What is osmosis?

Osmosis is defined as the diffusion of water across a selectively permeable membrane. This process occurs in response to differences in solute concentration on either side of the membrane. Water molecules move from an area of lower solute concentration (where there is more water and less solute) to an area of higher solute concentration (where there is less water and more solute) in order to achieve equilibrium. This movement of water is essential for maintaining cellular homeostasis, regulating fluid balance, and supporting various biological functions.

In contrast, the other processes listed do not accurately describe osmosis. Active transport, as mentioned in the first option, involves energy expenditure to move substances, such as glucose, against their concentration gradient and does not specifically refer to the movement of water. The third option describes the movement of solutes rather than water, and while that process, known as diffusion, is related, it does not define osmosis itself. Lastly, cell division pertains to the process by which cells reproduce and is unrelated to the movement of water across membranes. This highlights that only the diffusion of water across a selectively permeable membrane truly defines osmosis.