Plant and Animal Physiology
Plant and Animal Physiology
This domain tests how plants and animals carry out life processes: photosynthesis, respiration, transpiration and transport in plants; digestion, circulation, respiration and excretion in animals.
Core rules
- Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ in chlorophyll using light; light reactions make ATP and NADPH, the Calvin cycle fixes carbon.
- Aerobic respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy; anaerobic respiration in muscle gives lactic acid.
- Transpiration is water loss as vapour through stomata; it creates transpiration pull that lifts water in xylem. Phloem transports food.
- In humans, digestion breaks food into absorbable molecules; villi increase absorption. Blood carries oxygen, nutrients and wastes.
- The heart has four chambers; arteries carry blood away from the heart, veins return it, capillaries allow exchange.
- Nephrons filter blood in kidneys; urine contains water, urea and salts.
- Stomata open and close by guard-cell turgor.
Worked example
A plant uses 6 molecules of CO₂ to make 1 molecule of glucose. If 12 molecules of CO₂ are fixed, 2 molecules of glucose are produced and 12 molecules of O₂ are released, because the balanced equation uses 6 CO₂ : 1 glucose : 6 O₂. The oxygen released comes from water, not from carbon dioxide.
Traps
Photosynthesis and respiration are not reverse processes in every detail; respiration occurs all the time. Xylem carries water and minerals upward, phloem carries food. Arteries are not defined by oxygen content but by direction from the heart. Transpiration is not simply harmful; it drives water transport and cooling.