Plant Physiology
Plant Physiology covers photosynthesis, respiration, water relations, mineral nutrition and growth regulation.
Core rules
- Light reactions: PSII (P680) splits water, PSI (P700) reduces NADP⁺; non-cyclic photophosphorylation produces ATP and NADPH; cyclic produces ATP only.
- Calvin cycle: 3 ATP and 2 NADPH per CO₂ fixed. C4 plants use PEP carboxylase in mesophyll and RuBisCO in bundle-sheath cells, reducing photorespiration; CAM plants fix CO₂ at night.
- Respiration: glycolysis (cytoplasm), Krebs cycle (mitochondrial matrix), electron transport chain (inner membrane). NCERT accounts 38 ATP per glucose.
- Water: water potential, osmosis, transpiration pull, cohesion–tension theory; stomata regulated by guard cells.
- Growth regulators: auxin, gibberellin, cytokinin, ABA (stress hormone), ethylene (ripening).
Worked example
How many ATP and NADPH are needed to fix six CO₂ into one glucose? Each CO₂ requires 3 ATP and 2 NADPH, so 6 × 3 = 18 ATP and 6 × 2 = 12 NADPH. This is why the light reaction must keep supplying both.
Traps
RuBisCO can bind O₂ as well as CO₂, causing photorespiration. C4 plants do not lack RuBisCO; they confine it to bundle-sheath cells. ABA closes stomata; it is not a growth promoter. Ethylene promotes ripening, not elongation.