Question

The major function of the contractile vacuole is
a. Excretion
b. Storage
c. Osmoregulation
d. Circulation

Answer 1

Hint: contractile vacuole is an organelle which helps in expelling the excess water from the cell and protects the cell from excessive expansion.

Complete answer:
Contractile vacuoles are mainly found in protozoans and other aquatic animals like sponges.

These organisms mainly live in freshwater, so the concentration inside the cell is more than surrounding, so the water flows from the external environment to inside of the cell where the process is called osmosis.

The excessive entry of water into the cell may result in expansion so contractile vacuoles expels entry of excess water by contracting the cell.

At the same time along with water substances such as ammonia which are soluble in water are also extracted or expelled out of the cell. The function of contractile vacuole occurs in a periodic cycle by collecting water, it expands, and while releasing the water, it contracts.

The phase where water flows into the contractile vacuole is called diastole, whereas expulsion of water to the outside environment is called systole.

Not only in freshwater organisms, the contractile vacuole is also present in some marine water and soil organisms.
Slowly in the evolution process the contractile vacuole is eliminated in multicellular organisms.

So from the above explanation the correct option is osmoregulation.

Note: One should not confuse vacuole with contractile vacuoles. Where vacuole function is the storage of food or water. Contractile vacuoles are also called as pulsatile vacuoles where their function is to maintain osmoregulation.