What you'll learn
How cells capture, store, and use energy (~12–16% of the exam).
Enzymes
Biological catalysts that lower activation energy. Activity depends on temperature, pH, and substrate concentration; competitive inhibitors block the active site, noncompetitive inhibitors bind elsewhere and change shape (allosteric).
Photosynthesis (in chloroplasts)
- Light-dependent reactions (thylakoid): capture light → ATP + NADPH, release O₂ from water.
- Calvin cycle (stroma): uses ATP + NADPH to fix CO₂ into sugar.
Cellular respiration
- Glycolysis (cytoplasm): glucose → 2 pyruvate + small ATP/NADH.
- Krebs cycle (mitochondrial matrix): CO₂ + NADH/FADH₂.
- Oxidative phosphorylation (inner membrane): electron transport chain + chemiosmosis → most ATP; O₂ is the final electron acceptor.
- Anaerobic: fermentation regenerates NAD⁺ without O₂ (less ATP).
Exam tips
- Track energy/electron carriers (ATP, NADPH, NADH) between processes.
- Link photosynthesis and respiration as reciprocal.
Common mistakes
- Saying glycolysis needs oxygen (it doesn't).
- Confusing where each stage occurs.