Class 10 sa 2... 2017-2018

Study material (Science) (Class 10)

Page 1 Notes Assembled by Anupam Narang (8802442964)([email protected])

Need of light

Light is a form of energy. It is needed to see things

around us.

We detect light with our eyes.

It is only when light coming from an object enters

our eyes. That we are able to see the objects.

Light enables us to see objects from which it comes

or from which it is reflected.

Luminous and non-luminous objects

The objects like sun, stars, electric bulb, tube-light,

torch, candle are luminous objects.

The objects which do not emit their own light are

called luminous objects.

The objects which do not emit their own light are

called non luminous objects. They reflect light

coming from luminous object and we can see the

objects.

Light always travel in straight lines (rectilinear

propagation of light).

Nature of light

Light have dual nature: wave & particle nature.

Wave theory: light consists of electromagnetic

waves which do not require a material medium

(like solid, liquid or gas) for their propagation.

Particle theory: light is composed of particles

which travel in a straight line at very high speed.

The elementary particle is called photon.

Reflection of light

The process of sending back of the light rays which

fall on the surface of an object is called reflection

of light.

The objects having polished, shining surface reflect

more light than objects having unpolished, dull

surfaces.

Silver metal is the best reflector of light.

Making of ordinary mirrors: Ordinary mirrors

are made by depositing a thin layer of silver metal

on the back side of a plane glass sheet. The silver

layer is then protected by a coat of a red paint. The

reflection of light in the plane mirror takes place at

the silver surface in the mirror.

A ray of light is the straight line along which light

travels.

A bundle of light rays is called a beam of light.

Reflection of light from plane surfaces: Plane

mirror

The ray of light which falls on the mirror surface is

called the incident ray.

The point at which incident ray falls on the mirror

is called the point of incidence.

The ray of light which is sent back by the mirror is

called the reflected ray.

The normal is a line at right angle to the mirror

surface at the point of incidence.

The angle of incidence (i ) is the angle made by

the incident ray with the normal at the point of

incidence.

The angle of reflection (r ) is the angle made by

the reflected ray with the normal at the point of

incidence.

Laws of reflection of light

1. Incident ray, reflected ray & normal ray, all lie in

the same plane.

2. The angle of reflection is always equal to angle of

incidence.

A ray of light which falls normally on a mirror is

reflected back along the same path because the

angles of incidence as well as angle of reflection for

such ray of light are zero.

Laws of reflection apply to all kinds of mirrors,

plane mirrors and spherical mirrors. (Concave and

convex)

Light – Reflection and Refraction



Regular Reflection

Reflection of parallel beam of incident light from a

smooth surface in one direction is called Regular

reflection.

The particles of smooth surface are facing in on

direction due to this the angle of incidence for all

parallel rays of light falling on a smooth surface is

same & hence angle of reflection is same.

Diffused Reflection

Reflection of parallel beam of incident light from

rough surface like that of paper, chalk etc. in

different directions is called diffused reflection.

The particles of rough surface are all facing in

different directions. Due to this the angle of

incidence for all parallel rays are different and

hence all angles of Reflection are different due to

which the reflected rays go in different directions

Most of the objects cause diffuse reflection of light.

Objects & images:-

Anything which gives out light rays (either its own

or reflected by it) is called an object.

Image is an optical appearance produced when

light rays coming from an object are reflected from

a mirror or refracted by a lens.

Example:- when we see into the mirror, then our

face is object and its reflection is image.

Real images Virtual images

1. The image which can

be obtained on a

screen is called a real

image.

2. Real image is formed

when rays coming

from an object

actually meet at a

point after reflection

or refraction.

3. Real image formed on

a cinema screen is an

example of real

images.

1. The image which cannot be

obtained on screen is called

a virtual image. It can be

seen only by looking into a

mirror or a lens.

2. A virtual image is an

illusion; it is formed when

light rays coming from an

object only appear to meet

at a point when produced

backwards after reflection

or refraction.

3. Image of our face in mirror

is virtual image.

Formation of image of a point object in plane

mirror

Image of an extended object (or finite object)



Lateral inversion:-

When an object is placed in front of plane mirror,

then the right side of object appears to become the

left side of image, and the left side of object

appears to become the right side of image. This

change of sides of an object & its mirror image is

called lateral inversion.

Example:

The word RED

The phenomenon of Lateral inversion is due to the

reflection of light.

The word AMBULANCE on the hospital vans is

written in the form of because

when we are driving our car & see the hospital van

coming from behind in our rear view mirror then

we will get laterally image of AMBULANCE.

Characteristics of an image formed by a plane

mirror

Image is virtual. It cannot be received on a screen

The image is erect. It is same side up as the object.

The image is of same a size as of object.

The distance between object & mirror is same as

the distance between image & mirror.

The image formed in a plane mirror is laterally

inverted.

Uses of plane mirror

Used in our dressing tables & in bathrooms.

Used in jewellery shops to make them look bigger.

Used at blind turns of some busy roads so drivers

can see the vehicles coming from the other side. &

prevent accidents.

Used in making periscopes.

Spherical mirrors

The mirror in which reflecting surface is the part

of a hollow sphere of glass is called spherical

mirror.

Concave mirror: it is the spherical mirror in

which reflection takes place at concave surface. (Or

bent in surface)

It brings in the parallel beam of incident rays, after

reflection so, it is called converging mirror.

Convex mirror: It is the spherical mirror in which

reflection takes place at convex surface. (Or bent

out surface)

It spreads out the parallel beam of incident rays

after reflection, so it is called diverging mirror.

Some important terms

Centre of curvature (C):-

It is the centre of the hollow sphere of glass of

which the mirror is the part.

The Centre of Curvature of a concave mirror is in

front glass of which the mirror is a part.

The Centre of Curvature of a convex mirror is in

behind the glass of which the mirror is a part.

The Radius of Curvature (R)

The radius of Curvature of a spherical mirror is the

radius of the hollow sphere of glass of which the

mirror is a part.



Pole (P)

The centre of a spherical mirror is called its pole.

Principal axis (XY)

The straight line passing through the centre of

curvature and pole of a spherical mirror is called

its principal axis.

Aperture of the mirror

The diameter of reflective surface is called the

aperture of the mirror.

Principal focus & focal length of a Concave Mirror

The principal focus of a concave mirror is a point

on its principal axis to which all the light rays

which are parallel and from the concave mirror.

A Concave mirror has a real focus. The focus of a

concave mirror is in front of the mirror.

The focal length of a concave mirror is the distance

between its pole & principal focus.

Principal focus & focal length of a Convex Mirror

The principal focus of a convex mirror is a point on

its principal axis from which a beam of light rays,

initially parallel to the axis, appears to diverge

after being reflected from the convex mirror.

A Convex mirror has a virtual focus.

The focus of a convex mirror is situated behind the

mirror.

Relation between Radius of Curvature & focal

length of a Spherical Mirror.

The focal length of a spherical mirror of a concave

mirror or a convex mirror is equal to half its radius

of curvature.

F=R/2

Rules for obtaining images formed by Concave

Mirrors

The image is formed at that point where at least two

reflected rays intersect (or appear to intersect).

Rule 1:



A ray of light which is parallel to the principal axis

of a concave mirror passes through its focus after

reflection from the mirror.

Rule 2:

A ray of light passing through the centre of

curvature of a concave mirror is reflected back

along the same path.

Rule 3:

A ray of light passing through the focus of a

concave mirror becomes parallel to the principal

axis after reflection.

Rule 4:

A ray of light which is incident at the pole of a

concave mirror is reflected back making the same

angle with the principal axis.

Formation of different types of images by a

concave Mirror

Case 1: Object is placed b/w the pole & focus

Characters of image formed:

Behind the mirror.

Virtual & erect.

Larger than the object (Or magnified)

Case 2: Object is placed at the focus


At infinity,

Real & inverted, and

Highly magnified (or highly enlarged).

Case 3: Object between F and C


Between focus and centre of curvature.


Larger than the object (or magnified).



Case 4: Object at C)


At the center of curvature (C),


Same size as the object.

Case 5: Object beyond C)


Between the focus & centre of Curvature,

Real inverted, and

Smaller than the object (or diminished).

ase 6: Object is at infinity


At the focus (F),

Real & inverted. And

Much smaller than object (or highly diminished).

Uses of Concave Mirrors

Concave mirrors are used as shaving mirrors to

see a large image of the face. This is because when

the face is held within the focus of a concave

mirror, then an enlarged image of the face is seen

in the concave mirror.

Concave mirrors are used by dentists to see the

large images of the teeth of patients. This is

because when a tooth is within the focus of a

concave mirror, then an enlarged image of the

tooth is seen in the concave mirror. Due to this, it

becomes easier to locate the defect in the tooth.

Concave mirrors are used as reflectors in torches,

vehicle head-lights and search lights to get

powerful beams of light.

Concave reflectors are also used in room heaters.

The concave reflectors of room heaters direct heat

rays into the whole room.

Concave mirrors are used as doctor’s head-mirrors

to focus light coming from a lamp on to the body

parts of a patient (such as eye, ear, nose, throat,

etc.), to be examined by the doctor.

Concave dishes are used in T.V dish antennas to

receive T.V sequels from the distant

communications satellites. The Concave dish

collects a lot of T.V sequels & focuses them on to an

antenna (or aerial) fixed at its focus, so as to

produce strong sequels to run the television.

Large concave mirrors are used in the field of solar

energy to focus sun’s rays for heating solar

furnaces. The solar furnace is placed at the focus of

a large concave reflector. The concave reflector

focuses the sun’s heat rays on the furnace due to

which the solar furnace gets very hot.

Rules for obtaining images Formed by convex

mirrors

Rule 1



A ray of light which is parallel to the principal axis of a

convex mirror, appears to be coming from it focus

after reflection from the mirror.

Rule 2

A ray of light going towards the centre of curvature of

a convex mirror is reflected back along the same path.

Rule 3

A ray of light going towards the focus of a convex

mirror becomes parallel to the principal axis after

reflection.

Rule 4

A ray of light which is incident at the pole of a convex

mirror is reflected back making the same angle with

the principal axis.

Formation of image by a convex mirror

Case 1

Object is anywhere in front of mirror

Characteristics of image

Image is formed behind the mirror b/w Pole (P) &

focus (f).

Virtual & erect

Diminished (Smaller than the object).

Case 2

When the object is at infinity

Characteristics of image

Behind the mirror at F.

Virtual & erect.

Highly diminished.

Uses of convex mirror

Convex mirror are used as rear view mirrors in

vehicles to see the traffic at the back side.

Because :-



(a) Convex mirror produces erect images.

(b) The image formed in a convex mirror is highly

diminished or much smaller than object, due to

which is gives a wide field of view.

Big convex mirrors are used as ‘shop security

mirrors’. By installing a big convex mirror at a

strategic point in the shop, the shop owner can

keep an eye on the customers to look for thieves

and shoplifters among them.

Why we can’t use concave mirrors as rear view

mirror?

We cannot use concave mirrors as rear view mirror

because they produce inverted images.

How to distinguish between a plane mirror, a

concave mirror & a convex mirror without

touching them

By bringing our face close to each mirror, turn by turn.

A plane mirror will produce an image of the same size.

A Concave mirror will produce a magnified erect

image. A convex mirror will produce a diminished

erect image.

Sign convention for spherical mirrors

All distances are measured from pole of the mirror

and all heights are measured from principal axis.

Distances measured in the same direction as that

of incident light are taken as positive.

Distances measured against the direction of

incident light are taken as negative.

Heights measured upward & perpendicular to the

principal axis are taken as positive.

Distances measured downward & perpendicular to

the principal axis are taken as negative.

Some Important Conclusions

The object distance is always negative.

If an image is formed behind a concave mirror, the

image distance (v) is + ve.

If an image is formed in front of mirror, the image

distance (v) is –ve.

The focal length (f) of concave mirror is –ve &

convex mirror +ve.

The height of object is always +ve.

If the image is formed above the principal axis, it

height is +ve & if image is formed below the

principal axis then the height is –ve.

Mirror formula

The formula which gives the relationship b/w image

distance (v), object distance (u) and focal length (f) of

a spherical mirror is known as the mirror formula. 1

𝑓 =

1

𝑣 +

1

𝑢

Linear magnification produced by mirrors

The ratio of height of image to the height of object

is known as linear magnification (m).

m = 𝑕𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝑖𝑚𝑎𝑔𝑒

𝑕𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝑜𝑏𝑗𝑒𝑐𝑡 =

𝑕𝑖

𝑕𝑜

If the magnification has a plus sign, then the image

is virtual & erect.

If the magnification has a minus sign then the

image is real & inverted.

The linear magnification produced by a mirror is

equal to the ratio of the image distance to the

object distance, with a minus sign.

m = − 𝑖𝑚𝑎𝑔𝑒 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒

𝑜𝑏𝑗𝑒𝑐𝑡 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 =

−𝑣

𝑢



Refraction of Light

Define: The change in direction of light when it

passes from one medium to another obliquely is

called refraction of light. In other words, the

bending of light when it goes from one medium to

another obliquely is clled the refraction of light.

The refraction (or bending) of light takes place at

the boundary b/w the two media.

The angle b/w incident ray and normal ray (at the

point of incidence) is called the angle of

incidence.

The angle b/w the refracted ray & the normal (at

the point of incidence) are called the angle of

refraction.

In refraction of light, the angle of refraction is

usually not equal to the angle of incidence.

Causes of refraction

The refraction of light is due to the change in the

speed of the light on going from one medium to

another. When light go from one medium to

another its speed changes. And this change in

speed of light causes the refraction of light.

Greater the difference in the speeds of light in the

two media, greater will be the refraction of light.

Optically Rarer Medium & Optically Denser

Medium

A medium in which the speed of light is more is

known as optically rarer medium.

A medium, in which the speed of light is less, is

known as optically denser medium.

Rules of refraction

Rule 1: When a ray of light goes from a rarer medium

to a denser medium, it bends towards the normal (at

the point of incidence).

Rule2: When a ray of light goes from a denser

medium to a rarer medium, it bends away form the

normal (at the point of incidence).

Refraction from a rectangular glass slab



The light emerges from a parallel-sided glass slab

in a direction parallel with that in which it enters

the glass slab,

The perpendicular distance b/w the original path

of incident ray & the emergent ray coming out of

the glass slab is called lateral displacement of the

emergent ray of light.

The angle which the emergent ray makes with the

normal is called the angle of emergence.

Factors affecting lateral displacement

Lateral displacement is directly proportional to

(i) angle of incidence, (ii) thickness of glass-slab, (iii)

refractive index of glass slab.

The Case of Light falling Normally on a glass Slab

If the incident ray (or perpendicularly) to the surface

of a glass slab, then there is no bending of the ray of

light, & it goes straight.

Effects of Refraction of Light

Stick partly immersed in Water Appears to be bent

at the Water Surface.

When a pencil is partly immersed in water & held

obliquely to the surface, the pencil appears to send

at the water surface.

An object placed under Water appears to be raised.

When the coin is under water due to refraction of

light, a virtual image of the coin is formed nearer

to the water surface. And since the virtual image of

coin which we see, is nearer to the water surface,

so the coin appears to rise on adding water in the

begin.

A pool of water appears to be less deep than it

actually is.

When we look into a pool of water, we do not see

the actual bottom of the pool, we see a virtual

image of the bottom of the pool which is formed by

the refraction of light coming from the pool water

into the air.

Laws of Refraction of light

The incident ray, refracted ray & normal at the

point of incidence, all lie in the same plane.

The ratio of sine of angle of incidence to the sine of

angle of refraction is constant for a given pair of

media. This is also called Snell’s law. sin i

sin r= constant = refractive index of 2nd medium

Refractive Index & speed of light

The refractive index of two media can be written

as a ratio of speeds of light in the two media.

The refractive index of medium 2 with respect of

medium 1 is equal to the ratio of speed of light in

medium 1, to the speed of light in medium 2.

Refractive index, = 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑙𝑖𝑔𝑕𝑡 𝑖𝑛 𝑚𝑒𝑑𝑖𝑢𝑚 1

𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑙𝑖𝑔𝑕𝑡 𝑖𝑛 𝑚𝑒𝑑𝑖𝑢𝑚 2

When light is going from one medium to another

medium, then the value of refractive index is called

relative refractive index.



When the light is going from vacuum to another

medium, then the value of refractive index is called

the absolute refractive index.

Factors affecting refractive index

Refractive index depends on the nature of the

material of the medium and on the wavelength of

the light used.

Important points

A substance having higher refractive index is

optically denser than another substance having

lower refractive index.

Higher the refractive index of a substance, more it

will change the direction of a beam of light passing

through it.

Optical density is different from mass density.

Refraction of light by using spherical lenses

A lens is a piece of transparent glass bound by two

spherical surfaces.

Types of lenses

Convex lens: it is

thick at the centre

but thinner at edges.

It has two convex

surfaces.

Concave lens: It is

thin in the middle but

thick at the edges. It

has two concave surfaces.

Optical centre & principal axis of a lens:-

The centre point of a lens is known as its optical

centre.(O)

The principal axis of a lens is line passing through

the optical centre of the lens & perpendicular to

both to the faces of a lens.

Principal focus & focal length of a convex lens

The principal focus of a convex lens is a point on

its principal axis to which light rays parallel to the

principal axis converge after passing through the

lens.

A convex lens has a real focus because all light rays

actually pass through the focus of a convex lens.

The focal length of lens is the distance b/w

optical centre & principal focus of the lens.

A Convex lens is also known as converging lens

because it converges, a parallel beam of light rays

passing through it.

Factors affecting focal length

Higher the refractive index, shorter will be the

focal length.

More the curvature shorter the focal length.

Principal focus & focal length of a Concave lens

The principal focus of a concave lens is a point on

its principal axis from which light rays, originally

parallel to the axis appear to diverge after passing

through the concave lens.



A Convave lens is known as a diverging lens

because it diverge a parallel beam of light rays.

A Concave lens has a virtual focus because light

rays do not actually pass through the focus of a

concave lens.

The aperture of a spherical lens

Aperture of spherical lens is its

diameter.

Rules for obtaining images formed by convex

lenses

Rule 1: A ray of light which is parallel to the principal

axis of a convex lens, passes through its focus after

refraction through the lens.

Rule 2: A ray of light passing through the optical

centre of a convex lens goes straight after refraction

through the lens.

Rule3: A ray of light passing through the focus of a

convex lens becomes parallel to its principal axis after

refraction through the lens.

Formation of different types of images By convex

lens

Case 1: Object between optical centre & focus

The characteristics of image

Behind the object

Virtual & erect

Larger than the object

Case 2: Object at the focus of convex lens (at F1)


Image at infinity,

Real & Inverted,

Highly enlarged.

Case 3: Object is b/w F1 & 2F1

The characteristics of images

Beyond 2F2

Real & inverted,

Larger than the object.

ase 4: Object is at 2F1

The characteristics of image:

At 2F2 on the other side of lens.

Real & inverted.

Same size as the object.



Case 5: Object is beyond 2F1

The characteristics of image:

Between F & 2F on the other side of lens,

Real & inverted,

Smaller than the object.

Case 6: Object is at infinity


Image at focus.

Real & inverted.

Much smaller than the object (highly diminished).

Uses of convex lenses:-

Used in spectacles to correct the defect of vision

called hypermetropia.

Used to make simple camera.

Used as magnifying glass.

Used in making microscopes, telescopes and slide

projectors.

Sign convention for spherical Lenses:-

All the distances are measured from the optical

centre of the lens.

The distances measured in the same direction of

incident light are taken as positive.

The distances measured against the direction of

incident light are taken as negative.

The distances measured upward & perpendicular

to the principal axis are taken as positive.

The distances measured downward &

perpendicular to the principal axis are taken as

negative.

Focal length of lens

Focal length of convex lens is always + ve.

Focal length of concave lens is considered –ve.

Lens formula

The formula which gives the relationship between

distance (v), object distance(u) & focal length (f) of

a lens is called lens formula. 1

𝑓 =

1

𝑣 -

1

𝑢

Magnification produced by lenses

The linear magnification is the ratio the height of

the image to the height of the object.

m = 𝑕𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝑖𝑚𝑎𝑔𝑒

𝑕𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝑜𝑏𝑗𝑒𝑐𝑡 =

𝑕𝑖

𝑕𝑜

The linear magnification produced by a lens is

equal to the ratio of image distance to the object

distance.

m = 𝑖𝑚𝑎𝑔𝑒 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒

𝑜𝑏𝑗𝑒𝑐𝑡 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 =

𝑣

𝑢

Rules for obtaining images formed by Concave

lenses

Rule 1: A ray of light which is parallel to the principal

axis of a concave lens, appears to be coming from its

focus after refraction through the lens.

Rule 2: A ray of light passing through the optical

centre of a concave lens goes straight after passing

through the lens.

Rule 3: A ray of light going towards the focus of a

concave lens, becomes parallel to the principal axis

after refraction through the lens.



Formation of image by a concave lens:-

Case 1: Object is anywhere between infinity & O.


Between 2F & F.

Virtual & erect.

Diminished.

Case 2: Object is at F


Image is formed at F.

Virtual & erect.

Highly diminished.

How to distinguish b/w convex lens & concave lens

Keep the lens close to the page of a book & see the

image of the writings of the book through it. If the

letters of the book appear enlarged then it is convex

lens & if it appears diminished then it is concave lens.

Uses of concave lenses

Concave lenses are used in spectacles to correct

the defect of vision called myopia.

Concave lens are used as eye lens in Galilean

Telescope.

Concave lens are used in combination with convex

lenses to make high equality lens system of optical

instruments.

Concave lens is used in wide-angle spy hole in

doors.

Power of lens:-

The power of lens is a measure of the degree of

convergence or divergence of light rays falling on

it.

The power of a lens is defined as the reciprocal of

its focal length in meters.

P = 1/f

P – Power of lens, f - focal length of lens.

A lens of short focal length has more power

whereas a lens of long focal length has less power.

The unit of power is dioptre. One dioptre is the

power of a lens whose focal length is 1m.

The power of convex lens is +ve.

The power of concave lens is –ve.

Power of a combination of lenses

If a number of lenses are placed in close contact, then

the power of the combination of lenses is equal to the

algebraic sum of the power of individual lenses.

P = P1 + P2.



ASSIGNMENT:

1. A convex lens of focal length 0.1 m is placed at a

distance of 12 cm from a wall. How far from the

lens should an object be placed so as to form its

real image on the wall?

2. An object is placed at a distance of 0.5 m from a

concave lens of focal length 0.2 m. find the nature

and position of the image.

3. An object placed 50 m from a lens produces a

virtual image at a distance of 10 cm in front of the

lens. What is the focal length of the lens?

4. A diverging lens of focal length 15 cm forms an

image 10 cm from the lens. Prove that the object is

30 cm away from the lens.

5. An object 4 cm high is placed at a distance of 15 cm

in front of a concave lens of power – 10 D. find the

size of the image. Draw a ray diagram taking

suitable scale.

6. 4 cm tall object is placed perpendicular to the

principal axis of converging lens of focal length 20

cm. If distance of object from the lens is 30 cm, find

position, nature and size of image.

7. Concave lens of focal length form an image at a

distance of 10 cm from the lens. What is the

distance of object from the lens?

8. A needle 10 cm high is placed at 40 cm from a

convex lens of focal length 15 cm. Find position,

nature and size of the image.

9. Two thin lenses (concave and convex) of power

3.5D and 2.5D respectively are placed in contact.

Find the power and focal length of the lens

combination.

10. What is the angle of reflection if a ray falls

normally on a plane mirror? Also write the angle

between incident and reflected ray.

11. Identify a mirror having focal length -15 cm.

12. How do you draw normal at any point on a

spherical mirror?

13. If an object is placed at the focus of a concave

mirror, where is the image formed?

14. The refractive index of diamond is 2.47 and that of

glass is 1.51. How much faster does light travel in

glass than in diamond.

15. Out of convex mirror and concave mirror, whose

focus is situated behind the mirror?

16. For what position of an object, a real and

diminished image is formed by a concave mirror?

17. What is the value of focal length of a plane mirror?

18. Give the range of wavelength of visible light?

19. Define ray of light.

20. Which metal is the best reflector of light?

21. Is it possible that the laws of reflection change, if

we use spherical mirror instead of a plane mirror?

22. How can you draw normal to a spherical mirror at

a particular point?

23. Name the converging mirror.

24. Do a concave mirror form a virtual image of same

size as the object?

25. Name the mirror which has larger field of view.

26. Where is the image formed when an object is at

large distance from a concave mirror?

27. Arrange air, glass and water in terms of

descending order of refractive index.

28. If the refractive index of alcohol is 1.36 and carbon

disulphide is .63. which is optically denser?

29. Is it possible that the image formed by a convex

lens is real?

30. How is power of a lens related to its focal length?

31. Define number of lens.

32. A ray of light passing through centre of curvature

of a concave mirror retraces its path on reflection.

Why?

33. Where should an object be placed so that a real

and inverted image of the same size is obtained

using a convex lens?

34. For what position of an object will a convex lens

form a virtual and erect image?

35. Identify the lens which is thick at centre and thin

at the edges.

36. What is the nature of the image formed by a

concave mirror if the magnification produced by

the mirror is +3?

37. Between which two points of a concave mirror

should an object be placed to obtain a

magnification of -3?

38. On what factors does the focal length of a spherical

mirror depend?

39. What is the basic cause of refraction?

40. If the magnification of a body of size 1m is 2. What

is the size of the image?

41. Draw a labeled ray diagram to find the image of an

object formed by a convex lens of focal length 20

cm when an object is place 30 cm away from the

lens.

42. How are power and focal length of a lens related?

You are provided with two lenses of focal length

20 cm and 40 cm respectively. Which lens will you

use to obtain more convergent light?

43. A ray of light travelling in air is incident on a

rectangular glass slab. What will happen?



44. A convex lens of focal length 20 cm can produce a

magnified virtual as well as real image. Is this a

correct statement? If yes, where shall the object be

placed in each case for obtaining these images?

45. Can we change focal length of a given spherical

mirror by changing the object distance from the

mirror?

46. How is refractive index of a medium related to

velocity of light in a medium?

47. List out the factors on which refractive index of a

medium depends?

48. Under what conditions there won’t be any

refractive of light when it enters from one medium

to another?

49. A pencil when dipped in water in a glass tumbler

appears to be bent at the interface of air and water.

will the pencil appear to be bent to the same

extent, if instead of water we use liquids like

kerosene or turpentine. Support your answer with

reason.

50. Refractive index of diamond with respect to glass

is 1.6 and absolute refractive index of glass is 5.

Find out the absolute refractive index of diamond.

51. How can you identify the three types of mirrors

without touching?

52. What happens to a ray of light when it travels from

one medium to another having equal refractive

indices?

53. State the cause of refraction of light?

54. What should be the position of the object, when a

concave mirror is to be used

a. As a shaving mirror?

b. In torches producing parallel beam of

light?

55. A man standing in front of a mirror, finds his image

having a very small head and legs of normal size.

What type of mirrors are used in designing such a

mirrors?

56. The power of a lens is -1.5 D. find the focal length

of the lens and state its nature.

57. Two lenses of power -2.5 D and +1.5 D are placed

in contact. Find the total power of the combination

of lens. Calculate the focal length of this

combination.

58. Give one uses of each of the following

a. Regular reflection

b. Irregular reflection

59. State two factors which determine lateral

displacement of ray of light passing through a

rectangular glass slab.

60. State whether the following are positive or

negative when a concave lens forms a virtual

image

a. Distance of image from lens

b. Focal length of lens

61. Under what condition in an arrangement of two

plane mirror, incident ray and reflected ray will

always be parallel to each other, whatever may be

angle to incidence?

62. What is the name given to linear distance between

the pole and principal focus of a spherical mirror?

If this distance is 25 cm, how far is the centre of

curvature from the pole of the spherical mirror?

63. The focal length of the glasses of a short sighted

person is 37.5 cm. Find the power of the glasses

and their nature.

64. Identify the device used as spherical mirror or lens

in the following cases, when the image formed is

virtual and erect in each case.

a. Object is placed between device and its

focus, image formed is enlarged and behind

it.

b. Object is placed between the focus and

device, image formed is enlarged and on

the same side as that of the object.

c. Object is placed between infinity and

device, image formed is diminished and

between focus and optical centre on the

same side as that of the object.

65. A concave mirror is used as a head mirror by ENT

specialists. The same mirror can also be used as a

shaving mirror. Why?

66. State two uses of concave mirror and convex

mirror.

67. Identify the nature of the mirror and mention two

characteristics of the image formed by

magnification m = +6.

68. Give two uses of concave lens and convex lens.

69. A 6 cm tall object is placed perpendicular to the

principal axis of a convex lens of focal length 25 cm.

The distance of the object from the lens is 40 cm.

By calculating determine

a. The position and

b. The size of the image formed.

70. A real image one – fifth the size of an object is

formed at a distance of 18 cm from a mirror. What

is the nature if mirror? Calculate its focal length.

71. A man standing in front of a special mirror finds his

image having a small face, big tummy and legs of



normal size. What are the shapes of three parts of

the mirror?

72. Define power of a lens.

73. What is the unit of power?

74. Which of the two lens has a greater power?

a. A convex lens of focal length 5 cm?

b. A convex lens of focal length 50 cm?

75. A convex mirror used for rearview on an

automobile has a radius of curvature of 3 m. if a

bus is located at 5 m from this mirror. Find the

position, nature and magnification of the image.

76. State the sign of convention of u, v and i for a

concave mirror when it forms a virtual image.

77. Draw a labelled diagram showing how an image of

a small slide can be projected on large screen. State

two characteristics of an image.

78. A convergent terms of power 8 D is combined with

a divergent lens of power -10 D. calculate.

a. Power of combination.

b. Focal length of combination.

79. State the sign of convention of u, v and f for a

convex mirror.

80. If an object is held at a distance of 60 cm from a

concave mirror of focal length 20 cm. At what

distance from the convex mirror, should a plane

mirror be held so that images in the two mirrors

coincide?

81. A convex lens has focal length of 30 cm. Calculate at

what distance should an object be placed from the

lens so that it forms an image at 60 cm on the other

side of the lens. Also, calculate the magnification

produced by the lens.

82. A convex lens of focal length 40 cm and a concave

lens of focal length 50 cm are placed in contact

with each other. Find

a. power of the combination.

b. Focal length of the combination.

83. An object 3 cm high is placed perpendicular to the

principal axis of a concave lens of focal length 7.5

cm. The image is formed at a distance of 5 cm from

the lens. By calculating determine

a. Distance at which an object is placed

b. The size and nature of the image formed.

84. An object 50 cm tall is placed on the principal axis

of a convex lens. Its 20 cm tall image is formed on

the screen placed at a distance of 10 cm from the

lens. Calculate the focal length of the lens.

85. At what distance should an object be placed from a

convex lens of focal length 18 cm to obtain an

image at 36 cm from it? What will be the

magnification produced in this case?

86. What is linear magnification? Describe its

significance.

87. Draw ray diagrams showing the image formation

by a convex mirror when an object is placed.

a. At infinity

b. At finite distance from the mirror.

88. Why does a light ray incident on a rectangular glass

slab immersed in any medium emerges parallel to

itself? Explain using a diagram?

89. When an object is placed at a distance of 60 cm

from a convex spherical mirror, the magnification

produced is 1/2. Where should the object be placed

to get a magnification of 1/3?

90. Find the distance at which an object should be

placed in front of a convex lens of focal length 10

cm to obtain an image of double its size?

