The Sliding Filament Model of Muscle Contraction · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Ropes That Slide, Not Shrink

Science · The Human Body · ages 17-18
Name ______________________   Date ____________

  1. Which filament is which in the sliding model?

    • Actin is thick with heads and myosin is thin
    • Both filaments are identical ropes
    • Actin is thin and myosin is thick with heads

  2. What happens to the bands of a sarcomere during contraction?

    • I bands and H zone shrink while the A band stays constant
    • The A band shrinks while I bands stay constant
    • All bands shrink by the same amount

  3. How does calcium uncover the myosin binding sites?

    • It dissolves the actin filaments
    • It binds troponin, which moves tropomyosin aside
    • It fuses actin directly to myosin

  4. Where is ATP used in muscle contraction?

    • Only in the power stroke pull
    • Only in making new actin
    • In detaching and resetting heads plus pumping calcium back

  5. Put the cross-bridge cycle in order.

    • Power stroke, attach, detach, re-cock
    • Attach, power stroke, detach with ATP, re-cock
    • Detach, re-cock, power stroke, attach

  6. Why does the A band keep a constant length?

    • Because myosin filaments slide without shortening
    • Because actin dissolves as it moves
    • Because Z lines never move

  7. A student says ATP is only needed for the power stroke pull. This claim is true.

    Circle one:   True   False

  8. A muscle shortens although neither filament changes length. How?

    • The filaments coil up like springs
    • The filaments slide past each other so overlap grows
    • The Z lines dissolve to free space
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Answer key

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

Ropes That Slide, Not Shrink W1-mt_BsB4s4HfD8-s1

  1. Actin is thin and myosin is thick with heads · Thin actin is pulled inward by the heads of thick myosin.
  2. I bands and H zone shrink while the A band stays constant · Filaments slide, so I and H narrow while the A band keeps its myosin length.
  3. It binds troponin, which moves tropomyosin aside · Calcium binds troponin, and troponin tugs tropomyosin off the sites on actin.
  4. In detaching and resetting heads plus pumping calcium back · ATP breaks the cross-bridge, re-cocks the head, and pumps calcium back for relaxation.
  5. Attach, power stroke, detach with ATP, re-cock · Heads attach, pull, use ATP to detach, re-cock, and grab further along.
  6. Because myosin filaments slide without shortening · The A band spans the myosin, and myosin keeps its length while actin slides past.
  7. False · ATP also detaches heads, re-cocks them, and pumps calcium back so the muscle can relax.
  8. The filaments slide past each other so overlap grows · Sliding filaments pull the Z lines together, shortening the sarcomere with fixed length ropes.
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