Class 9 Science NCERT Summary Part - II

By Dr. Roman Saini

Contents8. Motion

9. Force and Laws of Motion

10. Gravitation

11. Work and Energy

12. Sound

13. Why do we fall ill?

14. Natural Resources

15. Improvement in Food Resources

8. Motion

● Simplest type of motion - motion along a straight line.

● Magnitude - numerical value of a physical quantity.

● Displacement - shortest distance measured from the initial to the final position of an object.

● Magnitude of displacement is not equal to the path length/distance.

● Magnitude of the displacement for a course of motion may be zero but the corresponding distance covered is not zero.

● Uniform motion - equal distances covered in equal intervals of time.

● Non-uniform motion - unequal distances covered in equal intervals of time.

● Speed - Rate of motion of an object or the distance covered by an object in unit time. SI unit - metre/second (m/s or ms-1).

○ Speed (v) = D/t (D - distance, t - time)

○ In most cases, objects will be in non-uniform motion. The speed of such objects is described as average speed.

○ Average speed = Total distance travelled/ Total time taken

● Velocity - speed of an object moving in a definite direction.

○ Velocity can be uniform or variable; can be changed by changing the object’s speed, direction of motion or both.

○ Average velocity for non-uniform motion - Displacement/Total time taken

○ Average velocity for uniform motion - (initial velocity + final velocity)/2

● Acceleration - measure of the change in the velocity of an object per unit time. SI unit - m/s2.

Acceleration = change in velocity/ time taken

○ Acceleration is positive if motion is in the direction of velocity and negative when it is opposite to the direction of velocity.

● Acceleration is uniform if an object travels in a straight line and its velocity increases or decreases by equal amounts in equal intervals of time. Eg. - motion of a freely falling body.

● Acceleration is non-uniform if velocity changes at a non-uniform rate. Eg. - a car travelling along a straight road increases its speed by unequal amounts in equal intervals of time.

Distance-Time graphs

Velocity-Time Graphs

Uniform acceleration

Non-uniform acceleration

Equations of Motion

1. v = u + at (velocity - time relation)

2. s = ut + ½ at2 (position - time relation)

3. 2 a s = v2 – u2 (position - velocity relation)

where u is the initial velocity of the object which moves with uniform acceleration a for time t, v is the final velocity, and s is the distance travelled by the object in time t.

Uniform Circular motion - motion in a circular path; accelerated motion where magnitude of velocity is constant but the direction keeps on changing.

9. Force and Laws of Motion

Balanced force - a force that does not change the state of rest or of motion of an object.

Eg. - an object does not move if equal forces (balanced forces) are used to pull it from either side.

Unbalanced force - a force that can cause change either in the speed or in the direction of motion of an object.

Eg. - an object moves to in the direction in which greater force is applied (greater than the force of friction).

Newton’s laws of Motion

First law of motion/ Law of inertia

“An object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force”.

● Inertia - the natural tendency of an object to resist a change in its state of motion or of rest. The mass of an object is a measure of its inertia. Heavier objects offer more inertia.

● Eg. - a person moves forward in when brakes are applied in a moving car, a person tends to move backwards when a bus starts moving from rest, a person moves sideways when a car makes a sharp turn, etc.

Second Law of Motion

“The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force”.

● Momentum (p) - It is the product of its mass and velocity. It has magnitude and has the same direction as that of the velocity. Its SI unit is kg m s–1.

p = mv

F = ma

● One unit of force is defined as the amount that produces an acceleration of 1 ms-2 in an object of 1 kg mass.

● The unit of force is kg m s-2 or newton, which has the symbol N.

● Eg. - a fielder pulls his hands backwards while catching a fast moving cricket ball, athletes are made to fall either on a cushioned bed or on a sand bed in a high jump athletic event, etc.

Third Law of Motion

“Every action has a equal and an opposite reaction”.

● Eg. - when a sailor jumps out of a rowing boat, the boat moves backwards; recoiling of the gun after it is fired, etc.

Conservation of Momentum

Total momentum is conserved provided there is no external force.

● Eg. - consider two objects moving in the same direction. After they collide, it is seen that the sum of momenta of the two objects before collision is equal to the sum of momenta after the collision, provided there is no external unbalanced force acting on them.

