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Biology 20

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Cellular respiration

Ten questions of mixed difficulty, covering Cellular respiration. Print it, or work through it on screen — the answer key starts on its own page.

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Cellular respiration

Biology 20 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. The electron transport chain is located in the

    1. a) matrix
    2. b) outer mitochondrial membrane
    3. c) inner mitochondrial membrane
    4. d) cytoplasm

  2. Most of the ATP from aerobic respiration is produced in the

    1. a) chloroplast
    2. b) mitochondrion
    3. c) cytoplasm
    4. d) nucleus

  3. The Krebs cycle takes place in the mitochondrial matrix and

    1. a) releases CO₂ while loading NADH and FADH₂ with electrons
    2. b) produces most of the cell's ATP directly
    3. c) converts pyruvate back into glucose
    4. d) consumes oxygen directly

  4. Aerobic respiration differs from anaerobic respiration in that aerobic respiration

    1. a) produces no carbon dioxide
    2. b) takes place in the cytoplasm
    3. c) requires oxygen
    4. d) happens only in animals

  5. The overall equation for aerobic cellular respiration is

    1. a) C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
    2. b) 6O₂ + 6H₂O → C₆H₁₂O₆
    3. c) 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
    4. d) C₆H₁₂O₆ → 2CO₂ + 2C₂H₅OH

  6. The final electron acceptor in aerobic respiration is

    1. a) carbon dioxide
    2. b) NAD⁺
    3. c) oxygen
    4. d) pyruvate

  7. Lactic acid fermentation is useful to a working muscle because it

    1. a) supplies oxygen to the muscle
    2. b) removes carbon dioxide
    3. c) regenerates NAD⁺ so glycolysis can keep producing ATP
    4. d) produces large amounts of ATP

  8. Aerobic respiration of one glucose molecule yields about

    1. a) 2 ATP
    2. b) 36 to 38 ATP
    3. c) 100 ATP
    4. d) 4 ATP

  9. ATP is described as the cell's energy currency because it

    1. a) stores energy permanently
    2. b) is the only molecule containing energy
    3. c) carries oxygen to the cells
    4. d) releases usable energy when its terminal phosphate bond is broken

  10. Glycolysis converts one glucose molecule into

    1. a) two pyruvate, with a net gain of 2 ATP and 2 NADH
    2. b) two pyruvate, with a net gain of 4 ATP
    3. c) six CO₂ and 2 ATP
    4. d) one pyruvate and 2 NADH

Answer key · Cellular respiration

Biology 20 · maddyhelps.com

  1. c) inner mitochondrial membrane — The inner membrane is folded into cristae, which multiplies the area available for the chain and for ATP synthase. Membrane location is essential, because the proton gradient needs two sides.
  2. b) mitochondrion — Glycolysis happens in the cytoplasm and yields a small amount, but the Krebs cycle and electron transport chain are both in the mitochondrion and produce the great majority.
  3. a) releases CO₂ while loading NADH and FADH₂ with electrons — The carbon dioxide you breathe out comes from here. The cycle makes very little ATP itself; its real product is the loaded electron carriers that feed the next stage.
  4. c) requires oxygen — Oxygen is the defining difference and it is also the reason aerobic respiration yields so much more ATP: it lets the electron transport chain keep running.
  5. a) C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy — Glucose and oxygen in, carbon dioxide and water out, with energy captured as ATP. The energy is not a substance in the equation — it is what the cell keeps.
  6. c) oxygen — Oxygen accepts the spent electrons and combines with protons to form water. Without it the chain backs up, NADH cannot be recycled, and the whole process grinds to a halt within seconds.
  7. c) regenerates NAD⁺ so glycolysis can keep producing ATP — The point is not the lactate but the recycled NAD⁺. Without it glycolysis stops within seconds, and even two ATP per glucose is better than none while the oxygen supply catches up.
  8. b) 36 to 38 ATP — Roughly 2 from glycolysis, 2 from the Krebs cycle and the rest from the electron transport chain. The number is given as a range because the yield depends on how the cytoplasmic NADH is shuttled in.
  9. d) releases usable energy when its terminal phosphate bond is broken — ATP is spent and remade constantly — a cell recycles its own body weight in it daily. It is a short-term carrier, not a store; that job belongs to fats and carbohydrates.
  10. a) two pyruvate, with a net gain of 2 ATP and 2 NADH — Four ATP are made but two were invested at the start, so the net gain is two. The 2 NADH matter as much as the ATP, because they carry electrons to the chain later.