A protein cell attains turgidity due to

E) Endosmosis
Turgidity in a cell occurs when water enters the cell through osmosis, creating internal pressure. This process is called endosmosis, where water moves from an area of lower solute concentration outside the cell to an area of higher solute concentration inside the cell. The influx of water causes the cell to swell, making it turgid and firm, which is important for maintaining cell structure and rigidity.