Number of Cells in Organism

Unicellular organisms are made up of single cell only. Multicellular organisms are made up of many cells. Only one cell carries out all life processes and behaves as a complete organism in unicellular organism . Bacteria, Amoeba, Protozoans and Algae are unicellular. In a multi-cellular organism some cells of similar type aggregate together to perform a function. Such an aggregation of cells is known as a tissue. In living kingdom majority of organism are formed of more than one cell. That is why majority of organisms are formed of more than one cell. That is why majority of plants and animals are multicellular. Tissues of different structures and functions are incorporated in the body organisation of multicellular organism. Plants like Marchantia, Fern Cycas Sunflower and Maize are multicellular. Animals like Sponge, Corals, Jelly fish, Earthworm, Slug, Cockroach, Fish, Frog, Wall lizard, Monkey and Men are all multicellular. On the basis of nuclei of cells, among multicellular animals human being is considered to be in the highest position. The cortex of the human brain consists of about 920 crores cells. In human blood there are 3 1013 Cells. The adult man weighs about 140 pounds and its body consists of 6 1015 cells. Each cell has two main components- Cytoplasm and nucleus. Usually there is a nucleus in the cell. Group Akaryota includes organisms having cells without any cytoplasmic organisation and devoid of definite nuclear material e.g. Virus Group Prokaryota [Monera] includes organism having primitive type of nucleus in cell e.g. Bacteria and Blue green algae. Group Eukaryota includes organisms having cell with well developed nucleus . e.g. Protista [Algae, Amoeba, Lichens], Fungi [Yeast, Mushroom], Metaphyta [Moss, Fern, Cycas, Sunflower and Maize] and Metazoa [Parazoa-animals like sponges and Eumetazoa the remaining animal kingdom.]