Lesson 3.6.3.1

3.6.3.1 Antagonistic muscles and the sliding filament mechanism Quiz: AQA Biology, Unit 6

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.6.3.1, Antagonistic muscles and the sliding filament mechanism: 20 multiple choice questions for the AQA Biology (7402), Unit 6: Organisms respond to changes in their internal and external environments, written with Revision Ninja.

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The 20 questions

  1. Why do skeletal muscles act in antagonistic pairs?

    • Antagonistic pairs store calcium ions for the next contraction
    • Each muscle contracts on both sides of a joint
    • Muscles can only contract and pull, so an opposing muscle is needed to move a joint back
    • Muscles can push and pull equally well

  2. Which protein forms the thick filaments of a myofibril?

    • Actin
    • Myosin
    • Tropomyosin
    • Phosphocreatine

  3. What is the role of tropomyosin in resting skeletal muscle?

    • It stores calcium ions in the sarcoplasmic reticulum
    • It covers the myosin-binding sites on actin, preventing contraction
    • It pumps protons across the membrane
    • It breaks down ATP to release energy

  4. What role do calcium ions play in muscle contraction?

    • They break down actin into smaller units
    • They move tropomyosin away from the binding sites, allowing myosin heads to bind actin
    • They make myosin heads detach from ATP
    • They stop the muscle relaxing

  5. What is the role of ATP in the sliding filament mechanism?

    • It binds to actin to form the thick filament
    • It is the enzyme that breaks down tropomyosin
    • It is the molecule that stores calcium ions
    • It is hydrolysed to provide energy for the myosin head to re-cock, and it binds to detach myosin from actin

  6. What is the role of phosphocreatine in muscle contraction?

    • It is the enzyme that breaks down actin
    • It regenerates ATP from ADP and phosphate, buffering ATP supply
    • It produces oxygen for the mitochondria
    • It binds calcium ions in the sarcoplasm

  7. What is a sarcomere?

    • The region of a myofibril between two Z-lines
    • The membrane of the sarcoplasmic reticulum
    • A bundle of muscle fibres enclosed by connective tissue
    • A single muscle fibre cell

  8. During contraction of a sarcomere, which length remains unchanged?

    • The H zone
    • The I band
    • The A band
    • The distance between Z-lines

  9. A biceps muscle contracts to bend the elbow. What happens to the triceps?

    • It relaxes, allowing the elbow to bend
    • It becomes longer by contracting
    • It produces calcium ions for the biceps
    • It contracts at the same time to hold the elbow still

  10. An earthworm moves using an incompressible skeleton. What is the role of the muscles in this movement?

    • Circular and longitudinal muscles work as antagonists against the fluid-filled body
    • Muscles only produce calcium ions for the skeleton
    • Muscles move the worm by pushing the skeleton away from the ground only
    • Muscles are not involved because the skeleton is rigid

  11. A muscle's calcium ion concentration falls. What is the most likely result?

    • The muscle contracts more strongly, because tropomyosin is destroyed
    • The muscle contracts permanently
    • The muscle produces more ATP by glycolysis
    • The muscle relaxes, because tropomyosin returns to block the binding sites

  12. Why does a muscle stay contracted after death when there is no ATP?

    • Myosin is converted into actin
    • Myosin heads cannot detach from actin without ATP, so the muscle remains in a stiff state
    • Calcium ions are stored permanently in the muscle
    • Tropomyosin is destroyed by the lack of ATP

  13. A sarcomere is 2.0 micrometres long at rest and 1.6 micrometres when contracted. What is the percentage shortening?

    • 25%
    • 0.4%
    • 80%
    • 20%

  14. Which sequence correctly describes one cycle of the actin-myosin interaction?

    • Myosin head binds actin, power stroke moves actin, ATP binds and detaches myosin, ATP is hydrolysed to re-cock the head
    • Calcium binds myosin, tropomyosin attaches to actin, ATP is made, myosin head releases
    • ATP binds actin, myosin head is destroyed, calcium binds tropomyosin, power stroke ends the cycle
    • Myosin binds tropomyosin, ATP is hydrolysed, actin is destroyed, calcium is released

  15. Why does the sliding filament mechanism shorten a muscle without the filaments themselves shortening?

    • Calcium ions physically compress the sarcomere
    • Actin molecules contract on their own
    • Myosin filaments coil up into a shorter shape
    • Myosin heads pull actin filaments past the myosin, so the filaments slide over each other

  16. Which ion is essential for muscle contraction because it moves tropomyosin?

    • Sodium
    • Hydrogen
    • Calcium
    • Chloride

  17. During intense short exercise, which energy store supplies ATP first?

    • Lactate
    • Phosphocreatine
    • Glycogen in the liver
    • Ethanol

  18. What is the role of the Z-line in a sarcomere?

    • It stores calcium ions for release
    • It marks the boundary at each end of a sarcomere
    • It produces ATP for the sarcomere
    • It contains the myosin heads that bind actin

  19. What happens to the H zone when a muscle contracts?

    • It becomes narrower
    • It stays exactly the same
    • It disappears entirely
    • It becomes wider

  20. Why does shortening of sarcomeres shorten the whole muscle fibre?

    • Sarcomeres contain the sarcolemma which contracts
    • Sarcomeres are joined to the membrane and lift the fibre
    • Sarcomeres are arranged end to end in series, so the shortening of each adds up
    • Sarcomeres are arranged side by side, so each shortens independently

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