What is osmosis?

• A. The movement of solutes across a semi-permeable membrane
• B. The active transport of water molecules into cells
• C. The passive movement of water from lower to higher solute concentration
• D. The active movement of water against a concentration gradient

Answer: (C)

Osmosis is best defined as the passive movement of water from a region of lower solute concentration to a region of higher solute concentration through a semi-permeable membrane. This movement occurs naturally as an attempt to equalize solute concentrations on both sides of the membrane. Water molecules are able to move freely across the semi-permeable membrane, while solutes are not, resulting in a net movement of water to where there are more solute particles.

This process does not require energy, as it is driven by the concentration gradient of solutes, making it a passive transport mechanism. Therefore, the correct understanding of osmosis involves recognizing that it specifically refers to the movement of water induced by differences in solute concentrations rather than the movement of solutes themselves or water against a gradient.