Life and Living
Cell Theory and Cell Structure
Cell theory tells us that all living organisms are made up of at least one cell.
Some organisms exist as single cells, that is are unicellular. This means that each cell has to carry out all the activities necessary for life.
Other organisms can exist a single cells, or as large complexes of single cells in which the tasks necessary to maintain life get shared out.
Animals, and most plants are multicellular, with groups of cells having different tasks being organised into tissues e.g. muscle tissue in animals.