Final answer:
When a cell gains water, both size and mass increase due to swelling from water absorption without a change in osmolarity.
Step-by-step explanation:
When a cell gains water, its size and mass both increase. This is due to water absorption, which often results in cellular growth or expansion. In biological terms, this process is known as osmosis where water moves across the cell membrane from an area of lower solute concentration to an area of higher solute concentration. Moreover, the main component of cells is water, and its acquisition is generally what drives cellular growth. When cells take in water, they swell due to water gain, which results in an increase in both cell size and mass. However, a cell's osmolarity, or the total concentration of all solute particles in a solution, will stay the same if water is moving in and out of the cell at the same rate.