OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What is osmosis?

1. A process for the active transport of nutrients

2. The net movement of water molecules across a membrane

3. A chemical reaction that occurs in cells

4. A method for generating energy in cells

The correct answer is: The net movement of water molecules across a membrane

Osmosis is defined as the net movement of water molecules across a selectively permeable membrane. This process occurs from an area of lower solute concentration (higher water concentration) to an area of higher solute concentration (lower water concentration) until equilibrium is reached. This movement relies on the principles of diffusion, where substances move to balance concentrations on either side of a membrane. Osmosis is crucial for maintaining cell turgor, nutrient transport, and overall cellular function in living organisms. The other options describe different biological processes. The active transport of nutrients, for instance, involves the movement of substances against their concentration gradient using energy, which is not applicable to osmosis. Chemical reactions in cells generally involve the transformation of substances, such as in metabolic pathways, rather than the passive movement of water. Lastly, methods for generating energy in cells typically refer to processes like cellular respiration or photosynthesis, which does not include the movement of water molecules. Hence, the correct characterization of osmosis as the movement of water across a membrane is accurately captured in the chosen answer.