In a process known as phagocytosis, amebas engulf their prey, or particles of appropriate size, with their pseudopodia, forming food vacuoles. Digestive enzymes, manufactured and secreted by the organism, are then poured into these vacuoles, and the particles are digested. Useful compounds are subsequently absorbed into the ameba's body. Freshwater amebas take up water constantly through the process of osmosis , and water content is regulated with a pulsating contractile vacuole. Marine amebas lack a contractile vacuole.
Respiration is by diffusion of gases through the cell membrane.
When an ameba is divided artificially, the portion containing the nucleus forms a new cell membrane and continues as a whole animal, while the other portion lives only as long as its present food supply lasts, ultimately dying, since it cannot ingest food or reproduce. If conditions are unfavorable, e.g., in the absence of food and water, amebas secrete a firm protective covering and encyst until conditions are again favorable to active division. The Columbia Encyclopedia, Sixth Edition.