How does the contractile vacuole of a paramecium maintain osmotic balance?

What is the function of the contractile vacuole in a paramecium?

A. To store excess nutrients
B. To expel excess water
C. To protect the cell from predators
D. To produce energy

Answer:

B. To expel excess water

The contractile vacuole of a paramecium plays a crucial role in maintaining osmotic balance within the cell. When a paramecium is placed in a hypotonic solution, where the surrounding environment has a lower concentration of solutes than the cell's cytoplasm, water tends to flow into the cell. This can cause the cell to swell and potentially burst from excess water intake. In order to prevent this, the contractile vacuole contracts rhythmically to expel the excess water from the cell, maintaining the proper osmotic balance.

In contrast, when a paramecium is placed in a hypertonic solution, where the surrounding environment has a higher concentration of solutes than the cell's cytoplasm, water tends to flow out of the cell. In this situation, the contractile vacuole fills up faster as it works harder to expel the excess water and prevent dehydration of the cell.

Overall, the contractile vacuole functions as a dynamic organelle that helps the paramecium adapt to different osmotic conditions to ensure its survival.