CHAPTER 2 Cell as a unit of life

2.1 WHAT IS A CELL?

� A cell is the basic unit of life.

� Its size is too small to be seen with the naked eye.

� We need an instrument called a microscope to

observe cells.

MICROSCOPE

THE FUNCTIONS OF MICROSCOPE’S PARTS

Part Function

Eyepiece To magnify the image formed by he objective

lens.

Objective lens To magnify the image of the object.

Stage clip To hold the microscope slide in position.

Adjustment knob To get a sharper focus of the object.

Diaphragm To control the amount of light entering the

objective lens.

Stage To support the microscope slide.

PLANT CELL AND ANIMAL CELL

SIMILARITIES BETWEEN PLANT AND

ANIMAL CELL

� Have cell membrane

– controls the movement of substances in

and out of the cell

Have nucleus � Have nucleus

– control all activities of a cell

� Have cytoplasm

– it’s a jelly like-substance fluid filled with cell

sap (where chemical processes take place)

DIFFERENCES BETWEEN PLANT AND

ANIMAL CELL

2.2

UNICELLULAR AND MULTICELLULAR ORGANISMS

� Organism consists of living things living things which

include microscopic of animals and plants

(bacteria, viruses and fungus)

� A life process is a process conducted by all living � A life process is a process conducted by all living

things to enable them to survive in the world

� Life process conducted by multicellular

organisms are more complex compare to a

unicellular organisms

UNICELLULAR ORGANISMS

� Organisms that consist of only one cell are called

unicellular organisms.

� These organisms usually live in water. Some of

them such as bacteria and yeast can even live in them such as bacteria and yeast can even live in

air and human body.

UNICELLULAR ORGANISMS THAT

PHOTOSYNTHESIZE

� Unicellular organisms such as euglena and

chlamydomonas which consists of chloroplasts

can produce food by themselves through the

process of photosynthesis

MULTICELLULAR ORGANISMS

� Multicellular organisms are complex organisms

that made up of many cells.

� Multicellular organisms have many types of

different cells with its special function. This

caused them to have a huge size in shape

Hydra Spirogyra Mucor

2.3

ORGANISATION OF CELLS IN THE HUMAN BODY

� Human body is the most complex multicellular

organism. It has about 60,000 billion of cells

� The cells differ by its size, shape and structure

to enables it to perform a particular functionto enables it to perform a particular function

� A speciallised cell is a cell that performs only one

specific function in order to carry out and

maintain the stability of a huge processes

HUMAN CELLS AND ITS FUNCTIONS

Carry oxygen from lungs

throughout the whole body

Send nerve impulses to the whole

body

Form the outer layer of skin Form the outer layer of skin

to protect the body surface

Fertilises the ovum in sexual

reproduction

Allows movement

Found in bones and functions in

the support system of the body

TISSUES

� A tissue is a group of similar cells that carry out

the same function. Example,

Tissues Function

Epithelium

tissue

to protect the tissues beneath it

Muscle tissue Made up of muscle cells that contracts and relaxes

to enable movements of body

Nervous

tissue

Carry massages from one part of the body to

another

Connective

tissue

To connect and join several tissues together for

support and

protect the organs and body.

ORGANS

� When different tissues co-operate to carry out a

certain function is called an organ

� For example, heart is an organ formed of muscle

tissues and connective tissues that co-operate to

carry out the function of blood circulation to the carry out the function of blood circulation to the

entire body

THERE ARE SOME EXAMPLES OF HUMAN ORGANS

AS SHOWN BELOW:

SYSTEMS

� A group of different organs that co-operate to

perform a certain function of life process is

known as the systems

� The body systems as a whole enable human to � The body systems as a whole enable human to

carry out life process normally and more

efficiently

� There are 10 main systems in a human body

SYSTEM AND ITS FUNCTIONS

� Digests food and

absorb nutrient

�� Transport oxygen

and digested food to

the body

�� Carries unwanted �� Carries unwanted

excretory materials to

organs to be disposed from the body

� Inhales oxygen into

the body and exhales

carbon dioxide out of

the body

� During respiration, the

exchange of oxygen

and carbon dioxide

gases occur in the alveolus

� Coordination of

body activities ,

such as digestion

and metabolism

SKELETAL SYSTEM

� Preserves the body

shape

� Provides support and

protection to internal protection to internal

organs such as the

heart, lungs and other

organs

MUSCULAR SYSTEM

� Enables body

movement

� Muscles usually react

as opposing pairs to as opposing pairs to

produce movement

REPRODUCTION SYSTEM

� Produces offspring to

continue the generation

EXCRETORY SYSTEM

� Dispose waste from the

body

� Lung − carbon dioxide

and water vapour

� Skin − Urea, mineral

salt and water

� Kidney − Urea, mineral

salt and water

� Co-ordinates and control

all activities in the body

� Responds to the stimuli

when the sensory

organs receive impulses

from brainfrom brain

LYMPHATIC SYSTEM

� Body defense

� Remove bacteria from

the tissue

ORGANISMS

� All systems in the body works together to perform a

life process that produce an independent organism

� Cell organisation allows different types of work in

body to work more smoothly and efficientlybody to work more smoothly and efficiently

2.4 THE HUMAN BEING– A COMPLEX ORGANISMS

� Human considered to

be a complex

organisms because

they have various

types of cells that form types of cells that form

tissues, organs and

systems. (cell

specialisation)