Cells and Tissues

THE CELL

The cell is the basic, structural and functional unit of living organisms. There are two types of cells:

ANIMAL CELL and PLANT CELL

PARTS OF THE CELL AND THEIR FUNCTIONS

NUCLEUS

It is usually found in the centre of the cell. It contains nucleolus which is rich in RIBONUCLEIC ACID (R.N.A) and chromosomes which is made up of DEOXYRIBONUCLEIC ACID(D.N.A).

FUNCTIONS

It is the powerhouse of the cell. That is it control all the metabolic activities in the cell.

It stores hereditary materials in the cell

It is responsible for cell division.

CELL MEMBRANE/ PLASMA MEMBRANE

It is a thin- flexible semi-permeable membrane which forms a boundary around the cell.

FUNCTIONS

It prevents the cell from injury

It is a channel through which substances enter or live the cell

VACUOLE

It is a sac containing watery fluid. It normally occupies a large volume of the cell.

FUNCTIONS

It is used to store foods in the cells

It stores waste products of individual cell

It imparts colour of food and flowers

MITOCHONDRION

It is a sausage-shaped organelle that is responsible for the breaking of food to release energy.

FUNCTIONS

It produces energy from respiration

It is responsible for the synthesis of amino acids

It is responsible for the synthesis of chlorophyll in plants.

CELL WALL

It is made up of cellulose and found outside the cell membrane of plant cells.

FUNCTIONS

It supports and protects the plants

It gives the cell its definite shape

CHLOROPLAST

These are small bodies containing the green-pigment call chlorophyll, which enables plants to manufacture their own food.

CYTOPLASM

It is a transparent fluid which contains smaller parts of the cell call organelles.

FUNCTIONS

All chemical reactions and life processes take place in the cytoplasm

It helps in the inter-cellular distribution of \molecules, enzymes and nutrients.

It helps in the breakdown of glucose.

DIFFERENCES BETWEEN PLANT CELL AND ANIMAL CELL

PLANT CELL	ANIMAL CELL
It has a cell wall	It has no cell wall
It has chlorophyll	It has no chlorophyll
It has a definite shape	It does not have a definite shape
It has a large vacuole	It has a small vacuole
It stores food as starch	It stores food as glycogen

SPECIALIZED CELLS

These are cells structurally adapted to perform specific functions. Some examples of specialized cells include the following:

Examples of specialized cells and functions:

Cell	Function
Muscle cell	Relaxes and contracts to produce movement
Red Blood Cell	Carry oxygen from lungs to tissue
White Blood Cell	Produces antibodies to fight against diseases
Nerve Cell	Transmit nerve impulses
Sperm Cell	Fertilizes egg
Palisade Cell	Contains chlorophyll to carry out photosynthesis
Leaf epidermal cell	Allow light to enter the leaf and reach photosynthetic tissues below them.

TISSUE

A tissue is a group of similar cells, which are specialized and perform the same function. Example include Nerve tissue, blood tissue, vascular tissue, etc.

SOME TYPES OF TISSUES AND THEIR FUNCTIONS:

TISSUE	FUNCTION
Adipose tissue	It insulates the body against heat.
Muscle tissue	It contracts and relaxes to bring about movement
Skeletal tissue	It provides support for the body
Nerve tissue	It conducts and co-ordinates impulse messages
Photosynthetic tissue	It produces food
Phloem tissue	It transports food
Epidermal tissue	It covers the surface of plants
Strengthening tissue	It provides support for plants
Xylem tissue	It transport water and mineral salts