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Flashcards · 9700 · A Level Topic 12

Energy and respiration (A Level) flashcards

15 cards on A Level Topic 12, subtopics 12.1 to 12.2. Pick a subtopic or study them all.

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12.1 Energy

Why is ATP the universal energy currency?
Hydrolysis to ADP + Pi is a single quick step releasing energy in small, usable amounts. ATP is small and soluble, so it moves easily, is quickly regenerated, and is found in all cells.
Substrate-linked phosphorylation vs chemiosmosis
Substrate-linked: a phosphate is transferred directly from a substrate to ADP (glycolysis, Krebs cycle). Chemiosmosis: protons diffuse through ATP synthase down a gradient (inner mitochondrial membrane, thylakoid membranes).
Energy per gram of respiratory substrates
Carbohydrate: about 16 kJ g⁻¹. Protein: about 17 kJ g⁻¹. Lipid: about 39 kJ g⁻¹. Lipids have more hydrogen atoms per gram, so more reduced NAD and FAD, more protons and more ATP.
Respiratory quotient (RQ), and typical values
RQ = CO₂ produced ÷ O₂ taken in. Carbohydrate 1.0; protein about 0.9; lipid about 0.7. Glucose: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, so RQ = 6 ÷ 6 = 1.0.
Finding RQ with a respirometer
With KOH (absorbs CO₂): movement x = O₂ uptake. With water: movement y = O₂ uptake − CO₂ output. CO₂ output = x − y, so RQ = (x − y) ÷ x. Control: glass beads of equal volume.
An RQ between 0.7 and 1.0 suggests…
A mixture of lipid and carbohydrate is being respired. A very high RQ points to some anaerobic respiration.

12.2 Respiration

Sites of the four stages of aerobic respiration
Glycolysis: cytoplasm. Link reaction and Krebs cycle: mitochondrial matrix. Oxidative phosphorylation: inner mitochondrial membrane.
Glycolysis: outline and products per glucose
Glucose (6C) is phosphorylated to fructose 1,6-bisphosphate, which splits into two triose phosphate (3C), then oxidised to two pyruvate (3C). Net 2 ATP and 2 reduced NAD.
Link reaction
In the matrix, pyruvate (3C) is decarboxylated and dehydrogenated to a 2C acetyl group, which combines with coenzyme A to form acetyl coenzyme A. Per glucose: 2 CO₂ and 2 reduced NAD.
Krebs cycle: outline and products per glucose
The acetyl group (2C) joins oxaloacetate (4C) to form citrate (6C), which is converted back to oxaloacetate by decarboxylation and dehydrogenation. Per glucose (two turns): 4 CO₂, 6 reduced NAD, 2 reduced FAD, 2 ATP.
Decarboxylation vs dehydrogenation
Decarboxylation: removing CO₂. Dehydrogenation: removing hydrogen, which reduces NAD or FAD.
Oxidative phosphorylation
Reduced NAD and FAD release hydrogen, which splits into protons and electrons. Electrons pass along the electron transport chain, releasing energy that pumps protons into the intermembrane space. Protons return by facilitated diffusion through ATP synthase, making ATP. Oxygen is the final electron acceptor, forming water.
Anaerobic respiration in mammals vs yeast
Mammals: pyruvate → lactate; no CO₂. Yeast: pyruvate → ethanal + CO₂, then ethanal → ethanol. Both oxidise reduced NAD so glycolysis can continue; net 2 ATP per glucose.
Three adaptations of rice for growing with its roots in water
Aerenchyma in roots lets oxygen diffuse to root cells; ethanol fermentation in roots, with tolerance of ethanol; faster stem growth keeps leaves above rising water.
Using DCPIP or methylene blue to measure respiration rate in yeast
The dye turns from blue to colourless when reduced by hydrogen removed by dehydrogenases. Rate = 1 ÷ time to decolourise. Control: boiled yeast. Do not shake: oxygen re-oxidises the dye.

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