Exam Tips: Plant Hormones

Auxin moves AWAY from light: This is the single most commonly confused fact. Auxin accumulates on the SHADED side, not the illuminated side. The shoot then bends TOWARDS light because the shaded side grows faster. Rehearse this direction until it is automatic.

Always explain the mechanism, not just the outcome: "The shoot bends towards light" is only 1 mark. To get full marks, explain: auxin redistribution → higher concentration on shaded side → greater cell elongation on shaded side → differential growth → bending. Each step is a mark.

Root vs shoot sensitivity: When comparing, always state that roots are MORE sensitive to auxin than shoots, and that the same concentration has opposite effects. This distinction earns the highest-difficulty marks in this topic.

Commercial uses require a mechanism: "Ethylene ripens fruit" is 1 mark. "Ethylene triggers breakdown of chlorophyll and softening of cell walls, causing ripening" is 2 marks. Always add the mechanism.

RPA8 practical questions: For the plant growth required practical, know: independent variable (direction of light/gravity), dependent variable (angle of bending or direction of growth), control variables (temperature, water, wavelength of light, age of seedlings), and why multiple seedlings are used (to improve reliability/take a mean).

Use correct terminology: Use "gravitropism" not "geotropism" (both are accepted by AQA, but gravitropism is preferred in current mark schemes). Use "cell elongation" not "cell growth" (growth implies cell division — elongation is more precise).