10. Gravitation

● Gravitational force - force of attraction between all objects

● Centripetal force - force acting towards the centre of the earth. It is provided by the force of attraction of the earth.

● The motion of the moon around the earth is due to the centripetal force. If there were no such force, the moon would pursue a uniform straight line motion.

Universal law of gravitation

● Every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance between them. The force is along the line joining the centres of two objects.

● SI unit of G is N m2 kg–2.

Importance of the Universal Law of Gravitation

It explains several phenomena like

(i) the force that binds us to the earth;

(ii) the motion of the moon around the earth;

(iii) the motion of planets around the Sun;

(iv) the tides due to the moon and the Sun.

Free fall - an object falling down due to force of gravity.

Acceleration due to gravity - the acceleration of object in free fall. It is denoted by g. The unit of g is ms-2.

g = 9.8 m s–2

The earth is not a perfect sphere. As the radius of the earth increases from the poles to the equator, the value of g becomes greater at the poles than at the equator.

Mass - mass of an object is the measure of its inertia; greater the mass, the greater is the inertia; mass of an object is constant and does not change from place to place.

Weight - force with which an object is attracted towards the earth; it is a force acting vertically downwards; it has both magnitude and direction; SI unit is N.

W = m x g

● Mass is always constant. So, weight depends on g or on the location of the object.

● Weight of the object on the moon = (1/6) × its weight on the earth.

Thrust - force acting on an object perpendicular to the surface.

● The effect of thrust depends on the area on which it acts.

● Eg. - The effect of thrust on sand is larger while standing than while lying.

Pressure - The thrust on unit area is called pressure.

● Pressure = Thrust/ Area

● SI unit of pressure as N/m2 or N m–2. SI unit of pressure is also called pascal, denoted as Pa.

● The same force acting on a smaller area exerts a larger pressure, and a smaller pressure on a larger area. Therefore, a nail has a pointed tip, knives have sharp edges and buildings have wide foundations.

● Pressure exerted by a fluid in any confined mass of fluid is transmitted undiminished in all directions.

Buoyancy - upward force exerted by the water on an object; magnitude of this buoyant force depends on the density of the fluid.

● Objects of density less than that of a liquid float on the liquid. The objects of density greater than that of a liquid sink in the liquid.

● Eg. a nail sinks in water as the gravitational attraction of the earth acting on the nail downwards is greater than the upthrust of water on the nail.

● A cork floats in water as its density is lighter than that of water.

Archimedes’ Principle

When a body is immersed fully or partially in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it.

Applications

● It is used in designing ships and submarines.

● Lactometers, which are used to determine the purity of a sample of milk and hydrometers used for determining density of liquids, are based on this principle.

Relative Density - ratio of an object’s density to that of water.

R.D = Density of a substance / Density of water

11. Work and Energy

● Work done by a force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force.

● Work done = force × displacement

W = F s

● Work has only magnitude and no direction.

● The unit of work is newton metre (N m) or joule (J).

● 1 J is the amount of work done on an object when a force of 1 N displaces it by 1 m along the line of action of the force.

● Work done is negative when the force acts opposite to the direction of displacement. Work done is positive when the force is in the direction of displacement.

Energy

● An object having a capability to do work is said to possess energy.

● The object which does the work loses energy and the object on which the work is done gains energy.

● The unit of energy is joule (J).

● 1 J is the energy required to do 1 joule of work.

● 1 kJ equals 1000 J.

Forms of Energy

The various forms include mechanical energy (potential energy + kinetic energy), heat energy, chemical energy, electrical energy and light energy.

Kinetic Energy

● Energy possessed by an object due to its motion.

● The kinetic energy of an object increases with its speed.

● A falling coconut, a speeding car, a rolling stone, a flying aircraft, flowing water, blowing wind, a running athlete etc. possess kinetic energy.

● The kinetic energy possessed by an object of mass, m and moving with a uniform velocity, v is mv2.1

2

Potential Energy

● The potential energy possessed by the object is the energy present in it by virtue of its position or configuration.

● An object increases its energy when raised through a height. The energy present in such an object is the gravitational potential energy.