91. In the way from Kanpur to Delhi they were four

friends. Sunil was driving the car and saw from his

side mirror that the car which was behind their car

had met an accident. He suddenly applied the brake

even after his friends asked him to leave the

situation as it is. But Sunil didn’t agreed and get

down of car and persuade his friends to help the

injured.

All of them took the injured person to the nearest

hospital. After taking first aid from hospital the

victim thanks and pleased them for saving their

life.

a. Name the type of mirror from which Sunil

saw the accident?

b. Why this mirror is used as a slide mirror in

vehicles?

c. What can you learn from the Sunil’s

character?

92. Draw ray diagram showing the image formation by

a concave mirror when an object is placed

a. Between pole and focus of the mirror.

b. Between focus and centre of curvature of

the mirror.

c. At centre of the curvature of the mirror.

d. A little beyond centre of curvature of the

mirror.

e. At infinity

93. Draw ray diagram showing the image formation by

a convex lens when an object is placed

a. Between optical centre and focus of the

lens.



b. Between focus and twice the focal length of

lens.

c. At twice the focal length of the lens.

d. At infinity

e. At the focus of the lens.

94. Define real image of an object.

95. Give the name of the mirror that

a. Can give real as well as virtual image of an

object.

b. Will always give virtual image of same size

of an object.

c. Will always give virtual and diminished

image of an object.

d. Is used by a doctor in examining teeth.

96. Draw a ray diagram in each of the following cases

to show the formation of an image, when an object

is placed

a. Between optical centre and principal focus

of a convex lens

b. Between F and 2 F of a concave lens.

c. At 2 F of a convex lens.

97. For a spherical mirror, we have 1

𝑣+

1

𝑢=

1

𝑓=

2

𝑅

where, u = distance of an object pole of mirror

v = distance of an image from pole of mirror

f = focal length of mirror

R = radius of curvature.

We called this formula as mirror formula and is

applicable equally to concave mirror as well as

concave mirror.

a. If we change the value of u by moving an object

then how is focal length f affected?

b. If the radius of curvature of a spherical mirror

is 30 cm. What is its focal length?

c. Focal length of a mirror depends neither on u

nor v but it depends only on radius of

curvature of the mirror. What values of life do

you learn from this fact?

98. A thin converging lens form real magnified image

and virtual magnified images of an object in front

of it.

a. Write the positions the object in each case.

b. Draw ray diagram to show the image

formation in each part.

c. How will the following be affected on

cutting this lens into two halves along the

principal axis?

d. Focal length?

e. Intensity of the image formed by half lens.



THE HUMAN EYE

The main parts of the human eye are: Cornea, Iris, Pupil, Ciliary muscles, Eye lens, Retina and optic nerve.

The eye – ball is approximately spherical in shape having a diameter of about 2.5 cm.

Construction of the Eye

The front part of the eye is called cornea. It is

made of a transparent substance and it is

bulging outwards. The outer surface of cornea

is convex in shape. The light coming from

objects enters the eye through cornea.

Behind the cornea is the iris (or coloured

diaphragm). Iris is a flat, coloured, ring-shaped

membrane behind the cornea of the eye. There

is a hole in the middle of the iris which is called

pupil of the eye. Thus pupil is a hole in the

middle of the iris. The pupil appears black

because no light is reflected from it.

The eye-lens is a convex lens made of a

transparent, soft and flexible material like a

jelly made of proteins. Being flexible, the eye-lens can change its shape (it can become thin or thick) to focus

light on to retina.

The eye-lens is held in position by suspensory ligaments. One end of suspensory ligaments is attached to the

eye-lens and their other end is attached to ciliary muscles. Ciliary muscles change the thickness of eye-lens

while focusing.

An eye differs from a camera. The focal length of the convex lens used in a camera is fixed and cannot be

changed but the focal length of the convex lens present inside the eye can be changed by the action of ciliary

muscles.

The screen on which the image is formed in the eye is called retina. The retina is behind the eye- lens and at

the back part of the eye. The retina of an eye is just like the film in a camera.

The retina is a delicate membrane having a large number of light sensitive cells called ‘rods’ and ‘cones’

which respond to the intensity of light and ‘colour of objects’ respectively, generating electrical signals.

At the junction of optic nerve and retina in the eye, there are no light sensitive cells (no rods or cones) due

to which no vision is possible at that spot. This is called blind spot. Thus, blind spot is a small area of the

retina insensitive to light where the optic nerve leaves the eye. When the image of an object falls on the

blind spot, it cannot be seen by the eye.

An eye-lid in front of the eye which is just like the shutter in a camera. When eye-lid is open, light can enter

the eye but when eye-lid is closed, no light enters the eye.

The space between cornea and eye-lens is filled with a watery liquid called ‘aqueous humour’. And the space

between eye-lens and retina is filled with a transparent jelly like substance called ‘vitreous humour’ which

supports the back of the eye.

The Function of Iris and Pupil

The iris controls the amount of light entering the eyes. The iris automatically adjusts the size of the pupil

according to the intensity of light received by the eye.

Human eye and the colourful world



How does iris and pupil perform their function?

If the amount of light received by the eye is large (as during the day time), then iris contracts the pupil

(makes the pupil small) and reduces the amount of light entering the eye.

If the amount of light received by the eye is small (as in dark room or during night), the iris expands the

pupil (makes the pupil large) so that more light may enter the eyes.

Why it takes some time to see clearly when we enter from bright sunlight into a room or hall?

The adjustment of the size of the pupil takes some time. In bright sunlight the pupil of our eye is small. So, when

we enter the darkened cinema hall, very little light enters our eye and we cannot see properly. After a short

time, the pupil of our eye expands and becomes large. More light then enters our eye and we can see clearly.

Rods and Cones

Rods are the rod- shaped cells present in the retina of an eye which are sensitive to dim light. Rods are the

most important for vision in dim light (as during the night).

Nocturnal animals (animals which sleep during the day and come out at night) like the owl have a large

number of rod cells in their retina which help them see properly during the night when there is not much

light.

Cones are the cone-shaped cells present in the retina of an eye which are sensitive to bright light (or normal

light). The cone cells of our retina also respond to colours.

Cone cells of the retina function only in bright light. The cones do not function in dim light. This is why when

it is getting dark at night, it becomes impossible to see colours of cars on the road.

Rays From Nearby Objects & Distant Objects



Accommodation of Human Eye

The eye is said to be unaccommodated because it is the relaxed state of the eye.

When the eye-lens becomes more convex to focus the nearby objects, then eye is said to be ‘accommodated’.

The ability of an eye to focus the distant objects as well as the nearby objects on the retina by changing the

focal length (or converging power) of its lens is called accommodation.

A normal eye has a power of accommodation which enables objects as far as infinity and as close as 25 cm

to be focused on the retina.

The power of accommodation of the eye for a person having normal vision (normal eyesight) is about 4

diopters.

Range of Vision of a Normal Human Eye

The farthest point from the eye at which an object can be seen clearly is known as the ‘’ far point’’ of the eye.

The far point of a normal human eye is at infinity.

The nearest point up to which the eye can see an object clearly without any strain, is called the ‘’near point’’

of the eye. The near point of a normal human eye is at a distance of 25 cm from the eye.

The minimum distance at which an object must be placed so that a normal eye may see it clearly without

any strain, is called the least distance of distant vision.

The least distance of distant vision for a normal human eye is about 25 cm.

The range of vision of a normal human eye is from infinity to about 25 cm.

DEFECTS OF VISION AND THEIR CORRECTION

There are three common defects of vision (or defects of eye).

Myopia (Short-sightedness or Near-sightedness)

Hypermetropia (Long-sightedness or Far- sightedness), and

Presbyopia

Cataract

Myopia (Short- Sightedness or Near- Sightedness)

Myopia (or short- sightedness) is that defect of vision due to which a person cannot see the distant objects

clearly (though he can see the nearby objects clearly).

The far point of an eye suffering from myopia is less than infinity.

Cause: Due to high converging power of eye-lens (because of its short focal length).Due to eye-ball being

too long.

Described cause:

1. The ciliary muscles attached to

the eye – lens do not relax

sufficiently to make the eye-

lens thinner to reduce its

converging power. Power of

lens in more than the normal

(40D).

2. The eye-ball is too long due to

which the retina is at larger

distance from the eye-lens and

the image forms in front of the

retina (even though the eye-

lens may have correct

converging power).



Correction

1. Myopia should be of such a focal length (or power) that it produces a virtual image of the distant

object (lying at infinity) at the far point of the myopic eye.

2. The concave lens used here decreases the converging power of the eye-lens and helps on forming

the image of distant object on the retina of the myopic eye.

Calculation of Power of Concave Lens to correct Myopia.

Object distance, U = ∞ (Infinity)

Image distance, V = given as Far point, in front of lens

And, Focal length, f = ? (To be calculated)

Hypermetropia (Long – Sightedness or Far – Sightedness)

Hypermetropia (or long- sightedness) is that defect objects due to which a person cannot see the nearby

objects clearly (though he can see the distant objects clearly).

The near-point of a hypermetropic eye is more than 25 cm away.

Cause:

1. Due to low converging power of eye- lens

(because of its large focal length), or

2. Due to eye-ball being too short.

Described cause:

1. The ciliary muscles attached to the eye- lens

weak and cannot make the eye-lens thicker to

increase its converging power.

2. The eye- ball is too short due to which the

retina is at a smaller distance from the eye-

lens and the image of a nearby object is formd

behind the retina (even though the eye-lens

may have correct converging power).

Correction:

1. The convex lens used for correcting

hypermetropia (or long- sightedness should

be of such a focal length (or power) that it

forms a virtual image of the object (placed at

the normal near point N of 25 cm), at the near

point N’ of the hypermetropic eye.

2. Convex lens increase the converging power of

the eye-lens.

Calculation of the Power of Convex Lens to correct Hypermetropia.

Object distance, U = -25 cm (Normal near point)

Image distance, V = given as Near point of this defective eye

And, Focal length, f = ? (To be calculated)

Presbyopia (old age hyper-metropia)

Presbyopia is that defect of vision due to which an old person cannot see the nearby due to loss of power of

accommodation of the eye.

The near –point of the old person having presbyopia gradually recedes and becomes much more than 25

centimetres away.



Presbyopia is the hypermetropia (or long – sightedness) caused by the loss of power of accommodation of

the eye due to old age. Presbyopia defect is corrected in the same way as hypermetropia by using spectacles

having convex lenses.

If a person suffering from myopia as well as hypermetropia

A person suffering from myopia as well as hypermetropia uses spectacles having bifocal lenses in which

upper part consists of a concave lens (to correct myopia) used for distant vision and the lower part consists

of a convex lens (to correct hypermetropia) used for reading purposes.

Cataract

The medical condition in which the lens of the eye of a person becomes progressively cloudy resulting in

blurred vision is called cataract.

Cataract develops when the eye-lens of a person becomes cloudy (or even opaque) due to the formation of a

membrane over it. Cataract decreases the vision of the eye gradually. It can even lead to total loss of vision

of the eye.

The vision of the person can be restored after getting surgery done on the eye having cataract. The opaque

lens is removed from the eye of the person by surgical operation and a new artificial lens is inserted in its

place.

WHY DO WE HAVE TWO EYES FOR VISION AND NOT JUST ONE

Having Two Eyes Gives a Wider Field of View. A human being has a horizontal field of view of about 1500

with one eye open but with two eyes open, the field of view becomes 1800.

Having Two Eyes Enables Us to Judge Distances More Accurately. Our two eyes are a few centimeters apart

from each other. Due to this, the two eyes see the same object from two slightly different angles and send

two slightly different images of the same object to the brain. The brain combines these two slightly different

images to build a three- dimensional picture of the object which enables us to judge the distance of the

object more accurately.

GLASS PRISM

The refraction of light on passing through a glass prism is different from that in a glass slab.

In refraction through a glass slab, the emergent ray is parallel to the incident ray but in refraction through a

glass prism, the emergent ray is not parallel to the incident ray. The emergent ray of light in a glass prism is

not parallel to the incident ray of light because the opposite faces of the glass prism (where refraction takes

place) are not parallel to one another.

Refraction of light through a glass

prism

When a ray of light passes

through a prism, it bends

towards the base of prism. In

other words, when a ray of light

passes through a prism, it bends

towards the thicker part of the

prism.

The angle between incident ray

and emergent ray is called angle

of deviation.



DISPERSION OF LIGHT

The splitting up of white light into seven colours on passing through a transparent medium like a glass

prism is called dispersion of light.

The dispersion of white light occurs

because colours of white light colours

of white light travel at different

speeds through the glass prism.

Cause: When white light consisting of

seven colours falls on a glass prism,

each colour in its refracted (or

deviated) by a different angles

because they all have different speeds

in glass. Speed of red is max and

speed of violet is min.

RE- Combination of Spectrum Colours to Give White Light

Newton showed that the reverse of this is also true. That is, the seven coloured lights of the spectrum can be

recombined to give back white

light.

A triangular glass prism P1 is

placed on its base and another

similar prism P are placed

alongside it in the inverted

position on its vertex A so that its

refracting surface is in the

opposite direction. When a beam

of white light is allowed to fall on

the first prism P1 , then a patch of

ordinary white light is obtained on a screen S placed behind the second prism P.

The Rainbow

The rainbow is an arch of seven colours visible in the sky which is produced by the dispersion of sun’s light

by raindrops in the atmosphere. The rainbow is

actually a natural spectrum of sunlight in the sky.

Optical phenomenon involved: A rainbow is

produced by the dispersion, total internal refraction

and refraction of white sunlight by raindrops (or

water drops) in the atmosphere.

How rainbow is produced: The raindrops in the

atmosphere act like many small prisms. A ray of white

sunlight enters the raindrops and undergoes

refraction and dispersion to form a spectrum. This

spectrum undergoes total internal reflection within

the raindrop and finally refracted out of the raindrop.

The red colour of spectrum appears at the top of the

rainbow whereas violet colour appears at its bottom.



ATMOSPHERIC REFRACTION

In the atmosphere we have air layers having different optical densities.

The refraction of light caused by the earth’s atmosphere (having air layers of varying optical densities) is

called atmosphere refraction.

Twinkling of Stars

The twinkling of a star is due to the atmosphere refraction of star’s light.

When the light coming from a star enters the earth’s atmosphere, it undergoes refraction due to the varying

optical densities of air at various altitudes. The atmosphere is continuously changing (due to which the

optical densities of air at different levels in the atmosphere keep on changing). The continuously changing

atmosphere refracts the light from the stars by different amounts. When the atmosphere refracts more star-

light towards us, the star appears to be bright and when the atmosphere refracts fewer star- light, then the

star appears to be dim. In this way, the star – light reaching our eyes increases and decreases continuously

due to atmospheric refraction. And the star appears to twinkle at night.

Why planets do not twinkle?

The planets appear to be quite big to us (because they are much nearer to the earth). So, a planet can be

considered to be a collection of a very large number of point sources of light. The dimming effect produced

by some of the point sources of light in one part of the planet is nullified by the brighter effect produced by

the point sources of light in its other part.

The brightness of a planet always remains the same and hence it does not appear to twinkle.

The Stars Seem Higher Than They Actually Are

Due to atmospheric refraction, the stars seem to be higher in the sky than they actually are.

Light from a star is refracted (bent) as it leaves space (a vacuum) and enters the earth’s atmosphere. Air

higher up in the sky is rarer but that nearer the earth’s surface is denser. So, as the light from a star comes

down, the dense air bends the light more. Due to this refraction of star’s light, the star appears to be at a

higher position.

Advance Sunrise and Delayed Sunset

We can see the about 2 minutes before the actual

sunrise and 2 minutes after actual sunset because of

atmospheric refraction.

The time from sunrise to sunset is lengthened by

about 2+2 = 4 minutes because of atmospheric

refraction.

Cause: When the sun is slightly below the horizon,

then the sun’s light coming from less dense air to

more dense air is refracted downwards as it passes

through the atmosphere. Because of this atmospheric

refraction, the sun appears to be raised above the horizon when actually it is slightly below the horizon.

SCATTERING OF LIGHT

Scattering of light means to throw light in various random directions. Light is scattered when it falls on

various types of suspended particles in its path.

Depending on the size of particles, the scattering can be of white sunlight as such or of the coloured lights

which make up the white sunlight.



Tyndall Effect

The scattering of light by particles in its path is called Tyndall effect.

When a beam of sunlight enters a dusty room through a window, then its path becomes visible to us. This is

because the tiny dust particles present in the air of room scatter the beam of light all around the room. And

when its scattered light enters our eyes, we can see the beam of light.

When white light consisting of seven colours is passed through a clear liquid having small suspended in it,

then the blue colour of white light having shorter wavelength is scattered much more than the red colour

having longer wavelength.

The blue coloured light present in white sunlight is scattered much more easily than the red light. The blue

light present in sunlight is scattered 10 times more than the red light.

The Colour of Scattered Light Depends on the Size of Scattering Particles

The larger particles of dust and water droplets present in the atmosphere scatter the lights as such

due to which the scattered light also appears white.

The extremely minute particles such as the air molecules (oxygen and nitrogen) present in the

atmosphere scatter all colours present in the white sunlight.

Why the Sky is Blue

The scattering of blue component of the white sunlight by air molecules present in the atmosphere causes

the blue colour of the sky.

The sunlight is made up of seven coloured lights mixed together. When sunlight passes through the

atmosphere, most of the longer wavelength lights such as red, orange, yellow, etc. Present in it did not get

scattered much by the air molecules and hence pass straight through. The shorter wavelength blue light is,

however, scattered all around the sky by air molecules in the atmosphere.

If the earth had no atmosphere

If the earth had no atmosphere consisting of air, there would have been no scattering of sunlight at all. In

that case no light from the sky would have entered our eyes and the sky would have looked dark and black

to us.

Sky in outer space

In outer space, the sky looks dark and black instead of blue. This is because there is no atmosphere

containing air in the outer space to scatter sunlight. Since there is no scattered light to reach our eyes in

outer space, therefore the sky looks dark and black there.

Why danger signals are red

The ‘danger’ signal lights are red in colour. This is because the red coloured light having longer wavelength

is the least scattered by fog or smoke particles. Due to this the red light can be seen in the same colour even

from a distance.

Why the Sun Appears Red at Sunrise and Sunset

At the time of sunrise and sunset when the sun is near the horizon, the sunlight has to travel the greatest

through the atmosphere to reach us. During this long journey of sunlight, most of the shorter wavelength

blue-colour present in it is scattered out and away from our line of sight. So, the light reaching us directly

from the rising sun or setting sun consists mainly of longer wavelength red colour due to which the sun

appears red.



Why the Sun Appears white when sun is

over head

When the sun is overhead (as at noon),

then the light coming from the sun has to

travel a relatively shorter distance through

the atmosphere to reach us. During this

shorter journey of sunlight, only a little of

the blue colour of the white light is

scattered. Since the light coming from the

overhead sun has almost all its component

colours in the right proportion, therefore,

the sun in the sky overhead appears white

to us.

ASSIGNMENT

1. How is the eye lens held its position?

2. What is meant by near point?

3. What is the least distance of distinct vision?

4. What is the nature of an image formed on the

retina of the eye?

5. Name the part of an which is equivalent to

(a) Diaphragm and

(b) Photographic plate, in a camera?

6. Name the part of the eye that controls the amount

of the light entering the eye.

7. Which liquid fills the space behind the cornea?

8. Define the power of accommodation.

9. What do you mean by far point?

10. Define cataract.

11. What is the approximate diameter of human eye?

12. Why does the sun at noon, i.e, the overhead sun

appears white?

13. On what factors does the angle of deviation of a

prism depends?

14. Where is the image formed in an eye suffering

from near sightedness?

15. Where is the image formed in an eye suffering

from long sightedness?

16. How is long sightedness corrected?

17. What is the other name of presbyopia?

18. What is the twinkling of stars due to?

19. Give one example of source of white light.

20. Which scientist first explains the dipersion of

light?

21. On what factor the colour of the scattered light

depends?

22. What is a function of Choroids?

23. What happens to the lens and the ciliary muscles

when u are looking at nearby objects?

24. Why do we observe random wavering or flicking of

the objects near a fire or on a very hot day?

25. Name any one source of polychromatic light.

26. Why are we not able to see things clearly when we

come out of a dark room?

27. Why does the sky appear black instead of blue to

an astronaut?

28. Can visible light be scattered by atoms / molecules

in Earth’s atmosphere?

29. Light of which wavelength deviates the maximum

and the least when passed through a prism?

30. Name the phenomenon responsible for rainbow

formation.

31. What is Tyndall effect?

32. When sunlight enters a dark smoke filled room, its

path become visible. Name the phenomenon

responsible for this.

33. Why are danger signals lights red in colour?

34. What would have been the colour of the sky, if the

earth had no atmosphere?

35. Give the numerical relation between wavelength of

red light and blue light.

36. How long does the light from an event stay in our

eye so as to form its image on retina?

37. What is a contact lens?

38. What is blind spot?

39. A man can read the number of a distant bus clearly

but he finds difficulty in reading a book. From

which defect of the eye he is suffering from? What

type of spectacles lens should be used to correct

the defect?

Sun nearly

over head

Less blue

scattered

Blue scattered away

sun appears reddish

Sun near

horizon



40. Draw a ray diagram each showing Myopic eye and

Hypermetropic eye.

41. A student sitting at the back of the classroom

cannot read clearly the letters written on the black

board.what advice will a doctor give to her? Draw

a ray diagram for the correction of this defect.

42. The sun near the horizon appears flattened at the

sunset and sunrise. Explain why?

43. Explain why and when the sun is overhead at

moon it appears white?

44. How will you use two identical prisms so that a

narrow beam of white light incident on one prism

emerges out of the second prism as white light?

Draw a ray diagram.

45. Draw a ray diagram showing the dispersion

through a prism when a narrow beam of white

light is incident on one of its refracting surfaces.

Also indicate the order of the colours of the

spectrum obtained.

46. What is astigmatism? How is it rectified?

47. What is the nature of the image formed on the

retina? What kind of lens is present in our eyes?

48. What is the role of ciliary muscles in the normal

functioning of an eye?

49. What is the cause of dispersion of light?

50. When the sunlight passes through the canopy of a

dense forest, the light is scattered. Explain

51. Why is it difficult to drive on a foggy day?

52. Explain the role of pupil and iris.

53. Explain the role or importance of ciliary muscles in

eye accomodation.

54. What is the colour of an emergent light when

white light is passed through a collloidal solution

of sulpher? Explain

55. Define spectrum and Dispersion of light.

56. Calculate maximum power of accommodation of a

person having normal vision.

57. Give the meaning of VIBGYOR. With which

phenomenon is it connected?

58. A person wants to read a book placed at 20cm,

whereas near point of his eye is 30cm. Calculate

the power of the lens required?

59. A myopic person can see things clearly only when

lie between 10cm and 100cm from the eye, which

lens will enable him to see the moon clearly?

60. How are we able to see nearby and also the distant

objects clearly?

61. A person needs a lens of power -4.5D for

correction of her vision. A) what kind of defect in

vision is she? B) what is the focal length of the

corrective lens? C) what is the nature of the

corrective lens?

62. What is pres-byopia? Give its causes? How can it

be treated?

63. Is the position of a star as seen by us its true

position? Justify

64. Why do we see a rainbow in the sky only after

rainfall?

65. Sun is visible 2 minutes before actual sunrise and 2

minutes after sunset. Give reason.

66. How scattering of light depends upon particle size.

67. Define: a) prism b) angle of prism

c) recomposing of dispersed white light

68. If the far point of eye lens is 1m. Find the power

required to correct the defect.

69. What happens to the eye when you enter a

darkened cinema hall from bright sunshine? Give

reason.

70. Give difference between hypermetropia and

presbyopia.

71. Draw a labeled diagram of rainbow formation. Also

explain the phenomenon of rainbow formation.

72. How do we see objects erect when the eye forms a

real, inverted image of them on its retina?

73. Draw a labeled diagram of human eye. What is the

significance of the blind spot and yellow spot?

74. What are the main parts of a human eye? What are

their functions? How does the eye work?

75. Explain the phenomenon of dispersion of white

light through a glass prism, using suitable diagram.

76. State two main causes of a person developing near

sightedness .with the help of ray diagram, suggest

how he can be helped to overcome his disability.

77. The far point of myopic person is 100cm in front of

the eye, calculate the focal length and power of

lens required to enable him to see distant object

clearly.



COVALENT BOND

The chemical bond formed by the sharing of electrons between two atoms is known as a covalent bond. The

sharing of electrons takes place in such a way that each atom in the resulting molecule gets the stable

electron arrangement of an inert gas.

A covalent bond is formed when both the reacting atoms need electrons to achieve the inert gas electron

arrangement.

Whenever a non-metal combines with another on-metal, sharing of electrons takes place between their

atoms and a covalent bond is formed. A covalent bond can also be formed between two atoms of the same

non-metal. The shared electrons are counted with both the atoms due to which each atom in the resulting

molecule gets an inert gas electron arrangement of 8 electrons (or 2 electrons) in the outermost shell.

Covalent bonds are of three types :

(i) Single covalent bond

(ii) Double covalent bond

(iii) Triple covalent bond.

SINGLE BOND

A single bond is formed by the sharing of one pair of electrons between two atoms. a single covalent

bond is formed by the sharing of 2 electrons between the atoms, each atom contributing one electron for

sharing.

1. Formation of a Chlorine Molecule, CL2

2. Formation of a Hydrogen Molecule, H2

3. Formation of a Hydrogen Molecule, HCl

4. Formation of a Methane Molecule, CH4

5. Formation of a Carbon Tetrachloride Molecule, CCl4

6. Formation of a Water Molecule, H2O

7. Formation of Ammonia Molecule, NH3

Carbon and its compounds



DOUBLE BOND

A double bond is formed by the sharing of two pairs of electrons between two atoms. A double covalent

bond is formed by the sharing of four electrons between two atoms, each atom contributing two electrons

for sharing.

1. Formation of Oxygen Molecule, O2

2. Formation of Carbon Dioxide Molecule, CO2

3. Formation of Ethane Molecule, C2H4

TRIPLE BOND

A triple bond is formed by the sharing of three pairs of electrons between two atoms. A triple bond is

formed by the sharing of six electrons between two atoms, each atom contributing three electrons for

sharing.

1. Formation of a Nitrogen Molecule, N2

2. Formation of Ethyne Molecule, C2H2

PROPERTIES OF COVALENT COMPOUNDS

1. Covalent compounds are usually liquids or gases. Only some of them are solids. For example, alcohol, ether, benzene, carbon disulphide, carbon tetrachloride and bromine are liquids; methane, ethane, ethene, ethyne, and chlorine are gases. Glucose, can sugar, urea, naphthalene and iodine are, however, solid covalent compounds. The covalent compounds are usually liquids or gases due to the weak force of attraction between their molecules.

2. Covalent compounds have usually low melting points and low boiling points. For example, naphthalene has a low melting point of 80°C and carbon tetrachloride has a low boiling point of 77°C.

3. Covalent compounds are usually insoluble in water but they are soluble in organic solvents. For example, naphthalene is insoluble in water but dissolves in organic solvents like ether. Some of the covalent compounds like glucose, sugar and urea, etc., are however, soluble in water. The polar covalent compounds like hydrogen chloride and ammonia are also soluble in water.

4. Covalent compounds do not conduct electricity. This means that covalent compounds are non-electrolytes. Covalent compounds do not conduct electricity because they do not contain ions. For example, covalent compounds like glucose, can sugar, urea, alcohol and carbon tetrachloride, etc., do not conduct electricity (because they do not contain ions).

Why covalent compounds have low melting and boiling points?

Covalent compounds are made up of electrically neutral molecules. So, the force of attraction between the molecules of a covalent compound is very weak. Only a small amount of heat energy is required to break these weak molecular force, due to which covalent compounds have low melting points and low boiling points.



Carbon

Carbon is an element. The symbol of carbon is C. it is a non-metal. The name carbon is derived from the Latin word ‘carbo’ which means ‘coal’. This is because carbon is the

main constituent of coal. The amount of carbon present in the earth’s crust and atmosphere is very small. For example, the

earth’s crust contains only 0.02% carbon in the form of minerals (like carbonates, coal and petroleum, etc.) and the atmosphere has only 0.03% of carbon dioxide gas.

Importance of carbon: 1. All the living things, plants and animals, are made up of carbon based compounds which are called

organic compounds. 2. Our food materials like grains, pulses, sugar, tea, coffee, fruits and vegetables, etc., are carbon

compounds. 3. The materials like cotton, silk, wool, nylon and polyester which are used for making clothes are

carbon compounds. 4. The fuels like wood, coal, kerosene, LPG (Liquefied Petroleum Gas), natural gas, CNG (Compressed

Natural Gas), petrol and diesel which we use for cooking food and running vehicles are carbon compounds. And paper, rubber, plastics, leather, drugs and dyes, are also made of carbon compounds.

How can we test the presence of carbon? Ans: We can test the presence of carbon in a material on the basis of the fact that carbon and its compounds burn in air to give carbon dioxide gas which turns lime water milky. This test can be performed as follows: Burn the given material in air. Pass the gas formed through lime water. If the lime water turns milky, then the given material contains carbon Why does Carbon Always Forms Covalent Bonds? Or Why carbon cannot form ionic bonds? Ans: The atomic number of carbon is 6. The electronic configuration of carbon is K, L 2,4 Carbon atom is very small due to which its outermost electrons are strongly held by the nucleus. So, it is not possible to remove 4 electrons from a carbon atom to give it the inert gas electron arrangement. It is also not possible to add as many as 4 electrons to a carbon atom due to energy considerations, and acquire the inert gas configuration. The carbon atoms have to acquire the inert gas structure of 8-electrons in their outermost shell by the sharing of electrons, therefore carbon always forms covalent bonds. Occurrence of Carbon In Free State, carbon occurs in nature in two forms: diamond and graphite. Another naturally occurring

form of carbon called buckminsterfullerene. In the combined state, carbon occurs in nature in the form of compounds such as:

Carbon dioxide gas in air, Carbonates (like limestone, marble and chalk), Fossil fuels like coal, petroleum and natural gas, Organic compounds like carbohydrates, fats and proteins, and Wood, cotton and wool, etc.

Allotropes of Carbon The various physical forms in which an element can exist are called allotropes of the element. The three allotropes of carbon are:

1. Diamond, 2. Graphite, and 3. Buckminsterfullerene.

Diamond and graphite are the two common allotropes of carbon which are known to us for centuries. Buckminsterfullerene is the new allotrope of carbon which has been discovered recently.



Different properties of Diamond and Graphite Diamond Graphite

Diamond is a colorless transparent substance having extraordinary brilliance (chamak).

Diamond is quite heavy. Diamond is extremely hard. It is the hardest natural

substance known. Diamond does not conduct electricity.

Graphite is a grayish-black opaque substance.

Graphite is lighter than diamond. Graphite is soft and slippery. Graphite conduct electricity.

Similar property of Diamond and Graphite Or How can we show that diamond and graphite is made of carbon? Diamond and graphite burn on strong heating to form carbon dioxide. If we burn diamond and graphite in

oxygen, then only carbon dioxide gas is formed and nothing is left behind. This shows that diamond and graphite is made up of carbon only. The carbon dioxide formed by burning diamond can turn lime water milky.

