Osmosis takes place in an amoeba much like any other single-celled aquatic organism, with water diffusing across its cell membrane into the cell because of the higher concentration of solutes in its cytoplasm. Indeed, in many freshwater amoebas, this water movement is constant and at a high rate, enough to damage or even burst the cell if not regularly removed. Fortunately, amoebas have a sophisticated system to remove excess water.
Amoebas are unique types of cells with extremely mutable shapes. They move and eat using structures known as pseudopods, which are appendages they form as needed from their extremely mutable forms. They respond to their environment using active movements of protein structures in their cytoplasm that push and shape their cell membranes. When moving by pseudopod, they reach out with the appendage and flow the rest of their bodies into the temporary structure.
Another structure they form that is constantly active in many amoebas is known as a contractile vacuole. Because of their constant intake of water via osmosis, water must actively be moved out of the cell with great frequency. Small, membrane-bound bubbles of pure water, collected from the cytoplasm, are brought to the contractile vacuole, which then contracts, pumping its contents back into the environment.