Respiration & Photosynthesis is a core part of IB Biology. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
Light-dependent reactionsThylakoid membrane; photosystems II and I split water, produce ATP via chemiosmosis and NADPH.
Calvin cycleStromal carbon fixation: RuBisCO joins CO2 to RuBP (Calvin & Benson 1948-50 using carbon-14).
ChemiosmosisATP synthesis driven by proton gradient across membrane (Mitchell 1961 chemiosmotic hypothesis).
GlycolysisCytoplasmic conversion of glucose to two pyruvate, net 2 ATP and 2 NADH.
Krebs cycleMitochondrial matrix oxidation of acetyl-CoA producing CO2, NADH, FADH2, ATP (Krebs 1937).
Electron transport chainInner mitochondrial membrane; electrons pass through complexes I-IV pumping H+; O2 final acceptor.
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
Where does most of a plant's mass come from?✗ From minerals taken up from the soil. ✓ From carbon dioxide in the air, via photosynthesis.
Does photosynthesis create energy?✗ Yes, plants create new energy from nothing. ✓ No — it stores light energy as chemical energy in glucose.
Where in the cell does photosynthesis happen?✗ In the mitochondria. ✓ In the chloroplasts, which contain chlorophyll.
Practise Respiration & Photosynthesis — free games
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