In a hypotonic solution
Explanation:
Contractile vacuoles are used mainly by protozoans like an amoeba in osmoregulation. When the organism environment becomes hypotonic to the cell's cytoplasm, the contractile vacuole pumps more rapidly. This is because, in the hypotonic environment, more water is getting into the cell by osmosis. To maintain the right osmotic pressure in the cell more water is needed to be pumped out – this is a function of the organelle.
