Cells are the basic units of life.
Cells can function as individual organisms or can be part of higher organizational units. The outer layer of cytoplasm is in a gel state and called ectoplasm , and the more fluid inner is called endoplasm . Single cells are small, since these organisms need lots of surface area for diffusion and other processes, but a small volume for the nucleus to control all of the cytoplasm. Membranes are fluid and constantly changing. This allows the controlled passage of material and to define inside from outside.