Structure of Diamond Each carbon atom in the diamond crystal is linked to four other carbon atoms by strong covalent bonds. The four surrounding carbon atoms are at the four vertices (four corners) of regular tetrahedron. Why diamond is hard or rigid? Ans. The diamond crystal is, made up of carbon atoms. Each carbon atom is powerfully bonded to four another carbon atoms by a network of strong covalent bonds. Due to this, diamond structure is very rigid. The rigid structure of diamond makes it a very hard substance. Use. It is the great hardness of diamond which makes it useful for making rock borers for drilling oil wells, etc., and for making glass cutters. Why diamond has high melting point? Ans. The diamond crystal is, made up of carbon atoms. Each carbon atom is powerfully bonded to four another carbon atoms by a network of strong covalent bonds. A lot of heat energy is required to break the network of strong covalent bonds in the diamond crystal due to which melting point of diamond is very high (3700C). Why diamond does not conduct electricity? Ans. A carbon atom has 4 valence electrons in it. In a diamond crystal, each carbon atom is linked to four other carbon atoms by covalent bonds, and hence all the 4 valence electrons of each carbon atom are used up in forming the bonds. Since there are ‘no free electrons’ in a diamond crystal, it does not conduct electricity. Uses of Diamond Since diamond is extremely hard, therefore, it is the right material for cutting and grinding other hard

materials, and for drilling holes in the earth’s rocky layers. Thus, diamonds are used in cutting instruments like glass cutters, saw for cutting marble and in rock drilling equipment. Diamond ‘dies’ are used for drawing thin wires like the tungsten filament of an electric bulb. All these uses of diamond are because of its great hardness.

Diamonds are used for making jewellery. The use of diamonds in making jewellery is because of their extraordinary brilliance, which is due to their great ability to reflect and refract and refract light.

Sharp-edged diamonds are used by eye-surgeons as a tool to remove cataract from eyes with a great precision.

Synthetic diamond Diamonds can be made artificially by subjecting pure carbon to very high pressure and temperature. These

are called synthetic diamonds. The synthetic diamonds are small but are otherwise indistinguishable from natural diamonds which are not

suitable for making jewellery are used in glass cutters, diamond-studded saws and drill bits.



Structure of Graphite Each carbon atom in a graphite layer is joined to three other carbon atoms by strong covalent bonds to form flat layers of hexagonal rings. The various layers of carbon atoms in graphite are held together by weak Vander Waals forces. Why graphite is soft and slippery? Ans. Each carbon atom in a graphite layer is joined to three other carbon atoms by strong covalent bonds to form flat layers of hexagonal rings. The various layers of carbon atoms in graphite are held together by weak Vander Waals forces. Since the various layers of carbon atoms in graphite are joined by weak forces, they can slide over one another. Due to the sheet like structure, graphite is a comparatively soft substance. It is the softness of graphite which makes it useful as a dry lubricant for machine parts. Why graphite is conductor of electricity? Ans. Graphite is a good conductor of electricity. This can be explained as follows: We know that a carbon atom has 4 valence electrons in it. Now, in a graphite crystal, each carbon atom is joined to only three other carbon atoms by covalent bonds. Thus, only the three valence electron of each carbon atom in graphite are used in bond formation. The fourth valence electron of each carbon atom is ‘free’ to move. Due to the ‘presence of free elections’ in a graphite crystal, it conducts electricity. Uses of Graphite Due to its softness, powdered graphite is used as a lubricant for the fast moving parts of machinery. Since

graphite is non-volatile, it can be used for lubricating those machine parts which operate at very high temperatures (where ordinary oil lubricants cannot be used). Graphite can be used as a dry lubricant in the form of graphite powder or mixed with petroleum jelly to form graphite grease. Graphite power can also be missed with lubricant oils.

Graphite is a good conductor of electricity due to which graphite is used for making carbon electrodes or graphite electrodes in dry cells and electric arcs. The black colored ‘anode’ of a dry cell is made of graphite. The carbon brushes of electric motors are also made of graphite.

Graphite is used for making the cores of our pencils called ‘pencil leads’ and black paints. Graphite is black in color and quite soft. So, it marks black lines on paper. Due to this property graphite is used for making the black cores of our pencils called pencil leads. For making pencil leads, graphite is usually mixed with clay.

Buckminsterfullerene Buckminsterfullerene is an allotrope of carbon containing clusters of

60 carbon atoms joined together to form spherical molecules. Since there are 60 carbon atoms in a molecule of buckminsterfullerene, its formula is C60 (C-sixty).

Shape: In Buckminsterfullerene 60 carbon atoms are arranged in interlocking hexagonal and pentagonal rings of carbon atoms. There are twenty hexagons and twelve pentagons of carbon atoms in one molecule of buckminsterfullerene.

Why it is Named as buckminsterfullerene? This allotrope was named buckminsterfullerene after the American architect Buckminster fuller because its structure resembled the framework of domeshaped halls designed by fuller for large international exhibitions. The arrangement of carbon atoms in buckminsterfullerene resembles a football.

Properties of Buckminsterfullerene Buckminsterfullerene is a dark solid at room temperature. Difference in properties of diamiond, graphite and Buckminsterfullerene:



1. Buckminsterfullerene differs from the other two allotropes of carbon, diamond and graphite, in the fact that diamond and graphite are giant molecules which consist of an unending network of carbon atoms, but buckminsterfullerene is a very small molecule made up of only 60 carbon atoms.

2. An important physical property in which the three allotropes of carbon differ is their hardness. Diamond is extremely hard whereas graphite is soft. On the other hand, buckminsterfullerene is neither very hard nor soft.

Similarity in diamond, graphite and Buckminsterfullerene OR how can we show that Buckminsterfullerene is made up or carbon: Just like diamond and graphite, buckminsterfullerene also burns on heating to form carbon dioxide. If we burn buckminsterfullerene in oxygen, then only carbon dioxide is formed and nothing is left behind. The formation of carbon dioxide can be verified by lime water test. This shows that buckminsterfullerene is made up of carbon only. Organic Compounds The compounds of carbon are known as organic compounds. Apart from carbon, most of the organic

compounds contain hydrogen and many organic compounds contain oxygen or other elements. So, most of the organic compound are hydrocarbons (containing only carbon and hydrogen), or their derivatives.

Examples of organic compounds are: Methane (CH4), Ethane(C2H6), Ethene(C2H4), Ethyne(C2H2), Trichloromethane (CHCI3), Ethanol (C2H5OH), Ethanal (CH3CHO), Ethanoic acid (CH3CHOOH), and Urea [CO(NH2)2].

Organic compounds occur in all living things like plants and animals. Why oxides of carbon, carbonates, hydrogencarbonates and carbides are not considered to be

organic compounds: because their properties are very different from those of the common organic compounds.

The study of carbon compounds (such as hydrocarbons and their derivatives) is called organic chemistry. Reason for the Large Number of Organic Compounds (or Carbon Compounds) 1. Carbon is Tetravalent: On carbon atom requires 4 electrons to achieve the eight-electron inert gas

structure, therefore, the valency of carbon is 4. Due to its large valency of 4, a carbon atom can form covalent bonds with a number of carbon atoms as well as with a large number of other atoms such as hydrogen, oxygen, nitrogen, sulphur, chlorine, and may more atoms.

2. Self Combination or catenation: The property of carbon element due to which its atoms can join with one another to form long carbon chains is called ‘catenation’. Example: Octane (C8H18), one of the constituents of petrol, has a chain of 8 carbon atoms, and some of the organic compounds like starch and cellulose contain chains of hundreds of carbon atoms. Carbon atoms combine with one another, three types of chains can be formed. These are: (i) Straight chains, (ii) Branched chains, and (iii) Closed chains or ring type chains.

3. The covalent bonds between the various carbon atoms are very strong and do not break easily. The reason for the formation of strong bonds by the carbon atoms is their small size. Due to the small size of carbon atoms, their nuclei hold the shared pairs of electrons between atoms strongly, leading to the formation of strong covalent bonds. The carbon atoms also form strong covalent bonds with the atoms of other elements such as hydrogen, oxygen, nitrogen, sulphur, chlorine, and many other elements.

Why catenation is considered as back bone for the existence of variety of carbon compounds? The property of self combination of carbon atoms to form long chains is useful to us because it gives rise to an extremely large number of carbon compounds (or organic compounds). This is because a long chain of carbon atoms acts as a backbone to which other atoms can attach in a number of ways to form a very large number of carbon compounds (or organic compounds).



Give an example of an element which shows catenation like carbon. Why there is not the variety of compounds of that element? Silicon element shows some catenation property due to which it forms compounds with hydrogen having chains of up to seven or eight silicon atoms. But due to weak bonds, these compounds are unstable, due to which there are very less compounds of silicon. Types of Organic Compounds

1. Hydrocarbons 2. Haloalkanes (Halogenated hydrocarbons) 3. Alcohols 4. Aldehydes 5. Ketones 6. Carboxylic acids (Organic acids)

HYDROCARBONS A compound made up of hydrogen and carbon only is called hydrocarbon. The most important natural source of hydrocarbons is petroleum (or crude oil) which is obtained from

underground oil deposits by drilling oil wells. The natural gas which occurs above petroleum deposits also contains hydrocarbons.

Types of hydrocarbons. Hydrocarbons are of two types: Saturated hydrocarbons and Unsaturated hydrocarbons.

Saturated Hydrocarbons (Alkanes) A hydrocarbon in which the carbon atoms are connected by only single bonds is called a saturated

hydrocarbon. Saturated hydrocarbons are also called alkanes. An alkane is a hydrocarbon in which the carbon atoms are connected by only single covalent bonds.

Methane (CH4), Ethane (C2H6), propane (C3H8) and butane (C4H10), are all saturated hydrocarbons which contain only carbon-carbon single bonds.

The general formula of saturated hydrocarbons or alkanes is CnH2n+2 where n is the number of carbon atoms in one molecule of the alkane.

Unsaturated Hydrocarbons (Alkenes and Alkynes) A hydrocarbon in which the two carbon atoms are connected by a ‘double bon’ or ‘triple bond’ is called an

unsaturated hydrocarbon. Unsaturated hydrocarbons are of two types:

(i) Those containing carbon-carbon double bonds (alkenes), and (ii) Those containing carbon-carbon triple bonds (alkynes).

Alkenes An unsaturated hydrocarbon in which the two carbon atoms are connected by a double bond is called an

alkene. Thus, alkenes contain a double bond between two carbon atoms which is formed by the sharing of two electron pairs.

The general formula of an alkene is C n H2n where n is the number f carbon atoms in its one molecule. Alkynes An unsaturated hydrocarbon in which the two carbon atoms are connected by a triple bond is called

alkynes. Thus, alkynes contain a triple bond between two carbon atoms which is formed by the sharing of three electron pairs (or six electrons).

The general formula of alkynes is CnH2n-2 where n is the number of carbon atoms in one molecule of the alkyne.

Alkyl Groups The group formed by the removal of one hydrogen atom from an alkane molecule is called an alky group. CYCLIC HYDROCARBONS Hydrocarbons in which the carbon atoms are arranged in the form of ring. Such hydrocarbons are called

cyclic hydrocarbons. The cyclic hydrocarbons may be saturated of unsaturated.



A saturated cyclic hydrocarbon is ‘cyclohexane’. An unsaturated cyclic hydrocarbon is ‘benzene’. NAMING OF HYDROCARBONS The number of carbon atoms in a hydrocarbon (or any other organic compound) is indicated by using the

following stems: One carbon atom is indicated by writing ‘Meth’ Two carbon atoms are indicated by writing ‘Eth’ Three carbon atoms are indicated by writing ‘Prop’ Four carbon atoms are indicated by writing ‘But’ (read as Bute) Five carbon atoms are indicated by writing ‘Pent’ Six carbon atoms are indicated by writing ‘Hex’ Seven carbon atoms are indicated by writing ‘Hept’ Eight carbon atoms are indicated by writing ‘Oct’ Nine carbon atoms are indicated by writing ‘Non’ Ten carbon atoms are indicated by writing ‘Dec’ (read as Dek)

A saturated hydrocarbon containing single bonds is indicated by writing the word ‘ane’ after the stem. An unsaturated hydrocarbon containing a double bond is indicated by writing the word ‘ene’ after the stem. An unsaturated hydrocarbon containing a triple bond is indicated by writing the word ‘yene’ after the stem. Naming of Saturated Hydrocarbons Naming of CH4

IUPAC name : Methane Common name : Methane

Naming of C2H6. IUPAC name : Ethane Common name: Ethane

Naming of C3H6. IUPAC name : Propane Common name : Propane

Naming of C4H10. IUPAC name : Butane Common name: n-butane

Naming of C5H12.

IUPAC name : Pentane Common name: n-pentane

IUPAC Nomenclature for Branched-Chain Saturated Hydrocarbons The longest chain of carbon atoms in the structure of the compound (to be named) is found first. The

compound is then named as a derivative of the alkane hydrocarbon which corresponds to the longest chain of carbon atoms (This is called parent hydrocarbon).

The alkyl groups present as side chains (braches) are considered as substituents and named separately as methyl (CH3—) or ethyl (C2H5—) groups.

The carbon atoms of the longest carbon chain are numbered in such a way that the alkyl groups (substituents) get the lowest possible number (smallest possible number).

The position of alkyl group is indicated by writing the number of carbon atom to which it is attached. The IUPAC name of the compound is obtained by writing the ‘position and name of alkyl group’ just before

the name of ‘parent hydrocarbon’.



Naming of Unsaturated Hydrocarbons Containing a Double Bond Naming of C2H4.’ IUPAC name : Ethene Common name: Ethylene Naming of C3H6. IUPAC name : Propene Common name : Propylene Naming of Unsaturated Hydrocarbons Containing a Triple Bond Naming of C2H2. IUPAC name : Ethyne Common name : Acetylene Naming of C3H4. IUPAC name : Propyne Common name : Mehyl-acetylene ISOMERS The organic compounds having the same molecular formula but different structures are known as isomers. The existence of two (or more) different organic compounds having the same molecular formula but

different structures is called isomerism. Why isomerism is only possible with hydrocarbons containing more than 4 carbon atoms?

Isomerism is possible only with hydrocarbons having 4 or more carbon atoms, because only then we can have tow or more different arrangement of carbon atoms. No isomerism is possible in hydrocarbons containing 1,2 or 3 carbon atoms per molecule because then only one arrangement carbon atoms is possible. For example, no isomerism is possible in methane, ethane and propane because they contain only one, two or three carbon atoms respectively.

ISOMERS OF BUTANE, PENTANE AND HEXANE



FUNCTIONAL GROUPS An’ atom’ or ‘a group of atoms’ which makes a carbon compound (or organic compound) reactive and decides its properties (or functions) is called a functional group. HALOALKANES When one hydrogen atom of an alkane is replaced by halogen atom, we get haloalkane (also called halogenoalkane). The general formula of haloalkanes is CnH2n+1-X (where X represents Cl, Br or I). Naming of Haloalkanes Name CH3Cl by IUPAC method. The IUPAC name of CH3Cl is chloromethane. The common name of chloromethane (CH3Cl) is methyl chloride. Name C2H5Cl by IUPAC method. The IUPAC name of C2H5Cl becomes chloroethane. The common name of chloroethane is ethyl chloride. Name C3H7Cl by IUPAC method. The IUPAC name of C3H7Cl becomes chloropropane. The common name of chloropropane (C3H7Cl) is propyl chloride. ALCOHOLS The hydroxyl group attached to a carbon atom is known as alcohol group. The general formula CnH2n+1—OH. Naming of Alcohols Name the compound CH3OH by IUPAC method The IUPAC name of CH3OH is methanol. The common name of methanol is methyl alcohol. Name C2H5OH by IUPAC method. The IUPAC name of C2H5OH is ethanol. The common name of ethanol is ethyl alcohol. Name C3H7OH by IUPAC method. The IUPAC name of C3H7OH is propanol. The common name of propanol is propyl alcohol.



ALDEHYDES The general molecular formula of aldehydes is CnH2no. Naming of Aldehydes The compound HCHO by IUPAC method. The IUPAC name of HCHO is methanal. The common name of methanal is formaldehyde. The compound CH3CHO by IUPAC method. The IUPAC name of CH3CHO is ethanal. The common name of ethanal is acetaldehyde. The compound C2H5CHO can be named. The IUPAC name of C2H5CHO is propanal. The common name of propanal (CH3CH2CHO) is propionaldehyde. KETONES Ketones are the carbon compounds (or organic compounds) containging the ketone group, -CO– group. The general molecular formula of ketones is CnH2nO. Naming of Ketones The IUPAC name of CH3COCH3 is propanone. The common name of propanone is acentone. Propanone is the simplest ketone. The compound CH3COCH2CH3 by IUPAC method. The IUPAC name of the compound CH3COCH2CH3 is butanone. The common name of butanone is ethyl methyl ketone. The compound CH3COCH2CH2CH3 by IUPAC method. IUPAC name of the compound CH3COCH2CH2CH3 is pentanone. The common name of pentanone is methyl proply ketone. CARBOXYLIC ACIDS (OR ORGANIC ACIDS) The general molecular formula of ketones is CnH2nO2 Naming of Carboxylic Acids (or Organic Acids) The compound HCOOH by IUPAC method IUPAC name of HCOOH is methanoic acid. The common name of methanoic acid (HCOOH) is formic acid.



The compound CH3COOH by IUPAC method The IUPAC name of CH3COOH is ethanoic acid. The common name of ethanoic acid (CH3COOH) is acetic acid. The compound CH3CH2COOH by IUPAC method The IUPAC name is propanoic acid. The common name is propionic acid. HOMOLOGOUS SERIES A homologous series is a group of organic compounds having similar structures and similar chemical

properties in which the successive compounds differ by CH2 group. Characteristics of a Homologous Series 1. All the members of a homologous series can be represented by the same general formula. 2. Any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.

That is, any two adjacent homologues differ by a CH2 group. 3. The difference in the molecular masses of any two adjacent homologues is 14 u. 4. All the compounds of a homologous series show similar chemical properties. 5. The members of a homologous series show a gradual change in their physical properties with increase in

molecular mass. COAL AND PETROLEUM A fuel is a material that has energy stored inside it. When a fuel is burned, the energy is released mainly as

heat (and some light). This heat energy can be used for various purposes like cooking food, heating water, and for running generators in thermal power stations, machines in factories and engines of motor cars.

Coal Define: Coal is complex mixture of compounds of carbon, hydrogen and oxygen, and some free carbon.

Small amounts of nitrogen and sulphur compounds are also present in coal. Where it is found: It is found in deep coal mines under the surface of earth. How Coal was Formed: Coal was formed by the anaerobic decomposition of large land plants and trees

buried under the earth millions of years ago. It is believed that millions of years ago, due to earthquakes and volcanoes, etc., the forests were buried under the surface of the earth and got covered with sand, clay and water. Due to high temperature and high pressure inside the earth, and in the absence of air, wood was converted into coal.

Petroleum Define: Petroleum is dark colored, viscous, and foul smelling crude oil. The name petroleum means rock oil

(petra = rock; oleum =oil). It is called petroleum because it is found under the crust of earth trapped in rocks.

The crude oil petroleum is a complex mixture of several solid, liquid and gaseous hydrocarbons mixed with water, salt and earth particles. Thus, the crude petroleum oil is not a single chemical compound, it is a mixture of compounds. The fuels such as petrol, kerosene, diesel and LPG are obtained from petroleum.

How Petroleum was Formed: Petroleum oil (and natural gas) were formed by the anaerobic decomposition of the remains of extremely small plants and animals buried under the sea millions of years ago. It is believed that millions of years ago, the microscopic plants and animals which lived in seas, died. Their bodies sank to the bottom of the sea and were soon covered with mud and sand. The chemical effects of pressure, heat and bacteria, converted the remains of microscopic plants and animals into petroleum oil and natural gas. This conversion took place in the absence of oxygen or air. The petroleum thus formed got trapped between two layers of impervious rocks (non-porous rocks) forming an oil trap. Natural gas is above this petroleum oil.



Why do Substances Burn with a Flame or without a Flam All the gaseous fuels burn with a flame but only those solid and liquid fuels which vaporize on heating (to

form a gas), burn with a flame. For example, cooking gas (LPG) is a gaseous fuel which burns with a flame but wax and kerosene oil are solid and liquid fuels respectively, which vaporize ( or form gas) on heating and hence burn with a flame.

Types of flames Flames are of two types : blue flame and yellow flame. On which factor does the type of flame depends: When fuels burn, the type of flame produced depends

on the proportion of oxygen (of air) which is available for the burning of fuel or combustion of fuel. Blue flame: When the oxygen supply (or air supply) is sufficient, then the fuel burns completely producing

a blue flame. This blue flame does not produce much light, so it is said to be non luminous (or non light-giving) flame.

Yellow flame: When the oxygen supply (or air supply) is insufficient, then the fuels burn incompletely producing mainly a yellow flame. The yellow color of flame is caused by the glow of hot, unburnt carbon particles produced due to the incomplete combustion of fuel. This yellow flame produces light, so it is said to be a luminous (light-giving) flame.

Blue flame in Gas stove: In a gas stove, cooking gas (LPG) burns with a blue, non-luminous flame. The gas stove has holes (or inlets) for air to mix properly with cooking gas. The cooking gas gets sufficient oxygen from this air and hence burns completely producing a blue flame. Thus, complete combustion of cooking gas takes place in a gas stove.

Yellow flame in candle: When a candle is lighted, the wax melts, rise up the wick and gets converted into vapours. In candle, there is no provision for the proper mixing of oxygen (of air) for burning wax vapours. So, in a candle the wax vapours burn in an insufficient supply of oxygen (of air) which leads to incomplete combustion of wax. The incomplete combustion of wax in a candle produces small unburnt carbon particles. These solid carbon particles rise in the flame, get heated and glow to give out yellowish light.

Which fuels do not burn with flame: Those solid and liquid fuels which do not vaporize on heating, burn without producing a flame. For example, coal and charcoal burn in an ‘angithi’ without producing a flame. They just glow red and give out heat.

Burning of “coal and charcoal” or “angithi”: Coal and charcoal contain some volatile substances. So, when coal or charcoal is ignited, the volatile substances present in them vaporize and they burn with a flame in the beginning. When all the volatile substances present in coal and charcoal get burnt, then the remaining coal or charcoal just glows red and gives heat without producing any flame.

CHEMICAL PROPERTIES OF CARBON COMPOUNDS 1. Combustion (or Burning) Define: The process of burning of a carbon compound in air to give carbon dioxide, water, heat and light, is

known as combustion. Combustion is also called burning. Why alkanes are excellent fuels: Alkane burn in air to produce a lot of heat due to which alkanes are

excellent fuels. Example: When methane (natural gas) burns in a sufficient supply of air, then carbon dioxide and water vapour are formed, and a lot of heat is also produced.

CH4 + 2O2 combustion CO2 + 2H2O + Heat + Light

Methane + Oxygen Carbon dioxide + Water + heat + light (Natural gas) (from air) Why LPG is an excellent fuel: The cooking gas (LPG) burns in air in the burner of gas stove, then it forms

carbon dioxide and water vapour, with the evolution of a lot of heat (and some light). Due to this, butane (or LPG) is an excellent fuel.

Why Carbon and its compounds are used as fuels because they burn in air releasing a lot of heat energy. The saturated hydrocarbons (alkanes) generally burn in air with a blue, non-sooty flame. This

because the percentage of carbon in the saturated hydrocarbon is comparatively low which gets oxidized completely by the oxygen present in air.

Incomplete combustion of saturated hydrocarbons: If, however, the supply of air (and hence oxygen) for burning is reduced (or limited), then incomplete combustion of even saturated hydrocarbons will take place and they will burn producing a yellow sooty flame.



The gas stove (and kerosene stove) used in our homes have tiny holes (or inlets) for air so that sufficient oxygen of air is available for the complete burning of fuel to produce a smokeless blue flame.

If the bottom of the cooking utensils in our homes are getting blackened, it shows that the air holes of the gas stove (or kerosene stove) are getting blocked and the fuel is not burning completely.

The unsaturated by hydrocarbons (alkenes and alkynes ) burn in air with a yellow, sooty flame (producing black smoke). For example, ethane and ethyne burn in air with a sooty flame. The unsaturated hydrocarbons (alkenes and alkynes ) burn with a sooty flame because the percentage of carbon in unsaturated hydrocarbons is comparatively higher (than that of alkanes), which does not get oxidesed completely in the oxygen of air.

Can unsaturated hydrocarbons burn with blue flame: If unsaturated hydrocarbons are burned in pure oxygen, then they will burn completely producing a blue flame (without any smoke at all).

Mixture of acetylene (ethyne) and pure oxygen: If a mixture of acetylene (ethyne) and pure oxygen is burned, then acetylene burns completely producing a blue flame. The oxygen – acetylene flame (called oxy-acetylene flame) is extremely hot and produces a very high temperature which is used for welding metals.

A mixture of acetylene (ethyne) in air produces a sooty flame (due to incomplete combustion), which is not hot enough to melt metals for welding.

Disadvantages of incomplete combustion of fuels: 1. Incomplete combustion in insufficient supply of air, leads to unburnt carbon in the form of soot which

pollutes the atmosphere, blackens cooking untensils, and blocks chimneys in factories. 2. The incomplete combustion also leads to the formaton of an extremely poisonous gas called carbon

monoxide. 3. The incomplete combustion of fuel produces less heat than that produced by complete combustion.

2. Substitution Reactions Saturated hydrocarbons, however, undergo substitution reactions with chlorine in the presence of sunlight. Define: The reaction in which one (of more) hydrogen atoms of a hydrocarbon are replaced by some other

atoms (like chlorine), is called a substitution reaction. If the substitution of hydrogen atoms takes place by chlorine, it is also called chlorination. Substitution reactions (like chlorination) are a characteristic property of saturated hydrocarbons or alkanes

(Unsaturated hydrocarbons do not give substitution reactions with halogens, they give addition reactions). Substitution Reaction of Methane with Chlorine.

CH4 + Cl2 sunlight CH3Cl + HCl

Methane + Chlorine Chloromethane (or Methyl chloride) + Hydrogen chloride We can obtain three more compounds: Dichloromethane or Methyl dichloride, CH2Cl2, Trichlomethane or

Chloroform, CHCl3 and Tetrachloromethane or Carbon tetrachloride, CCl4. 3. Addition Reactions Addition reactions (like the addition of hydrogen, chlorine or bromine) are a characteristic property of

unsaturated hydrocarbons. Addition reactions are given by all unsaturated hydrocarbons containing a double bond or a triple bond. That is, addition reactions are given by all the alkenes and alkynes (like ethane and ethyne).

Addition Reaction of Ethene with Hydrogen.

CH2 =CH2 + H2 Ni catalyst

Heat CH3 – CH3

Ethene Hydrogen Ethene The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydrocarbon is called

hydrogenation. The process of hydrogenation takes place in the presence of nickel or palladium metals as catalyst.

Industrial application of hydrogenation: It is used to prepare vegetable ghee (vanaspati ghee) oils. Hydrogenation of Oils (The addition of hydrogen (or hydrogenation) to the vegetable oils leads to the formation of vegetable ghee or vanaspati ghee) The vegetable oils (like groundnut oil, cotton seed oil and mustard oil) are unsaturated compounds

containing double bonds. They are in the liquid state at room temperature. Due to the presence of double



bonds, vegetable oils undergo addition of hydrogen just like alkenes to form saturated products called vegetable ghee or vanspati ghee which are solid (or semi-solid) at the room temperature.

Vegetable oils containing unsaturated fatty acids are good for our health. The common cooking oils are sunflower oil, kardi oil, soyabean oil and groundnut oil. The saturated fats like vegetable ghee, obtained by the hydrogenation of oils, are not good for health. The animal fats (like butter and desi ghee) are also saturated fats containing saturated fatty acids which are

said to be harmful for health. Test to distinguish between saturated and unsaturated hydrocarbons Bromine water has a red-brown color due to the presence of bromine in it. All the unsaturated compounds (alkenes and alkynes, etc.) declourise bromine water but saturated

compounds (alkanes) do not decolourise bromine water. Distinguish between cooking oil and butter: We can distinguish chemically between a cooking oil and

butter by the bromine water test. Add bromine water to a little of cooking oil and butter taken in separate test-tubes. Cooking oil decolourises bromine water (showing that it is an unsaturated compound). Butter does not declourise bromine water (showing that it is a saturated compound).

SOME IMPORTANT CARBON COMPOUNDS Two commercially important carbon compounds (or organic compounds) : Ethanol and Ethanoic acid. ETHANOL (OR ETHYL ALCOHOL) Ethanol is the second member of the homologous series of alcohols (the first member being methanol). The

formula of ethanol is C2H5OH (which can also be written as: CH3—CH2OH or CH3—CH2—OH). The common name of ethanol is ethyl alcohol. Ethanol is the most common and most widely used alcohol and sometimes ethanol is also called just alcohol.

Physical Properties of Ethanol Ethanol is colorless liquid having a pleasant smell and a burning taste. Ethanol is a volatile liquid having a low boiling point 78oC (351 K). It is lighter than water. Ethanol mixes with water in any proportion. The solubility of ethanol in water is due to the presence of

hydroxyl group in it. Ethanol is a covalent compound. Ethanol does not contain any hydrogen ions, so it is a neutral compound.

Thus, ethanol has no effect on any litmus solution. Rectified spirit Ethanol containing 5 per cent water is called rectified spirit. Rectified spirit is the commercial alcohol.

100% pure ethanol is called absolute alcohol. Chemical Properties of Ethanol 1. Combustion. Ethanol is a highly inflammable liquid. It catches fire easily and starts burning. Ethanol burns readily in air

to form carbon dioxide and water vapour, and releasing a lot of heat and light:

C2H5OH + 3O2 combustion 2CO2 + 3H2O + Heat & light

Ethanol + Oxygen Carbon + Water vapour (Ethyl (From air) dioxide alcohol) Ethanol as a Fuel A material which is burnt to obtain heat is called a fuel. Since ethanol burns with a clear flame giving a lot of

heat, therefore, it is used as a fuel. Some countries add ethanol to petrol to be used as a fuel in cars. Thus, ethanol is used as an additive in petrol. In Brazil, a mixture of ethanol and petrol is used as a fuel for cars.



Ethanol is a clean fuel because it gives only harmless products carbon dioxide and water vapour on burning. It does not produce any poisonous gas like carbon monoxide. So the addition of ethanol to petrol has the advantage of reducing the emission of carbon monoxide from cars.

Production of ethanol: Ethanol is produced on a large scale from sugar cane crop. Sugar cane juice is used to obtain sugar by the process of crystallization. After the crystallization of sugar from concentrated sugar cane juice, a thick, dark brown liquid called molasses is left behind. Molasses still contains about 30% of sugar which could not be separated by crystallization. Ethanol is produced by the fermentation (breakdown by enzymes) of the cane sugar present in molasses.

Oxidizing agents A substance which gives oxygen (for oxidation) is called an oxidizing agent. Alkaline potassium

permanganate and acidified potassium dichromate are strong oxidizing agents (because they provide oxygen for oxidizing other substances).

An aqueous solution of potassium permanganate containing sodium hydroxide is called alkaline potassium permanganate solution. Thus, alkaline potassium permanganate solution is KMnO4+ NaOH.

The potassium dichromate solution containing sulphuric acid is called acidified potassium dichromate solution. In other words, acidified potassium dichromate solution is K2Cr2O7+ H2SO4.

2. Oxidation Oxidation ‘means controlled combustion’. When ethanol is heated with alkaline potassium permanganate

solution (or acidified potassium dichromate solution), it gets oxidized to ethanoic acid.