● The gravitational potential energy of an object at a point above the ground is defined as the work done in raising it from the ground to that point against gravity.

● The potential Energy, Ep, possessed by an object of mass m, raised through a height, h from the ground is mgh.

● An object in a given position can have a certain potential energy with respect to one level and a different value of potential energy with respect to another level.

Law of Conservation of Energy

Energy can only be converted from one form to another; it can neither be created or destroyed.

Power

● Power is defined as the rate of doing work or the rate of transfer of energy.

● If an agent does a work W in time t, then power is given by:

Power = work/time or W = P/t

● The unit of power is watt.

● 1 watt is the power of an agent, which does work at the rate of 1 joule per second.

● 1 watt = 1 joule/second or 1 W = 1 J s–1.

● The power of an agent may vary with time.

● Average power is obtained by dividing the total energy consumed by the total time taken.

● Commercial unit of energy - kilowatt hour (kW h); 1 kW h = 3.6 × 106 J

For example, electrical energy used during a month is expressed in terms of ‘units’ where 1 ‘unit’ means 1 kilowatt hour.

12. Sound

● Sound is a form of energy which produces a sensation of hearing in our ears.

● Sound is produced due to vibration.

● The sound of the human voice is produced due to vibrations in the vocal cords.

● Sound moves through a medium from the point of generation to the listener. The medium can be a solid, liquid or a gas.

● Sound is transmitted as sound waves. They are characterised by the motion of particles in the medium and are called mechanical waves.

● Medium of propagation - Sound is a mechanical wave which requires a medium for propagation. It cannot travel in vacuum.

● Longitudinal waves - The particles in a sound wave in a medium move in a direction parallel to the direction of propagation of the disturbance.

[Transverse wave - the individual particles of the medium move about their mean positions in a direction perpendicular to the direction of wave propagation. Light is a transverse wave.]

How does sound propagate?

● Sound is carried forward through compressions and rarefactions.

● When a vibrating object moves forward, it pushes and compresses the air in front of it creating a region of high pressure. This region is called a compression (C) which starts to move away from the vibrating object.

● When the vibrating object moves backwards, it creates a region of low pressure called rarefaction (R).

● More density of the particles in the medium gives more pressure and vice versa.

● Thus propagation of sound is propagation of density variations or pressure variations in the medium.

Density variations

Pressure variations

Characteristics of a sound wave

1. Frequency

2. Amplitude

3. Speed

● Compressions are the regions where particles are crowded together and represented by the upper portion of the curve.

● The peak represents the region of maximum compression. It represents regions of high density and pressure.

● Rarefactions are the regions of low pressure where particles are spread apart and are represented by the valley, that is, the lower portion of the curve.

● A peak is called the crest and a valley is called the trough of a wave.

● The distance between two consecutive compressions (C) or two consecutive rarefactions (R) is called the wavelength.

● The wavelength is usually represented by λ. Its SI unit is metre (m).

● The change in density from the maximum value to the minimum value, then again to the maximum value, makes one complete oscillation.

● The number of such oscillations per unit time is the frequency of the sound wave. It is usually represented by ν (Greek letter, nu). Its SI unit is hertz (symbol, Hz).

● The time taken by two consecutive compressions or rarefactions to cross a fixed point or the time taken for one complete oscillation is called the time period of the sound wave. It is represented by the symbol T. Its SI unit is second (s).

● ν = 1/T

● Pitch is a measure of the frequency of the wave. Higher the frequency, higher the pitch.

● Thus, a high pitch sound corresponds to more number of compressions and rarefactions passing a fixed point per unit time.

● The magnitude of the maximum disturbance in the medium on either side of the mean value is called the amplitude of the wave. It is usually represented by the letter A.

● The loudness or softness of a sound is determined basically by its amplitude.

● The quality or timber of sound is that characteristic which enables us to distinguish one sound from another having the same pitch and loudness.

● A sound of single frequency is called a tone.

● The sound which is produced due to a mixture of several frequencies is called a note.

● The speed of sound is defined as the distance which a point on a wave, such as a compression or a rarefaction, travels per unit time.

● Speed, v = λ/T

● Or, v = λν [speed = wavelength × frequency]

● Sound propagates through a medium at a finite speed.

