Concept:The contractile vacuole regulates water balance in freshwater organisms.
Explanation:Paramecium lives in fresh water.
Its cytoplasm has more solutes than the surrounding water.
Therefore, water enters the cell by osmosis.
The contractile vacuole collects this excess water.
It then swells and expels the water out through the cell membrane.
This process prevents the cell from bursting and is called osmoregulation.
Answer:Gets rid of excess water. (Option D)