CHAPTER 2

CELL-THE BASIC UNIT of LIFE

2.1 WHAT IS A CELL?

• All living things are made up of basic units.• The basic unit that makes up living thing is the

cell.• Cell is the basic unit that can carry out all

living processes.• Cells are very small. Thus, they can only be

seen with the help of microscope. • So, we need to know how to use a

microscope.

microscope

Learning How To Use A Microscope

• A microscope is used to look at very small things.

• We must handle a microscope with care. • Make sure that the microscope is always clean

and dry.

How to carry a microscope?

The correct way to carry a microscope is to hold the arm of the microscope with one hand and support the base with another hand.

Types of cell

Plant cell Animal cell

Animal Cell

Plant Cell

• Protoplasm=nucleus and cytoplasm

Structures of animal and plant cells and their functions

Structures Functions

Cell Membrane

Controls the movement of substances into or out of the cell

Cell Wall Support and gives the cell a regular shape

Cytoplasm -A place for storing food and waste materials-Chemical reactions take place here.

Structures Functions

Nucleus Controls all activities of the cell

Vacuole Salt solution and sugar solutions are stored here.

Chloroplast Carries out photosynthesis

2.2 Unicellular and multicellular Organisms

• Living things are also called as organisms.• Some organisms are made up of one cell.

These are called as unicellular organisms.• They are very small and can only be seen by

using a microscope.• For examples, Yeasts, Euglena, Paramecium

and Amoeba.

Paramecium

Euglena

Amoeba

Yeast

Multicellular Organisms

• Organisms that are made up of more than one cell.

• Eg: Hydra, Spirogyra, birds, and ferns

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2.4 Cells in the Human Body

• Human body is made up of different kinds of cells.

• Examples: muscle cells, blood cells, nerve cells, epithelial cells and reproductive cells.

• Each type of cell plays an important role in carrying out certain functions.

A)Muscle cell Function: Contract and relax providing elasticity for

movements of different parts of the body.

B) White Blood Cell Function: Protect the body from being attacked by

microorganisms

C) Reproductive Cells (Ovum and Sperm)

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Function: Take part in fertilisation to produce young generations.

D)Red Blood Cell

Function: Transport oxygen in the body.

ORGANISATION OF CELLS

CELL

TISSUE

ORGAN

SYSTEM

ORGANISM

• The organisation of cells in the human body is far more complex compared to those Hydra and Spirogyra.

• The organisation of cells in this way enable multicellular organisms to carry out various processes of life such as moving, breathing and reproduction.

- There are 200 types of cells in our body.- Cells of the same type that the same function

form a tissue.- Muscle tissue, for example, is made up of muscle

cells and nervous tissue is made up of nerve cells. Different tissues working together to carry out a certain function form an organ.

- An organ consists of two or more types of tissue that perform a certain function. For examples, ear, brain, lung and stomach.

- Different organs working together to carry out a certain function form a system.

- Different systems make up the whole organism.

Organisations of cells in the human body

Organ

Tissue

Cell

System

Organism (human)

HUMAN SYSTEMS

A) Skeletal system

Function: To support weight of the

body and protect soft organs.

B)Muscular system

Function: To help the body to move.

Lymphatic system

Function:To defend the body against

disease with the help of lymphocytes.

C) Endocrine system

Function: To produce hormones to control

the body’s activities and development.

D) Digestive system

Function:To digest food so that it can be

absorbed easily and used by the body.

E) Nervous system

Function: To help the body to respond to changes inside and outside the

body.

F) Reproductive system

Reproductive system

• Produce young for the next generation

G) Blood circulatory system

Function: To carry oxygen and food to all

parts of the body and waste substances to the kidneys.

H) Excretory System

• TO REMOVE TOXIC SUBSTANCES FROM THE BODY