● The speed of sound depends on the properties of the medium through which it travels.

● Sound travels with a speed which is much less than the speed of light. Eg. - sound of a thunder is heard a little later than the flash of light is seen.

● The speed of sound in a medium depends on temperature of the medium.

● The speed of sound decreases when we go from solid to gaseous state.

Reflection of sound

● Sound gets reflected at the surface of a solid or liquid and follows the same laws of reflection.

● The directions in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence, and the three are in the same plane.

Echo

● The sound that is reflected from an object is called an echo.

● To hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1s.

● Echoes may be heard more than once due to successive or multiple reflections.

● The rolling of thunder is due to the successive reflections of the sound from a number of reflecting surfaces, such as the clouds and the land.

Reverberation

● The sound that persists after repeated reflections until it is reduced to a value where it is no longer audible.

● To reduce reverberation, the roof and walls of the auditorium are generally covered with sound-absorbent materials like compressed fibreboard, rough plaster or draperies.

Uses of multiple reflection of sound

● Megaphones or loudhailers, horns, musical instruments such as trumpets and shehanais.

● Stethoscope - medical instrument used for listening to sounds produced within the body, mainly in the heart or lungs.

3. Curving of the the ceilings of concert halls, conference halls and cinema halls.

Range of Hearing

● The audible range of sound for human beings extends from about 20 Hz to 20000 Hz (one Hz = one cycle/s).

● Children under the age of five and some animals, such as dogs can hear up to 25 kHz (1 kHz = 1000 Hz).

● Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound.

● Rhinoceros, Whales and elephants produce infrasonic sound.

● Earthquakes produce low-frequency infrasound before the main shock waves begin which possibly alert the animals.

● Frequencies higher than 20 kHz are called ultrasonic sound or ultrasound.

● Ultrasound is produced by animals such as dolphins, bats and porpoises.

Hearing aid - It is an electronic, battery operated device. The microphone converts the sound waves to electrical signals which are amplified by an amplifier. The amplified electrical signals are given to a speaker which converts it to sound and sends to the ear for clear hearing.

Applications of ultrasound

● Cleaning - parts located in hard-to-reach places, for example, spiral tube, odd shaped parts, electronic components etc.

● Detect cracks and flaws in metal blocks

● Echocardiography - formation of image of the heart

● Ultrasonography - for getting images of internal organs of the human body to detect abnormalities; examination of the foetus during pregnancy to detect congenial defects and growth abnormalities.

● Break small ‘stones’ formed in the kidneys into fine grains which is flushed out through urine.

Sonar

● SOund Navigation And Ranging

● Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

● Sonar consists of a transmitter to transmit ultrasonic waves which get reflected after striking an object and a detector which converts the ultrasonic waves into electrical signals. It is installed in a boat or a ship

● It uses the echo-ranging technique to determine the depth of the sea and to locate underwater hills, valleys, submarine, icebergs, sunken ship etc.

Structure of human ear

● The outer ear is called ‘pinna’ which collects sound from surroundings.● The collected sound passes through the auditory canal at the end of which

there is a thin membrane called the eardrum or tympanic membrane.● The eardrum vibrates inward due to compressions of the medium and

outward when a rarefaction reaches it.● The vibrations are amplified several times by three bones (the hammer, anvil

and stirrup) in the middle ear.● The middle ear transmits the amplified pressure variations received from the

sound wave to the inner ear where they are turned into electrical signals by the cochlea.

● These electrical signals are sent to the brain via the auditory nerve, and the brain interprets them as sound.

13. Why do we fall ill?

● Health is a state of well being physically, mentally and socially.

● Diseases can be classified as

○ Acute diseases - those which last for a short period of time

○ Chronic diseases - those which last for a long time, even as much as a lifetime.

● Chronic diseases have very drastic long-term effects on people’s health as compared to acute diseases.

Causes of diseases

● Immediate causes

○ Microorganisms - Diseases where microbes are the immediate causes are called infectious diseases.

○ Non-infectious causes - due to internal problems of the body. Eg. - cancer, high blood pressure etc.

● Contributory causes

○ Hygiene - unclean areas, unclean drinking water, etc.

