7.2.1 Overall aerobic respiration and enzyme-controlled steps Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 7

The 20 questions

1. The overall equation for aerobic respiration of glucose is:

   • C6H12O6 + 6O2 yields 6CO2 + 6H2O, with energy released as ATP
   • C6H12O6 yields 2C2H5OH + 2CO2, with energy released as ATP in the cytoplasm
   • C6H12O6 + 6H2O yields 6CO2 + 12H2, with no net release of energy
   • C6H12O6 + 6CO2 yields 6O2 + 6H2O, with energy released as heat only

2. In aerobic respiration, the final electron acceptor is:

   • Oxygen, which combines with electrons and hydrogen ions to form water
   • Carbon dioxide, which accepts electrons and is reduced to form glucose again
   • ATP synthase, which accepts electrons and becomes the final product of the chain
   • Pyruvate, which accepts electrons from reduced NAD and is converted into lactate

3. Which statement describes respiration as a many-stepped process?

   • Each step happens outside the cell in the blood plasma, using enzymes secreted into the blood
   • Each step is uncatalysed, so that energy is released as heat from the glucose molecule
   • Each step releases all of the energy at once, using a single non-specific enzyme in the cytoplasm
   • Each step is controlled and catalysed by a specific intracellular enzyme

4. Where does glycolysis take place in a eukaryotic cell?

   • The nucleus, where the enzymes of glycolysis are made and assembled into complexes
   • The mitochondrial matrix, where the Krebs cycle takes place in aerobic conditions
   • The inner mitochondrial membrane, where the electron transport chain is found
   • The cytoplasm

5. Why is the aerobic respiration equation described as splitting the substrate and reuniting hydrogen with oxygen?

   • Glucose is broken down to carbon dioxide
   • Oxygen is split into two atoms that combine with glucose to form carbon dioxide and water
   • Glucose is combined with carbon dioxide to form oxygen, and hydrogen is released as a gas
   • Glucose is split into two molecules of ethanol, and hydrogen is combined with carbon dioxide

6. Which molecule is the respiratory substrate in the overall equation for aerobic respiration?

   • Water, which is split into hydrogen and oxygen by ATP synthase in the inner membrane
   • Oxygen, which is split into carbon dioxide and water during the first step of respiration
   • Carbon dioxide, which is reduced to glucose by the electron transport chain in mitochondria
   • Glucose, which is oxidised completely to carbon dioxide and water

7. Why is aerobic respiration much more energy efficient than anaerobic respiration?

   • Aerobic respiration takes place in the cytoplasm, which is more efficient than the mitochondria
   • Complete oxidation of glucose releases far more energy
   • Oxygen converts glucose into ethanol, which stores more energy than glucose does
   • Anaerobic respiration uses oxygen to make lactate, which wastes most of the energy as heat

8. The energy released in aerobic respiration is captured mainly as:

   • Glycogen, which is formed directly from glucose and stored in the muscle fibre
   • Lactate, which stores the energy until it is converted back to glucose in the liver
   • Carbon dioxide, which is produced in large amounts and stores energy as a gas
   • ATP, which is synthesised from ADP and inorganic phosphate

9. A student measures oxygen consumption by a respiring organism. What does this measurement indicate?

   • The rate of aerobic respiration
   • The rate of photosynthesis, since oxygen is produced by plants during respiration
   • The rate of glycolysis alone, since oxygen is used only in the first step of the pathway
   • The rate of anaerobic respiration, since oxygen is produced when lactate is made in the cell

10. Which statement about the products of aerobic respiration is correct?

    • Ethanol and oxygen are produced, along with a large amount of heat and glycogen
    • Lactate and carbon dioxide are produced, along with a small amount of ATP in each cell
    • Carbon dioxide and water are produced, along with a large amount of ATP
    • Pyruvate and water are produced, along with ADP that is recycled to glucose

