7.2.4 Oxidative phosphorylation and ATP synthase Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 7

The 20 questions

1. Oxidative phosphorylation takes place on:

   • The outer mitochondrial membrane, where the Krebs cycle enzymes are attached to its surface
   • The matrix of the mitochondrion, where the acetyl CoA is oxidised to carbon dioxide and water
   • The cytoplasmic membrane of the cell, where glycolysis enzymes are found in the lipid bilayer
   • The inner mitochondrial membrane, where the electron transport chain and ATP synthase are located

2. In chemiosmosis, the energy from electron transfer is used to:

   • Pump protons from the matrix into the intermembrane space, creating an electrochemical gradient
   • Pump electrons from the matrix into the cytoplasm, creating an electrical charge across the membrane
   • Pump oxygen from the intermembrane space into the matrix, where it is converted to water
   • Pump glucose from the intermembrane space into the matrix so that it can be split by the Krebs cycle

3. ATP synthase produces ATP when:

   • Oxygen is combined with it to form water, which releases ATP as a by-product of the reaction
   • Electrons flow through it from the matrix to the intermembrane space, releasing energy as heat
   • Protons flow back through it down their electrochemical gradient, driving ADP and phosphate together
   • Glucose binds to it and is split into pyruvate, which enters the Krebs cycle directly

4. What is the final electron acceptor in the electron transport chain?

   • ATP synthase, which accepts electrons and releases them as heat to the environment
   • Oxygen, which combines with electrons and protons to form water
   • NAD+, which accepts electrons and is reduced to form lactate in the cytoplasm
   • Carbon dioxide, which accepts electrons and is reduced to glucose in the matrix

5. Why does a lack of oxygen stop oxidative phosphorylation?

   • Electrons cannot be passed to oxygen at the end of the chain
   • Oxygen is needed to split glucose in glycolysis, which is the source of all the electrons
   • Oxygen is needed to make ATP directly from ADP, so no ATP can form without it at all
   • Oxygen is converted into carbon dioxide in the chain, which blocks the proton channels

6. Reduced NAD and reduced FAD both feed into oxidative phosphorylation. Which statement is correct?

   • Reduced NAD donates electrons at an earlier point in the chain than reduced FAD
   • Reduced NAD and reduced FAD donate electrons to the same point in the chain and yield the same ATP
   • Reduced FAD donates electrons at an earlier point in the chain than reduced NAD, so it yields more ATP
   • Reduced NAD and reduced FAD are not used in oxidative phosphorylation, which uses only water as donor

7. Which description best matches the role of the cristae in the inner mitochondrial membrane?

   • They separate the cytoplasm from the nucleus, preventing the movement of ribosomes
   • They increase the permeability of the membrane to glucose, which is needed for glycolysis
   • They increase the surface area for the electron transport chain and ATP synthase
   • They increase the volume of the matrix so that more Krebs cycle enzymes can be stored

8. Why do most of the ATP molecules from one glucose molecule come from oxidative phosphorylation rather than substrate-level phosphorylation?

   • Substrate-level phosphorylation produces lactate, which is then converted to ATP by oxidative phosphorylation
   • Substrate-level phosphorylation takes place only in the cytoplasm, which has no enzyme for ATP production
   • Oxidative phosphorylation uses ADP made by the cell's nucleus, which is more abundant than ADP in the cytoplasm
   • Reduced coenzymes from glycolysis, link reaction and Krebs cycle feed large numbers of electrons into the chain

9. Which of the following is the correct sequence of electron transfer?

   • ATP synthase, Krebs cycle, oxygen, producing ethanol in the intermembrane space
   • Reduced coenzyme, electron transport chain, oxygen as the final acceptor
   • Glucose, ATP synthase, reduced coenzyme, producing carbon dioxide in the cytoplasm
   • Oxygen, electron transport chain, reduced coenzyme, producing lactate in the matrix

10. Which statement describes proton movement in oxidative phosphorylation?

    • Protons are pumped into the intermembrane space and return through ATP synthase into the matrix
    • Protons are pumped out of the cell and return through the nuclear membrane into the matrix
    • Protons are pumped into the matrix and return through the outer membrane into the cytoplasm
    • Protons are not moved at all, since the chain works by transferring electrons alone

11. Which statement evaluates the claim that oxidative phosphorylation produces ATP without any direct involvement of oxygen?