○ Lack of nourishment

○ Poverty or lack of public services

Infectious Diseases

Infectious Agents

● Microorganisms like bacteria (typhoid fever, cholera, tuberculosis and anthrax), fungi (skin infections) and viruses (common cold, influenza, dengue fever and AIDS).

● Single celled animals or protozoans (malaria and kala-azar).

● Multicellular organisms, such as worms of different kinds (eg. - elephantiasis)

Means of spread

● Diseases that spread from an infected person through air and water are called communicable diseases.

○ Through air - eg. - common cold, pneumonia and tuberculosis.

○ Through water - occurs if the excreta from someone suffering from an infectious gut disease, such as cholera, get mixed with the drinking water used by people living nearby.

● Sexually transmitted diseases - syphilis, AIDS (can also spread through blood-to-blood contact with infected people or from an infected mother to her baby during pregnancy or through breast feeding).

● Vectors - animals that carry the infecting agents from a sick person to another potential host; eg. - mosquitoes.

Organ specific and tissue specific manifestations

● The signs and symptoms of a disease will depend on the tissue or organ which the microbe targets.

● Other effects include inflammation caused by the response of the body’s immune system.

● In some cases, the tissue-specificity of the infection leads to very general-seeming effects as the immune system is weakened by the infection.

● The severity of disease manifestations depend on the number of microbes in the body.

Principles of Treatment

● There are two ways to treat an infectious disease - reduce the effects of the disease and kill the cause of the disease.

● Antibiotics blocks the bacterial synthesis pathway without affecting the body’s own mechanism.

● Making anti-viral medicines is harder than making antibacterial medicines as viruses have few biochemical mechanisms of their own. They use the body’s machinery for their life processes.

Principles of Prevention

● Two methods - general ways and ways specific to each disease.

○ The general ways of preventing infections mostly relate to preventing exposure.

○ Eg. - avoiding overcrowded conditions, using safe drinking water, clean environments, etc.

● Availability of proper and sufficient food will keep the body healthy.

● Immunisation through vaccination - developing a memory for a particular infection by putting something, that mimics the microbe into the body.

14. Natural Resources

● Resources on earth - air, water and land.

● Water covers 75% of the Earth’s surface.

● Biosphere - lithosphere, hydrosphere and atmosphere exist together.

● Two components

○ Biotic components - living things

○ Abiotic components - non-living things like air, water and soil.

Air

● It is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour.

● In planets such as Venus and Mars, carbon dioxide constitutes up to 95-97% of the atmosphere.

● CO2 is controlled in the earth’s atmosphere in two ways:

(i) Green plants convert carbon dioxide into glucose in the presence of Sunlight

(ii) many marine animals use carbonates dissolved in sea-water to make their shells.

Role of atmosphere in climate control - atmosphere prevents the sudden increase in temperature during the daylight hours and slows down the escape of heat into outer space at night.

Wind

● Land gets heated faster than water. Thus, during daytime, the air over land would be heated faster than the air over water bodies, rises and a low pressure area is created over land. Air moves from over the sea to the low pressure area producing winds.

● At night, both land and sea start to cool. Since water cools down slower than the land, the air above water would be warmer than the air above land. Therefore, winds blow from land to sea.

● Similarly, all the movements of air resulting in diverse atmospheric phenomena are caused by the uneven heating of the atmosphere in different regions of the Earth.

● Other factors that influencing winds – the rotation of the Earth and the presence of mountain ranges in the paths of the wind, etc.

Rain

● Water vapour due to heating of water bodies and other biological activities rises up, expands and cools down to form tiny droplets.

● Water droplets condense around dust particles which act as the nucleus for cloud formation.

● When the drops have grown big and heavy, they fall down in the form of rain.

● Sometimes, when the temperature of air is low enough, precipitation may occur in the form of snow, sleet or hail.

● Rainfall patterns are decided by the prevailing wind patterns.

Air Pollution

● Burning of fossil fuels produces oxides of nitrogen and sulphur. These gases are poisonous and mixes with water to form acid rain.

● The combustion of fossil fuels also increases unburnt carbon particles or substances called hydrocarbons which lowers the visibility of air and creates smog. These cause allergies, cancer and heart diseases.

