Fuel Homeostasis and the Fed to Fasted Switch · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Fed or fasted: how your body switches fuels

Science · The Human Body · ages 21-22
Name ______________________   Date ____________

  1. In the fasted state, what does the liver do?

    • Stores glucose as glycogen
    • Breaks down glycogen and releases glucose
    • Absorbs fatty acids from the blood

  2. After a meal, which hormone dominates the blood?

    • Insulin
    • Glucagon
    • Somatostatin

  3. In the fed state, insulin drives cells to store glucose as glycogen and fat.

    Circle one:   True   False

  4. How do muscle and fat differ during a fast?

    • Muscle keeps its glycogen locally while fat releases fatty acids
    • Fat stores glycogen while muscle releases glucose
    • Muscle makes glucose while fat stores protein

  5. Why do two opposing hormones control the same enzymes instead of one?

    • Because muscle needs a separate hormone of its own
    • Because one hormone acts too slowly to matter
    • To brake and accelerate at once without overshooting

  6. Glycogen is running low during a fast. What happens next?

    • The body breaks down muscle protein right away
    • The body burns fat while the liver keeps making glucose for the brain
    • The liver stops releasing glucose and lets blood sugar fall

  7. During a days-long fast, which fuel store is spent last?

    • Muscle protein
    • Liver glycogen
    • Adipose fat

  8. A student claims muscle protects blood sugar by releasing its glycogen as glucose. What is wrong with this claim?

    • Muscle stores no glycogen at all
    • Muscle never uses glucose for its own work
    • Muscle lacks the machinery to release free glucose
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Answer key

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

Fed or fasted: how your body switches fuels W1-mt_zZrXwbWqw--s1

  1. Breaks down glycogen and releases glucose · Glucagon tells the liver to clip glycogen apart and release the glucose.
  2. Insulin · Rising glucose after a meal makes beta cells release insulin, which drives storage.
  3. True · That is the fed program: take up glucose and store the surplus.
  4. Muscle keeps its glycogen locally while fat releases fatty acids · Muscle spends glycogen on itself, and fat ships fatty acids to other tissues.
  5. To brake and accelerate at once without overshooting · An opposing pair holds glucose steady by pushing both directions at once.
  6. The body burns fat while the liver keeps making glucose for the brain · Fat becomes the bulk fuel, and new glucose is reserved for the brain.
  7. Muscle protein · Protein is the last resort, used only after glycogen and fat cannot cover the need.
  8. Muscle lacks the machinery to release free glucose · Muscle stores plenty of glycogen but spends it locally, so the liver guards blood sugar alone.
Worksheet · LightMySky