The outline of the single-celled body changes constantly as it moves and has no permanent shape. The freshwater amoeba is typical of this group. Oxygen and carbon dioxide for respiration pass freely through the delicate cell membrane. Amoebas multiply by simply dividing in two. If food or water becomes scarce, they can survive as inactive cysts until conditions improve.
Amoebas feed themselves by trapping food particles in the surrounding water.
Their cell parts can become more fluid to stretch out and form 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.