Water

Water is one of the major resources which determine life on land.

Water Pollution

● The addition of undesirable substances to water-bodies like fertilisers and pesticides used in farming or poisonous substances like mercury salts used in paper industry, disease causing organisms etc.

● It also means the removal of desirable substances like dissolved oxygen and other nutrients from water bodies.

● Changes in temperature also affects the living organisms in water bodies as their eggs may not survive the same.

Minerals in soil● The outermost layer of our Earth is called the crust and minerals are found in

this layer of soil.● The minerals found in the soil depend on the type of rocks it was formed

from.● Soil is a mixture of rock particles, microorganisms and decayed living

organisms called humus.● Humus makes the soil porous and allows water and air to penetrate deep

underground.● Top soil - contains soil particles, humus and living organisms.● The quality of the topsoil is an important factor that decides biodiversity in

that area.

Factors that make soil

● Sun - expansion of rocks due to heating during daytime and contraction at night times creates cracks in rocks ultimately breaking them into smaller pieces.

● Water - water entering into cracks of rocks freezes to widen the cracks and break the rocks; flowing water wears away the rocks and carries the rock particles downstream causing further wearing and breaking them into smaller pieces;

● Wind - erodes rocks and carries the particles to far away places.

● Living organisms - Roots of big trees, moss growing on rocks and lichens help in breaking down of rocks.

Removal of nutrients

● Fertilisers and pesticides - kills soil microorganisms that recycle nutrients in the soil and earthworms which make humus.

● Soil pollution - Removal of useful components from the soil and addition of other substances, which adversely affect the fertility of the soil and kill the diversity of organisms that live in it.

● Soil erosion - by flowing water or wind.

● Deforestation - exposes the top soil for erosion.

Biogeochemical Cycles

Water cycle

● The whole process in which water evaporates and falls on the land as rain and later flows back into the sea via rivers is known as the water-cycle.

● Water rises in the form of water vapour through evaporation and transpiration.

● It condenses at higher altitudes and precipitates in the form of rain, snow, etc.

● Some of the water that falls on the land flows into the sea, some seeps underground and forms underground water which are used by plants, animals and humans.

● Rivers carry many nutrients from the land to the sea, and these are used by the marine organisms.

● The nitrogen from the atmosphere is converted to nitrates and nitrites by the ‘nitrogen-fixing’ bacteria found in the root nodules of legumes.

● During lightning, the high temperatures and pressures created in the air also convert nitrogen into oxides of nitrogen. These oxides dissolve in water to give nitric and nitrous acids and fall on land along with rain.

● Plants generally take up nitrates and nitrites and convert them into amino acids which are used to make proteins which are are subsequently consumed by animals.

● Once the animal or the plant dies, other bacteria in the soil convert the various compounds of nitrogen back into nitrates and nitrites which are then converted into nitrogen by denitrifying bacteria.

Carbon cycle

● Photosynthesis by plants converts carbon dioxide from the atmosphere or dissolved in water into glucose molecules.

● Combustion of fuels for various needs like heating, cooking, transportation and industrial processes also add CO2 to the atmosphere.

● The utilisation of glucose to provide energy to living things involves the process of respiration in which oxygen may or may not be used to convert glucose back into carbon dioxide which then goes back into the atmosphere.

● An increase in the carbon dioxide content in the atmosphere would cause more heat to be retained by the atmosphere and lead to global warming.

Oxygen cycle

● Oxygen is found in the atmosphere and in combined form as the oxides of most metals and minerals in the Earth’s crust and as CO2.

● Oxygen from the atmosphere is used up in three processes, namely combustion, respiration and in the formation of oxides of nitrogen.

● Oxygen is returned to the atmosphere in only one major process, that is, photosynthesis.

● Ozone or O3 is a protective covering against ultraviolet radiation in the stratosphere. It is getting depleted by man-made compounds like CFCs (carbon compounds having both fluorine and chlorine which are very stable and not degraded by any biological process).

15. Improvement in Food Resources

● In order to feed India’s growing population, it is necessary to increase our production efficiency for both crops and livestock.

● Green revolution and white revolution had helped in increasing food-grain production and milk production and its efficient use respectively.

