Some detail about single celled organisms and multicelluar organisms

Single celled organisms

            Nearly all living organisms are made up of either single cell or group of cells.

    In unicellular organisms, the single cell performs the vrious  biological functions. There is no division of labour

eg. Bacteria, Blue green algae, Chlorella, Amoeba, Euglene and Paramecium.

    Chlorella is simple non-motile unicellular green algae. The cell is more or less spherical in shape. They lack flagella, eyespot and contractile vacuoles. They are able to carry out all important activities of life. Thus they lead an independent life.

Multicellular organisms 

         Most of the plants and animals are made up of many cells. Hence they are called multicellular organisms.

            In mutlicellular organisms, the cells do not lead a totally independent life. The different group of cells perform different functions in the body of a multicellular organism. This is called division of labour.

For example

In Animals

1. Epithelial cell-protection

2. Sex cell-reproduction

3. Muscle cell-contraction

4. Nerve cell-sensory impulse and motor activities

In Plants

1. Epidermal cell-protection

2. Root hair-absorption

3. Xylem-transportation of water

4. Phloem- transportation of food materials.

         In addition, multicellular organisms have a great capacity for survival than unicellular organisms. For example, blood cells are continuously destroyed and replaced in the bone marrow where as damage may result in the death of the unicellular organisms.