Which term describes the diffusion of water across a semipermeable membrane?

Which term describes the diffusion of water across a semipermeable membrane?

• A. Osmosis
• B. Diffusion
• C. Osmolarity
• D. Transpiration

Answer: (A)

Osmosis is the diffusion of water across a semipermeable membrane. Water moves from the side with more water (fewer dissolved particles) to the side with more dissolved particles, because the membrane allows water to pass but restricts most solutes. This flow continues until the solute concentrations are balanced or opposing pressure stops it. Osmosis explains why a cell placed in salty or sugary solutions loses water and shrivels, while in pure water it tends to swell. Diffusion, by contrast, is the general spread of any molecules from high to low concentration and doesn’t have to involve a semipermeable membrane. Osmolarity is a measure of how concentrated a solution is with dissolved particles, not the movement itself. Transpiration is the process of water loss from a plant’s leaves due to evaporation, not transport across a membrane.

Osmosis is the diffusion of water across a semipermeable membrane. Water moves from the side with more water (fewer dissolved particles) to the side with more dissolved particles, because the membrane allows water to pass but restricts most solutes. This flow continues until the solute concentrations are balanced or opposing pressure stops it. Osmosis explains why a cell placed in salty or sugary solutions loses water and shrivels, while in pure water it tends to swell.

Diffusion, by contrast, is the general spread of any molecules from high to low concentration and doesn’t have to involve a semipermeable membrane. Osmolarity is a measure of how concentrated a solution is with dissolved particles, not the movement itself. Transpiration is the process of water loss from a plant’s leaves due to evaporation, not transport across a membrane.