● However, these have increased the use of natural resources thereby disrupting the balance of the environment.

● Therefore, there is a need for sustainable practices in agriculture and animal husbandry.

Crop Variety Improvement

Crop improvement is done through

● Hybridisation - crossing between genetically dissimilar plants which may be intervarietal (between different varieties), interspecific (between two different species of the same genus) or intergeneric (between different genera).

● Genetic modification by introducing genes to produce desirable characteristics.

Crop improvement is done for

● Higher yield: increase the productivity of the crop per acre.

● Improved quality: like baking quality for wheat, protein quality in pulses, oil quality in oilseeds and preserving quality in fruits and vegetables.

● Biotic and abiotic resistance: against diseases, insects and nematodes and drought, salinity, water logging, heat, cold and frost.

● Change in maturity duration: Shorter duration of crops from sowing to harvesting allows farmers to grow more crops in a year and reduces the cost of crop production.

● Wider adaptability: towards different environmental conditions.

Desirable agronomic characteristics: Tallness and profuse branching for fodder crops, dwarfness for cereal crops, etc gives higher productivity.

Crop Production Management

1. Nutrient Management - Plants require macronutrients (those required in large quantities) and micronutrients (those required in minor quantities) which are supplied from air (carbon, oxygen), water (hydrogen, oxygen) and soil.

● Macronutrients: nitrogen, phosphorus, potassium, calcium, magnesium, sulphur.

● Micronutrients: iron, manganese, boron, zinc, copper, molybdenum, chlorine

● Nutrients can be supplied through manures and fertilisers.

Manures

● Manure is prepared by the decomposition of animal excreta and plant waste.

● It enriches the soil fertility with nutrients and organic matter which helps in increasing the water holding capacity in sandy soils and prevents water logging in clayey soils.

● Based on the kind of biological material used, manure can be classified as:

1. Compost and vermi-compost: The process in which farm waste material like livestock excreta (cow dung etc.), vegetable waste, animal refuse, domestic waste, sewage waste, straw, eradicated weeds etc. is decomposed in pits is known as composting. Vermi-compost is prepared by using earthworms to hasten the process of decomposition of plant and animal refuse.

2. Green manure: plants like sun hemp or guar are grown and then mulched by ploughing them into the soil which thus turn into green manure which helps in enriching the soil in nitrogen and phosphorus.

Fertilisers

● Fertilizers supply nitrogen, phosphorus and potassium.

● They should be applied carefully in terms of proper dose, time, and observing pre and post-application precautions for their complete utilisation.

● Excessive use of fertilisers can cause water pollution when they are washed away during irrigation.

2. Irrigation

● Irrigation is necessary as the monsoon rains are irregular and are not available throughout the year sufficiently in all areas.

● Different types of irrigation are

○ Wells: two types: dug wells (water is collected from water bearing strata) and tube wells (water is collected from the deeper strata).

○ Canals: water collected from rivers or reservoirs are supplied to the fields through main canal or through distributaries of the canal.

○ River Lift Systems: Water is directly drawn from the rivers for supplementing irrigation in areas close to rivers.

● Tanks: small storage reservoirs, which intercept and store the run-off of smaller catchment areas.

● Other initiatives: rainwater harvesting, watershed management and building small check-dams.

3. Cropping Patterns

Different cropping patterns are chosen to satisfy the nutrient requirements of the soil and prevent pests and diseases.

● Mixed cropping - growing two or more crops simultaneously on the same piece of land. Eg. - wheat + gram, or wheat + mustard, or groundnut + sunflower, etc.

● Inter-cropping - growing two or more crops simultaneously on the same field in a definite pattern. Eg. - soyabean + maize, or finger millet (bajra) + cowpea (lobia).

● Crop Rotation - growing of different crops on a piece of land in a pre-planned succession; crop is decided according to the availability of moisture and irrigation facilities.

Crop Protection Management

● Crops should be protected against weeds, insect pests and diseases.

● Weeds are unwanted plants in the cultivated field which compete for food, space and light. Eg. - Xanthium, Parthenium, Cyperinus rotundus, etc.