C2H5OH + 2[O]

4

2 2 7

alkaline KMnOor acidified K Cr O

heat

CH3COOH + H2O

Ethanol + Nascent Ethanoic acid(Acetic acid) + Water (Ethyl oxygen alcohol) (from oxidizing agent) This reaction can be carried out by adding a 5 per cent aqueous solution of potassium permanganate in

sodium hydroxide solution to ethanol dropwise till the purple color of potassium permanganate solution longer disappears. On warming the test-tube containing ethanol and alkaline potassium permanganate solution gently in a hot water bath, ethanol is oxidized to ethanoic acid. Thus, ethanoic acid is formed by the oxidation of ethanol by using a strong oxidizing agent. This ethanoic acid (or acetic acid) formed by the oxidation of ethanol can turn blue litmus to red.

3. Reaction with Sodium Metal. Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas. 2C2H5OH + 2Na 2C2H5𝑂

−𝑁𝑎+ + H2 Ethanol Sodium Sodium ethoxide Hydrogen (Ethyl alcohol) This reaction is used as a test for ethanol. When a small piece of sodium metal is put into ethanol in a dry

test-tube, rapid effervescence due to the evolution of hydrogen gas is produced. The hydrogen gas produced can be tested by burning. When a burning splinter is brought near the mouth of the test-tube, the gas burns with a ‘pop’ sound, which is a characteristic of hydrogen gas.

4. Dehydration Dehydration an alcohol means removal of water molecule from it. When ethanol is heated with excess of

concentrated suphuric acid at 170oC (443 K), it gets dehydrated to form ethane (which is an unsaturated hydrocarbon):

C2H5OH 2 4

o

conc H SO

170 C

CH2=CH2 + H2O

Ethanol (Dehydration) Ethene Water (Ethyl alcohol) Concentrated sulphuric acid acts as a dehydrating agent (which removes water molecule from the ethanol

molecule).



5. Reaction with Ethanoic Acid (Formation of Ester). Ethanol reacts with ethanoic acid on warming in the presence of a few drops of concentrated sulphuric acid

to form a sweet smelling easter, ethyl ethanoate.

CH3COOH + C2H5OH 2 4conc H SO

heat

CH3COOC2H5 + H2O

Ethanoic Ethanol Ethyl ethanoate + water acid (Ethyl alcohol) (Ethyl acetate) (Acetic acid) (Sweet smelling ester) The reaction in which a carboxylic acid combines with an alcohol to form an ester is called esterification.

Esterification takes place in the presence of a catalyst like concentrated sulphuric acid. Test for an Alcohol Sodium metal Test. Add a small piece of sodium metal to the organic liquid (to be tested), taken in a dry

test-tube. If bubbles (or effervescence) of hydrogen gas are produced, it indicates that the given organic liquid is an alcohol.

Ester Test for Alcohols. The organic compound (to be tested) is warmed with some glacial ethanoic acid and a few drops of concentrated sulphuric acid. A sweet smell (due to the formation of ester) indicates that the organic compound is an alcohol.

Uses of Ethanol (Ethyl Alcohol) Ethyl alcohol (ethanol) is used in the manufacture of paints, varnishes, lacquers, medicines, perfumes, dyes,

soaps and synthetic rubber. Ethyl alcohol (ethanol) is used as a solvent. Many organic compounds which are insoluble in water, are

soluble in ethyl alcohol. Being a good solven, ethyl alcohol (ethanol) is used in medicines such as tincture iodine, cough syrups and

may tonics. Ethyl alcohol (ethanol) is used as a fuel in cars alongwith petrol. It is also used as a fuel in spirit lamps. Ethyl alcohol (ethanol) is used in alcoholic drinks (beverages) like whisky, wine, beer and other liquors.

Whisky contains about 35% of ethyl alcohol, wine contains 10% to 20% of ethyl alcohol, and beer contains about 6% of ethyl alcohol.

Ethyl alcohol (ethanol) is used as an antiseptic to sterilize wounds and syringes in hospitals and dispensaries.

Harmful Effects of Drinking Alcohol Alcohol slows down the activity of the nervous system and the brain due to which the judgment of a person

is impaired and his ‘reaction’ becomes slow. So, a person driving a car under the influence of alcohol cannot judge a situation properly and act quickly in case of an emergency. In this way, drunken driving leads to increased road accidents

Alcohol drinking lowers inhibitions (mental restrain) due to which a drunken man becomes quarrelsome. This leads to quarrels and fights which increases violence and crime in society.

Drinking alcohol heavily on a particular occasion leads to staggered movement, slurred speech (unclear speech), blurred vision, dizziness, and vomiting. Drinking of large quantities of alcohol makes a man unconscious. He may even die.

Heavy drinking of alcohol makes a person alcoholic (addicted to alcohol). This makes the person financially bankrupt (diwaliya).

Heavy drinking of alcohol over a long period of time can damage the stomach, liver, heart and even brain. The liver disease known as ‘cirrhosis’ caused by alcohol can lead to death.

The drinking of adulterated alcohol containing methyl alcohol (methanol), causes severe poisoning leading to blindness and even death.

Denatured Alcohol (or Denatured Ethanol) Why alcohol is denatured: To prevent the misuse of industrial alcohol for drinking purposes (or black

marketing), ethyl alcohol meant for industrial purposes is denatured by adding small amounts of poisonous substances like methanol, pyridine or copper sulphate, etc. The addition of these poisonous substances makes the ethyl alcohol unfit for drinking.

Define: Denatured alcohol is ethyl alcohol which has been made unfit for drinking purposes by adding small amounts of poisonous substances like methanol, pyridine, copper sulphate, etc.



Harmful effect of drinking Methanol Effect: When taken internally, methanol is a poison. So, unlike ethanol, drinking methanol even in very

small quantity can cause severe poisoning leading to blindness and even death. How methanol affects our body: Methanol damages the optic nerve causing permanent blindness in a

person. Methanol is oxidized to methanol in the liver of a person. This methanol reacts rapidly with the components of the cells causing coagulation of their protoplasm. Due to this the cells stop functioning normally. This leads to the death of the person who drinks methanol.

ETHANOIC ACID (OR ACETIC ACID) Ethanoic acid is a colorless liquid having a sour taste and a smell of vinegar. The boiling point of ethanoic acid is 118oC (391K). When pure ehtanoic is cooled, it freezes to form a colorless, ice-like solid (which looks like a glacier). Due to

this, pure ethanoic acid is called glacial ethanoic acid (or glacial acetic acid). Ethanoic acid is miscible with water in all proportions. Chemical Properties of Ethanoic Acid 1. Action on Litmus. Ethanoic acid is acidic in nature. Being acidic in nature, ethanoic acid turns blue litmus

solution red. In fact, all the carboxylic acids turn blue litmus to red. Dilute ethanoic acid turns universal indicator paper to orange, showing that its pH is about 4. This tells us that ethanoic acid is a weak acid.

2. Reaction with Carbonates and Hydrogencarbonates. Or Reaction with Sodium Carbonate Ethanoic acid reacts with sodium carbonate to form sodium ehtanoate and carbon dioxide gas.

2CH3COOH + Na2CO3 2CH3COONa + CO2 + H2O Ethanoic Sodium Sodium Carbon Water Acid carbonate ethanoate dioxide (Acetic acid) (Sodium acetate)

When sodium carbonate is added to a solution of ethanoic acid, brisk effervescence of carbon dioxide is given off. The salt formed in this reaction is sodium ethanoate. The common name of sodium ethanoate is sodium acetate. Reaction with Sodium Hydrogencarbonate(sodium bicarbonate) Ethanoic acid reacts with sodium hydrogencarbonate to evolve brisk effervescence of carbon dioxide gas:

CH3COOH + NaHCO3 CH3COONa + CO2 + H2O Ethanoic Sodium Sodium Carbon Water Acid bicarbonate ethanoate dioxide (Acetic acid) (Sodium acetate)

This reaction is used as test for ethanoic acid (or acetic acid).

3. Reaction with Sodium Hydroxide Ethanoic acid reacts with bases (or alkalis) to form salts and water. For example, ethanoic acid reacts with sodium hydrxide to form a salt called sodium ethanoate and water:

CH3COOH + NaOH CH3COONa + H2O Ethanoic Sodium Sodium Water Acid hydroxide ethanoate 4. Reaction with Alcohol:

Ethanoic acid reacts with alcohols in the presence of a little of concentrated sulphuric acid to form esters. Fro example, when ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid, a sweet smelling ester called ethyl ethanoate is formed:

CH3COOH + C2H5OH 2 4conc H SO

heat

CH3COOC2H5 + H2O

Ethanoic Ethanol Ethyl ethanoate + water acid (Ethyl alcohol) (Ethyl acetate) (Acetic acid) (Sweet smelling ester)

The reaction of a carboxylic acid with an alcohol to form an ester is called esterification.



Use of esters: Esters are usually volatile liquids having sweet smell or peasant smell. They are also said to have fruity smell. Esters are used in making artificial perfumes (artificial scents). This is because of the fact that most of the esters have a pleasant smell. Esters are also used as flavouring agents. This means that esters are used in making artificial flavours and essences used in ice-cream, sweets and cold drinks.

Hydrolysis of Esters When an ester is heated with sodium hydroxide solution then the ester gets hydrolysed (breaks down) to

form the parent alcohol and sodium salt of the carboxylic acid. For example, when ethyl etthanoate ester is boiled with sodium hydroxide solution, then sodium ethanoate and ethanol are produced.

CH3COOC2H5 + NaOH heat CH3COONa + C2H5OH

Ethyl Sodium Sodium Ethanol ethanoate hydroxide ethanoate (Ethyl acetate) (sodium acetate) The alkaline hydrolysis of esters (using alkali like sodium hydroxide) is known as saponification (soap

making). This is because of the fact that this reaction is used for the preparation of soaps. When the esters of higher fatty acids with glycerol (oil and fats) are hydrolysed with sodium hyroxide solution, we get sodium salts of higher fatty acids which are called soaps.

Test for Carboxylic Acid 1. Sodium Hydrogencarbonate Test. The organic compound (to be tested) is taken in a test-tube and a pinch

of sodium hydrogencarbonate is added to it. Evolution of carbon dioxide gas with brisk effervescence shows that the given organic compound is a carboxylic acid.

2. Ester Test for Acids. The organic compound (to be tested) is warmed with some ethanol and 2 or 3 drops of concentrated sulphuric acid. A sweet smell (due to the formation of ester) shows that the organic compound is a carboxylic acid.

3. Litmus Test. Some blue litmus solution is added to the organic compound (to be tested). If the blue litmus solution turns red,it shows that the organic compound is acidic in nature and hence it is a acidic in nature and hence it is a carboxylic acid.

Uses of Ethanoic Acid (or Acetic Acid) Dilute ethanoic acid (in the form of vinegar) is used as food preservative in the preparation of pickles and

sauces (like tomato sauce). As vinegar, it is also used as an appetizer for dressing food dishes. Ethanoic acid is used for making cellulose acetate which is an important artificial fiber. Ethanoic acid is used in the manufacture of acetone (propanone) and esters used in perfumes. Ethanoic acid is used in the preparation of dyes, plastics and pharmaceuticals. Ethanoic acid is used to coagulate rubber from latex. SOAPS AND DETEGENTS Ay substance which has cleansing action in water is called a detergent. There are two types of detergents: soapy and non-soapy. In everyday language, soapy detergents are

called soaps and non-soapy detergents are called ‘synthetic detergents’ or just detergents’ Soaps and detergents are used for washing clothes (laundry), cleaning our body(sanitation), shaving

soaps, hair shampoos, cleaning utensils and in textile manufacture. SOAPS A soap is the sodium (or potassium salt) of a long chain carboxylic acid (fatty acid) which has cleaning

properties in water. A soap has large non-ionic hydrocarbon group and an ionic group, CO𝑂−𝑁𝑎+. Examples of the soaps are : Sodium stearate and Sodium palmitate.

Sodium Stearate, C17H35CO𝑂−𝑁𝑎+. Sodium stearate ‘soap’ is the sodium salt of a long chain saturated fatty acid called stearic acid. C17H35COOH. Sodium stearate soap has a long alkyl group C17H35 and an ionic carboxylate group CO𝑂−𝑁𝑎+.

Sodium Palmitate, C15H31CO𝑂−𝑁𝑎+. Sodium palmitic acid, C15H31COOH. A soap solution turns red litmus paper to blue.



Manufacture of Soap Soap is made from animal fat or vegetable oils. Fats and vegetable oils are naturally occurring esters of

higher fatty acids (long chain carboxylic acids) and an alcohol called glycerol. When fats and oils (obtained from animals and plants) are heated with sodium hydroxide solution, they split to form sodium salt of higher fatty acid (called soap) and glycerol.

Soap is made by heating animal fat or vegetable oil with concentrated sodium hydroxide solution (caustic soda solution). The fats or oils react with sodium hydroxide to form soap and glycerol.

Fat or Oil + Sodium hydroxide heat Soap + Glycerol

(An ester) ( An alkali) (Sodium salt of fatty acid) ( An alcohol) Preparation of Soap in Laboratory (or at Home) The main raw materials required for preparing soap in a school laboratory or at home are: (i) Vegetable oil (like Castor oil, Cottonseed oil, Linseed oil or Soyabean oil) (ii) Sodium hydroxide (Caustic soda) (iii) Sodium chloride (Common salt) Why Common Salt (Sodium Chloride) is Added in Soap Making Common salt is added to the mixture to make the soap come out of solution. Though most of the soap separates out on its own but some of it remains in solution. Common salt is added to precipitate out all the soap from the aqueous solution. Actually, when we add common salt to the solution, then the solubility of soap present in it decreases, due to which all the soap separates out from the solution in the form of a solid. Structure of a Soap Molecule A soap molecule is made up of two parts: a long hydrocarbon part and a short ionic part containing –

CO𝑂−𝑁𝑎+ group.

The long hydrocarbon chain is hydrophobic (water-repelling), so the hydrocarbon part of soap molecule is

hydrophobic (insoluble in water) but soluble in oil and grease. The ionic portion of the soap molecule is hydrophilic (water-attracting) due to the polar nature of water molecules.

The ionic portion of soap molecule is soluble in water but insoluble in oil and grease. Micelle formation The hydrocarbon part of the soap molecule

is soluble in oil or grease, so it can attach to the oil and grease particles present on dirty clothes. On the other hand, the short ionic part of the soap molecule (having negative charge) is soluble in water, so it can attach to the water particles (in which the soap is dissolved and dirty cloth is dipped).

A ‘spherical aggregate of soap molecules’ in the soap solution in water is called a ‘micelle’.

Cleansing Action of Soap When soap is dissolved in water, it forms a

colloidal suspension in water in which the soap molecules cluster together to form spherical micelles. In a soap micelle, the soap molecules are arranged radially with hydrocarbon ends directed towards the centre and ionic ends directed outwards (The ionic ends are directed outwads because negative charges at the ends repel one another).



When a dirty cloth is put in water containing dissolved soap, then the hydrocarbon ends of the soap molecules in the micelle attach to the oil or grease particles present on the surface of dirty cloth. In this way the soap micelle entraps the oily or greasy particle by using its hydrocarbon ends.

The ionic ends of the soap molecules in the micelles, however, remain attached to water . When the dirty cloth is agitated in soap solution, the oily and greasy particles present on its surface and

entrapped by soap micelles get dispersed in water due to which the soap water becomes dirty but the cloth gets cleaned. The cloth is cleaned thoroughly by rinsing in clean water a number of times.

Why micelle formation only takes place in ionic solution but not in organic solution? Micelle formation takes place when soap is added to water because the hydrocarbon chains of soap

molecules are hydrophobic (water repelling) which are insoluble in water, but the ionic ends of soap molecules are hydrophilic ( water attracting) and hence soluble in water.

Micelle formation will not take place when soap is added to organic solvents like ethanol because the hydrocarbon chains of soap molecules are soluble in organic solvents like ethanol.

Limitation of Soap When soap is used for washing clothes with hard water, a large amount of soap is wasted in reacting with

the calcium and magnesium ions of hard water to form an insoluble precipitate called scum, before it can be used for the real purpose of washing. So, a larger amount of soap is needed for washing clothes when the water is hard.

The scum (or curdy precipitate) formed by the action of hard water on soap, sticks to the clothes being washed and interferes with the cleaning ability of the additional soap. This makes the cleaning of clothes difficult.

DETERGENTS Detergents are also called ‘soap-less soaps’ because though they act like a soap in having the cleansing

properties, they do not contain the usual ‘soaps’ like sodium stearate, etc. detergents are better cleansing agents than soaps because they do not form insoluble calcium and magnesium salts with hard water, and hence can be used for washing even with hard water. Unlike soap, a detergent can lather well even with hard water.

We would not be able to check whether a sample of water is hard by using a detergent (because a detergent forms lather easily even with hard water)

A detergent is the sodium salt of a long chain benzene sulphonic acid (or the sodium salt of a long chain alkyl hydrogensulphate) which has cleansing properties in water. A detergent has large non-ionic hydrocarbon group and an ionic group like sulphonate group,S𝑂3

−𝑁𝑎+, or sulphate group S𝑂4−𝑁𝑎+

Example of detergents: Sodium n-dodecyl benzene sulphonate CH3—(CH2)11—C6H4—𝑆𝑂3−𝑁𝑎+ (A

common detergent) and sodium n-dodecyl sulphate CH3—(CH2)10—CH2— S𝑂4−𝑁𝑎+ (Another detergent)

Differences between Soaps and Detergents Soaps Detergent 1. Soaps are the sodium salts (or potassium salts) of

the long chain carboxylic acids (fatty acids). The ionic group in soaps is –CO𝑂−𝑁𝑎++.

2. Soaps are not suitable for washing purposes when

the water is hard. 3. Soaps are biodegradable. 4. Soaps have relatively weak cleaning action.

1. Detergents are the sodium salts of long chain benzene sulphonic acids or long alkyl hydrogensuphates. The ionic group in a detergent

is –S𝑂3−𝑁𝑎+ or –S𝑂4−𝑁𝑎+. 2. Detergents can be used for washing even when the

water is hard. 3. Some of the detergents are not biodegradable. 4. Detergents have a strong cleansing action.

Advantages of detergents over soaps Detergents are better than soaps because of the following reasons: 1. Detergents can be used even with hard water whereas soaps are not suitable for use with hard water. 2. Detergents have a stronger cleansing action than soaps. 3. Detergents are more soluble in water than soaps.



Disadvantage of detergent over soap Disadvantage of detergent over soap is that some of the detergents are not biodegradable, that is, they cannot be decomposed by micro-organisms like bacteria and hence cause water pollution in lakes and rivers.

ASSIGNMENT

1. Give reasons for existence of large number of

carbon compounds?

2. Why does carbon atom not form ion?

3. Define isomers.

4. Expand IUPAC?

5. Draw all isomers of pentane and write their IUPAC

names.

6. Draw all isomers of butane and write their IUPAC

names.

7. Draw all isomers of hexane and write their IUPAC

and common names.

8. Draw all isomers of heptane and write their IUPAC

and common names.

9. What is the difference between two consecutive

homologues of alkenes in terms of mass and

chemical composition?

10. Which hydrocarbon are present in (i) LPG(ii) CNG?

11. Name the next homologue of pentyne.

12. Give IUPAC and common name of the simplest

alkane, alkene and alkyne.

13. Give IUPAC name of the simplest alkane, alkene

and alkyne which have isomers.

14. How can unsaturated hydrocarbons be converted

into saturated? Name the process?

15. Write one use of each : methane, ethane and

ethyne.

16. Which hydrocarbon has highest calorific value and

why?

17. Write structural formula of

(a) 1, 2- dichloroethane

(b) 1, 1, 2- tribromoethane

(c) Tetreachloroethane

18. Carbon exists in the atmosphere in the form of

(a) Carbon monoxide only

(b) Carbon monoxide in traces and carbon dioxide

(c) Carbon dioxide only

(d) Coal

19. Which of the following statements are usually

correct for carbon compounds? These

(a) Are good conductors of electricity?

(b) Are poor conductors of electricity?

(c) Have strong forces of attraction between their

molecules.

(d) Do not have strong forces of attraction

between their molecules

20. A molecule of ammonia ( NH3 ) has

(a) Only single bonds

(b) Only double bonds

(c) Only triple bonds

(d) Two double bonds and one single bond

21. In the soap micelles

(a) The ionic end of soap is on the surface of the

cluster while the carbon chain in the interior of

the cluster.

(b) Ionic end of soap is in the interior of the cluster

and the carbon chain is out of the cluster

(c) Both ionic end and carbon chain are in the

interior of the cluster

(d) Both ionic end and carbon chain are on the

exterior of the cluster

22. Buckminster fullerence is an allotrophic form of

(a) Phosphorus (b) Sulphur (c) Carbon (d) Tin

23. What is the formula of sodium acetate?

(a) CH3COONa (b)C2 H5COONa (c) C3 H7COONa

(d) C4 H7COONa

24. The first member of alkyne homologous series is

(a) Ethyne (b) Ethene (c) Propyne (d)Methane

25. Vinegar is a solution of

(a) 50% - 60% acetic acid in alcohol

(b) 5% - 8% acetic acid in alcohol

(c) 50% - 60% acetic acid in water

(d) 5% - 8% acetic acid in water

26. Chlorine reacts with saturated hydrocarbons at

room temperature in the

(a) Absence of sunlight

(b) Presence of sunlight

(c) Presence of water

(d) Presence of hydrochloric acid

27. Carbon forms four covalent bonds by sharing its

four valence electrons with four univalent atoms,

e.g., hydrogen. After the formation of four bonds,

carbon attains the electronic configuration of

(a) Helium (b) Neon (c) Argon (d) Krypton

28. Mineral acids are stronger acids than carboxylic

acids because

I. Mineral acids are completely ionised

II. Carboxylic acids are completely ionised



III. Mineral acids are partially ionised

IV. Carboxylic acids are partially ionised

(a) I and IV (b) II and III (c) I and II (d) III and IV

29. Pentane has the molecular formula C5H12 . it has

(a) 5 covalent bonds

(b) 12 covalent bonds

(c) 16 covalent bonds

(d) 17 covalent bonds

30. The name of the compound CH3CH2CHO is

(a) Propanal

(b) Propanone

(c) Ethanol

(d) Ethanal

31. Ethanol reacts with sodium and forms two

products. These are

(a) Sodium ethanoate and hydrogen

(b) Sodium ethanoate and oxygen

(c) Sodium ethoxide and hydrogen

(d) Sodium ethoxide and hydrogen

32. Which of the following does not belong to the same

homologous series?

(a) CH4 (b) C2 H6 (c) C3 H8 (d) C4 H8

33. C15 H31 COOH is commonly known as

(a) Oleic acid

(b) Stearic acid

(c) Luric acid

(d) Palmitic acid

34. On treating ethanoic acid with Na metal, it forms

(a) Sodium salt of acetic acid

(b) Sodium salt of propionic acid

(c) Ester

(d) Aldehyde

35. Main constituent of biogas is

(a) Methane

(b) Ethane

(c) Propane

(d) Butane

36. Number of valence electrons in nitrogen is

(a) 4 (b) 5 (c) 6 (d) 7

37. Shape of graphite is

(a) Hexagonal

(b) Octahedral

(c) Tetrahedral

(d) Square planar

38. The soap molecules has a

(a) Hydrophilic head and a hydrophobic tail

(b) Hydrophobic head and hydrophilic tail

(c) Hydrophobic head and hydrophobic tail

(d) Hydrophilic head and hydrophilic tail

39. Identify the unsaturated compounds from the

following :

I. Propane

II. Propene

III. Propyne

IV. Chloropropane

(a) I and II (b) II and IV (c) III and IV (d) II and III

40. Write the name and structure of an aldehyde with

4 carbon atoms.

41. Draw the structure of simplest ketone.

42. How is scum formed?

43. Why do carbon compounds not conduct

electricity?

44. “ Saturated hydrocarbons burn with a blue flame

while unsaturated hydrocarbons burn with a sooty

flame.” Why?

45. Draw the electron dot structure of ethane, C2H6 .

46. What will you observe on adding a 5% alkaline

potassium permanganate solution drop by drop to

some warm ethanol taken in a test tube? Write the

name of the compound formed during the above

chemical reaction?

47. Which two of the following compounds belong to

same homologous series?

C2 H6 O, C2 H6O2 , C2 H6 , CH4 O

48. What happens when a small piece of sodium is

dropped into a ethanol?

49. How ethanoic acid got its name as glacial acetic

acid?

50. Identify the compounds those contain double

bond? C5H8 , C5 H10 , C5 H12

51. What are catalysts?

52. Name the reactions which esters get converted to

soap by adding NaOH?

53. Convert alcohol into carboxylic acid.

54. What are the two allotropic forms of carbon?

55. Give the formula for the functional group ketone?

56. What are the two types of hydrocarbon?

57. Mention two properties of ethanol.

58. Give litmus test for carboxylic acid.

59. Draw the electron dot structure for NH3 .

60. Define catenation.

61. Name the upper and lower homologue of C2 H5 OH.

62. Draw the structural formula of ethyl ethanoate.

63. Convert ethanol to ethane.

64. Graphite is soft and slippery. Why?

65. Which property of diamond make it lustrous?

66. Draw the electron dot structure of ethyne and also

draw its structural formula.



67. Why detergents are better cleansing agents than

soaps?

68. How is ethane prepared from ethanol? Give the

reaction involved in it.

69. Intake of small quantity of methanol can be lethal.

Comment.

70. Carbon, group (14) element in the Periodic Table,

is known to form compounds with many elements.

Write an example of a compound formed with

(a) Chlorine ( Group 17 of Periodic Table)

(b) Oxygen ( Group 16 of Periodic Table)

71. Ethane is formed when ethanol at 443 K is heated

with excess of concentrated sulphuric acid. What is

the role of sulphuric acid in this reaction? Write

the balanced chemical equation of this reaction?

72. On burning a hydrocarbon in air, a student obtains

sooty flame. What does it indicates?

73. Define denaturated alcohol.

74. Write the structural formulae of all the isomers of

hexane.

75. Write the formula and draw electron dot structure

of carbon tetrachloride.

76. What is saponification? Write the reaction

involved in this process?

77. What is vinegar?

78. Describe with a chemical equation, what happens

when sodium hydrogen carbonate reacts with

ethanoic acid?

79. Mention four differences between saturated and

unsaturated hydrocarbons.

80. Give general formula and an example of alkyne and

alkene.

81. What is substitution reaction? Give an example.

82. What is esterification?

83. What happens when ethyl alcohol and acetic acid

react with each other in the presence of

concentrated H2SO4 ?

84. Unsaturated hydrocarbons contain multiple bonds

between the two C – atoms and show addition

reaction. Give the test to distinguish ethane from

ethane.

85. Write the names and molecular formula of two

organic compounds having functional group

suffixed as ‘ –oic acid’ . with the help of a balanced

chemical equation explain. What happens when

any one of them reacts with sodium hydroxide.

86. Write the names and molecular formula of an

organic compound having its name suffixed with

‘–ol’ and having two carbon atoms in the molecule.

With the help of a balanced chemical equation

indicates what happens when it is heated with

excess of concentrated H2SO4.

87. Draw the possible isomers of the compound with

molecular formula C3 H6 O and also give their

electron dot structures.

88. Name the reaction which is commonly used in the

conversion of vegetable oils to fats. Explain the

reaction involved in detail.

89. How would you bring about the following

conversions? Name the process and write the

reaction involved?

(a) Ethanol to ethane.

(b) Propanol to propanoic acid.

90. In electron dot structure, the valence shell

electrons are represented by crosses or dots.

(a) The atomic number of chlorine is 17. Write its

electronic configuration.

(b) Draw the electron dot structure of chlorine

molecule.

91. Catenation is the ability of an atom to form bonds

with other atoms of the same element. It is

exhibited by both carbon and silicon. Compare the

ability of catenation of the two elements. Give

reasons.

92. What are the advantages of synthetic detergents

over soaps?

93. What is meant by saponification? Give an example.

94. Why soaps cannot be used in hard water?

95. What is flame? Under what conditions it is called

luminous and non – luminous?

96. A gas is evolved when ethanol reacts with sodium.

Name the gas evolved and also write the balanced

chemical equation of the reaction envolved?

97. Name the functional groups present in the

following compounds.

(a) CH3 COCH2 CH2CH2 CH3

(b) CH3 CH2CH2 COOH

(c) CH3 CH2CH2CH2 CHO

(d) CH3 CH2 OH

98. A compound X is formed by the reaction of a

carboxylic acid C2 H4O2 and an alcohol in the

presence of a few drops of H2 SO4 . the alcohol on

oxidation with alkaline KMnO4 followed by

acidification gives the same carboxylic acid as used

in this reaction. Give the names and structures of

(a) carboxylic acid, (b) alcohol

(c) the compound X.

Also write the reaction.

99. An organic compound A on heating with

concentrated H2SO4 forms a compound B which on



addition of one mole of hydrogen in the presence of

Ni forms a compound C. One mole of the compound

C on combustion forms two moles of CO2 and three

moles of H2 O. Identify the compounds A, B and C

write the chemical equation of the reactions

involved.

100. Arvind was sufferning from cough and cold. He

went to the chemist shop and asked for ‘Corex’

cough syrup. But the chemist refused him to give

‘ Corex’ and told Arvind that the sale of this

syrup has been banned by the government.

Answer the given questions based on the above

text

(a) What is the main constituent of ‘Corex’

cough syrup?

(b) According to you, why the sale of ‘Corex’ has

been banned?

(c) What values you have learnt from the given

text?

101. Draw the structural isomers of hexane.

102. Complete the following reactions. Also balance

them.

(a) CH3 - CH2 OH

(b) C2 H5 OH + O2

(c) C2 H5 OH + Na

103. Complete the following reactions :

1. C2 H5 OH + CH3 COOH

2. CH3 COOC2 H5 + NaOH

3. CH3 COOH + NaOH

104. (a) Name the compound CH3 COOH and

identify its functional group. (b) Give a chemical

test to identify this compound. (c) Name the

gas evolved when this compound acts on solid

sodium carbonate. How would you identify this

gas?

105. (a) What are hydrocarbons ?give examples?

(b) Give the structural differences between

saturated and unsaturated hydrocarbons with

two examples Each?

(c) What is functional group? Give examples of

four different functional groups.

106. A son was travelling in a CNG auto with his

mother. The auto driver took the auto to the CNG

filling station for filling the empty cylinder. The

son asked his mother about the gas which was

filled in the auto. His mother replied, this gas in

CNG. CNG is used in place of petrol or diesel

because it is cheaper, pollution free and eco

friendly.

Answer the following questions on the basis of

the above text

(a) What is the full form of CNG?

(b) Name the main constituent of CNG. Also draw

its structure.

(c) What values you have learnt after reading

the text?

107. Explain the given reactions with the examples

(a) Hydrogenation reaction

(b) Oxidation reaction

(c) Substitution reaction

(d) Saponification reaction

(e) Combustion reaction

108. (a) The structural formula of an ester. Write

the structural formula of the corresponding

alcohol and the acid. (b) (i) Mention the

experimental conditions involved in obtaining

ethane from ethanol. (ii) Write the chemical

equation for the above reaction. (c) Explain the

cleansing action of soap.

109. Describe a chemical test to distinguish between

ethanol and ethanoic acid.

110. Write a chemical equation to represent what

happens when hydrogen gas is passed through

an unsaturated hydrocarbons in the presence of

nickel as a catalyst.

111. Complete the following reactions and name the

main product formed in each case.

(a) CH3 CH2 OH + 2[O] Acidified

1. K2 Cr2 O7

(b) CH3 COOH + NaHCO3

(c) Ch3 COOC2 H5 + NaOH

112. Seema have seen advertisements stating that

some vegetables oils are healthy. Although

saturated fatty acids are said to be harmful for

health. She got confused and want to know the

reason for this. So she ask this to her science

teacher who tell her why unsaturated fats are

healthier. From her answer she got satisfied.