    • The claim is accurate, since oxygen is produced by the electron transport chain and needs no supply
    • The claim is accurate, since oxygen is needed only in the Krebs cycle and not at any later step
    • The claim is inaccurate, since oxygen is required only in glycolysis and not in oxidative phosphorylation
    • The claim is inaccurate, since oxygen is the final electron acceptor and its absence stops the chain and ATP production

12. Which structural feature of the inner membrane is most closely linked to chemiosmosis?

    • Its high permeability to oxygen, which allows oxygen to diffuse into the matrix
    • Its lack of proteins, which allows electrons to pass freely through the membrane
    • Its high permeability to glucose, which allows the sugar to diffuse into the matrix
    • Its impermeability to protons

13. Using 2.5 ATP per reduced NAD and 1.5 ATP per reduced FAD, how much ATP does oxidative phosphorylation yield from 10 reduced NAD and 2 reduced FAD?

    • 28 ATP, since (10 x 2.5) + (2 x 1.5) = 28
    • 25 ATP, since only the reduced NAD contributes ATP through the chain
    • 30 ATP, since every reduced coenzyme gives three ATP regardless of its type
    • 12 ATP, since 10 + 2 = 12 coenzymes each give one ATP

14. A poison makes the inner membrane leaky to protons. What is the most likely effect on oxidative phosphorylation?

    • Electron transport stops immediately, so no oxygen is consumed by the mitochondria at all
    • The Krebs cycle speeds up, because protons leak back into the matrix and drive the cycle
    • More ATP is made, because the gradient becomes stronger when protons leak across the membrane
    • Electron transport continues but the gradient dissipates as heat

15. A poison blocks ATP synthase but not the electron transport chain. What happens to the proton gradient and ATP production?

    • Both the chain and the gradient are unaffected, but oxygen consumption falls to zero
    • ATP production rises, because the gradient is no longer lost through the synthase channel
    • The gradient builds up but cannot be used
    • The gradient collapses at once and the chain stops, so ATP production stops entirely

16. Which statement best describes why oxidative phosphorylation is described as coupled?

    • Oxygen and glucose combine into a single molecule before they enter the electron transport chain
    • Electron transfer and ATP synthesis are linked through the proton gradient across the inner membrane
    • ATP and ADP are produced in exactly equal numbers at every step of the electron transport chain
    • Electron transfer and glycolysis take place at the same location in the cytoplasm of the cell

17. Which coenzyme donates electrons at the start of the electron transport chain in mitochondria?

    • Pyruvate, which donates electrons directly to the outer membrane of the mitochondrion
    • Carbon dioxide, which is reduced by the first complex of the chain to form glucose
    • Lactate, which donates electrons to the ribosomes in the matrix for protein synthesis
    • Reduced NAD, which delivers electrons to the first complex of the chain

18. During intense exercise, muscle ADP levels rise. How does this affect oxidative phosphorylation?

    • It stops the chain, because ADP binds to oxygen and removes it from the final acceptor site
    • It has no effect, because ADP is used only in glycolysis and never in oxidative phosphorylation
    • It decreases the rate, because ADP is a product that blocks the electron transport chain
    • It increases the rate, because ADP is a substrate that ATP synthase needs in order to make ATP

19. Which statement describes the proton gradient in terms of energy?

    • It stores energy as a difference in proton concentration and charge across the inner membrane
    • It stores energy as a difference in glucose concentration between the cytoplasm and the matrix
    • It stores energy as a difference in oxygen concentration between the cristae and the outer membrane
    • It stores energy as a difference in the number of ribosomes on the inner and outer membranes

20. Which statement evaluates the claim that oxidative phosphorylation would work without any membrane?

    • The claim is inaccurate, since the membrane is needed to hold the proton gradient that drives ATP synthase
    • The claim is accurate, since ATP synthase does not need protons to work in any environment
    • The claim is accurate, since the gradient can form across a water droplet without any membrane present
    • The claim is inaccurate only for animals, since plant mitochondria can produce ATP without membranes

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