Physiology of Plants and Animals
What this domain tests
This domain examines how plants gain carbon, move water and food, take up minerals, and respond to stimuli - plus the general principle of homeostasis that applies to animals.
Core rules
- Photosynthesis: 6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O, in chloroplasts. Light reaction on the thylakoid membranes splits water (photolysis), releasing O2 and making ATP and NADPH; the Calvin cycle in the stroma fixes CO2 using RuBisCO.
- Stomata open when guard cells become turgid (K+ and water enter) and close when they lose water.
- Transpiration pull, cohesion of water molecules and root pressure together raise water through xylem; transpiration also cools leaves and pulls minerals up.
- Guttation is water loss as droplets from hydathodes, driven by root pressure - different from transpiration.
- Phloem translocates sucrose from source (leaf) to sink (root, fruit, growing tip) by pressure flow.
- Macronutrients N, P, K, Ca, Mg, S; magnesium is the core of chlorophyll, nitrogen of proteins and nucleic acids.
- Hormones: auxin (phototropism, apical dominance), gibberellin (stem elongation), cytokinin (cell division), abscisic acid (stomatal closure, stress), ethylene (fruit ripening).
- Animal physiology runs on homeostasis: negative feedback holds temperature, pH, glucose and water within narrow limits.
Worked example
A potted plant is kept in darkness for 48 hours, then tested with iodine. Reasoning: without light the light reaction stops, so no ATP and NADPH reach the stroma, the Calvin cycle halts and no new starch forms. The leaf decolourised and treated with iodine stains brown, not blue-black - proof that light is essential for starch synthesis.
Traps that cost marks
Saying the Calvin cycle runs at night; confusing guttation with transpiration; claiming root pressure alone lifts water to the top of tall trees; writing that stomata open when guard cells are flaccid.