Question

What is the function of contractile vacuole in amoeba?

Answer 1

Hint: An amoeba is a type of cell or unicellular organism that belongs to the family amoebidae, which has the ability to alter its shape, primarily by extending and retracting pseudopodia. Amoebae do not have cell walls and they move and feed by using pseudopods, which are bulges of cytoplasm formed by the coordinated action of actin filaments pushing out the plasma membrane that surrounds the cell.

Complete answer:
Like many other protists, species of amoeba control osmotic pressures with the help of a membrane-bound organelle called the contractile vacuole. Amoeba proteus has one contractile vacuole which slowly fills with water from the cytoplasm (diastole), then, while fusing with the cell membrane, quickly contracts (systole), releasing water to the outside by exocytosis, this process regulates the amount of water present in the cytoplasm of the amoeba. Thus, a contractile vacuole helps in keeping the internal environment constant.

Species that possess a contractile vacuole generally always use the organelle, even at very hypertonic (high concentration of solutes) environments, since the cell tends to adjust its cytoplasm to become even more hyperosmotic than the environment. The amount of water expelled from the cell and the rate of contraction are related to the osmolarity of the environment.
The membrane of the contractile vacuole crumples immediately after the contraction vacuole.
Soon after many small vacuoles appear surrounding the membrane of the contractile vacuole, these small vacuoles are split from the contractile vacuole membrane.
These small vesicles gradually increase in size as they take in water and fuse with the contractile vacuole. The function of these small vesicles is to channel excess cytoplasmic water into the contraction vacuole. Now the contractile vacuole swells and contracts to expel the water outside, and this cycle repeats multiple times.
The membrane of contractile vacuoles and small vesicles has aquaporins which facilitate the water passage through the membrane.

Note:
Not all aquatic organisms have contractile vacuole for example in marine organisms there is no contractile vacuole present as the outside water is of high salinity so water does not diffuse inside the cell therefore there is no need for contractile vacuole whereas the cellular environment of a freshwater organism being hypersonic the water diffuses inside the cell constantly and gets collected in the contractile vacuole, which squeezes the extra water out of the cell periodically.