Variety in cell number

Question 1 What are single-celled organism? Give example?

Question 2 What are multicellular organism? Give example?

Question 3 What is fertilised egg cell?

Question 4 How a single cell organism behave like a complete organism?

The various organisms differ in the number of cells which make up their body; they differ in the shapes of cells in their body ; also they differ in the size of cells in their body.

Variety in number of cell

Different organism have different number of cells in their bodies.The number of cells varies from organism to organism.Some are made up of just one cell while other are made up of large number of cells.

The organism which are made up of only one cell are called unicellular organism or single-celled organism.

For Ex:Amoeba, paramecium, Euglena, Chlamydomonas etc.

A unicellular organism perform all necessary life functions with the help of just one cell.All basic function such as taking of food, digestion, respiration, movement, response to environment, excretion , reproduction etc are performed by single cell.

The organism which are made up of only many cell are called multicellular organism.

A multicellular organism is made up of millions, billions, trillions of cell joined together.Most of the plants and animals are multicellular.

In multi cellular organism different cells perform different functions.

The number of cell being less in small organism does not in any way affect the functioning of the small organism.Even an organism made of million, billions or trillions of cells begin its life as a single cell called fertilised egg cell.The fertilised egg cell divides and multiplies due to which the number of cell increases as the development of the organism proceeds.