Plant Physiology
Plant Physiology covers transport in plants, mineral nutrition, plant growth and development, and respiration in plants. The exam tests water potential, transport pathways, deficiency symptoms, hormones, and respiratory pathways.
Core rules
- Water moves from higher water potential to lower water potential. Water potential = solute potential + pressure potential.
- Apoplast is the cell-wall route; symplast is the cytoplasmic route through plasmodesmata. Transpiration pull drives xylem transport; phloem translocates sugars.
- Macronutrients: C, H, O, N, P, K, Ca, Mg, S. Micronutrients include Fe, Mn, Zn, Cu, B, Mo, Cl, Ni. Deficiency symptoms include chlorosis and necrosis.
- Growth regulators: auxin promotes apical dominance; cytokinin promotes lateral buds; gibberellin promotes stem elongation; abscisic acid closes stomata; ethylene ripens fruit.
- Respiration: glycolysis, Krebs cycle, electron transport chain; plants respire day and night.
Worked example
A cell has solute potential -0.8 MPa and pressure potential +0.3 MPa. Find its water potential and state whether it will gain or lose water in a solution of -0.8 MPa. Reasoning: water potential = -0.8 + 0.3 = -0.5 MPa. The cell has higher water potential (-0.5) than the solution (-0.8), so water moves out of the cell; the cell loses water.
Traps
Pure water has water potential zero, the highest value. Guttation is not transpiration. Micronutrients are essential despite small amounts. Auxin and cytokinin have opposing effects on lateral buds. Respiration is not limited to night.