Plant Physiology
Plant Physiology tests water and mineral transport, photosynthesis, respiration, and growth regulation. Questions often require linking a process to its site, energy source, or hormone effect.
Core rules and concepts
- Water moves down a water-potential gradient. Transpiration pull, cohesion, and adhesion drive xylem transport. Stomata regulate gas exchange and water loss.
- Minerals are classified as macronutrients or micronutrients. Deficiency symptoms include chlorosis and necrosis; mobile nutrients show symptoms first in older leaves.
- Photosynthesis: PSII splits water and releases O₂; non-cyclic photophosphorylation produces ATP and NADPH; the Calvin cycle fixes CO₂ using RuBisCO. C4 plants use the Hatch-Slack pathway and reduce photorespiration.
- Respiration: glycolysis, Krebs cycle, and electron transport chain. The respiratory quotient is CO₂ released divided by O₂ consumed.
- Growth regulators include auxin, gibberellin, cytokinin, ABA, and ethylene. Photoperiodism controls flowering in many plants.
Worked example
A tissue consumes 200 mL O₂ and releases 140 mL CO₂. RQ = 140/200 = 0.7. This value is typical of fats, which are more reduced and require more oxygen per carbon than carbohydrates, whose RQ is about 1.0.
Traps that cost marks
Water is split at PSII, not PSI. RuBisCO acts as both carboxylase and oxygenase. Auxin causes apical dominance; cytokinin promotes lateral bud growth. Transpiration pull depends on cohesion-tension, not on active pumping by xylem.