Lesson 7.1.2

7.1.2 Sliding filament theory of muscle contraction Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 7

20 questions

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Lesson 7.1.2, Sliding filament theory of muscle contraction: 20 multiple choice questions for the Pearson Edexcel Biology A (Salters-Nuffield) (9BI0), Unit 7: Run for your Life, written with Revision Ninja.

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The 20 questions

  1. Which molecule binds to the myosin head and causes it to detach from actin during the cycle of contraction?

    • Calcium ions, which bind to the myosin head and hold it firmly onto the actin filament
    • Tropomyosin, which binds to the myosin head and prevents it from detaching from actin
    • ATP, which binds to the myosin head and causes it to release from the actin filament
    • Troponin, which binds to myosin and drives the power stroke that moves the filament

  2. What is the role of calcium ions in the contraction of skeletal muscle?

    • They bind directly to the myosin head, which prevents it from attaching to the actin filament
    • They act as the energy source for the power stroke, replacing ATP in the myosin head
    • They bind to troponin, which moves tropomyosin and exposes the binding sites on actin
    • They bind to the Z line and pull the sarcomere apart, lengthening the muscle fibre

  3. In the sliding filament theory, which change occurs in the sarcomere during contraction?

    • The actin and myosin filaments both shorten, so the A band becomes twice as long
    • The H zone and I band shorten, while the A band stays the same length
    • The A band shortens, while the H zone and I band stay the same length
    • The myosin filaments slide to the outside of the sarcomere, so the Z lines move apart

  4. During the power stroke, what happens to the myosin head?

    • It pivots, pulling the actin filament towards the centre of the sarcomere after ADP and phosphate are released
    • It detaches from the actin, which is then pulled towards the outside of the sarcomere by ATP
    • It attaches to troponin, which then moves the tropomyosin away from the calcium-binding site
    • It splits ATP into ADP and phosphate, which releases energy that lengthens the sarcomere

  5. The enzyme ATPase in muscle is needed to:

    • Synthesise ATP from ADP and phosphate, which is used to attach the myosin head to troponin
    • Break the bonds between actin and tropomyosin, which releases calcium into the sarcoplasm
    • Digest the sarcolemma so that the calcium ions can enter the muscle fibre during relaxation
    • Hydrolyse ATP to ADP and phosphate, providing energy to recock the myosin head

  6. Which structure in the muscle fibre stores calcium ions for release during contraction?

    • The T-tubules, which store calcium ions permanently and release them during rest
    • The sarcoplasmic reticulum
    • The sarcolemma, which stores calcium ions in the outer membrane of the muscle fibre
    • The myofibrils, which contain calcium ions in their actin and myosin filaments

  7. Why does a muscle relax after a contraction?

    • Troponin is activated by ATP and so pulls the tropomyosin into the Z line, lengthening the sarcomere
    • Calcium ions are released from the myosin head, which then binds to the sarcolemma to block contraction
    • ATP is used to split the actin filaments into smaller fragments, which stops the cross-bridge cycle
    • Calcium ions are pumped back into the sarcoplasmic reticulum

  8. Which molecules form the thick and thin filaments of a myofibril?

    • Haemoglobin forms the thick filament and keratin forms the thin filament in the sarcoplasm
    • Collagen forms the thick filament and elastin forms the thin filament along the Z lines
    • Actin forms the thick filament and myosin forms the thin filament, with troponin in the middle
    • Myosin forms the thick filament and actin forms the thin filament

  9. Which best explains why a muscle cannot contract without ATP?

    • ATP is needed to bind calcium to troponin, which then causes the sarcomere to shorten by itself
    • ATP is needed to detach the myosin head from actin, and to recock it for the next power stroke
    • ATP is needed to make the sarcolemma permeable, so the sarcoplasmic reticulum can release calcium
    • ATP is needed only to start the first contraction, after which the muscle contracts with no further energy

  10. Which event directly triggers the release of calcium from the sarcoplasmic reticulum?

    • An action potential travelling along the axon of the motor neurone to the nucleus of the fibre
    • A rise in ATP concentration inside the sarcoplasm, which causes the reticulum to release calcium
    • A fall in the pH of the blood, which causes the reticulum to open and release calcium into the fibre
    • An action potential travelling down the T-tubules

