Single-celled organisms perform all essential life functions inside single cell.
However no cell can provide the best conditions for all functions, as each function requires a different type of cellular structure.
Cells of multicellular organisms = each adapted with different structure to perform a particular role.
Initially all cells in organism = identical.
However cells differentiate as they mature, have their own characteristics for function it is performing = cell differentiation.
All cells derived by mitotic divisions of fertilised egg, so they all contain the same genes but different genes are switched on in different cells.
Different genes switched on cause cells to develop into certain type of cell with the structure to perform a certain function.
Cells vary in the shape of the cell and the number of each of their organelles:
- Muscle or sperm cells have many mitochondria but bones have very few.
- White blood cells have many lysosomes but muscle cells have few.
Cells of multicellular organism have evolved to become more and more suited to specialised functions but lose ability to carry out other functions, so rely on other cells to do these activities…