11. Which statement best evaluates the claim that aerobic respiration releases energy in one large step?

    • The claim is inaccurate, since respiration releases no energy at all and relies only on heat
    • The claim is accurate, since all of the glucose energy is released at once in the cytoplasm
    • The claim is inaccurate, since energy is released in many small enzyme-controlled steps and captured as ATP
    • The claim is accurate, since the enzymes of respiration act on the whole glucose molecule together

12. In a student practical measuring respiration rate, which variable would be the dependent variable?

    • The temperature of the water bath, which the student deliberately sets at the start
    • The type of respiratory substrate, which is chosen before the investigation begins
    • The rate of oxygen uptake or carbon dioxide production by the respiring organisms
    • The mass of the organisms, which the student keeps constant throughout the practical

13. Which statement about aerobic respiration in a muscle cell during exercise is accurate?

    • Oxygen supply falls as exercise increases, so respiration switches entirely to lactate production
    • The rate of respiration falls as exercise increases, because the muscle uses less energy in activity
    • Oxygen supply and the rate of respiration increase together, so more ATP is made as demand rises
    • Oxygen supply and respiration are unrelated, since oxygen is needed only at rest and not during exercise

14. Which of these is a true statement about the link between respiration and oxygen?

    • Oxygen is used only for the production of lactate, which is essential for the Krebs cycle
    • Oxygen is produced during the Krebs cycle, so it is not needed from outside the cell at any stage
    • Oxygen is needed in glycolysis to split glucose into two pyruvate molecules in the cytoplasm
    • Oxygen is needed to keep the electron transport chain running

15. Which statement about the reaction catalysed by each respiratory enzyme is correct?

    • Each enzyme works only outside the cell, so respiration depends on enzymes in the blood plasma
    • Each enzyme is specific to one reaction
    • Each enzyme is non-specific, so any enzyme can catalyse any step of respiration equally well
    • Each enzyme catalyses all steps of respiration at once, so a single enzyme controls the whole pathway

16. Which factor would most directly increase the rate of aerobic respiration in a muscle fibre?

    • A decrease in oxygen supply, which forces the cell to speed up its aerobic pathway
    • An increase in lactate concentration, which directly activates the electron transport chain
    • An increase in ADP and inorganic phosphate, which signals a high demand for ATP
    • An increase in ATP concentration, which signals that the cell has plenty of energy available

17. Which statement compares aerobic and anaerobic respiration in terms of the products formed from glucose?

    • Aerobic and anaerobic respiration both produce only carbon dioxide and water as their products
    • Aerobic respiration produces lactate and water, whereas anaerobic respiration produces carbon dioxide only
    • Aerobic respiration produces carbon dioxide and water, whereas anaerobic respiration in animals produces lactate
    • Aerobic respiration produces ethanol and carbon dioxide, whereas anaerobic respiration produces water

18. A student says that aerobic respiration is simply the reverse of photosynthesis. Which statement best evaluates this?

    • The claim is incorrect, since photosynthesis produces carbon dioxide while respiration produces oxygen
    • The claim is partly correct for overall reactants and products, but the pathways are different and use different enzymes
    • The claim is fully correct, since the two processes are identical in every enzyme and location in cells
    • The claim is incorrect, since neither process involves any exchange of gases with the environment

19. What is the main purpose of the electron transport chain in aerobic respiration?

    • To pass electrons from reduced coenzymes to oxygen, pumping protons that drive ATP synthesis
    • To split glucose into pyruvate in the cytoplasm, releasing ATP directly in the process
    • To make carbon dioxide from acetyl CoA in the mitochondrial matrix without any electron transfer
    • To convert lactate back into glucose in the liver after strenuous exercise

20. Complete aerobic oxidation of one glucose releases how many molecules of carbon dioxide in total?

    • 12, since each of the two pyruvates releases six carbon dioxide molecules in turn
    • 2, since only the link reaction produces carbon dioxide from the glucose molecule
    • 6, since 2 are released in the link reaction and 4 in the Krebs cycle
    • 4, since only the Krebs cycle releases carbon dioxide from the pathway

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