Answer the following questions.

(a) Why vegetables oils are considered healthy

than saturated fatty acids (ghee)?

(b) What precautions you would take in

selecting a cooking oil?

(c) What values did the learner learn from the

above text?

(d) What values are shown by Seema and her

teacher?

113. (a) Draw the structure of ethyne( C2 H2 ).



(b) Define esterification. Write a chemical

equation to illustrate it.

(c) List any two differences between soaps

and detergents.

114. (a) How is vinegar made?

(b) What is glacial acetic acid? What is its

melting point?

(c) Why are carboxylic acids called weak

acids?

(d) Write the name and the formula of the

two compounds formed when the ester CH3

COOC2H5 undergoes saponification.

115. Esters are sweet smelling substances and are

used in making perfumes. Suggest some activity

and the reaction involved for the preparation of

an ester with well labelled diagram.

116. Ethanol is used on a large scale. At commercial

level this is a very useful chemical. It is

commonly called alcohol and is the active

ingredient of alcoholic drink. But consumption

of alcohol also causes drunknness and this

practise is socially condemned.

Read the above text and answer the following

questions

(a) As a responsible student of class what steps

you would take to discourage the use of

alcohol.

(b) What values did learners have learn from the

above text?

117. A compound C ( molecular formula C2 H4 O2 )

reacts with Na metal to form a compound R and

evolves a gas which burns with a pop sound.

Compound C on treatment with an alcohol A in

the presence of an acid forms a sweet smelling

compound S ( molecular formula, C3 H6 O2 ). On

addition of NaOH to C, it also gives R and water.

S on treatment with NaOH solution gives back R

and A. identify C, R, A, Sand write down the

reactions involved.

118. Mrs. Anita observed that her cooking utensils

are becoming black in colour and the flame of

her gas stove is yellowish is colour. Her

neighbour Mrs Anand when came to her, told the

reason why her utensils becomes black and

advise her to clean the stove or gas burner time

to time.

Answer the following questions.

(a) (i) What can be the reasoned for this sooty

flame.

(ii) How is this problem harmful for our

environment

(b) What steps should be taken to stop this

process.

(c) What is the associated value that the

learners get from this passage?

119. A salt X is formed and a gas is evolved when

ethanoic acid reacts with sodium hydrogen

carbonate. Name the salt X and the gas evolved.

Describe an activity and draw the diagram of the

apparatus to prove that the evolved gas is the

one which you have named. Also, write the

chemical equation of the reaction involved.



Q.) What is the need of the periodic classification of elements?

Ans. There are 115 elements known at present and it is very difficult to study the properties of all these

elements separately. So, all the elements have been divided into a few groups in such a way that elements in the

same group have similar properties. This is the reason for the periodic classification of elements.

DOBEREINER’s TRIADS

Dobereiner’s law of triads: When elements are arranged in the order of increasing atomic masses, groups of

three elements (known as triads), having similar chemical properties are obtained. The atomic mass of the

middle elements of the triad being equal to the arithmetic mean of the atomic masses of the other two elements.

Three groups made by Dobereiner.

1) The Alkali Metal group.

The elements lithium, sodium and potassium show similar chemical properties.

All these elements are metals

All of them react with water to form alkalis and hydrogen gas

All of them have a valency of 1 (they are monovalent).

Atomic mass of lithium = 7u

Atomic mass of potassium = 39u

Arithmetic mean of atomic masses = 7+39

2 u of lithium and potassium =

46

2 =23u

Actual atomic mass of sodium = 23u

Q.)Why Lithium, sodium and potassium are called alkali metals?

Ans. Lithium, sodium and potassium are called alkali metals because they form alkalis (Caustic solutions) on

reaction with water.

2) The Alkaline Earth Metal Group.

The elements calcium, strontium and, barium show similar chemical properties.

All these elements are metals,

The oxides of all them are alkaline in nature, and

All these elements have a valency of 2 (they are divalent).

The arithmetic mean of atomic masses of the first and third members of this triad (calcium and barium) will

come to be 40+137

2 = 88.5 u. And the actual atomic mass of the middle element of this triad (strontium) is 88 u.

Q.) Why the elements calcium, strontium and barium are called alkaline earth metals?

Ans. The elements calcium, strontium and barium are called alkaline earth metals because their oxides are

alkaline in nature which existed in the earth. These oxides were called “alkaline earths” and hence their metals

as alkaline earth metals.

3) The Halogen Group.

The elements chlorine, bromine and iodine show similar chemical properties.

All these elements are non-metals,

All these elements react with water to form acids, and

All these elements have a valency of 1 (they are monovalent).

Periodic classification of elements

Name of element Atomic mass Lithium (Li) 7 u Sodium (Na) 23 u Potassium (K) 39 u

Name of element Atomic mass Calcium (Ca) 40 u Strontium (Sr) 88 u Barium (Ba) 137 u

Name of element Atomic mass Chlorine (Cl) 35.5 u Bromine (Br) 80 u Iodine (I) 127 u



The arithmetic mean of the atomic masses of the first and third members of this triad (chlorine and iodine) will

come to be 35.5+127

2 = 81.2u. And the actual atomic mass of the middle element of this triad (bromine) is 80u.

Q.) Why the elements chlorine, bromine and iodine are known as halogens?

Ans.) The elements chlorine, bromine and iodine are known as halogens because they react with metals to form

salts (halo = salt, gene = producer).

Limitation/ drawback of Dobereiner’s classification

The limitation of Dobereiner’s classification was that it failed to arrange all the then known elements in the

form of triads of elements having similar chemical properties. Dobereiner could identify only three triads form

the elements known at that time. So, his classification of elements was not much successful.

NEWLANDS’ LAW OF OCTAVES

In 1864, Newlands arranged the 56 known elements in the order of increasing atomic masses and found

that the properties of every eighth element are similar to the properties of the first element.

The Newlands law of octaves: When elements are arranged in the order of increasing atomic masses, the

properties of the eighth element (starting from a given element) are a repetition of the properties of the

first element.

Newlands divided the elements into horizontal rows of seven elements.

H Li Be B C N O

F Na Mg Al Si P S

Cl K Ca Cr Ti Mn Fe

Co and Ni Cu Zn Y In As Se

Br Rb Sr Ce and La Zr - -

Newlands could classify elements only up to calcium in this way. As more and more new elements were

discovered, they could not be fitted into the octave structure.

Q.) What is the significance of the Newlands’ classification of elements?

Ans. Newlands’ classification of elements based on his law of octaves, however, gave a very important

conclusion that there is some systematic relationship between the order of atomic masses and repetition of

properties of elements.

Limitations of Newlands’ classification of elements

Newlands’ law of octaves was applicable to the classification of elements up to calcium only. After calcium,

every eighth element did not possess the properties similar to that of the first element.

Newlands assumed that only 56 elements existed in nature and no more elements would be discovered in

the future. But later on, several new elements were discovered. Whose properties did not fit into Newlands’

law of octaves.

In order to fit elements into his table, Newlands put even two elements together in one slot and that too in

the column of unlike elements having very different properties. For example the two elements cobalt (Co)

and nickel (Ni) were put together in just one cell , and that too in the column of elements like fluorine,

chlorine and bromine which have very different properties from these elements.

Iron element (Fe) which resembles cobalt and nickel elements in properties, was placed far away from

these elements.

Existence of Dobereiner’s triad in Newlands’ classification of elements

Dobereiner’s triads also exist in the columns of Newlands’ classification of elements based on the law of

octaves. For example, the second column of Newlands’ classification has the elements lithium (Li), Sodium

(Na), and potassium (K) which constitute a Dobereiner’s triad.

Dobereiner’s

triad



Q .) What is the meaning of the periodic table?

Ans. The periodic table is a chart of elements prepared in such a way that the elements having properties occur

in the same vertical column or group. It is called periodic because the elements having similar properties are

repeated after certain intervals or periods, and it is called a table because the elements are arranged in the

tabular form. A periodic table consists of horizontal rows of elements called periods and vertical columns called

groups.

Q .) Which chemical properties of elements were considered by the Mendeleev to study the periodicity

in the properties?

Ans. The elements having similar chemical properties form oxides having similar formulae. They also form

hydrides having similar formulae.

Mendeleev took the formulae of the oxides and hydrides formed by the elements as the basic properties of

elements for their classification in the form of a periodic table.

In Mendeleev’s periodic table, the general formulae of the oxides and hydrides of elements in every group are

written at the top of the group.

MENDELEEV’S PERIODIC TABLE

A Russian scientist Mendeleev found that when elements are arranged in the order of increasing atomic

masses, the elements with similar properties occur at regular intervals.

Mendeleev gave a periodic law in1869.

Mendeleev’s periodic law: The properties of elements are a periodic function of their atomic masses.

Mendeleev’s periodic law means that if elements are arranged in the order of increasing atomic masses,

then the properties of elements are repeated after regular intervals or periods.

There were seven periods (horizontal rows) and eight groups (vertical columns) in the original periodic

table of Mendeleev. Out of eight groups, first seven groups are of normal elements and eighth group is of

transition elements.

Noble gases were not known at that time. So there was no group of noble gases in Mendeleev’s original

periodic table.

Mendeleev was guided by two factors :

Increasing atomic masses.

Grouping together of elements having similar properties.



Merits of Mendeleev’s classification of elements

Mendeleev’s periodic law predicted the existence of some elements that had not been discovered at

that time.

In order to make sure that the elements having similar properties fell in the same vertical column or group,

Mendeleev left some gaps in his periodic table. These gaps were left for the elements not known at that

time.

The undiscovered elements (or unknown elements) at that time for which gaps were left in the periodic

table were named by Mendeleev as eka - boron, eka - aluminium and eka - silicon by prefixing the term’eka’

to the name of the preceding element in the same group. The term ‘eka’ is derived form Sanskrit and means

‘first’.

These elements were discovered later on, then eka - boron means was named as scandium (symbol Sc), eka

- aluminium was named as gallium (symbol Ga), and eka - silicon was named as germanium (symbol Ge).

Mendeleev’s periodic table could predict the properties of several elements on the basis of their

positions in the periodic table.

The properties of the then undiscovered elements like gallium, scandium and germanium were predicted in

this way. The missing elements of Mendeleev’s periodic table were discovered later on and their properties

were found to be very close to those predicted by Mendeleev.

Mendeleev’s periodic table could accommodate noble gases when they were discovered.

When a whole new group called noble gases was discovered, it got a place in the periodic table in the form

of a separate group. The noble gases are placed in a separate because they are chemically unreactive.

The noble gases were discovered very late because they are unreactive (or

Inert), and present in extremely low concentration in the atmosphere.

Anomalies (or Limitations) of Mendeleev’s classification of Elements

The position of isotopes could not be explained. Isotopes are the atoms of the same element having similar

chemical properties but different atomic masses.

According to atomic masses the isotopes should be placed in different groups of the periodic table. The

isotopes were not given separate places in Mendeleev’s periodic table. The isotopes are placed at the same

place in the Mendeleev’s periodic table.

Wrong order of atomic masses of some elements could not be explained. When certain elements were put in

their correct group on the basis of their chemical properties it was found that the element with higher

atomic mass comes first and the element with lower atomic mass comes later.

Example – When put in the correct group on the basis of its chemical properties, the element cobalt (Co)

having higher atomic mass of 58.9 comes first and nickel (Ni) element with slightly lower atomic mass of

58.7 comes later.

A correct position could not be assigned to hydrogen in the periodic table. Hydrogen (H) has been placed in

group I with alkali metals. This is because like alkali metals, (Say sodium), hydrogen also combines with

halogens (Chlorine, etc.), oxygen and sulphur to form compounds having similar formulae. Hydrogen also

resembles halogens in some of the properties.

PRESENT BASIS FOR THE CLASSIFICATION OF ELEMENTS

Q.) Why atomic number is more fundamental property of an element tan atomic mass?

Ans. In 1913, Moseley showed that the atomic number of an element is a more fundamental property than

atomic mass and hence atomic number is a better basis for the classification of elements.

The atomic number increase regularly by 1 form element to element but atomic mass does not very regularly

from one element to the next. The atomic number of every element is fixed. No two elements can have the same

number.



Modern Periodic Law

The properties of elements are a periodic function of their atomic numbers. When elements are arranged

according to increasing atomic numbers, there is a periodicity in the electronic configurations of elements.

The periodicity in electronic configurations of elements leads to the periodicity in their chemical properties.

Explanation of Modern Periodic Law

When the elements are arranged according to increasing atomic numbers, then the elements having some

number of valence electrons occur at regular intervals (or periods). Since the number of valence electrons

in the elements show periodicity (regular repetition), the chemical properties also show periodicity.

The real significance of the modern periodic classification based on atomic numbers is that it relates

the periodicity in the properties of elements to the periodicity in their electronic configurations.

MODERN PERIODIC TABLE (OR LONG FORM OF PERIODIC TABLE)

The modern periodic table was prepared by Bohr.

The arrangement of elements in the modern (long form) periodic table is based on their electronic

configurations.

The horizontal rows of elements in a periodic table are called periods. There are seven periods in the long

form of periodic table. The elements in a period have consecutive (continuous) atomic numbers.

1st period contains 2 elements. It is called very short period.

2nd period contains 8 elements. It is called short period.

3rd period contains 8 elements. It is also a short period.

4th period contains 18 elements. It is called long period.

5th period contains 18 elements. It is also a long period.

6th period contains 32 elements. It is called very long period.

7th period contains rest of the elements. It is incomplete.

The number of elements in a period is fixed by the maximum number of electrons which can be

accommodated in the various shells of an atom.

The figures 2, 8, 18, 32 etc., representing the number of elements in various periods actually correspond

to the maximum number of electrons which can be put in the various shells of the atoms.

It is the number of valence electrons in the atoms of elements that decides, which element will be the

first element in a period and which element will be the last element in the period.

The vertical columns in a periodic table are called groups. There are 18 groups in the long form of periodic

table.

The element in a group do not have consecutive atomic number.

The groups 1 and 2, and 13 to 17 contain the normal elements (typical elements or representative

elements). In the normal elements all the inner shells are completely filled with electrons, only the

outmost shells are incomplete.

All the elements in a group have similar electronic configurations and show similar properties.

The valence shells of all the noble gases (group 18) are completely filled with electrons.

The groups 3 to group 12 elements are called transition elements. In these elements the outmost

shells as well as the next to outermost shell (penultimate shell) are incomplete.

The elements with atomic numbers 57 to 71 are called lanthanide series (because their first element is

lanthanum). And the elements with atomic numbers 89 to 103 are called actinide series (because their

first member is actinium).

These are two series of elements having similar properties and they have been placed in two rows at the

bottom of the periodic table.

In the periodic table, metals have been separated from non –metals by some elements called ‘metalloids’

which are placed diagonally in the periodic table. These metalloids are boron (B); Silicon (Si); Germanium

(Ge); Arsenic (As); Antimony (Sb); Tellurium (Te); and Polonium (Po).



The properties of metalloids are intermediate between those of metals and non- metals.

Explanation of the Anomalies of Mendeleev’s Classification of Elements

Explanation for the Position of Isotopes.

Since all the isotopes of an element have the same atomic number they can be put at one place in the same

group of the periodic table.

Explanation for the Position of Cobalt and Nickel.

The atomic number of cobalt is 27 and that of nickel is 28. Cobalt with lower atomic number (27) should

come first and nickel with higher atomic number (28) should come later, even if their atomic masses are in

the wrong order.

Explanation for the Position of Hydrogen

Hydrogen element has been placed at the top of group 1, above the alkali metals because the electronic

configuration of hydrogen is similar to those of alkali metals. Both, hydrogen as well as alkali metals has 1

valence electron each.

CHARACTERISTICS OF PERIODS

Group

Group

1

Group

2

---------------------- Group

13

Group

14

Group

15

Group

16

Group

17

Group

18

Valence

Electrons

the number of valence electrons in elements increases from 1 to 8

Valency 1 2 3 4 3 2 1 0

the valency of elements increase from 1to 4 and then decrease to 0 (Zero)

Size of

Atoms

the size of atoms decreases increases

Metallic

Character

Metallic character decreases and non metallic character increases

Chemical

Reactivity

reactivity of Metals decreases reactivity of non Metals increases

Nature of

Oxides

the basic nature of oxides decreases and the acidic nature of oxides increases

1) Valence Electrons (or Outermost Electrons)

On moving from left to right in a period, the number of valence electrons in elements increases from 1 to 8.

2) Valency

On moving from left to right in each short period, the valency of elements increase from 1to 4 and then

decrease to 0 (Zero).

The valency of an element is determined by the number of valence electrons (or outermost electrons)

present in the atom of the element.

The number of electrons lost or gained (or shared) by one atom of an element to achieve the nearest inert

gas electron configuration, gives us the valency of the element.

3) Size of Atoms (or Atomic size)(Atomic radius”unit is picometre”)(1 picometre = 10-12 metre)

On moving from left to right in a period of the periodic table, the size of atoms decreases (or atomic size

decreases).

On moving from left to right in a period of the periodic table, the atomic radius of elements decreases.

Q .) Why the size of atoms decreases on moving from left to right in a period of the periodic table?

Ans. As we move from left to right in a period, the atomic number of elements increases which means that the

number of protons and electrons in the atoms increases (the extra electrons being added to the same shell). Due



to large positive charge on the nucleus, the electrons are pulled in more close to the nucleus and the size of

atom decreases.

Q .) Why the size of the atom of an inert gas (group 18) is bigger than that of the preceding halogen atom

(group 17)?

Ans. The size of the atom of an inert gas is bigger than that of the preceding halogen atom. The greater size of

the inert gas atom (or noble gas atom) in a period is due to the structural stability of its outermost shell

consisting of an octet of electrons.

4) Metallic Character

On moving from left to right in a period, the metallic character of elements decreases (but the non-metallic

character increases).

Metals lose electrons and form positive ions, so metals are called electropositive elements. On the other

hand, non- metals accept electrons and form negative ions, so non-metals are called electronegative

elements.

On moving from left to right in a period, the electropositive character of elements decreases, but the

electronegative character increases.

Q.) Why the electropositive character of elements decreases, but the electronegative character

increases on moving from left to right in a period?

Or

Q.) Why the chemical reactivity of elements first decreases and then increases on moving from left to

right in a period?

Ans. As we move from left to right in a period of the periodic table, the nuclear charge (positive charge on

nucleus) increases due to gradual increase in the number of protons. Due to the increase in nuclear charge the

valence electrons are pulled in more strongly by the nucleus and it becomes more and more difficult for the

atoms to lose electrons. Thus, on moving from left to right in a period, the tendency of atoms to lose electrons

decreases. So the reactivity of metals decreases

On the other hand, due to the increased nuclear charge, it becomes easier for the atoms to gain electrons. So,

moving from left to right in a period, the tendency of atoms to gain electrons increases. So the reactivity of

nonmetals increases.

5) Chemical Reactivity

On moving from left to right in a period, the chemical reactivity of elements first decreases and then

increases.

6) Nature of Oxides

On moving from left to right in a period, the basic nature of oxides decreases and the acidic nature of oxides

increases.



CHARACTERISTICS OF GROUPS

Period

Group

1

Group

2

---------------------- Group

13

Group

14

Group

15

Group

16

Group

17

Group

18

Period 1

All the elements of a group of the periodic table have the same number of valence

electrons.

All the elements in a group have the same valency.

On going down in a group of the periodic table, the size of atoms increases

the metallic character of elements increases

the electronegative character (non – Metallic character) of elements decreases

The chemical reactivity of metals increases on going down in a group.

The chemical reactivity of non – metals decreases on going down in a group of the

periodic table.

There is no change in the nature of oxides of elements

Period 2

Period 3

Period 4

Period 5

Period 6

Period 7

1) Valence Electrons (or Outermost Electrons)

All the elements of a group of the periodic table have the same number of valence electrons.

Group 1 elements are monovalent (having Valency of 1).

On moving down in a particular group of the periodic table, the number of valence electrons in the elements

remains the same.

Group 2 elements are divalent (having valency of 2).

Group 13 elements have 3 valence electrons each, group 14 elements have 4 valence electrons each, group

15 elements have 5 valence electrons, and group 16 elements have 6 valence electrons each in their atoms.

Similarly, all the elements of group 17 have 7 valence electrons each in their atoms.

All the elements of group 18 have 8 valence electrons each in their atoms, except helium which has only 2

valence electrons in its atom.

If some elements have the same number of electrons (n electrons) in the outermost shell of their atoms,

then they belong to the same group of the periodic table.

Q.) How to find the group number of an element in the periodic table from the number of valence

electrons in its atom.

Ans. The group number of elements having up to two valence electrons is equal to the number of valence

electrons.

The group number of elements having more than two valence electrons is equal to the number of valence

electrons plus 10.

2) Valency

All the elements in a group have the same valency.

3) Size of Atoms (or Atomic Size)

On going down in a group of the periodic table, the size of atoms increases (or atomic size increases).

The smallest atomic size will be found at the top of a group whereas the largest atomic size is found in the

lowest part of a group.



Q .) Why the size of atoms increases (or atomic size increases) on going down in a group of the periodic

table?

Ans. When we move from top to bottom in a group, a new shell of electrons is added to the atoms at every step.

In this way, the number of electron shells in the atoms increases gradually due to which the size of atoms also

increases.

For example, lithium atom (Li) has only two electron shells K and L in it whereas a sodium atom (Na) has three

electron shells K, L, and M in it.

4) Metallic Character

On going down in a group of the periodic table, the metallic character of elements increases.

The greatest metallic character is found in the elements in the lowest part of a group.

On going down in a group of the periodic table, the electronegative character (non – Metallic character) of

elements decreases.

Q.) Why the metallic character of elements increases on going down in a group of the periodic table?

Ans. As we go down in a group of the periodic table, one more electron shell is added at every stage and size of

the atom increases. The valence electrons become more and more away from the nucleus and hold of the

nucleus on valence electrons decreases. Due to this the atom can lose valence electrons more easily to form

positive ions and hence the electropositive character increases.

The tendency of an atom to lose electrons increases on moving down in a group of the periodic table.

Q.) Why the non - metallic character of elements decreases on going down in a group of the periodic

table?

Ans. As we go down in a group of the periodic table, one more electron shell is added to the atom at every step

and size of the atom goes on increasing. Due to this increase in the size of the atom, its nucleus goes more deep

inside the atom. The attraction of nucleus for the incoming electron decreases, due to which the atom cannot

form negative ions easily and electronegative character decreases.

The tendency of an atom to gain electrons decreases on going down in a group of the periodic table.

5) Chemical Reactivity

The chemical reactivity of metals increases on going down in a group of the periodic table.

The chemical reactivity of non – metals decreases on going down in a group of the periodic table.

Q.) Why the chemical of metals increases on going down in a group of the periodic table?

Ans. As we move down in a group of metal elements, the size of their atoms goes on increasing. Due to increase

in the size of atoms, the valence electrons of metal atom (which take part in chemical reactions) become more

and more far away from the nucleus and hence can be removed easily. Thus as we go down in a group of metals,

the tendency of their atoms to lose electrons increases, and hence their chemical reactivity also increases.

Q.) Why the chemical of non - metals decreases on going down in a group of the periodic table?

Ans. As we move down in a group of non – metal elements, the size of their atoms goes on increasing. Due to

increase in the size of atom, the nucleus of atom goes more deep inside it and hence its attraction for the

incoming electrons decreases. Thus, as we go down in a group of non-metals, the tendency of their atoms to

gain electrons decreases, due to which their reactivity also decreases.

6) Nature of Oxides

On going down in a group of the periodic table, there is no change in the nature of oxides of elements.

Merits of the Modern Periodic Table

The modern periodic table is based on the atomic numbers of elements which is the most fundamental

property of elements.



The modern periodic table helps us understand why elements in a group show similar properties but

elements in different groups show different properties.

The modern periodic table explains the reasons for the periodicity in properties of elements.

The modern periodic table tells us why the properties of elements are repeated after 2, 8, 18 and 32

elements.

There are no anomalies in the arrangement of elements in the modern periodic table.

Advantage of the Periodic Table

The periodic table has made the study of chemistry systematic and easy. It acts as an aid to memory.

It is easier to remember the properties of an element of an element if its position in the periodic table is

known.

The type of compounds formed by an element by an element can be predicted by knowing its position in the

periodic table.

A periodic table chart is used as a teaching –aid in chemistry in schools and colleges.

Periodic Table and Chemical Bonding

Whenever an element from groups 1, 2, or 13 combines with an element from groups 14, 15, 16, or 17, an

ionic bond is formed.

Whenever two elements from groups 14, 15, 16 and 17 combine together, covalent bonds are formed.

ASSIGNMENT : 1. An element belongs to 14th group and 3rd period.

Identify it. 2. An element A belongs to 3rd group. Other element

B belongs to 17th group. Write formula between them.

3. Did Dobereiner’s triads also exist in the columns of Newlands octaves?

4. What were the limitations of Dobereiner’s classification?

5. State one limitation of Newland’s law of octaves? 6. What is a metalloid? Name any two of them? 7. Write the formula of the product formed when the

element A (atomic number 19) combines with the element B (atomic number 17). Draw its electron dot structure. What is the nature of the bond formed?

8. In Mendeleev’s Periodic Table the elements were arranged in the increasing order of their atomic masses. However cobalt with atomic mass of 58.93 u was placed before nickel having an atomic mass of 58.71 u, Give reason for the same.

9. Write the formulae of chlorides of Eka – silicon and Eka – aluminium the elements predicted by Mendeleev.

10. If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride?

11. Arrange the following metals with increasing order of their atomic number Li, N, AI, H, Na.

12. State Modern Periodic Law. 13. State Mendeleev’s Periodic Law. 14. A metal M belongs to 13th group in the Modern

Periodic Table. Write the valency of the metal. 15. Chlorine, bromine and iodine form a Dobereiner’s

triad. The atomic masses of chlorine and iodine

are 35.5 and 126.9 respectively. Predict the atomic mass of bromine.

16. Lithium, sodium and potassium form a Dobereiner’s triad. The atomic masses of lithium and potassium are 7 and 39 respectively. Predict the atomic mass of sodium.

17. Write the isotopes of chlorine. 18. Name the first and last element of lanthanoids. 19. Name all the metalloids. 20. An element X is present at the left corner of

Modern Periodic Table. State whether it would be a metal or a non – metal. State limitations of Newland’s octaves.

21. An atom has electronic configuration 2, 8. Predict the group in which it have been placed.

22. Elements have been arranged in the following sequences on the basis of their increasing atomic masses. F, Na, Mg, AI, Si, P, S, CI, Ar, K (a) Pick two sets of elements which have similar

properties. (b) The given sequences represents which law of

classification of element? 23. Can the following groups of elements be classified

as Dobereiner’s triads? (a) Na, Si, CI (b) Be, Mg, Ca [Atomic mass of Be 9; Na 23; Mg 24; Si 28; CI 35; Ca 40]Explain by giving reason.

24. “Hydrogen occupies a unique position in the Modern Periodic Table”. Justify the statement.

25. Arrange the following elements in the increasing order of their metallic character Mg, Ca, K, Ge, Ga.

26. Compare the radii of two species X and Y. give reasons for your answer. (a) X has 12 protons and 12 electrons. (b) Y has 12 protons and 10 electrons.



27. Arrange the following elements in the increasing order of their atomic radii. (a) Li, Be, F, N (b) Cl, Ar, Br, I

28. Identify and name the metals out of the following elements whose electronic configuration are given below : (a) 2, 8, 2 (b) 2, 8, 1 (c) 2, 8, 7 (d) 2, 1

29. Why the atomic radius decreases on moving left to right along a period?

30. Fluorine (atomic number 9) and chlorine (atomic number 17) are members of Periodic Table. (a) Write their electronic configuration. (b) Which one is more electronegative? Give one

reason. 31. State any two changes in the properties of I –

group elements of Modern Periodic Table, if we move downwards.

32. What is meant by the term atomic size? How it will change on moving down a group?

33. A metal M forms an oxide having the formula MO. It belongs to 2nd period in the Modern Periodic Table. Write its atomic number and valency.

34. How were the locations of nickel and cobalt resolved in the Modern Periodic Table?

35. Write the electronic configuration of the following ions. (a) Br - (b) O2- (c) Mg2+ (d) Li+

36. Give reason for the following (a) Lithium atom is smaller than sodium atom. (b) Chlorine (atomic number 17) is more

electronegative than sulphur (atomic number 16).

37. State the reason for the following (a) The elements of the same group have similar

chemical properties. (b) The elements of the same period have

different properties. 38. Why group 18 elements are called zero valent? 39. The three elements X, Y and Z with similar

chemical and physical properties have atomic masses A, B and C. Mass of Y is approximately equal to the average atomic masses of X and Z. How will you call such an arrangement of elements? Give an example too.

40. The elements of the second period of Period of the Periodic Table are given below Li Be B C N O F (a) Give reason to explain why atomic radii

decreases from Li to F. (b) Identify the most

(i) Metallic and (ii) Non – metallic element.

41. Name (a) Three elements having two electrons in their

outermost shells.

(b) Three elements with completely filled outermost shells, having atomic number more than 25.

42. (a) How many groups and periods are there in Modern Periodic Table? (b) Whose law of octaves was similar to the music notations?

43. Which group of elements could be placed Mendeleev’s Periodic Table without disturbing the original order? Give reason.

44. Ria and Rama are students of Class – X. Ria is very much organised and maintained. The teachers love her. She earns a great respect in the class whereas Rama is unorganised and always faces a lot of problems in handling life situations. Read the above passage and answer the following questions. (a) In your opinion how organisation help in

daily life? (b) How classification of elements help us in

studying them properly? (c) What is the associated value the learner gets

from the given passage? 45. A mother always wants her child to drink milk.

Milk is a boon for health. If one do not drink milk, one can face severe health problems. Answer the following questions on the basis of above text. (a) Name the major constituent/ nutrient

present in milk. (b) Write the chemical symbol, atomic number

and valency of that nutrient. (c) What value do you infer from the given text?

46. An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide. (a) What is the position of element X and Y in the

Periodic Table? (b) What will be the nature of oxide of element

Y? identify the nature of bonding in the compound formed?

47. (a) State the statement of modern periodic law. (b) How many Groups and Periods are present in the Modern Periodic Table? (c) State how the problem of placing Hydrogen and Isotopes of an element has been solved in this Periodic Table.

48. An element ‘X’ placed in 2nd group and 4th period of the Periodic Table burns in the presence of oxygen to form a basic oxide. (a) Identify the element. (b) Write its electronic configuration. (c) Write a balanced equation for the reaction

when this oxide is dissolved in water. 49. Three elements A, B and C have 3, 4 and 2

electrons respectively. Give the group number to which they belong in the Modern Periodic Table. Also, give their valencies.



50. The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.

51. An element is placed in 2nd group and 3rd period of the Periodic Table burns in the presence of oxygen to form a basic oxide. (a) Identify the element. (b) Write its electronic configuration. (c) Write a balanced equation for the reaction

when this oxide is dissolved in water. (d) Write the balanced equation when it burns in

the presence of air. (e) Draw the electron dot structure for the

formation of this oxide. 52. Properties of the elements are given below.

Where would you locate the following elements in the Periodic Table? (a) A soft metal stored under kerosene. (b) An element with variable (more than one)

valency stored under water. (c) An element which is tetravealent and forms

the basis of organic chemistry. (d) An element whose thin oxide layer is used to

make other elements corrosion resistant by the process of ‘anodising’?

53. An element X (atomic number 7) reacts with an element Y (atomic number 20) to form a divalent halide. (a) Where in the Periodic Table are elements X

and Y placed? (b) Classify X and Y as metal (s), non – metal (s)

or metalloid (s). (c) What will be the nature of oxide of element

Y? identify the nature of bonding in the compound formed?

