The three main parts of the cell theory are:
- All living things are made of cells.
- The cell is the basic unit of structure and function in all living things.
- Cells only come from other pre-existing cells by cell division.
While some organisms are single-celled, others are made up of many cells. These organisms are called multicellular (having many cells). Cells differ in their size and complexity.
Eukaryotes are organisms which are made up of large and complex cells, whereas prokaryotes are organisms which are made up of small and simple cells. Animals and plants are examples of eukaryotes (have eukaryotic cells) while bacteria are examples of prokaryotes (have prokaryotic cells).