  11. A fibre has its troponin mutated so that it cannot bind calcium. Which result is most likely?

    • The fibre contracts continuously, because tropomyosin is permanently removed from the actin
    • The fibre cannot contract, because tropomyosin continues to block the actin binding sites
    • The fibre contracts normally, because calcium can bind directly to the myosin head instead
    • The fibre lengthens, because the mutation causes the sarcomere to stretch to its maximum length

  12. Which statement describes the role of tropomyosin in the resting muscle fibre?

    • It blocks the myosin binding sites on actin so that no cross-bridges form
    • It binds to the ATP molecules, which prevents them from being hydrolysed by ATPase
    • It blocks the calcium channels in the sarcolemma, so calcium cannot leave the reticulum
    • It binds to the myosin head and cocks it so that it is ready for the power stroke

  13. During muscle contraction, how many ATP molecules are hydrolysed per cross-bridge cycle at minimum?

    • At least one, since each cycle requires ATP to detach the myosin head and to recock it
    • Exactly two, since one ATP is used per calcium ion that binds troponin in each cycle
    • None, since the energy comes from the calcium ions that bind to troponin during contraction
    • Exactly four, since each actin subunit binds two calcium ions and one ATP molecule

  14. Which statement evaluates the claim that muscles shorten because the filaments themselves shorten?

    • The claim is inaccurate, since the filaments keep their lengths and slide past each other to shorten the sarcomere
    • The claim is inaccurate, since muscles shorten by swelling in volume, not by any change in length
    • The claim is accurate, since calcium ions shorten the filaments by breaking their protein chains
    • The claim is accurate, since the actin and myosin filaments both contract to half their length

  15. Which feature of the sarcomere helps to define its structure?

    • The sarcolemma, which is a single membrane that surrounds the whole sarcomere in every muscle
    • The Z lines, which mark the boundaries of each sarcomere and anchor the thin filaments
    • The nuclei, which are found between each pair of thick filaments in the sarcomere
    • The mitochondria, which fill the sarcomere and are the sites of the cross-bridge attachment

  16. Which event immediately follows the power stroke in the cross-bridge cycle?

    • Myosin splits ATP while still attached to actin, so that the power stroke repeats without release
    • Tropomyosin moves back over the binding sites on actin, which is the cause of the power stroke
    • ATP binds to the myosin head, which causes it to detach from the actin filament
    • Calcium binds to the myosin head, which locks it firmly onto the actin filament

  17. Where does cross-bridge formation take place in the sarcomere?

    • Between the Z lines and the myosin tails, which are anchored to the sarcolemma of the fibre
    • Between the folds of the sarcolemma and the myosin heads, which are anchored by collagen
    • Between tropomyosin strands projecting from the thin filament and binding sites on the myosin
    • Between myosin heads projecting from the thick filament and binding sites on the actin of the thin filament

  18. A sarcomere shortens from 2.4 micrometres to 1.8 micrometres during contraction. What is the percentage shortening?

    • 0.6%, since 2.4 minus 1.8 gives 0.6 and this is the percentage directly
    • 75%, since 1.8 divided by 2.4 gives 0.75 and the shortening is 75%
    • 33%, since (2.4 - 1.8)/1.8 x 100 is approximately 33
    • 25%, since (2.4 - 1.8)/2.4 x 100 = 25

  19. Which statement about the H zone during full contraction is correct?

    • It moves to the centre of the sarcomere and doubles in length as the sarcomere shortens
    • It stays the same width because it contains only actin filaments, which do not move
    • It becomes narrower and may disappear, because thin filaments overlap across it
    • It becomes wider because the myosin filaments are pulled apart by the contracting actin

  20. Myosin heads bound to actin with no ATP present are in which state?

    • The detached state, in which the head is free to bind calcium ions in the sarcoplasm
    • The relaxed state, in which tropomyosin blocks binding even though ATP is abundant
    • The cocked state, in which ATP has been hydrolysed and the head is ready to bind actin
    • The rigor state, in which cross-bridges stay locked because the heads cannot detach

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