Amoebas get their name from the Greek word for change, amoibe. They have no permenant shape, and the outline of the single-celled body changes constantly as it moves. The amoeba has two kinds of cytoplasm: at the surface, a stiff, gellike cytoplasm forms a semisolid layer that acts as a membrane. It holds the inner, more watery cytoplasm and its contents together. Oxygen and carbon dioxide for respiration pass freely through the cell membrane.
Amoebas feed by trapping food particles in the surrounding water. Their cells stretch out and form pseudopods (false feet) around food bits. They are predators of other protozoans and minute animals. They can detect vibrations, and when stalking active prey, they will avoid contact until their false foot has surrounded the prey completely. The food is then enclosed in a bubble-like food vacuole, which disappears when it is digested completely.
Amoebas multiply by simply dividing in two. This process (fission) takes less than an hour.
If food or water becomes scarce, they can survive as inactive cysts until conditions improve.