● Insect pests attack the plants in three ways:

(i) they cut the root, stem and leaf,

(ii) they suck the cell sap from various parts of the plant, and

(iii) they bore into stem and fruits.

● Diseases in plants are caused by pathogens such as bacteria, fungi and viruses.

● All these can be controlled by the use of pesticides, which include herbicides, insecticides and fungicides.

● However, excessive use can be poisonous to many plant and animal species and cause environmental pollution.

● Other preventive methods

○ Proper seed bed preparation, timely sowing of crops, intercropping and crop rotation.

○ Use of resistant varieties, and summer ploughing, in which fields are ploughed deep in summers to destroy weeds and pests.

Storage of grains

● Biotic storage losses - insects, rodents, fungi, mites and bacteria.

● Abiotic storage losses - inappropriate moisture and temperatures in the place of storage.

● These factors cause degradation in quality, loss in weight, poor germinability, discolouration of produce, all leading to poor marketability.

● Preventive and control measures before grains are stored - strict cleaning of the produce before storage, proper drying of the produce first in sunlight and then in shade, and fumigation using chemicals that can kill pests.

● Proper treatment and systematic management of warehouses can decrease losses.

Animal Husbandry

It is the scientific management of animal livestock which includes feeding, breeding and disease control.

1. Cattle Farming

● Cattle husbandry is done for two purposes— milk and draught labour for agricultural work such as tilling, irrigation and carting.

● Milk-producing females are called milch animals (dairy animals), while the ones used for farm labour are called draught animals.

● The breeds having more lactation period and those having increased disease resistance are cross bred to produce the desired characteristics.

● The shelters should be properly cleaned and should be well-ventilated roofed sheds.

● Animals should be regularly brushed.

● The food requirements of dairy animals are of two types:

(a) maintenance requirement, which is the food required to support the animal to live a healthy life, and

(b) milk producing requirement, which is the type of food required during the lactation period.

● Animal feed includes: (a) roughage, which is largely fibre, and (b) concentrates, which are low in fibre and contain relatively high levels of proteins and other nutrients.

● Animals should be protected from external parasites (live on skin and cause skin diseases), internal parasites (like worms, affect stomach and intestine while flukes damage the liver and diseases.

● They should be properly vaccinated to prevent diseases.

2. Poultry farming

● It is undertaken to raise domestic fowl for egg production and chicken meat.

● The following traits are desired in cross breds

○ number and quality of chicks

○ dwarf broiler parent for commercial chick production

○ summer adaptation capacity/ tolerance to high temperature

○ low maintenance requirements;

○ reduction in the size of the egg-laying bird with ability to utilise more fibrous cheaper diets formulated using agricultural by-products

● Broiler chickens are fed with vitamin-rich supplementary feed (vitamins A and K is kept high) for good growth rate and better feed efficiency.

● Good management practices include maintenance of temperature and hygienic conditions in housing and poultry feed, as well as prevention and control of diseases and pests.

● Proper cleaning, sanitation, and spraying of disinfectants at regular intervals and vaccination are required to prevent diseases caused by virus, bacteria, fungi, parasites and those from nutritional deficiencies.

3. Fish Production

● It includes the finned true fish as well as shellfish such as prawns and molluscs.

● There are two ways of obtaining fish

○ Natural resources, which is called capture fishing.

○ Fish farming, which is called culture fishery.

● The water source of the fish can be either seawater or fresh water, such as in rivers and ponds.

Marine Fisheries

● Popular marine fish varieties include pomphret, mackerel, tuna, sardines, and Bombay duck.

● Some marine fish of high economic value are also farmed in seawater. This includes finned fishes like mullets, bhetki, and pearl spots, shellfish such as prawns , mussels and oysters as well as seaweed.

Inland Fisheries

● Fresh water resources - canals, ponds, reservoirs and rivers.

● Brackish water resources - seawater and fresh water mix together, such as estuaries and lagoons.

● Fish culture is sometimes done in combination with a rice crop, so that fish are grown in the water in the paddy field.

● Composite fish culture systems - intensive fish farming; local and imported fish species are used; a combination of five or six fish species is used in a single fishpond; these species are selected so that they do not compete for food among them having different types of food habits; increases the fish yield from the pond.