The number of cell varies in a body or an organism. Organisms are divided into two types Unicellular and multi-cellular. The main difference between unicellular and multicellular organisms is, some organisms are made-up of single cell termed as unicellular while multicellular are made-up of two or more cells.
Single celled organism is called unicellular organism. They depend on simple diffusion to ride out and live. Unicellular organisms have greater surface area to volume ratio. They are so small that can only be seen through microscope. They are not visible to naked eye. An example of unicellular organism is amoeba. Generally they come under the heading of prokaryotes that are not specialized cells. For movement they form pseudopodia by which it drags itself in forward direction. They do not have structure called cell nuclei. It does not have internal cell organelles or the membranous coat of organelles. They survive in a habitat which are very hazardous for example highly acidic environment. The single cell is responsible for an organism to survive. The single cell membrane protects the cell from external environment. If the progenitor cell dies the organism dies completely.
Multicellular are those that harbor multiple numbers of cells. The Multicellular organism is actually the aggregation of cells. They are more large, huge and specialized cells. They are classified as eukaryotes. It has all membrane bound organelles plus the nuclei. They have their DNA’s individually placed from the surplus of the cell. These cells are placed next to each other growing exponentially to amazing sizes. They vary from microscopic (Myxozoa) to enlarged cells that can be seen through naked eye. They can conduct more complex activity and functions. Animal, plants and fungi are its examples. If one cell of a Multicellular organism dies the cell survives with the remaining ones. The cellular practice and division of the work leads to the development of Multicellular organism. Same group of cell join together to form one tissue system for example a nerve cell forms nerve tissue.
- The unicellular body is formed by single cell while body of Multicellular is of multiple cells.
- In unicellular organism the work is divided at the organelle level, while in Multicellular it involves cellular, tissue, organ and organ system level.
- In unicellular organism a single cell is responsible to carry the life, while in Multicellular organism special cells are focused to carry out distinct cellular duties.
- From all sides the cell of a unicellular organism is exposed to the environment while in Multicellular organism the outer cell face the environment and the inner cells are specialized to do the cell basic function.
- In unicellular organism a simple cellular trauma can cause its death while in Multicellular organism it does not cause the death of the tissue.
- In unicellular organism the cell body cannot attain a large size, due to surface area volume ratio while Multicellular can.
- In unicellular organism the life span is short due to heavy load work while in Multicellular life span is long.
- In unicellular organism the power of division is not lost but in Multicellular organism some non reproductive specialized cells lose this power.
- The cell has same role as the organism while in Multicellular organism are multipurpose.