(d) Draw the electron dot structure of the divalent halide.

54. Atomic number of a few elements are given below:- 10, 20, 7, 14 (a) Identify the elements. (b) Identify the group number of these elements

in the Periodic Table. (c) Identify the periods of these elements in the

Periodic Table. (d) What would be the electronic configuration

for each of these elements? (e) Determine the valency of these elements.

55. Mendeleev predicted the existence of certain elements not known at that time and named two of them as Eka – silicon and Eka – aluminium. (a) Name the elements which have taken the

place of these elements. (b) Mention the group and the period of these

elements in the Modern Periodic Table.

(c) Classify these elements as metals, non – metals or metalloids.

(d) How many valence electrons are present in each one of them?

56. An element X which is a yellow soild at room temperature shows catenation and allotropy. X forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and are the major air pollutants. (a) Identify the element X. (b) Write the electronic configuration of X. (c) Write the balanced chemical equation for the

thermal decomposition of ferrous sulphate crystals.

(d) What would be the nature (acidic / basic )of oxides formed?

(e) Locate the position of the element in the Modern Periodic table.

57. Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at “ periodic law”?

58. (a) Why do we classify elements? (b) What were the two criteria used by Mendeleev in creating his Periodic Table? (c)Why did Mendeleev leave some gaps in his Periodic Table? (d)In Mendeleev’s Periodic Table why was there no mention of noble gases like helium, neon and argon. (e)Would you place the two isotopes of chlorine, CI – 35 and CI – 37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.

59. (a)Electropositive nature of the element(s) increases down the group and decreases across the period. (b)Electronegative nature of the elements decreases down the group and increases across the period (c)Atomic size increases down the group and decreases across a period (left to right). (d)Metallic character increases down the group and decreases across a period.

60. On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic number 3 to 9. (a) Name the most electropositive element

among them. (b) Name the most electronegative element. (c) Name of the element with smallest atomic

size. (d) Name the element which is a metalloid. (e) Name the element which shows maximum

valency.



The production of new organisms from the existing organisms of the same species is called reproduction.

Q. Why reproduction is essential? Ans. So, living organisms produce more organisms of their kind to maintain the life of their species on the earth. Example: Reproduction by human beings ensures that the human beings will survive on the earth. Types of reproduction Asexual reproduction Sexual reproduction.

Asexual reproduction The production of the new organisms from the

single parent without the involvement of the sex cells (gametes) is called asexual reproduction.

It is called asexual reproduction because it does not use the gametes for producing the new organism.

It is a rapid mode of multiplication.

Cell division takes place either mitotically or

amitotically.

The new individuals produced after cell divisions

are always genetically identical to their parents, i.e.,

clone.

A single parent is involved, i.e., opposite sexes are

not involved.

It does not involve the fusion of gametes.

Example: - binary fission in amoeba, budding in hydra, formation of bread mould, regeneration in planaria etc.

Sexual reproduction The production of new organism from two parents

by making use of their sex cells is called sexual reproduction.

It is called sexual reproduction because it uses the gametes of two different organisms male and female.

It is not a rapid mode of multiplication.

Cell division involves meiosis at some stages.

The new individuals produced after cell division

exhibit variation, i.e., offspring.

It requires the involvement of two parents (a male

and a female).

It involves the formation and fusion of gametes.

Example: - most of the multicellular animals and most of the flowering plants reproduce by sexual reproduction.

Asexual reproduction It takes place by six different methods.

Fission Budding Spore formation Regeneration Fragmentation Vegetative propagation

Fission The type of asexual reproduction in which a

unicellular organism splits to form two or more new organisms is called fission

Types of fission Binary fission Multiple fission Binary fission The type of asexual reproduction in which the

parent organism splits in two new organisms is called binary fission.

In binary fission the parent organism ceases to exist and two new organisms are formed.

Example: - amoeba, paramecium, leishmania, etc. Binary fission in amoeba

How do organisms reproduce?



When the amoeba cell has reached the maximum size of growth then first the nucleus of amoeba lengthens and divides in two parts.

Then the cytoplasm of the amoeba divides in two parts one part around each nucleus.

In this method, parent organism divides into two identical daughter organisms with definite orientation.

Binary fission paramecium Paramecium is a unicellular organism having short

thread like structures called cilia over its body surface.

In a fully grown paramecium the division of the nucleus is followed by the method of division of cytoplasm to form two smaller paramecia.

Binary fission in leishmania Leishmania is a protozoan, which has greater

degree of organization in its body, it has a whip like structure called flagellum at its one end.

The splitting of parent leishmania during binary fission takes place longitudinally with respect to the flagellum at its one end.

Multiple fission The type of asexual reproduction in which the

parent organism splits to form many new organisms at the same time is called multiple fission.

In unfavorable condition a cyst or a protective wall is formed around the unicellular organism.

Inside the cyst the nucleus of the cell splits several times to form many smaller nuclei called daughter nuclei.

Little bit of cytoplasm collects around each

daughter nuclei and thin membranes are formed

around them.

Many daughter cells are formed from a single parent cell with in the cyst.

Under the favorable conditions cyst breaks open

and many daughter cells are released, each to form a new organism.

Example: - plasmodium (malaria causing protozoan) divides by the process of multiple fission forming around 1000 daughter cells at one time.

Budding The type of asexual reproduction in which a small

part of the parent organism grows out as a bud which then detaches and become a new organism.

Example: - hydra, a colony of sponges and corals is formed by this method.

A bud is the small outgrowth from the body of living organism.

Budding in Hydra Hydra is the simple multicellular organism.



In hydra, first a small outgrowth called bud is

formed on the side of its body by repeated mitotic divisions of its cells.

This bud then grows gradually to form a small hydra by developing mouth and tentacles.

Finally the tiny new hydra detaches itself from the body of parent hydra and lives as a separate organism.

Budding in Yeast Yeast is a tiny, unicellular, non-green plant (fungus). First a bud appears on the outside of the cell wall. The nucleus of the parent cell divides in two parts and one part of the nucleus then moves into the bud. The bud then separates from

the parent yeast cell and forms a new yeast cell.

The budding in the yeast is so fast that the first bud starts forming their buds and all of them remain attached to the parent yeast forming a chain of yeast cells.

After some time each bud separates from one another forming individual yeast cells.

Spore formation It is the type of asexual reproduction in which the

parent plant produces hundreds of microscopic reproductive units called spores. When the spore case of the plant bursts then the spores spreads into air. When these spores land on the food under favorable conditions they germinate to produce new plants.

Example: - rhizopus fungus, bacteria and non flowering plants.

Spore formation in Rhizopus fungus (bread mould) The tiny spores of rhizopus are everywhere present

in the air. These spores settle on the moist bread kept aside

for few days and germinate to grow to form a new fungus.

The common bread mould plant consists of a fine

thread like projections called hyphae and thin

stems having knob like structures called sporangia.

Each sporangium contains hundreds of minute

spores enclosed in spore case.

When the spore case bursts, the tiny spores are dispersed in air. These spores are asexual reproductive units which can produce more bread moulds under favorable conditions.

Q. Can spores exist in unfavorable condition? Explain. Ans. Spores can also exist in unfavorable condition. Spores are covered by a hard protective layer. This coat enables them to survive under unfavorable conditions like lack of food, lack of water and extreme temperature conditions.



Regeneration It is the process of getting back a full organism from

its body parts. Example: - Hydra, Planaria. Regeneration in planaria

Planaria is a flatworm found in fresh water ponds

and slow streams. If the body of the planaria is some how cut into

pieces then each piece give rise to a complete planaria by growing all missing parts.

Regeneration in Hydra If the body of Hydra gets cut into a number of

pieces, then each piece of Hydra can grow into the complete Hydra.

Q. Why Regeneration is not reproduction? Ans. Regeneration is not reproduction because most of the animals would not depend on being cut into pieces to be able to reproduce. Process of regeneration The regeneration of an organism occurs by the

process of growth and development. The cells of cut body part of the organism divide

rapidly to make a ball of cells. The cells present in the ball of cells move to their

proper places within the ball where they have to form various organs and body parts of the organism.

The cells then change their shapes or become specialized to form different types of tissues. These tissues then form various organs and body parts of the organism.

In this way the whole organism is regenerated.

Q. Why complex multicellular organisms can not give rise to the complete organism from their cut body parts? Ans. In complex multicellular organisms, specialised cells make up tissues, tissues make up organs and organs make up organ systems. Since in the complex multicellular organism there is a higher degree of organization so they can not be reproduced from their cut body parts by the process of regeneration. Example: - dog can not be regenerated from the cut tail because the cells present in the tail of the dog are not sufficient to produce the organs like heart, lungs, etc. which are needed to make the complete dog. Fragmentation The breaking of the body of the simple multicellular

organism into two or more parts on maturing, each of which subsequently grows to form a complete new organism is called fragmentation.

Example: - Spirogyra, Sea anemones. Fragmentation in spirogyra

Spirogyra is a green filamentous algae plant which

is found in ponds, lakes and slow moving streams. Spirogyra filament rapidly breaks into two or more

fragments on maturation and each fragment then grows into a new spirogyra.

Difference b/w fission and fragmentation In fission unicellular organism breaks into two or

more daughter cells but in fragmentation a multicellular organism breaks into two or more parts, each part producing new organism.

Difference b/w fragmentation and regeneration In fragmentation the multicellular organism divides

in two or more parts on maturation but in regeneration the multicellular organism accidently divides in two or more parts.

Vegetative propagation (Vegetative reproduction) The type of asexual reproduction in which new

plants are obtained from the parts of old plants like stems, roots and leaves, without the help of any reproductive organ.

The buds of old plants are in dormant state under unfavourable conditions. These buds grow to form a new plant when they are provided with the favourable conditions like warmth, moisture, etc.



Vegetative propagation in grass The dry stems of grass have buds which are in

inactive state. By getting warmth and moisture from rain water, these buds gets activated and grow to produce new grass plants.

Vegetative propagation in Bryophyllum

Buds are present on the stems as well as the leaves

of the bryophyllum plant which can be reproduced by vegetative propagation by using either its stem or its leaves.

Leaves of the plant have special buds in their margins. These buds may get detached from the leaves and fall to the ground or buds can also drop to the ground together with leaf and then grow to produce new plants.

Sometimes buds starts to grow even before a leaf drops off from the plant. Such a mature leaf of the bryophyllum plant falls on the ground ten each plantlet can grow into new plant.

Vegetative propagation in potato tuber

A tuber is a thickened part of the plant which is

swollen with the stored food. The tuber has number of buds called eyes.

There are two types of tubers potato is stem tuber and sweet potato is root tuber.

The buds on the body of the tuber act as organs for vegetative propagation and grow as a new plant when planted in soil.

The vegetative propagation method of producing potato plants by tubers is much faster than the production of the potato plant from seeds.

Example: - bryophyllum, guava (buds are present in roots), potato, sweet potato, garlic, water hyacinth, tulip, mint, strawberry can be produces by this method.

Artificial propagation of plants The process of growing many plants from one plant

by man made methods is called artificial propagation of plants.

Methods of Artificial propagation Cutting, Layering, Grafting Cutting A small part of plant which is removed by making a

cut with a sharp knife is called the cuttings. A cutting may be a piece of stem, root or leaf.

Each cutting should have some buds on it. A cutting of the parent plant having some buds on it

taken and its lower part is buried in moist soil. After few days the cuttings develop roots and shoots, and grow into a new plant.

Ex: - Rose, Bougainvillea, Chrysanthemum, grapes, sugarcane, bananas and cactus.

Layering A branch of the plant is pulled towards the ground

and a part of it is covered with moist soil leaving the tip of the branch exposed above the ground.

After some time new roots develop from the part of branch buried in the soil. The branch is then cut off from the parent plant. The part which has developed roots grows to become a new plant.

Ex:- jasmine, strawberry, raspberry, lemon, guava, hibiscus, bougainvillea

Grafting It is the method in which the cut stems of two

different plants (one with roots and one without roots) are joined in such a way that the two stems join and grow as a single plant.

The cut stem of the plant having roots and fixed in the soil is called stock.

The cut stem of the plant without roots is called scion.

Process of grafting Two plants are chosen which are which are to be

used as scion and stock. The stem is removed from the plant chosen to be

made scion by making a slant cut.



The stem of the plant to be used in grafting is also cut in a slanting way. The lower part of the plant is called stock.

The scion is placed over the stock. The cut surfaces are fitted together & bound tightly with a piece of cloth & covered properly with polyethene sheet to prevent harmful infection by bacteria or fungus & loss of water & plant sap from the cut & joined ends of stock and scion.

The cut soon heals and the stock and scion of two plants grow together and become one plant.

The scion continues to produce its original leaves, flowers and fruits but it gets water and minerals for making food from the chosen stock. So the fruits will have the characteristics of both the plants.

Ex: - apple, peach, apricot and pear trees are often grafted.

Advantages of the grafting method It enables to combine the most desirable

characteristics of two plants. By this method very young scion can be made to

flower and produce fruits faster. It enables us to obtain flowers and fruits having

desired characteristics by grafting scions from different varieties of plants on the same stock.

By this method we can produce the varieties of seedless fruits.

Advantages of Artificial vegetative propagation The new plant exactly similar to the parent plant

having desired characteristics can be produced. The fruit trees from the cuttings or by grafting start

to bear fruit much earlier. The plants grown by this method needs less

attention in their early years than the plants grown from seeds.

Many plants can be grown from just one parent plant.

Seedless plants can also be grown by this method. Tissue culture The production of the new plants from a small piece

of plant tissue or cells removed from the growing tips of a plant in a suitable growth medium is called tissue culture.

The growth medium used for growing plant tissues is very important in this process because it contains various plant nutrients in the form of jelly called agar.

ADVANTAGES OF TISSUE CULTURE It is very fast technique. Thousands of the plantlets

can be produced in a few weeks time from a small amount of plant tissue.

The new plants produced by tissue culture are disease free.

Tissue culture can grow the plants round the year, irrespective of weather and seasons.

Very little space is needed for developing new plants by tissue culture.

SEXUAL REPRODUCTION Sexual reproduction takes place by the combination

of special reproductive cells called ‘sex cells’. The cells involved in sexual reproduction are called

gametes. Gametes are of two types: male gametes and female

gametes. In sexual reproduction, a male gamete fuses with a

female gamete to form a new cell called ‘Zygote’. This Zygote then grows and develops into a new organism in due course of time.

Gametes are also sometimes called germ cells. SEXUAL REPRODUCTION IN FLOWERING PLANTS The plants in which the sex organs are carried

within the flowers and the seeds are enclosed in a fruit are called angiosperms. Angiosperms are commonly known as flowering plants.

The sex organs (or reproductive organs) of a plant are in its flowers.

The function of a flower is to make male and female gametes and to ensure that fertilization will take place to make new seeds for the reproduction of plant.

The sexual reproduction in plants takes place in the following steps: The male organ of flower called ‘stamen’ makes the

male gametes (male sex cells) of the plant. These male gametes are present in pollen grains.

The female organ of a flower called ‘carpel’ makes the female gametes (female sex cells) of the plant. These female gametes are present in ovules. The female gametes present in ovules are also called ‘ova’, ‘egg cells’ or just ‘eggs’.

The male gametes present in pollen grains fertilise the female gametes or eggs cells present in ovules.

The fertilise egg cells grow within ovules and become seeds.

The seeds produce new plants on germination (under suitable condition of water, warmth, air and light, etc.).

STRUCTURE OF FLOWER The main parts of a flower are: Receptacle, sepals,

petals, stamen, and carpel. Receptacle:-



The base of a flower to which all the parts of a flower are attached is called receptacle.

Sepals:- The green, leaf-like parts in the outermost

circle of a flower are called sepals. All the sepals taken together are called ‘calyx’.

The function of sepals (OR Calyx) is to protect the flower in its initial stages when it is the from of a bud.

Petals:- The colourful parts of a flower are called

petals. The petals lie inside the sepals. All the petals taken together are called ‘Corolla’.

The petals are usually scented. The function of petals (or Corolla) is to attract insects (for pollination) and to protect the reproductive organs which are at the centre of the flower.

Stamen:-

The little stalks with swollen tops just inside the ring of petals in a flower are called stamens. Stamen is the male reproductive organ of the plant. Stamen produces pollen grains.

The stamen is made of two parts: a filament and an anther. The stalk of stamen is called filament and the swollen top of stamen is called anther. It is actually the anther of a

stamen which makes the pollen grains and stores them (The pollen grains appear to be yellow, powder-like substance to us). Pollen grains contain the male gametes (or male sex cells) of the plant.

Carpel:-

In the centre of a flower, there is a flask-shaped organ called carpel. Carpel is the female reproductive organ of the plant.

A carpel is made of three parts: stigma, style and ovary. The top part of carpel is called stigma. Stigma is for receiving the pollen grains from the anther of stamen (during pollination). Stigma is sticky so that pollen can stick to it. The middle part of carpel is called style. Style is a tube which connects stigma to the ovary. The swollen part at the bottom of a carpel is called ovary (see figure). The ovary makes ovules and stores them. Ovules contain the female gametes (or female sex cells) of the plant. There are usually many ovules in the ovary (but we have shown only one ovule in the ovary in figure 45). Each ovule contains only one female gamete of the plant. The female gamete (or female sex cell) of the plant which is present inside the ovule is called ‘ovum’ or ‘egg’.

The flowers which contain only one sex organ, either stamens or carpels, are called unisexual flowers. The flowers of papaya and watermelon plants are unisexual flowers.

The flowers which contain both the sex organs, stamens as well as carpel, are called bisexual flowers. The flowers of Hibiscus and mustard plants are bisexual flowers.

A new seed of the plant is formed when the male gamete present in a pollen grain unites with the female gamete present in the ovule.



Pollination The transfer of pollen grains from the anther of a

stamen to the stigma of a carpel is called pollination.

When the pollen grains from the anther of a flower are transferred to the stigma of the same flower (or another flower on the same plant), it is called self- pollination.

When the pollen grains from the anther of a flower on one plant are transferred to the stigma of a flower on another similar plant, it is called cross- pollination.

Insects help in cross- pollination as follows: When an insect sits on the flower of a plant for sucking nectar, then the pollen grains from the anther of this flower stick to its body. And when this insect now sits on another flower of another similar plant, then the pollen grains sticking to its body are transferred to the stigma of this second flower.

Fertilisation

After a pollen grain falls on the stigma, the next step is fertilization.

Fertilisation occurs when the male gamete present in pollen grain joins with the female gamete (or egg) present in ovule.

When a pollen grain falls on the stigma of the carpel, it bursts open and grows a pollen tube downwards through the style towards the female gamete in the ovary.

A male gamete moves down the pollen tube. The pollen tube enters the ovule in the ovary. The tip of pollen tube bursts open and male gamete comes out of pollen tube. In ovary, the male gamete of pollen combines with the nucleus of female gamete or egg present in ovule to form a fertilised egg (called zygote).

Formation of Fruit and Seeds

Seed: The fertilised egg (or zygote) divides several

times to form an embryo within the ovule. The ovule develops a tough coat around it and is gradually converted into a seed (containing the baby plant).

Fruit: The ovary of flower develops and becomes a fruit (with seeds inside it). The other parts of flower like sepals, petals, stamens, stigma and style dry up and fall off. Only the ovary is left behind. So, at the place on plant where we had a flower originally, we now have a fruit (which is the ovary of the flower containing seeds).

Function of fruit: A fruit protects the seeds. Some fruits are soft, sweet and juicy like mangoes and oranges. But some fruits are hard, dry and woody like the peanuts and almonds, etc.

Structure of seed: The seed contains a body plant (or embryo) and

food for the baby plant. The part of baby plant in seed which develops

into shoot with leaves is called plumule. The part which develops into root is called

radicle. The part of seed which contain stored food for

the baby plant is called cotyledon. The wheat grains, gram (chana), corn, peas, and

beans, are all seeds.



Germination of Seeds In dry state, the seeds remain alive but inactive for

long periods. The beginning of the growth of seeds is called

germination of seeds. Germination begins when the seed absorbs water, swells and bursts through the seed coat. The water helps the enzymes to function in the seed. The enzymes digest the stored food in cotyledons and make it soluble. This soluble food makes the radicle and plumule present in the seed to grow.

The radicle of the seed grows first it form the root. The root pushes down into and begins to absorb water and minerals from the soil. After this plumule grows upwards to form the shoot.

SEXUAL REPRODUCTION IN ANIMALS Male and Female An animal having male sex cells called ‘sperms’ in

its body is called male. An animal having female sex cells called ‘ova’ (or

‘eggs’) in its body is called female. Gametes

Structure of egg: The ovum or egg contains water

and stored food. The important part of ovum or egg is its nucleus.

Structure of sperm: The sperm cell is hundreds or even thousands of times smaller than the ovum or egg and it has a long tail. The sperms are motile which can move independently with the help of their tails.

The cell which is formed by the fusion of a male gamete and a female gamete is called zygote.

Fertilisation The fusion of a male gamete with a female to form a

zygote during the sexual reproduction, is called fertilisation

The zygote (or fertilised egg) grows and develops to form a new baby. The unborn baby in the uterus

in the early stages of development (when its body parts are not much developed) is called an embryo.

The unborn baby in the uterus in the later stages of development (when all its body parts are well developed and can be identified) is called a foetus.

Types of fertilization Two modes of fertilization in animals : internal

fertilization and external fertilisation Internal fertilization:- The fertilisation which occurs inside the

female body is called internal fertilisation. In internal fertilization, the female animal’s eggs are fertilised by sperms inside her body.

Internal fertilization takes place in mammals (including human beings), birds and reptiles.

Copulation is the act by which the male animal transfers his sperms into the female animal’s body.

External fertilization:- The fertilisation which occurs outside the

female body is called external fertilization. In external fertilisation, the female animal’s eggs are fertilised by sperms outside its body.

In amphibians (like frogs and toads) and fishes, external fertilisation takes place.

The males and female of frogs and fishes release their sperms and eggs in water in which they live. The sperm then collide with the eggs and fertilise them outside the body of female frog or fish.

Method of development of zygote. In human beings the zygote grows and

develops into a baby inside the female body (mother’s body). And then the mother gives birth to the baby.

A hen sits on its fertilised eggs for a considerable time to give them warmth. During this period, the zygote grows and develops to form a complete chick. This chick then comes out of the eggs by breaking its shell.

The Advantages of Sexual Reproduction In asexual reproduction, the offsprings are almost

identical to their parent because they have the same genes as their parent. So, much genetic variation is not possible in asexual reproduction. This is a disadvantage of asexual reproduction because it inhibits the further evolution of the organism.

The sexual reproduction the offsprings, although similar to their parents, are not identical to them or to one another. This is because the offsprings receive some genes from the mother and some from the father. Because of the mixing of genes of mother and father in various different combinations, all the offsprings have genetic



variations. In this way, sexual reproduction leads to a greater variety in population.

Sexual reproduction plays an important role in the origin of new species having different characteristics. This genetic variations leads to the continuous evolution of various species to form better and still better organisms.

Why the Amount of DNA Does Not Get Doubled Sexual Reproduction The gametes are special type of cells called

reproductive cells which contain only half the amount of DNA (or half the number of chromosomes) as compared to the normal body cells of an organism. So, when a male gamete combines with a female gamete during sexual reproduction, then the new cell ‘zygote’ will have the normal amount of DNA.

The human sperm has 23 chromosomes and the human egg (or ovum) has also 23 chromosomes. So, when a sperm and an egg fuse together during fertilization, then the zygote formed will have 23+23 = 46 chromosomes, which is the normal number of chromosomes.

How Sexual Reproduction Takes Place in Animals The male parent produces male gametes (male sex

cells) called sperms. The sperm is a small cell with a long tail (flagellum) for movement.

The female parent produces female gametes (female sex cells) called ova (or eggs). The ovum (or eggs) is a much bigger cell than the sperm, having a lot of cytoplasm.

The sperm enters into the ovum (or eggs) and fuses with it to form a new cell called ‘zygote’. This process is called fertilization. So, the zygote is a fertilised ovum (or fertilized eggs).

The zygote then divides again and again to form a large number of cells (all of which remain together). And ultimately zygote grows and develops to become a new baby.

Puberty The age at which the sex hormones (or gametes)

begin to be produced and the boy and girl become sexually mature (able to reproduce) is called puberty.

Age for puberty: Boys (13 to 14 years) and girls (10 to 12 years).

The various changes which occur in boys at puberty are:- Primary sexual characters: - The penis and

testes become larger. The testes start to make sperms. Feelings and sexual drives associated with adulthood begin to develop.

Secondary sexual characters: - Hair grows under armpits and in public regions (genital area) between the thighs. Hairs also grow on other parts of the body like chest and face (moustache, beard, etc.). Body becomes more muscular due to the development of muscles. The voice deepens (or cracks). Chest and shoulders broaden.

The various changes which occur in girls at puberty are:- Primary sexual characters: - Fallopian

tubes, uterus and vagina enlarge. Ovaries start to release eggs. Menstruation (monthly period) start. Feelings and sexual drives associated with adulthood begin to develop.

Secondary sexual characters:-Hairs grow under armpits and public region. Mammary glands (or breasts) develop and enlarge. The hips broaden. Extra fat is deposited in various parts of the body like hips and thighs.

Hormones responsible for changes in males and females body: males(testosterone) and females(estrogen and progesterone)



THE MALE REPRODUCTIVE SYSTEM Parts Details

Testes Paired oval – shaped male sex glands.

Consist of seminiferous tubules, where the sperms are produced.

Produce a male sex hormone called testosterone.

Scrotum Small pouch that contains testes.

Present outside the abdominal cavity as sperm are formed here and these requires

a lower temperature than the normal body temperature (3 C lower than the body).

Epididymis Coiled tube – like structure firmly attached to the testis and serves as the

storehouse of sperms.

Inside the epididymis, sperms become mature and develop motility.

Vas Deferens Also known as sperm duct.

Connects testes to the urethra in order to allow the passage of semen.

Urethra Common passage for both the sperms and urine, but never carries both of them at

the same time.

Prostate Gland

and Seminal

Vesicles

Secretes seminal fluid and nutrients.

Fluid and nutrients combine with sperm to form semen. Milky, viscous fluid

contains fructose proteins and other chemicals for nourishing and stimulating

sperms.

Penis External male genital organ.

Transfer sperms into the vagina of the female during copulation.

Sperms Tiny and motile bodies that use their long tail to move through the female tract.

THE FEMALE REPRODUCTIVE SYSTEM

Parts Details

Ovaries Paired, oval – shaped organs located in the abdominal cavity near the kidney.

Ovary consist of millions of follicles (immature eggs).

Produces thousands of ova or egg cells.

Secretes female sex hormones like oestrogen and progesterone.



Oviduct

(fallopian

tube)

It has a funnel shaped opening near the ovary.

Carries ova or egg from ovary to the uterus.

It is the site of fertilisation.

These open into an elastic bag from both sides known as uterus.

Uterus

( Womb)

Hollow, bear shaped, bag like structure.

Here, the growth and development of foetus takes place.

Rhythmic contractions of the muscles in the uterus causes labour pain.

Cervix It is the lower and the narrower portion of uterus which opens into the vagina.

Vagina Receives the sperms from the male partner.

Serve as a birth canal.

FERTILISATION Vagina receives the penis for putting sperms into

the women’s body. The sperms made in the testes of man are

introduced into the vagina of the women through penis during copulation (or matting).

The sperms are highly active and mobile (moving). The sperms move up through cervix into the uterus. From uterus, the sperm pass into the oviducts.

One of the oviducts contains an ovum (or egg cell) released by the ovary during ovulation. Only one sperm fuses with the ovum (or egg) in the oviduct to form a zygote. This is called fertilisation.

Development of Embryo and foetus 1. The zygote divides rapidly by mitosis as it moves

down slowly in the oviduct and forms a hollow ball of hundreds of cells (called an embryo).

2. Embryo sinks into soft and thick lining of the uterus and gets embedded in it. The embedding of embryo in the thick lining of the uterus is called implantation.

3. After implantation, a disc- like special tissue develops between the uterus wall and the embryo which is called placenta (The foetus is connected to placenta in mother’s body through umbilical cord).

4. During the gestation period (38 weeks or 9 months), the foetus grows to become a baby and is born.

Importance of placenta: It is through the placenta that all the requirements of the developing foetus like nutrition, respiration, and excretion, etc., are met from the mother’s body. Gestation period: The time period from the fertilisation up to the birth of the baby is called gestation. The average gestation period in humans is about 9 months (or about 38 weeks). Birth of baby: The rhythmic contraction of uterus muscles gradually pushes the baby out of the mother’s body through vagina. This is how a baby is born.

Zygote Embryo Foetus A zygote is formed by the fusion of male and female gametes (sperm and egg)

An embryo is formed by the repeated cell division of a zygote.

A foetus is formed by the growth and development of an embryo

A zygote is the beginning of the Formation of a baby.

An embryo is an unborn baby in the uterus in the early stages of Development (up to 8 weeks after Fertilization).

A foetus is an unborn baby in the uterus in the later stages of Development (after 8 Weeks till birth).

A zygote is a single cell. It is Smaller than a full stop.

An embryo is multicellular. The body features of growing baby embryo are not much developed.

A foetus is also multicellular. The body features of developing Baby (like hands, legs, head, eyes and ears, etc.) can be identified.

Ovulation: The release of an ovum (or egg) from a matured follicle in ovary is called ovulation. Sexual cycles in females or Menstruation (occurs every 28 days starting from puberty) In a normal, healthy girl (or woman), ovulation

takes place in the middle of menstrual cycle on the 14th day of the beginning of menstrual cycle of 28 days.

Before every ovulation, the inner lining of the uterus becomes thick and soft with lot of blood capillaries in it to supply food and oxygen for growth of zygote into a baby if fertilization takes place.

If a sperm is not available at the time of ovulation, then fertilization of ovum does not take place. So, the thick and soft uterus lining having lot of blood capillaries in it is not required.



The unfertilised ovum dies within a day and the uterus lining also breaks down. That the breakdown and removed of the inner, thick and soft lining of the uterus along with its blood vessels in the form of vaginal bleeding is called menstrual flow or menstruation.

Menarche and Menopause The first occurrence of menstruation (or periods) at

puberty is called menarche. Menarche is the beginning of the reproductive life of a girl (or women).

The permanent stoppage of menstruation (or periods) in a women is called menopause. Menopause occurs in women at the age of about 45 to 50 years. A woman stops ovulating at menopause and cannot longer become pregnant.

Reproductive Health: Reproductive health can be defined as the rate of physical, mental and social fitness to lead a healthy reproductive life. The good reproductive health provides:- Both male and female, the fertility control

methods. Awareness of limiting their family size. Protection from infection and sexually transmitted

diseases. A limited size of family and no partial views about the sex of the population should be there in our society. For this, we need to maintain sex ratio and population size. Sex Ratio: It is the ratio of the number of females to the number of males in a population. The female – male sex ratio should be maintained in order to have a healthy society. Due to reckless female, foeticides, sex ratio is declining rapidly in some sections of our society. BIRTH CONTROL Birth control can be done by preventing pregnancy

in females (or women). The prevention of pregnancy in women (by

preventing fertilization) is called contraception. Device or chemical (drug) which prevents

pregnancy in women is called a contraceptive. Methods used to Prevent Pregnancies: (i) Natural Method: If copulation is avoided

around the days of ovulation, then there will be no fertilization. This is a self-vigilance.

