Question

Some protists, like the paramecium pictured, live in freshwater. Paramecium have contractile vacuoles, which act to pump water out of the cell. Why?
A. There is a lower solute concentration inside so water is moving into the cell constantly
B. There is a higher solute concentration inside so water is moving into the cell constantly
C. There is a lower solute concentration inside so water is moving out of the cell constantly
D. There is a higher solute concentration inside so water is moving out of the cell constantly

Answer 1

The correct answer is option B, that is, there is a higher solute concentration inside so water is moving into the cell constantly.  

The contractile vacuole functions to pump out an extra amount of water from the cell. Paramecium lives in freshwater, where the water exhibits lower solute concentration in comparison to the cytoplasm within the cell. Therefore, due to osmosis, the water will flow within the cell.

The extra amount of water can be accumulated at the contractile vacuole and then be withdrawn out. The frequency and rhythm of the contraction rely on the surrounding and also on the number of contractile vacuoles present.