The basic unit of all living organisms is the cell.
Most animals and plants contain trillions of them
and are called multicellular. However, life forms,
such as bacteria, which are composed of just one,
are called unicellular. Cells are made up of protein
material and are the fundamental machines of
biology, within which all the processes responsible
for sustaining life take place: energy production,
tissue growth, homeostasis and hormone
production. ----