Question

Major function of the contractile vacuole is of Amoeba and others are
A) Excretion
B) Circulation
C) Osmoregulation
D) All the above

Answer 1

Hint: Amoeba is a unicellular organism that can change its shape by retracting and extending its pseudopodia. Pseudopodia means false foot. These pseudopodia help in catching food and in locomotion. Amoeba are either free-living in damp environments or parasitic.

Complete answer: The contractile vacuole of Amoeba is a clear and single rounded pulsating structure. These contractile vacuoles are filled with watery fluid and enclosed by a unit membrane. They work by expanding (water-absorbing) and contracting (water expulsion) and their function is to pump water out of the cell through a process called osmoregulation, the regulation of osmotic pressure. For osmoregulation, the solvent (water) needs to be in balance with the solute (other material). As water moves across a semipermeable membrane, water moves to a lower concentration of water and a higher concentration of solute. The contractile vacuole acts as a protective mechanism that prevents the cell from absorbing too much water and thus preventing rupture of the cell (lysis) because of excessive internal pressure.
Hence, the correct answer is option C.
Additional information:
Water always flows from outside into the cell cytoplasm first and only then it is moved from the cytoplasm into the contractile vacuole. The movements of the contractile vacuole are periodical. The entering of water into the contractile vacuole is called Diastole and the expelling of water out of the cell by contraction of the vacuole is called Systole.

Note: Amoeba can be marine or freshwater. In freshwater amoeba, the contractile vacuole is necessary as freshwater has a lower concentration of solutes than the Amoeba’s internal fluids. The marine Amoeba doesn’t possess a contractile vacuole due to the concentration of the solutes in the cell are in balance with the toxicity of the surrounding water. So, they do not need osmoregulation.