Cells are specialised to perform specific functions. Similar cells are then grouped together into tissues, tissues into organs and organs into organ systems for increased efficiency.
- Single-celled organisms perform all essential life functions inside the boundaries of a single cell. Although they perform all functions adequately, they cannot be totally efficient at all of them, because each function requires a different type of cellular structure.
- For example, one activity may be best carried out by a long, thin cell, while another might suit a spherically shaped cell.
- No one cell can provide the best conditions for all functions, for this reason the cells of multicellular organisms are adapted in different ways to perform a particular role.
- All cells in an organism are indentical; but as it matures, each cell takes on its own individual characteristics that suit it to the function that it will perform when it is mature - the cell becomes specialised; this is known as cell differentiation.
- All cells in an organism are derived by mitotic divisions of the fertilised eggs and all cells contain exactly the same genes.
- Cells become differentiated because, only a few of the genes that the cell possess are switched on (expressed).
- Different genes are switch on (expressed) in each type of differentiated cell, the rest of the genes are switched off.
- Both shape and number of organelles within each cell varies from cell to cell, e.g. muscle or sperm cell have many mitochondria, while a bone cell has very few.
- The cells of a multicellular organism have therefore evolved to become more and more suited…