Anaerobic Respiration · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Anaerobic Respiration: Energy Without Oxygen

Science · Organisms & Life Processes · ages 12-14
Name ______________________   Date ____________

  1. Anaerobic respiration needs oxygen to happen.

    Circle one:   True   False

  2. What does anaerobic respiration in animal muscles produce, along with a little energy?

    • Lactic acid
    • Carbon dioxide and water
    • Oxygen

  3. Why do your legs start to ache and burn during a hard sprint?

    • The muscles run out of glucose
    • Lactic acid builds up in the muscles
    • The muscles produce too much oxygen

  4. Look at the chart. Aerobic respiration releases 18 units of energy from a set amount of glucose, anaerobic releases 2 units. How many times more energy does aerobic respiration release?

    Aerobic18Anaerobic2

    Answer: ______________

  5. A runner sprints 100m using anaerobic respiration, then jogs 5km using aerobic respiration. Which uses the same amount of glucose to release more energy?

    • The sprint, because anaerobic respiration is faster
    • Both release the same amount of energy
    • The jog, because aerobic respiration breaks glucose down completely

  6. After a hard sprint, why does your breathing stay fast and heavy even once you've stopped running?

    • The body needs extra oxygen to break down the lactic acid that built up
    • The muscles need more glucose delivered quickly
    • The heart needs to cool down

  7. Two friends use up the same amount of glucose in a muscle. One respires aerobically, one anaerobically. Who ends up with a bigger oxygen debt afterwards?

    • Neither, they both build up the same oxygen debt
    • The one who respired aerobically, because they used more oxygen overall
    • The one who respired anaerobically, because lactic acid needs breaking down afterward

  8. Jamal writes this equation for anaerobic respiration: glucose + oxygen → lactic acid + energy. What's wrong with it?

    • Anaerobic respiration doesn't release any energy
    • Anaerobic respiration doesn't use oxygen
    • The equation should include carbon dioxide
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Anaerobic Respiration: Energy Without Oxygen W1-mt_TKZefYXaVS-s1

  1. False · Anaerobic means 'without oxygen' - that's the whole point of this type of respiration.
  2. Lactic acid · Anaerobic respiration breaks glucose down only part way, into lactic acid, without needing oxygen.
  3. Lactic acid builds up in the muscles · Lactic acid collects in the muscle when oxygen can't keep up with the demand for energy.
  4. 9 · 18 divided by 2 is 9, so aerobic respiration releases 9 times more energy from the same glucose.
  5. The jog, because aerobic respiration breaks glucose down completely · Aerobic respiration fully breaks down glucose using oxygen, releasing far more energy than the incomplete breakdown in anaerobic respiration.
  6. The body needs extra oxygen to break down the lactic acid that built up · This is called repaying the oxygen debt. The extra oxygen breaks down the lactic acid made during anaerobic respiration.
  7. The one who respired anaerobically, because lactic acid needs breaking down afterward · Aerobic respiration uses oxygen as it happens, so there's no debt. Anaerobic respiration skips oxygen at the time, so the body has to catch up afterward by breaking down lactic acid.
  8. Anaerobic respiration doesn't use oxygen · Anaerobic respiration happens when oxygen is in short supply, so oxygen isn't a reactant. The correct equation is glucose → lactic acid (+ a little energy).
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