1. MECHANISMS & PATHWAYS
Explain how NAD is reduced in glycolysis
→ Accepts 2 hydrogen atoms (2e⁻ + H⁺) via dehydrogenase
Link oxidation and reduction in respiration
→ Oxidation = loss of H, reduction = gain of H → always occur together
Why does anaerobic respiration produce less ATP?
→ No oxidative phosphorylation / only substrate-level phosphorylation
RQ = 1.0 → what substrate?
→ Carbohydrate
Is ATP made directly in ETC?
→ No → made by chemiosmosis
Why must oxaloacetate be regenerated in the Krebs cycle?
→ Allows acetyl groups to continue entering cycle / prevents pathway stopping
Explain link between hydrogen carriers and ATP yield
→ More reduced coenzymes → more electrons → more proton pumping → more ATP
Why must NAD be regenerated in anaerobic conditions?
→ Without NAD → glycolysis stops → no ATP production
RQ ≈ 0.7 → explain
→ Lipid / less CO₂ per O₂ used
Does oxygen combine with hydrogen to make ATP?
→ No → forms water
Explain how ATP synthase works
→ Proton gradient → protons flow through channel → rotational change → ADP + Pi → ATP
300
Why does glycolysis occur in cytoplasm but Krebs in mitochondria?
→ Enzymes compartmentalised / mitochondria provide membrane for ETC
Explain why lactate causes muscle fatigue
→ Lowers pH → affects enzyme activity
A toxin blocks ATP synthase — what happens?
→ Proton gradient builds → ETC stops → no ATP
Is glycolysis aerobic?
→ No → does not require oxygen
Why does electron transport release energy in steps?
→ Prevents energy loss as heat / allows controlled ATP production
Explain relationship between structure of cristae and ATP production
→ Increased surface area → more ETC proteins + ATP synthase → higher ATP yield
Why does oxygen increase ATP yield?
→ Final electron acceptor → keeps ETC running → maintains proton gradient
Inner membrane damaged — effect?
→ No proton gradient → no chemiosmosis → no ATP
Does Krebs cycle produce ATP directly?
→ Only small amount (substrate-level)
Explain how reduced NAD leads to ATP formation
→ Donates electrons → ETC → energy released → proton gradient → chemiosmosis → ATP
Link chemiosmosis to facilitated diffusion
→ Proton flow down gradient via ATP synthase (protein channel)
Explain why fats have higher energy value than carbohydrates
→ More hydrogen atoms → more reduced coenzymes → more ATP
Cyanide blocks electron transport — explain death mechanism
→ No ATP → cells fail → especially brain/heart
Is NAD energy?
→ No → carrier of electrons/hydrogen