(ii) Barrier methods: These methods prevent the entry of sperms into the female genital tract and fusion of sperm with ova does not take place. All external contraceptives such as condom, and internal contraceptives such a diaphragm and cervical caps or copper-T, are common in this method.

(iii) Chemical methods: To prevent pregnancy certain drugs are also used, they change the hormones related to reproductive system. They are of two types: (a) Oral pills and (b) Vaginal pills (a) Oral pills: They are hormonal preparations and they are taken by the females daily. They are called oral contraceptives (OCs). In some women, oral pills may cause some side effects such as hormonal changes. (b) Vaginal Pills: The pills are placed inside the vagina. They cause no side effects.

(iv) Intra- Uterine Contraceptive Device (IUCD): The use of intrauterine contraceptive device called copper-T is also very effective in preventing pregnancy. A copper-T is placed inside the uterus by a doctor or a trained nurse. The IUCD or copper-T prevents the implantation of fertilised egg in the uterus.

(v) Surgical Methods In males, a small portion of the sperm duct

(or vas deferens) is removed by surgical operation and both the cut ends are ligated (or tied) properly. This prevents the sperms from coming out. The surgical procedure carried out in males is called ‘vasectomy’.

In females, a small portion of the oviducts is removed by surgical operation and the cut ends are ligated (or tied). This prevents the ovum (or egg) from entering into the oviducts. The surgical procedure carried out in females is called tubectomy.

Female Foeticide In order to have a male child (son), some misguided

people in our country get the sex of their unborn child determined by ultrasound technique (though it is illegal to do so), and if it is a female foetus, they get it removed by surgery. This killing of the unborn girl child is called female foeticide. Female foeticide is reducing the number of girls drastically in some societies of our country.

Sexually Transmitted Diseases (STDs): The sexually transmitted diseases (STDs) are caused by different pathogens transmitted by sexual contact between a healthy person and an infected person. These pathogens may reside in warm and moist environment of vagina, urethra, anus and mouth. AIDS (Acquired Immuno Deficiency Syndrome) It is a fatal syndrome, caused by a retrovirus-HIV (Human Immunodeficiency Virus): In this syndrome, the immune system of the body is seriously affected. AIDS is transmitted through: (i) sexual contact with an infected person, (ii) transmission of blood of infected person,



(iii) infected needle used for injection, (iv) children of infected mothers can get AIDS

infection from their mother’s milk, and (v) the use of contaminated blade or razor and other

equipments of barbers. Symptoms: (i) In the early stage, the patient is more or less

symptom-free, although lymph nodes become swollen.

(ii) Decreased blood platelets count, sweating at night and weight loss.

(iii) Haemorrhage and fever. (iv) Failure of immunity i.e., the resistance of body to

attack by pathogens is greatly reduced, thereby patient gets affected by every disease quickly.

(v) The patient then loses memory and cannot speak properly.

(vi) Finally, the patient dies due to total breakdown of the immune system.

Prevention: (i) Using only sterilized needle for injection. Better

use disposable needles and syringes. (ii) Do not allow the use of common razor at the

barber’s shop. Ask barber to use to use a few blade for shaving.

(iii) Avoid blood transfusion from excessive drug user. A blood donor must be first tested HIV negative.

(iv) Remain usually faithful to your spouse only. (v) Avoid prostitutes and maintain good moral

character. (vi) Avoid homosexuality.

Some Common STDs

Infection Examples Bacterial Infections

(i) Gonorrhoea (ii) Syphilis

Viral Infections

(i) AIDS (Acquired Immune Deficiency Syndrome)

(ii) Genital warts

ASSIGNMENT 1. What kind of reproduction is observed in

following organisms? Hydra, Planaria, Spirogyra 2. Name the reproduction in which new organisms

arise from the fusion of male and female gametes? 3. In which organisms fission occur and how? 4. How does reproduction occur by regeneration? 5. Name the reproductive parts of a flower with

their subparts? 6. Classify the pollination in its different types. 7. When does pollen tube develop in a flower? 8. Explain the term primary sex characters. 9. What is the composition of semen plasma? 10. At which age eggs or follicles start maturing in

females? 11. What is fertilisation and its product? 12. Write the age of menarche and menopause in

females. 13. What is the first sign of pregnancy in a woman? 14. Define the term reproductive health. 15. Write the function of epididymis. 16. In which mode, hormonal methods of

contraception act? 17. List out a disadvantage of abortion? 18. List out the basic features of reproduction. 19. What are the products and conditions of multiple

fission? In which organisms it occurs? 20. How does fragmentation occur in Spirogyra? 21. Which process is shown in the following diagram?

Explain. 22. How can one justify this statement that ‘ Like

physical, mental and social fitness, human beings need fitness of reproductive life’ i.e., ‘Reproductive Health’. Read the above text and answer the following questions a. Why is ‘Reproductive Health’ important? b. What value will the learners infer from this

passage? 23. (a) Which plants reproduce by sexual

reproduction? (b) What is the function of a flower in relation to sexual reproduction?

24. During sexual reproduction the amount of DNA does not get doubled. Explain.

25. List out two characteristic of zygote. 26. When does reproductive life starts in a woman

and when it ends? 27. What is contraception? How it can be achieved? 28. What are sexually transmitted diseases? Give two

reasons. 29. Write the functions of the following male

reproductive organ. (a) Testes (b) Seminal vesicles

30. What is gestation period and the next event after its completion?

31. (a) Which glands provide fluid to the semen?



(b) State two advantages of semen in relation to sperms.

32. Write the answers. (a) Name the site of implantation and

development of baby in human female. (b) Mention any two benefits of using barrier

method during sexual act. (c) Differentiate between reproduction and

regeneration. (d) Which organisms grow by regeneration?

33. We hear and read about female foeticide, which is really a wrong practice. In some families, be it in rural or urban, females are tortured for giving birth of a boy or a girl. Read the given passage and answer the following questions (a) In your opinion, the approach of the society

towards mother in this regard is correct or not? Explain the scientific reason.

(b) What value will the learners infer from this passage?

34. Define the terms unisexual and bisexual giving one example of each.

35. Answer the following.

(a) Label the following diagram. (b) Which process is being shown in this? (c) How is the process of binary fission different

from budding? (d) List any three advantages of vegetative

propagation? (e) When does ovulation occur during the

menstrual cycle in a normal healthy woman? (f) Draw a labelled diagram to show

reproductive system of human female. 36. Write three differences between primary sex

organs and secondary sex organs. 37. What is pollination? Name its two types. How do

they differ from each other? 38. Describe the process of budding in yeast with the

help of diagram. 39. List out the differences between menarche and

menopause. 40. What is vegetative propagation? How does it

occur naturally in plants? 41. Define the following terms.

(a) Placenta (b) Implantation

42. It is a well known fact that pregnant woman’s health is a backbone of every family and society. Read the above text and answer the following questions. (a) Which tissue is responsible for providing

nutrition from mother to growing embryo?

(b) According to you what can be the likely measures to maintain woman health during pregnancy?

(c) What value will the learners infer from this passage?

43. Trace out the movement and fate of egg in female body.

44. Name the following (a) The body part in which the testes are present

in a human life. (b) The part where the sperms are produced in

the testes. (c) The fully developed part of the ovary

containing a mature egg. (d) The accessory fluid in human males, whose

secretion activates the sperms. 45. Distinguish between pollination and fertilisation.

Mention site and product of fertilisation in a flower. Draw a well – labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.

46. List out the various components of female reproductive system with their functions.

47. Describe the menstrual cycle. 48. Explain the process of seed and fruit formation in

plants. 49. List out the advantages of artificial vegetative

propagation. 50. Give two reasons for avoiding frequent

pregnancies by woman. Explain the following methods of contraception giving one example each. (a) Barrier method (b) Chemical Method

(c) Surgical Method 51. Answer the following

(a) Explain the term grafting as a means of vegetative propagation in plants.

(b) Define stock and scion. (c) Which fruit trees are usually propagated by

grafting method? 52. Mr. R Sharma was suffering from various types of

diseases presently. He went for through health check ups and was diagnosed as HIV + ve. Soon this news spread in his neighbourhood and on account of this, he faced social isolation. Read the passage and answer the following questions (a) Do you think people’s indifference towards

HIV+ve people is justifiable? (b) What kind of approach should we have

towards the persons suffering from AIDS? (c) How can one protect oneself from this

diseases? (d) What value will the learners infer from the

passage?



A recognizable feature of a human being (or any other organism) like height, complexion, shape of hair, colour of eyes, and shape of nose and chin, etc, are called ‘characters’ or ‘traits’.

The transmission of characters (or traits) from the parents to their offsprings are called heredity.

Gametes are the reasons for heredity. Variations The differences in the characters (or traits) among

the individuals of a species is called variation. Example of variations in human beings which

involves our ears. The lowest part of our ear is called earlobe. In most of the people, the earlobe is ‘hanging’ and it is called free earlobe. In some people, however, the earlobe is closely attached to the side of the head and it is called attached earlobe. Thus, most people have free earlobes whereas some people have attached earlobes. So, the free earlobes and attached earlobes are two variations found in human population.

The variation is a necessity for organic evolution. Genetic Variation :-Majority of the variations caused by genetic differences in a population may arise due to mutation, meiosis and sexual reproduction, while many other characteristic are influenced by both environment and gene. Causes of Variation:-

1. Genetic variations a. Mutation b. Meiosis c. Sexual reproduction

2. Environmental factors a. Diet b. Radiation chemicals c. Pollution

Points stating importance of variation are (i) Variations are the basis of heredity. (ii) Adaptability to adverse conditions is due to

variations. (iii) New varieties of an organism may arise due to

genetic variations and form raw materials for evolution.

Accumulation of Variations Example. Suppose a bacterium produces two

bacteria by sexual reproduction. Again suppose that one of the offspring bacterium has a variations due to which it can tolerate a little higher temperature (or little more heat) than the other one. Now, these variations of little more heat

resistance will go on accumulating in the offsprings of successive generations of this bacterium. And this will ultimately give rise to a variant of bacteria which will be highly heat resistance and able to survive even at very high temperatures.

Some terms to be defined for mendel’s experiment

Terms Definition Gene A functional unit of heredity

present in chromosome of cell nucleus. It composed of DNA and codes for one polynucleotide (protein). It determines a particular character (phenotype).

Allele One of the different forms of a particular gene, e.g., hair colour.

Dominant gene A gene, whose phenotype will be expressed even in the presence of another allele of that gene. Represented by a capital letter, e.g., T.

Recessive gene Both the genes present must be of this type for the phenotype to be expressed. Represented by a small letter, e.g., t.

Genotype Representation of genetic composition of an individual.

Phenotype The expression of the genotype, which is an observable or measurable characteristic.

Chromosomes A long rod – like structure in a nucleus. It appears at cell division and is thought to carry genes.

Hybrid An individual having two different alleles for the same trait.

Monohybrid cross A hybridisation cross in which inheritance of only one pair of contrasting character is studied.

Dihybrid cross A cross in which inheritance of two pairs of contrasting character is simultaneously studied.

Heredity and Evolution



Homozygous A condition in which an individual possesses a pair of identical genes controlling a given character and will breed true for this character

Heterozygous A condition in which an individual has a pair of contrasted genes for any one character and will breed true for this character

Rules for the Inheritance of Traits – Mendel’s Contributions:- The heredity of most of the living organisms is found to be regulated by certain definite principles. Some of the basic laws of inheritance were proposed by Gregor Johann Mendel ( 1822 – 1884).

Mendel opted garden peas to conduct his experiments. His experiments with garden peas and the inferences together with his interpretations constitute the foundation of modern genetics. Mendel selected garden peas for his experiments because:- (i) They grow quickly and easily. (ii) It is easy to recognise their different traits. (iii) Pea plants can be crossed or self – pollinated and

have a flower structure that limits accidental contact.

(iv) Garden pea has a number of clear cut differences.

Monohybrid Inheritance and the Law of Segregation (monohybrid cross by Mendel)Character of pea plant studied was height. More pea pants were tall and few were dwarf. So, tallness was controlled by a dominant gene (T) and dwarfness was controlled by recessive gene (t).



Phenotypic ratio in monohybrid cross will be : Tall plants : Dwarf plants = 3 : 1

Dihybrid Inheritance and the Law of Independent Assortment The two pairs of contrasting characteristics chosen by Mendel were shape and colour of seeds : round – yellow seeds, and wrinkled – green seeds. Number of round seeds were much more than wrinkled seeds so roundness is controlled by a dominant gene (R) and wrinkled shape was controlled by recessive gene (r). Number of yellow seeds were much more than wrinkled seeds so yellow colour is controlled by a dominant gene (Y) and green colour was controlled by recessive gene (y). Mendel collected a total of 556 F2 seeds and counted them shape wise and colour wise. He got the following result :

Round – yellow seeds 315 Round – green seeds 108 Wrinkled – yellow seeds 101 Wrinkled – green seeds 32

The phenotypic ratio of different type of seeds can be written as : Round Round wrinkled Wrinkled Yellow : Green : Yellow : Green = 315 : 108 : 101 : 32 Seeds Seeds Seeds Seeds = 9 : 3 : 3 : 1





Law Statement Dominance Any appeared trait is always decided by a pair of genes. The trait controlled by dominant gene

always appear in next generation

Segregation or inheritance

Dominant and recessive both type of genes are inherited to the progeny. The dominant and recessive genes though remain together for long time but do not mix with each other and segregate at the time of gamete formation.

Independent Assortment

The inheritance of one character is always independent to the inheritance of other character within the same individual.

HOW ARE CHARACTERISTICS (OR TRAITS) TRANSMITTED TO PROGENY The characteristics or traits of parents are

transmitted to their progeny (offsprings) through genes present on their chromosomes during the process of sexual reproduction.

Genes work in pairs. There is a pair of genes for each characteristics of an organism (one is dominant gene and the other is recessive gene).

The male gamete and female gamete carry one gene for each characteristic from the gene pairs of parents.

When a male gamete fuses with a female gamete during fertilisation, they make a new cell called Zygote with a full set of genes (on a full set of chromosomes). The Zygote grows and develops to form a new organism having characteristics (or traits) from both the parents which it has inherited through genes.

How Blood Groups are Inherited A person has one of the four blood groups : A, B,

AB or O. Genes IA and IB both are dominant over the genes

IO. If the genotype (gene combination) is IA IA, then

the blood group of the person is A. And if the genotype is IA IO even then the blood group is A (because IO is a recessive gene).

If the genotype is IB IB, then the blood group of the person is B. And if the genotype is IB IO even then the blood group is B (because IO is a recessive gene).

If the genotype is IA IB, then the blood group of the person is AB.

If the genotype is IO IO, then the blood group of the person is O.

Sex Determination The process by which the sex of a person is

determined is called sex determination. The chromosomes which determine the sex of a

person are called sex chromosomes There are two types sex chromosomes, one is called X

chromosome and the other is called Y chromosome.

A male (man or father) has one X chromosome and one Y chromosome. This means that half the male gametes or half the sperms will have X chromosomes and the other half will have Y chromosomes.

A female (woman or mother) has two X chromosomes (but no Y chromosomes). This means that all the female gametes called ova (or eggs) will have only X chromosomes.

The sex of a child depends on what happens at fertilization.

If a sperm carrying X chromosome fertilises an ovum (or egg) which carries X chromosome, then the child born will be a girl (or female). This is because the child will have XX combination of sex chromosomes.

If a sperm carrying Y chromosome fertilizes an ovum (or egg) which carries X chromosome, then the child born will be a boy (or male). This is because the child will have XY combination of sex chromosomes.

There is a 50 per cent chance of a boy and a 50 per cent chance of a girl being born to the parent.

Father (man or husband) is responsible for the sex of the baby (boy or girl) which is born.

ACQUIRED AND INHERITED TRAITS A trait (or characteristics) of an organism which is

‘not inherited’ but develops in response to the environment is called an acquired trait.

The acquired traits of organism cannot be passed on to their future generations.

Example, If we breed some mice, all the progeny of mice will have tails, just like these first generations mice surgically and breed them, we will get new mice, all with full tails. The cut tail of mice is an acquired trait which is never passed on to their progeny. This is because cutting the tails of mice does not change the genes of their reproductive cells (or gametes).

A trait (or characteristics) of an organism which is caused by a change in its genes (or DNA) is called an inherited trait.



Inherited traits can be passed on to the progeny of the organism because they have produced changes in the genes (or DNA) of the organism.

There is a population of red beetles in the green bushes. Again suppose that a colour variation arises during reproduction so that there is one beetle which is green in colour (instead of red). This change of green colour in the beetle has been brought about by a change in the genes (or DNA) of the reproductive cells. The green colour of this beetle is an inherited trait which can be passed on to the next generations.

EVOLUTION Evolution is the sequence of gradual changes

which takes place in the primitive organism over millions of years in which new spices are produced.

Since the evolution is lot of the living organism, so it is also called ‘organic’ evolution.

EVIDENCES FOR EVOLUTION

Homologous organs Analogous organs, and Fossils

Homologous Organs Provide Evidence for Evolution Define: Those organs which have the same basic

structure (or some basic design) but different functions are called homologous organs.

Example, the forelimbs of a man, a lizard (reptile), a frog (amphibian), a bird and a bat (mammal) seem to be built from the same basic design of bones (as shown in Figure 27), but they perform different functions.

Evidence: They are derived from the ancestor who had the ‘basic design’ of the organ on which all the homologous organs are based.

Analogous Organs Provide Evidence for Evolution Define: Those organs which have different basic

structure (or different basic design) but have similar appearance and perform similar functions are called analogous organs.

Example, the wings of an insect and a bird have different structures (the insects have a fold of membranes as wings which are associated with a few muscles whereas a skeleton, flesh and feathers support bird’s wings) but they perform the same functions of flying.

Evidence: They are not derived from common ancestors, they can still evolve to perform similar functions to survive, flourish and keep on evolving in the prevailing environment.

Fossils Provide Evidence for Evolution The remains (or impressions) of dead animals or

plants lived in the remote past are known as fossils.

How the fossils of plants and animals are formed? When organisms (plant or animals) die, their

bodies will decompose by the action of micro-organisms in the presence of oxygen, moisture, etc. organism which we get as fossils on digging the earth.

In many cases the soft parts of the organisms get decomposed and what we get as a fossils is a skeleton of hard parts (like bones etc).

The soft parts of the plants and animals (which usually decompose quickly) are sometimes preserved as fossils in the form of their impressions inside the rocks For example, if a dead leaf gets caught in mud, it will not decompose quickly. The mud around the leaf will set around it as a mould, gradually harden to form a rock and retain the impression of the whole leaf. This forms a leaf fossils which can be dug out from the earth a long time later.

Fossils are obtained by digging into the earth. (age of fossils) The age of fossils can be estimated in two ways :

by the relative method, and by the carbon dating method.

The relative method: When we dig into the earth, we find fossils at different depths. The fossils which we find in layers closer to the surface of the earth are more recent; the fossils which are found in deeper layers of earth are older; whereas the fossils found in the deepest layers of earth are the oldest ones.

The carbon dating method: All the living objects contain some carbon-14 atoms which are radioactive. When a living object dies and forms fossils, its carbon-14 radioactivity goes on decreasing gradually. In the carbon dating method, the age of fossils is found by comparing the carbon -14 atoms radioactivity left in fossils with the carbon 14 radioactivity present in living objects today.

Examples of fossils There are various kinds of fossils. The important

fossils which have been studied are those of ammonite, trilobite and dinosaur.

Ammonities were the invertebrate animals (molluscs) with a flat, coiled, spiral shell which lived in the sea.

Another invertebrate animal fossils which has been studied is that of trilobite.



Dinosaurs are extinct carnivorous or herbivorous reptiles.

Darwin’s Theory of Evolution Charles Robert Darwin gave the theory of

evolution in his famous book ‘The Origin of Species’. The theory of evolution proposed by Darwin is known as ‘The theory of Natural Selection’.

This theory is called the theory of natural selection because it suggests that the best adapted organisms are selected by nature to pass on their characteristics (or traits) to the next generation.

Darwin’s theory of evolution can be described as follows : 1) Within any population, there is natural variation.

Some individuals have more favourable variations than others.

2) Even though all species produce a large number of offsprings, populations remain fairly constant naturally.

3) This is due to the struggle between members of the same species and different species for food, space and mate.

4) The struggle for survival within populations eliminates the unfit individuals. The fit individuals possessing favourable variations survive and reproduce. This is called natural selection (or survival of the fittest).

5) The individuals having favourable variations pass on these variations to their progeny from generation to generation.

6) These variations when accumulated over a long period of time, lead to the origin of a new species.

Example, one of the progeny may be tall (having long legs) than the other progeny. Thus, there may be a variation of height in the progeny. Now, the advantage of long legs to the progeny is that when no food (grass, etc.) is available on the ground, then this progeny having long legs can reach the leaves on tall trees, eat them as food and survive. On the other hand, the progeny which have short height (due to short legs) cannot reach the leaves on tall trees, they will not get any food, they will starve and hence die. Thus, nature has selected the animal with long legs to survive (because it is the fittest animal under these circumstances). Now, since long legs help in survival, the long-legged animals will live long enough to produce their offsprings. The offsprings will inherit long legs. So, all the future generations will have long-legged animals. In this way, the animals having short legs have evolved into animals having long legs due to variation.

Genetic variation is the raw material of evolution.

Synthetic Theory of Evolution: in which the origin of species is based on the interaction of ‘genetic variation’ and ‘natural selection’.

Once a species is extinct, its genes are lost for ever. It cannot re-emerge at all. The small of surviving tigers are a cause of worry from the point of view of genetics because if they all die out and become extinct, their genes will be lost for ever.

SPECIATION The process by which new species develop from

the existing is known as speciation. In simple words, the formation of new species is called speciation.

The important factors for speciation Geographical isolation of a population caused by

various types of barriers (such as mountain ranges, rivers and sea). The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of population.

Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.

Variations caused in individuals due to natural selection.

How Geographical isolation is the major factor in the speciation of sexually reproducing animals ? Geographical isolation is the major factor in the

speciation of sexually reproducing animals because it interrupts the flow of genes between their isolated populations through the gametes.

Why geographical isolation is not a major factor in the speciation of a self-pollinating plant species ? The geographical isolation, cannot be a major

factor in the speciation of a self-pollinating plant species because it does not have to look to other plants for its process of reproduction to be carried out.

Why geographical isolation is not a major factor in the speciation of asexually reproducing animals The geographical isolation, cannot be a major

factor in the speciation of asexually reproducing animals because it does not require any other organism to carry out reproduction.

Evolution of Eyes The eye is a complicated organ which cannot be

generated by a single DNA change. The complex body organs of animals such as eyes have been created in ‘stages’ over many generations.

First of all the rudimentary eye (basic eye) like that of a flatworm (Planaria) was formed. The eyes



of flatworm are very simple that are actually just ‘eye-spots’ which can detect light.

Even these rudimentary eyes provide a survival advantage to flatworm. Starting from this basic design, more and more complex eyes were then evolved in various organisms.

Most of the animals have eyes. For example, the insects, octopus and invertebrates, all have eyes.

Evolution of Feathers Sometimes an evolutionary change produced in an

organism for one purpose later on becomes more useful for an entirely different function.

Birds evolved feathers as a means of providing insulation to their bodies is cold weather but later on these feathers became more useful for the purpose of flying.

Even some dinosaurs had feathers though they could not fly by using these feathers. Birds, however, adapted feathers for flying.

The presence of feathers on birds tells us that the birds are very closely related to reptiles dinosaurs (which had feathers) were reptiles.

Evolution by Artificial Selection Different looking organism can in fact be created

from the same basic design of the ancestor. The wild cabbage plant is a good example to prove

that entirely different looking organism can evolve from the same organism by the process of evolution.

The farmers have been cultivating wild cabbage as a food plant for over two thousand years and have produced (or evolved) entirely different looking vegetables like cabbage, broccoli, cauliflower, Kohlrabi and Kale from it by artificial selection. 1) Some farmers wanted to have very short

distances between the leaves of wild cabbage and produced the common variety of ‘cabbage’.

2) When farmers opted for the arrested flower development of wild cabbage plant, it led to the production of another variety of cabbage called ‘broccoli’.

3) Some farmers went in for sterile flowers of wild cabbage and developed another variety of cabbage called ‘cauliflower’.

4) When farmers opted for the swollen parts of wild cabbage, it led to the evolution of a yet another variety of cabbage called ‘Kohlrabi’.

5) And finally, the farmers wanted to grow large leaves of wild cabbage and ended up producing a leafy vegetable called ‘Kale’ which is also a variety of wild cabbage.

Evolution Should Not be Equated With Progress There is no real progress in the concept of

evolution. Evolution is just the production of diversity of life forms and shaping of this diversity by the environmental selection. The only progress in evolution appears to be that more and more complex body designs of organisms have emerged over the ages.

Origin of Life on Earth A British scientist J.B.S. Haldane suggested in 1929

that life must have developed from the simple inorganic molecules (such as methane, ammonia, hydrogen sulphide etc.) Which were present on the earth soon after it was formed. He said that the conditions on earth at that time (including frequent lightning) could have converted simple inorganic molecules into complex organic molecules which were necessary for life. These complex organic molecules must have joined together to form first primitive living organism. Haldane also suggested from theoretical considerations that life (or living organism) originated in the sea water.

The theory of origin of life on earth proposed by Haldane was confirmed by experiments conducted by Stanley L. Miller and Harold C. Urey in 1953. They assembled an apparatus to create an early earth atmosphere which was supposed to consist of gases like methane, ammonia and hydrogen sulphide, etc., (but no oxygen), over water. This was maintained at a temperature just below 1000 C and electric sparks were then passed through the mixture of gases (to simulate lighting) for about one week. At the end of one week, it was found that about 15 per cent of carbon (from methane) had been converted into simple compounds of carbon including ‘amino acids’ which make up protein molecules found in living organisms. This experiment provides the evidence that the life originated from inanimate matter (or lifeless matter) like inorganic molecules.



ASSIGNMENT 1. Define inheritance. 2. Name the scientist who established the laws of

inheritance. 3. What is gene? 4. What is the function of genes in an organism? 5. In terms of evolution, what is the significance of

homology between a human hand and a wing of a bird?

6. Name the scientist, who gave an experimental support to Haldane’s theory of origin of life.

7. What is reproductive isolation? 8. Give examples of vestigial organs present in

human body. 9. What is the evolutionary significance of the fossil

Archaeopteryx? 10. Give an example of characteristic being used to

determine of what relationship does two species have in terms of evolution.

11. Define a variant. 12. What is hybrid? 13. What are germ cells? 14. Why does reproduction lead to variation? 15. Which vestigial organ in man suggests that he is a

descendent of herbivorous mammals? 16. State one of the evolutionary forces leading to the

origin of a new species according to the synthetic theory of evolution.

17. Give two characteristic of homologous organs. 18. What is the cause of variation in asexually

reproducing organisms? 19. What is carbon dating? 20. What are connecting links? How they do provide

us information about the evolution of an organism?

21. A chimpanzee can hold objects by its hand and an elephant by its trunk. Are these two organs analogous or homologous? Give reason in support of your answer.

22. Define genetic drift and gene pool. 23. Mention three important features of fossils which

help in the study of evolution. 24. What are dominant and recessive traits? 25. A very small population of a species faces a greater

threat of extinction than a larger population. Provide a suitable genetic explanation.

26. Do genetic combination of mothers play a significant role in determining the sex of a newborn? Explain.

27. Manu visited the hospital with her mother, where she observed a poster sex determination is a crime. She discussed the issue with her mother and realised that sex determination was banned as there was an increase in female infanticide across our country.

a. How can we determine sex of a baby? b. What values are promoted by the hospital?

28. Give the pair of contrasting traits of the following characters in pea plant and mention, which is dominant and recessive.

a. Yellow seed b. Round seed 29. Summarise the modern synthetic theory of

evolution. 30. In Mendel’s experiment of inheritance in which he

took two contrasting characters, i.e., round green and wrinkled yellow seeds.

a. What was the phenotype of offspring in F1 – generation?

b. What was the ratio of offspring in F2 – generation?

31. How is the sex of a newborn determined in humans?

32. Mita observed that her grandmother was preparing a family tree. On enquiring why it was done, she explained that it was necessary to know our roots as we have inherited many traits from our ancestors. She also mentioned that now everbody wants to live in nuclear families and joint families had disappeared?

33. Explain Mendel’s observation when he crossed a homozygous tall (TT) plant with homozygous dwarf (tt) plant followed by self cross.

34. A woman has only daughters. Analyze the situation genetically and provide a suitable explanation.

35. Enumerate the functions of chromosomes. 36. Why Mendel selected pea for his experiment? 37. What are the key factors in the modern concept of

evolution? 38. In human beings, the statistical probability of

getting either a male or female child is 50 : 50. Give a suitable explanation.

39. Explain the two kinds of variations. Which of the two is heritable?

40. What are homologous structure? Give an example. Is it necessary that homologous structure always have a common ancestor?

41. Give some application of genetics. 42. What is Paleontology and embryology? 43. Why did Mendel choose pea plant for his

experiments? 44. A village recorded highest cases of atrocities

against women. The health officer of the village organised a skit to convey the fact that women should not be punished for the birth of a girl child. They should be given due respect in society. The villagers were greatly motivated. a. What is the method of sex determination in

humans? b. What are the sex chromosomes in males? c. What values was the officer trying to highlight

through the skit? 45. Can sexual reproduction lead to the variations in

characters, speciation and evolution. Explain.



46. Anita had a huge scar on her cheek after she met with an accident during her school days. She is worried if her baby would inherit the scar had acquired. Her doctor, a sincere medical practitioner explained and successfully convinced Anita.

a. What are acquired traits? b. How is it different from inherited traits? c. Mention the values of the doctors that he

shows in the passage. 47. Give reasons why acquired characters are not

inherited. 48. Explain the importance of variation. 49. What is speciation? Mention the factors due to

which this can happen? 50. Give the basic features of the mechanism of

inheritance. 51. In human, if gene B gives brown eyes and gene b

gives blue eyes. What will be the colour of eyes of the persons having the following combination of genes?

a. Bb b. bb c. BB 52. Define fossils. How do they help in tracing the

process of organic evolution? 53. Define genetics. What is the contribution of Mendel

in this branch of biology? 54. Differentiate between inherited and acquired

characters. Give one example for each type. 55. Does geographical isolation of individuals of a

species lead to formations of a new species? Provide a suitable explanation.

56. Explain homologous and analogous organs and their significance.

57. Explain the mechanism of sex determination in humans.

58. Kalawati often blame her daughter – in – law for having only daughters and no son. As being a biology student how will you convince Kalawati that her daughter – in – law has no role in giving birth to girls or boys?

59. Given reason for your choice. A person first crossed pure bred pea plants having round – yellow seeds with pure bred pea plants having wrinkled green seeds and found that only A – B type of seeds were produced in the F1 generation. When F1 generation pea plants having A – B type of seeds were cross bred by self – pollination, then in addition to the original round yellow and wrinkled green seeds, two new varieties A – D and C – B type of seeds were also obtained. (a) What are A – B type of seeds? (b) State whether A and B are dominant traits or

recessive traits. (c) What are A – D type of seeds? (d) What are C – B type of seeds?

(e) Out of A – B and A – D types of seeds, which one will be produced in (i) minimum numbers, and (ii) maximum numbers, in the F2 generation?

