The cell theory says that:
- All organisms are composed of one or more biological cells.
- The cell is the basic unit of organization of organisms.
- All cells come from preexisting cells.
Microscopes continued to be improved upon by scientists that studied cells. As a result, the scientists could see closer and begin to understand the internal structures of an individual cell. The internal structures of a cell are called organelles
, which means "little organs." Just as our bodies are made up of organs, the "bodies" of cells are made up of organelles.
There are two basic types of cells:
- prokaryote: do not have a nucleus or membranes surrounding its organelles. Example: bacteria.
- eukaryotes: do have a nucleus and organelles with membranes surrounding them. Example: plants, animals.
See also: germ theory