Question

If an amoeba is kept in distilled water, its contractile vacuole
(a) Works slowly
(b) Works faster
(c) Remains unaffected
(d) Disappears

Answer 1

The process in which the cells absorb water when they are placed inside the hypotonic solution and result in the swelling of the cell is known as endosmosis. The cells swell due to the presence of a lower solute concentration in the surrounding than inside the cell.

Complete answer
Contractile vacuoles are the organs in the cells that help in maintaining the quantity of water and regulate the osmotic balance in the cell. If an amoeba is kept in distilled water, the rate of endosmosis is increased due to the movement of water inside the cytoplasm of their cell thus resulting in the contractile vacuole to work faster. In the case of amoeba, Its function is to manage the water content of the cell. It's also a way of excreting its waste from the cell (out through the cell membrane) via diffusion.

Additional information
‘Vacuole’ is often defined as a membrane-bound space found in the cytoplasm. It can contain sap, water, enzymes, organic acids, excretory products, or other materials which may not be useful for the cell. Hence, it is also known as the ‘storage sac of the cell.’ The vacuole is surrounded by a single, semipermeable membrane which is called tonoplast. This membrane enables the transport of a number of ions and other materials against the concentration gradient.
As osmotic pressure is to be maintained, to regulate osmotic pressure in amoeba's, most freshwater amoebae have a contractile vacuole that expels excess water from the cell. The freshwater has a lower concentration of solutes such as salt than the amoeba's own internal fluids (cytosol).
Without a contractile vacuole, the cell would fill with excess water and, eventually, burst, because the surrounding water is hypotonic with respect to the contents of the cell, water is transferred across the amoeba's cell membrane by osmosis.

So, the correct answer is ‘Works faster’.

Note:
In every amoeba species the contractile Vacuole may not be present. In the case of the marine species of amoeba, the The contractile vacuole is found to be absent as the concentration of the solute inside the cell cytoplasm is balanced as in comparison to the solute concentration present outside the cell that is in the surrounding water.