60. The person A has only B chromosomes in all its gametes. On the other hand another person C has chromosomes D in half of gametes and chromosomes E in the other half of gametes. When chromosomes B and D combine during fertilisation, a female zygote results. On the other hand, combination of B and E chromosomes produced a male zygote.

a. What are chromosomes i. B ii. D iii. E?

b. Out of B, D and E, which two chromosomes are of the same type?

c. Which chromosomes is smaller in size? d. What is the general name of chromosomes

such as B and E? e. Out of the two persons A and C, which one

is (i) male, and (ii) female? 61. X, Y and Z are three animals. The animal X can fly

but animal Y can only run on ground or walls. The forelimbs of animals X and Y have the same basic design but they are used for different purpose such as flying and running respectively. The animal Z became extinct a long time ago. The study of fossils of Z tells us that it had some features like those of X and some like those of Y. in fact, Z is said to form a connecting link in the evolutionary chain of X and Y.

a. What should the animals X, Y and Z be? b. What name is given to the forelimbs like

those of X and Y which have the same basic design but different functions?

c. Name one feature in which Z resembled X. d. Name one feature in which Z resembled Y. e. Which is the correct evolutionary chain

involving X, Y and Z X Z Y or Y Z X?

62. The organs P and Q of two animals have different structures but similar functions. One the other hand, the two organs R and S of two other animals have the same basic structure but different functions.

a. What are the organs like P and Q known as?

b. Name the organs like P and Q. Also name the animals which have such organs.

c. What are the organs like R and S called? Name the organs like R and S. also name the

animals which have such organs.



Environment: The sum total of all the external factors present in the surroundings influence an organism, it is called Environment. Simply environment is the surrounding of an organism that influences the life. WHAT HAPPENS WHEN WE ADD OUR WASTE TO THE ENVIRONMENT? Human population size has grown enormously over the last hundred years. The demand has been increased for food, water, automobiles and numerous other commodities. These demands are exerting tremendous pressure on our environment and are also contributing to pollute the environment. Thus, in daily activities a lot of waste materials are thrown to the environment. It creates pollution. Biodegradable and Non-biodegradable substances All wastes generated can be categorised into two categories: (a) Biodegradable substances: The substances that are broken down by biological processes are called

biodegradable substances. The biodegradable substances are broken into simpler, harmless, and non-toxic substances in nature. This decomposition is completed by the action of microbes like, bacteria, fungi etc. These substances cannot be transformed into resources, as these are biological in origin. Sewage (faecal matter), cattle dung, house hold garbage, human urine are the important examples of biodegradable substances. Besides these, domestic waste products, agricultural residue, paper, cloth, wool, silk and manure are also biodegradable substances.

(b) Non-biodegradable substances: The substances that are not broken down by the biological processes are called non-biodegradable substances. These substances may be inert and simply persist in the environment for a long time. It may harm the various members of the ecosystem. The non-biodegradable substances cannot be broken into simpler, non-toxic and harmless substances in nature because these are not degraded by microbes. Since, these are mainly man made, so, these cannot be easily recycled. These substances may exhibit biological magnification. Polythene bags, glass objects, pesticides like DDT, industrial chemicals, heavy metals like mercury, lead, arsenic, etc. Synthetic fibres, plastic objects, ballpoint pen refill etc. are non-biodegradable substances. Thus, the solid wastes and municipal solid wastes from homes, offices, stores, schools, hospitals etc. are collected and disposed by the municipality.

ECOSYSTEM – WHAT ARE ITS COMPONENTS? The term ‘ecosystem’ was coined by Tansley. An ecosystem is the structural and functional unit of nature (biosphere) where living organisms interact with the physical environment and shows interplay of matter and energy. An ecosystem is a self-contained, self-regulated and complete system that exchanges matter and energy for the existence of organisms. All organisms such as plants, animals, microorganisms and human beings as well as the physical surroundings interact with each other and maintain a balance in nature. Components of Ecosystems Ecosystem is a basic functional unit which includes the living organisms (biotic components) and non-living (abiotic components), both interacting with each other and both are necessary for maintenance of life on the earth. Abiotic components: The abiotic components consist of the following three parts: (a) Climatic factors: These include the physical environment that consists of light, temperature, wind, water,

humidity, soil etc. (b) Inorganic substances: These include carbon dioxide, oxygen, nitrogen, water, phosphorus, sulphur,

potassium and calcium. Most of them have own cycle as well as constitute nutrients. (c) Organic compounds: These include carbohydrates, proteins, lipids, nucleic acid, etc. These are a link

between biotic and abiotic components. Biotic components: These include living organisms of an ecosystem. These are classified on the basis of the food habits as follows:

Our Environment



(i) Producers: These are autotrophs which synthesize food from inorganic substances. All green plants and certain blue-green algae act as producer in an ecosystem.

(ii) Consumers: These are organisms which depend on other organisms for food. All animals which eat plants or other animals are called consumers. The herbivores are called primary consumers, the primary carnivores are called secondary consumers and the secondary carnivores are called tertiary consumers. If it is the ultimate or final plants and plant products, it is called top consumers.

Herbivores – Animals eating only Producers: These are autotrophs which synthesize food from inorganic substances. All green plants and certain blue-green algae act as producer in an ecosystem. e.g., cow, deer, rabbits, etc. Carnivores – Animals eating both plants and animals. e.g., snake, hawks, tigers, etc. Omnivores – Animals eating both plants and animals. e.g., crow, man, etc. Parasites – Animals that suck food from the living hosts. e.g., mosquito, Plasmodium, tapeworm etc.

(iii) Decomposers: These are also known as micro consumers or saprotrophs or osmotrophs. These include many bacteria and fungi. These organisms feed on dead plants and animals. They breakdown many bacteria and fungi. These organisms feed on dead plants and animals. They breakdown the complex compounds of dead organic matters and release inorganic nutrients after decomposition. These inorganic substances together with other organic substances are used as energy soured by producers. Thus, the biotic components include five groups of organisms as follow: (i) Producers, (ii) Primary consumers, (iii) Secondary consumers, (iv) Tertiary or Top consumers and, (v) Decomposers. Trophic Levels The energy is transferred from one step to another sequentially in a food chain. The various steps in a food chain are called Trophic levels. The trophic levels are also known as feeding levels or energy levels. There may be five categories of trophic levels of an ecosystem: Trophic level-one (T1): It includes all autotrophs like photoautotrophs (all green plants and photosynthetic bacteria i.e., green sulphur bacteria or purple sulphur bacteria) and chemoautorophs i.e., nitrifying bacteria, sulphur bacteria. All autotrophs are also known as convertors or transducers because they utilize radiant energy of sun to synthesize their organic molecules i.e., chemical bond energy (Glucose). Trophic level-two (T2): It includes all herbivorous organisms like rats, rabbits, camels, deer, grasshoppers etc. Trophic level-three (T3): It includes organisms or predators and feed directly on the herbivorous organisms like frog, predatory fishes, eagles, snakes etc. Trophic level-four (T4): It includes top consumers or giant predators or omnivorous and feed on the herbivores and carnivores. It may be tigers, lions, whales, sharks etc. Flow of Energy Energy from the sun enters the living world through producers and passes on from one generation to another in the form of food energy or chemical energy. Thus a continuous flow of energy from sun to biotic components and then to physical environment and their mechanism of flow is called Flow of energy or Energy flow. The sun is the ultimate source of energy and is trapped by the producers. The producers use up some energy for their own life processes. Only a portion of the energy trapped can be taken up by the primary consumers. Animals being more active than plants also use much of the energy acquired before they are consumed by the next trophic level. So, at each stage of energy transfer, a considerable amount of energy is lost from the different trophic levels. The amount of energy transferred to the next higher level gradually decreases. The decomposition of dead organisms also releases chemical energy. Eventually, all the solar energy that entered the living system through the producers goes back into the non-living world not as light but as heat.



Ten Per-Cent Law The ratio of energy flowing between various trophic levels are called as ecological efficiency. The ecological efficiencies are different for different species populations. In an ecosystem, the ecological efficiency also varies or reduces from primary producers to top consumers. Only 10% of energy of lower trophic level can be captured by the organism of next higher trophic level. This is known as Ten per cent law. It was proposed by Lindeman. Producers only stores 1% to 3% of solar energy. Herbivores can store only 10% of this energy and the remaining 90% is used by then in life processes. In this way, only 10% of the trophic level energy is being transferred upto the top consumers. Food Chain The food acts as a fuel to provide energy to do work. The autotrophs capture the energy present in sunlight and convert it into chemical energy. A series of organisms feeding on one-another. This series of organisms taking part at various biotic levels constitute a food chain. Thus, the energy transfer from producers through a series of other organisms with repeated eating and being eaten form a food chain. Characteristic Features of Food Chain: 1. The interactions among the various components of the environment involves flow of energy from one

component of the system to another. 2. From autotrophs, the energy goes to the heterotrophs and decomposers. 3. The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their

leaves and convert it into food energy. 4. An average of 10% of the food eaten is turned into its own body and made available for the next level of

consumers. 5. About 80% to 90% of energy is lost as heat to the environment. Some amount of energy goes into

digestion and in doing work and the rest goes towards growth and reproduction. 6. Food chains generally consist of only three or four steps. 7. The flow of energy is unidirectional in food chain. It does not revert back. 8. The energy moves progressively through the various trophic level. It is no longer available to the previous

levels. The number of trophic levels in different ecosystems may be upto five as follows: (i) Producers, (ii) Primary consumers (Herbivores), (iii) Secondary consumers (Primary carnivores) (iv) Tertiary consumers (Secondary carnivores) (v) Tertiary carnivores (Top consumers) Food Web In nature, the food relationship cannot be explained only in terms of a single food chain. With many food chains and cross-connecting links, there is greater opportunity for the prey and predator population to adjust to the changes. All the food chains in a community exist in a network and this is called a Food web. Depending upon the availability and choice of food, different organisms at each level have food relationship with more than one organism at the lower levels. For example, a rat feeds on various kinds of stems, roots, fruits and grains. A rat is in turn, is consumed by a snake which is eaten be a falcon. The snake feeds on both frogs and rats. This network of food chains constitute food web. It becomes more complicated. Significance of Food Web 1. The food web exhibits interlinked food chains as well as provides alternative pathways of food resources. 2. It makes the ecosystem more stable. Types of food chain: There are two types of food chain as follows:



Grazing food chain Detritus food chain 1. 2. 3.

It starts from producers or green plants. It is the most common type of food chain. Example: Grasses(T1) Grasshopper(T2) Birds(T3) Hawks(T4)

It starts from dead organic matters. It is the shortest food chain. Example: Dead organic matter(T1) Earthworms(T2) Frogs(T3) Snakes(T4) Hawks(T5)

Biological Magnification Some harmful chemicals may enter in the bodies of organisms through food chain. Several pesticides and

other chemicals are used to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals. These are taken up from the water bodies by aquatic plants and animals. Thus, these chemicals enter the food chain. These get accumulated progressively at each trophic level as these are non-degradable in nature. Thus, the process by which non-degradable chemicals are progressively increased by accumulation at different trophic levels in a food chain is known as biomagnification.

As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies.

Biomagnification is the reason why our food grains such as wheat and rice, vegetables and fruits even meat, contain varying amounts of pesticide residues. They cannot always be removed by washing or other means.

Example: There is biomagnifications of DDT in an aquatic food chain. The concentration of DDT is increased at successive trophic levels 𝑖. 𝑒., 0.003 ppb (Part per billion) in water can reach 25 ppm in fish eating birds. Disadvantage: High concentration of DDT disturb calcium metabolism in birds. It causes thinning of egg shell and their premature breaking causes decline in bird populations. HOW DO OUR ACTIVITIES AFFECT THE ENVIRONMENT? We are integral part of the environment. Changes in the environment due to undesirable changes in physical, chemical or biological characteristics of air, water, soil and land. It adversely affects human life, natural resources etc. Our activities change the environment around us. About 99.95% of pollution is natural while only 0.05% of pollution is man-made or by human activities. Human activities are also causing changes in atmosphere like global warming, ozone depletion etc. Waste disposal is also a major cause of environmental imbalance. Waste Management State governments across the countries are trying to push for reduction in use of plastics and use of

ecofriendly packaging. We can do our bit by carrying cloth or other natural fibre carry – bags when we go shopping and by refusing polythene bags.

Municipal solid wastes are wastes from homes, offices, stores, schools, hospitals etc. The municipal solid wastes generally comprise paper, food wastes plastics rubber, leather etc. Sanitary landfills were adopted as the substitute for open burning dumps. In sanitary landfills, wastes are dumped in a depression or trench after compaction and covered with dirt every day.

Hospitals generate hazardous wastes that contain disinfectants and other harmful chemicals, and also pathogenic microorganisms. Such wastes also require careful treatment and disposal. The use of incinerators is crucial to disposal of hospital waste.

Irreparable computers and other electronic goods called electronic wastes (e-wastes). E-wastes are buried in landfills or incinerated. More than 50% of the e-wastes generated in the developed world are exported to China, India and Pakistan where metals like Cu, Fe, Si, Ne and Au are recovered during recycling process.

Integrated organic farming must be adopted. It is a cyclic, zero-waste procedure farming where waste products from one process are cycled in as nutrients for other processes.



Ozone Layer Ozone (O3) is a molecule formed by three atoms of oxygen. It is deadly poisonous and also known as

chemical weed. The ‘band zone’ forms in the lower atmosphere 𝑖. 𝑒.,troposphere, that harms plants and animals. There is ‘good zone’ in the upper part of the atmosphere 𝑖. 𝑒., stratosphere. It acts as a shield absorbing

ultraviolet (UV) radiation from the sun. UV rays are highly injurious to living organisms. It damages DNA (Nucleic acid) and protein by

denaturation due to high breaking energy of UV-radiation. It also causes skin cancer in human beings. The thickness of ozone in the atmosphere is measured in terms of Doson Unit (DU). Ozone at the higher

levels of the atmosphere is a product of UV radiations acting on oxygen (O2) molecule. The higher energy UV-radiation split apart some molecular oxygen (O2) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone.

Ozone Depletion an Ozone Hole The amount of ozone in the atmosphere began to drop sharply in 1980s due to some synthetic chemicals, called Ozone Depleting substances (ODS). These are mainly Chlorofluorocarbons (CFC), methane, Nitrous oxide, Carbon tetrachloride etc. CFCs are most harmful among all.

ASSIGNMENT

1. What is meant by the term Environment? 2. Name any two non – biodegradable wastes. 3. Name any two biodegradable substances. 4. Rearrange the following according to their

ascending trophic levels in a food chain. “ Hawk, Grass, Snake, Frog, Grasshopper”.

5. In a harmful chemical enters a food chain comprising fishes, phytoplanktons and birds, which of the organism is likely to have minimum concentration of the harmful chemicals in its body?

6. In the following food chain, 20 J of energy was available to the hawks. How much would yhave been present in the plants?

Plants rats snake hawks 7. In a food chain comprising lion, grass and deer,

which will a. Transfer the maximum amount of energy. b. Receive minimum amount of energy.

8. Rearrange the following according to their ascending trophic levels in a food chain. “ Fish, zooplankton, seal, phytoplankton”.

9. In a harmful chemical enters a food chain comprising snakes, peacock , mice and plants, which of the organism is likely to have maximum concentration of the harmful chemicals in its body?

10. Give the technical terms for the graphical representation of the trophic structures in a food chain.

11. What is biological magnification? 12. Name ant two carnivores 13. Name any two omnivores. 14. What are decomposers? Write the role of

decomposers in the environment. 15. Name the group of chemical compounds which

adversely affects the ozone layer. 16. Which of the following materials are non –

biodegradable? a. Paper, leather, nylon, egg shell, glass

b. Tea leaves, glass, glucose, cotton cloth, silver foil

c. Glass, glucose, leather, silver foil, nylon cloth 17. State one difference between autotrophs and

hetrotrophs. 18. Write a food chain in a forest ecosystem. 19. Name any four modes of disposal of waste. 20. How depletion of ozone layer caused and what is

the effect of each of them on our environment? 21. How do food chains get shortened? How does their

shortening affect the biosphere? 22. Which of the following belong to the first trophic

level? a. Grasshopper, rose plant, neem tree, cockroach b. Sunflower plant, grasshopper, cockroach,

banyan tree 23. Which of the following belong to the second

trophic level? a. Frog, spider, butterfly, rice weevil b. Parrot, frog, spider, butterfly

24. Give an example of a chain consisting of four organisms at different trophic levels. Give the scientific term used ti indicate the first and third trophic level.

25. Write the food chain operation in a freshwater pond. Mention the food habit of each trophic level in this food chain.

26. What would happen if all the decomposers were eliminated from the earth? explain.

27. Describe how ozone present in the atmosphere is important for sustaining life on earth.

28. Draw schematic diagrams of a food chain and a food web.

29. Define ecosystem. Name the two components of ecosystem.

30. How are biotic and abiotic components of an ecosystem dependent on each other?

31. What is the 10% law of energy transfer? Explain.



32. Newspaper reports about the alarming increase in pesticides level in packed food items some of the states have banned these food items.

a. What are the sources of these pesticides in these food items?

b. Name the biological phenomenon associated with accumulation of pesticides in the food chain.

33. Why is pyramid of energy always erect? 34. Give some examples of each natural and man –

made ecosystem? 35. Why are micro organisms called scavengers of the

environment? 36. What is ecological pyramid? Give examples. 37. What are biodegradable and non- biodegradable? 38. What would happen, if all the micro organisms are

removed from the environment? 39. Why is the flow of energy from one trophic level to

another unidirectional? 40. What are the advantages of cloth bags over plastic

bags during shopping? 41. Explain how pesticides get accumulated in the

environment. 42. What method could be applied to reduce our

intake of pesticides? 43. Why is improper disposal of waste a curse to

environment? 44. ‘ Vegetarian food habits can sustain a larger

number of people’. Justify the statement in terms of food chain.

45. Name the radiations absorbed by ozone layer. Give any two causes of the depletion of the ozone layer. Name the disease likely to be caused due to depletion.

46. What is environment pollution? 47. Distinguish between biodegradable and non –

biodegradable pollutants? 48. Choose the biodegradable pollutants from the list

given – sewage, DDT, radioactive waste, agriculture waste.

49. How are consumers classified? Explain by giving examples.

50. How would you dispose the following wastes a. Domestic wastes like vegetable peels? b. Industrial wastes like metallic cans? c. Plastic materials?

51. Define producers, consumers and decomposers in the context of biosphere?

52. Explain why food chain consists of few steps only. 53. What is food web? Give example. 54. How do pesticides enter a food chain? Explain. 55. Plastic production is increasing day by day in spite

of the fact that plastic is harmful for the environment.

Based on the above statement, answer the following:-

a. What are the harmful effects of plastic usage?

b. In our day by day situation what are the alternative that we can instead of plastics.

c. What can we learn as a good citizen as in concern for this issue?

56. Number of vultures is decreasing remarkably. Now a days which is a matter of concern.

a. Vultures belong to which category of animals?

b. What is their role in nature to maintain ecological balance?

c. What value of the learner do we see to show concern towards this topic?

57. Suggest one word for each of the following a. The physical and biological word where we

live in. b. The physical factors like temperature,

rainfall, wind and soil of an ecosystem. c. Organisms which depend on the producers

either directly or indirectly for food. 58. Select the mis- matched pair and correct it.

a. Biomagnifications Decreases of chemicals atthe successive trophic levels of a food chain.

b. Ecosystem Biotic components of environment.

c. Aquarium Natural ecosystem. 59. What harm to skin does ultraviolet rays do? 60. At which level, pesticides enter the food chain? 61. How are most of the solid wastes in urban areas

disposed of? 62. Suggest any five activities in daily life which are

eco – friendly. 63. Write in detail about garbage management. 64. Consider the following food chain.

Grass Mice Snakes Peacocks If in this chain 2000 J of energy is available at the producers level, then calculate the nergy transferred to the peacocks as food. Also state the law used above.

65. What is the significance of food chain? 66. It is so often advised to stop our vehicles engine at

red light and also to drive car / vehicles at constant speed. Based on the above statement, answer the following questions.

a. Which type of fuel is used in vehicles? Is it renewable or non – renewable?

b. How can you contribute towards saving these fuels at your level?

c. What value will be depicted by this behaviour?



Anything in the environment which can be used is called natural resources. Controlling system for the use of natural resources in such a way as to avoid their wastages and to use

them in the most effective way is called management of natural resources. The reasons to manage our natural resources are: The proper management can ensure that the natural resources are used judiciously so that to fulfill the

needs of presents generation and also last for the generations to come. The proper management of natural resources takes into consideration long term perspective and

prevents their exploitation to the hilt for short gains. The proper management can ensure equitable distribution of natural resources so that all the people can

benefit from the development of these resources. The proper management will take into consideration the damage caused to the environment during the

‘extraction’ or ‘use’ of the natural resources and find ways and means to minimise this damage. The three R’s to save the environment are Reduce, Recycle and Reuse. Ganga Action Plan: Ganga along with its tributaries is the largest river system of India. Ganga is not only held sacred, it also supplies water to more than 50 million persons. The river originates as Bhagirathi from Gangotri glaciers, five miles x 15 miles at 4000m height in Garhwal Himalayas. Downstream it meets Alaknanda and Mandakini in Devapryag to from Ganga. Ganga runs a distance of over 2500 km from Gangotri to Ganga Sagar in Bay of Bengal. In the way, it passes through innumerable villages and over 100 towns and cities of Uttrakhand, Uttar Pradesh, Bihar and West Bengal. Over the years, the river has been grossly misused. Cities and towns along the banks of the river had been discharging some 1000 million litres of untreated sewage. Thousands of industries had been pouring their untreated effluents into the river. Garbage and excreta were poured into it by all the inhabitants living near the banks of the river. Immersion of ashes and throwing of unburnt corpses into river had also been a practice since several hundred years. bathing and washing of animals and clothes are other pollution causing activities. The result was that BOD of the river had risen to 9.7 mg/l instead of the maximum of 2 mg/l/ pollution load and toxicity had started killing of fish in large sections of the river. Ganga Action Plan was formulated to reduce pollution load of river Ganga by more than 75%. The plan has been carried out in two phases since, 1985. The water quality has been tested from time to time by checking coliform number/ 100 ml. The important aspect of GAP has been (i) Diversion of sewers away from river (ii) Treatment of sewage and changing it into an energy source (iii) Construction of community toilets (iv) Establishment of electric crematoria (v) Development of solid waste management system (vi) Enforcement of setting up of effluent treatment plants by the industry (vii) Development of ghats and interception. Forest and wild life: Forests are vast areas, located far away from human inhabitation where wild plants of various kinds grow

and animals of different varieties live without intervention of humans. Forests are “ biodiversity hot spot”. One of the main aims of conservation is to try and preserve the biodiversity we have inherited.

Experiments and field studies suggest that a loss of diversity may lead to a loss of ecological stability. A person with an interest or concern in something is called stakeholder. To consider the conservation of forests, we need to look at the stakeholders who are :-

The people who live in or around forests, are dependent on forest products for various aspects of their life.

The forest department of the government which owns the land and controls the resources from forests.

The industrialists – from those who use ‘ tendu’ leaves to make bidis to the ones with paper mills who use various forest produce.

Management of Natural Resources



The wild life and nature enthusiasts who want to conserve nature in its pristine form. A major programme called silviculture has been started to replenish the forest by growing more trees and

plants. The silviculture programme has many advantages:

It produces a large quantity of raw materials for industry. It increases the area of earth under forests. It maintains a perfect water cycle in nature. It prevents soil erosion. It prevents floods.

Steps for conservation of energy resources are :- Save electricity, water etc by not using useless . Use energy efficient electricity appliances to save electricity. Use pressure cooker for cooking food. Use solar cookers. Fuel efficient motor vehicle should be designed to reduce consumption of petrol and diesel. Encourage the use of biogas as domestic fuel.

When coal and petroleum based fuels are burnt, the products of combustion are : carbon dioxide, water, sulphure dioxide and nitrogen oxides. And if combustion take place in an insufficient supply of air, then some carbon monoxide is also produced. Out of all the products of combustion of these fuels, only water is harmless and does not affect the environment. All other products are harmful and hence pollute the environment.

The harnessing of water resources by building dams has social, economic and environmental implications. Alternatives to large dams exist. These are locate specific and may be developed so as to give local people control over their local resources.

The fossil fuels, coal, petroleum, will ultimately be exhausted. Because of this and because their combustion pollutes our environment, we need to use these resources judiciously.

The destruction of forests affects not just the availability of forest products but also the quality of soil and the sources of water.

Traditional Water Harvesting Systems

Large scale killing of snakes disrupts the food chains in which snakes occur and creates and imbalance in nature.

The various sources of water which are available to us are : Rains, Rivers, Lakes, Ponds, Wells, Ocenas and Glaciers. Rain is a very important source of water.

The pollution of river water is caused by the dumping of untreated sewage and industrial wastes into it.

State/ Union territory

Traditional water harvesting system

Description

Himachal Pradesh Kulh Khatri

Head wall across a ravine to divert water from the natural stream for irrigation. Chambers carved in hard rock for storing water.

Rajasthan Khadin Tanks Nadi

Embankment across lower hill slopes. Underground tank Village pond

Maharashtra Bandharas Check dams Madhya Pradesh Bundhis Reservoir ( Talab) Uttar Pradesh Bundhis Reservoir ( Talab)

Bihar Ahar and Pynes Embanked catchment basin and channels.

Jammu and Kashmir Ponds and kul Water channels in mountain area is called kul

Tamil Nadu Eris Ooranis

Tank Pond

Kerala Surangams Horizontal well

Karanataka kattas Embankment across a drainage line.



The contamination of river water can be usually found from two factors : The presence of coliform bacteria in river water, and Measurement of pH of river water.

Rain water harvesting is an age old practice in India. Water harvesting techniques used depend on the location where it is to be used.

Various advantages of water stored in the ground are :- The water stored in ground does not evaporate. The water stored in ground spreads out to recharge wells and provides moisture for crops over a

wide area. The water stored in ground does not promote breeding of mosquitoes. The water stored in ground is protected from contamination by human and animal wastes. The water stored in ground is utilised for the benefit of the local population.

ASSIGNMENT

1. When did Ganga Action Plan come into action? 2. What is the first step before recycling any article? 3. Which quality of water is generally studied to

study its level of contamination? 4. What will happen if loss of biodiversity occurs? 5. Which of the following is / are biodegradable?

Agricultural wastes. Vegetable peels, polythene bags, aluminium foils, sewage.

6. Which of the following pollutants of air would affect the capacity of blood in human bodies to absorb O2 from lungs? NO2 , SO4 , CO, CO2

7. What is economic development linked to? 8. Where was ChipkoAndolan started? 9. What are the two major benefits of dams? 10. Give an example to show that exploitation of

resources lead to pollution. 11. Define deforestation. 12. What are the kulhs? 13. List any two systems of water harvesting? 14. Name any two endangered plant species and fossil

fuels. 15. A person lives near a forest. Enlist four items,

which he can get from forests to meet his daily needs.

16. How is the increase in demand for energy affecting atmosphere?

17. Mention the four main types of resources affected the most by their over utilisation.

18. Name a bacteria found in human intestine? 19. Why are forest called biodiversity hot spot? 20. Write at least two ways by which people of ancient

India managed water resources. 21. Name a few minerals being mined out from sea

floor. 22. In which part of the world is a hole created in the

atmosphere due to ozone depletion? 23. Why did Amrita Devi Bishoni sacrifice her life for

and in which year? 24. Mention the names of any two dams whose

construction faced opposition. 25. Name a few industries based on forest products. 26. What is the importance of monoculture plantation?

27. Hydroelectricity power is also an indirect form of solar energy. How?

28. Why must we conserve our forests? List any two causes for deforestation taking place.

29. What are the harmful effects of the negligence of the local knowledge and local needs in the forest management practices?

30. List two advantages associated with water harvesting at the community level.

31. Why do we say that reuse of articles is better than its recycle?

32. Prepare a list of items that you use daily in the school. Identity from the list such items that can be recycled.

33. In a village in Karnataka, people started cultivating crops all around a lake, which was always filled with water. They added fertilisers to their field in order to enhance the yield. Soon, they discovered that the water body was completely covered with green floating plants and fishes started dying in large numbers. Analyse the situation and give reasons for excessive growth of plants and death of fish in the lake.

34. What measures would you take to conserve electricity in your home?

35. What is meant by biodiversity ?why do we need to conserve biodiversity?

36. Explain the concept of sustainable development? 37. What happened during ChipkoAndolan? Write in

brief. 38. Write a short note on the water harvesting

structures used in largely level terrains. 39. Although coal and petroleum are produced by

degradation of biomass, yet we need to conserve them. Why?

40. Suggest a few measures for controlling carbon dioxide levels in the atmosphere?

41. Write some of the simple choices that can make a difference in our energy consumption patterns.

42. Give an example showing the benefits of traditional use of forest areas by local people.

43. What had led to the loss of local peoples control over the local water resources in India?



44. What are the various actors to be considered while we exploit our natural resources?

45. Coal and petroleum are converted forms of solar energy. Is this statement correct? Why?

46. What was the cause behind the ChipkoAndolan and what happened during it? What was the result of the movement?

47. Write a short note on the pollution of the Ganga. 48. Mention any three problems addressed by

criticisms about large dams. 49. Why do we need to manage our resources

carefully? Also, explain how do we need to manage our resources?

50. Why is replenishment of forests necessary? 51. Why are the Arabari forest of Bengal known to be a

good example of conserves forest? 52. What does watershed management mean and aim

at? What are the advantages of watershed management?

53. Distinguish between inexhaustible and exhaustible resources.

54. Write a note on the kulhs in Himachal Pradesh. 55. What are the causes leading to the damage of

forests? 56. List few activities that have led to the

contamination of the river Ganga. 57. The major energy resources are fossil fuels. The

increase in the use of fossil fuels, has led to the problem of environmental damage and depletion. Therefore, it is usually recommended to use renewable source of energy as they provide clean energy. One of the fast developing renewable energy sources in our country is wind.

a. Can you tell us about the principle of producing electricity through the use of wind?

b. Why is this energy preferred over others? c. Name the states of our country leading in

its problems? 58. Who are the three types of stakeholders we need

to look at while considering the conservation of forest?

59. Give an example where participation of local people has led to the efficient management of forests.

60. Prepare a list of five activities that you perform daily in which natural resources can be conserved or energy utilisation can be minimised.

61. Explain the three R’s. 62. In the context of conservation of natural resources,

explain the terms reduce, recycle and reuse. From among the materials that we use in daily life, identify two materials for each category.

63. Suggest a few useful ways of utilising waste water. 64. What direct value does a forest have for man? 65. Find out about the traditional systems of water

harvesting. 66. Reena is a student of class X of a Government

School is a member of Eco – club of her school. a. What would you suggest Reena to improve

the environment in her school? b. What value would she attain by doing so?

67. Water finds a necessary place in our life. However, a large proportion of would population has no access to drinking water. Also, around four million people died of various water borne diseases every year. The availability of safe drinking water is given priority as a human right. Can you think about it? Read the above passage and answer the following questions.

a. What makes water unsafe for drinking? b. What steps are taken to be aware to make

water fir for drinking? c. What values you have learnt from the

above passage? 68. ChipkoAndolan was started in 1970 in a small

village of Garhwal high up in Himalayas villagers stood against greedy contractors. Women folk hugged the trees. The ChipkoAndolan spread slowly to all nearby areas under the leadership of Shri Sunder LalBahuguna. Read the above passage and answer the following questions. a. Do you feel inspired by this movement which

prevented felling of trees? b. Do you think that local people are real stake

holders? c. Which old beliefs has been challenged by

ChipkoAndolan? d. What value would the students learn from

this?



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Date post:	22-Jan-2018
Category:	Education
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Class 10 sa 2... 2017-2018

Education