AP Biology Unit 2 Topic 5: Cell regulatory mechanisms (like osmosis and selective permeability)

Cell regulatory mechanisms (like osmosis and selective permeability) belongs to Unit 2: Cells. Cells regulate internal water and solute balance through selective membranes, osmosis, and controlled movement of materials. Treat the topic as a relationship between structure, process, evidence, and biological function instead of memorizing an isolated definition.

Key relationships: Water moves across membranes in response to differences in solute concentration and water potential. Aquaporins can increase water movement without making the membrane freely permeable to every solute. Tonicity predicts whether cells gain water, lose water, or stay near equilibrium in a solution.

Model to use: Compare a cell in hypertonic, hypotonic, and isotonic environments and predict net water movement. A clear model should label the parts, show the direction of movement or information flow when relevant, and connect the diagram back to the biological outcome.

AP-style move: When a question includes mass change, swelling, or shrinking, translate the observation into water movement and solute concentration differences. Strong answers name the concept, apply it to the scenario, and explain the reasoning in complete sentences.