Microtubules, Dynamic Instability and the Spindle · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How the spindle finds every chromosome

Science · Organisms & Life Processes · ages 20-22
Name ______________________   Date ____________

  1. What flips the switch between growth and shrinking?

    • A change at the growing tip
    • A change in the room temperature only
    • A signal from a neighboring cell

  2. What is dynamic instability?

    • Slow steady growth that never reverses
    • Switching between growth and rapid shrinking
    • Splitting one tube into two tubes

  3. What happens to the microtubule end that reaches a chromosome?

    • It dissolves at once
    • It leaves the cell
    • It is captured and held

  4. A drug freezes all microtubules in place. What happens to new attachments?

    • None form, because the search stopped
    • They form faster than before
    • They form only at the cell edge

  5. How does the spindle find chromosomes without knowing where they are?

    • It aims each fibre with a sensor
    • It searches blindly and captures hits
    • It waits for chromosomes to line up alone

  6. Most searching microtubules miss, shrink back, and try again.

    Circle one:   True   False

  7. A frozen spindle can still finish capturing every chromosome.

    Circle one:   True   False

  8. A student claims the spindle aims each fibre at a chromosome. What is wrong?

    • Fibres cannot grow at all
    • There is no aiming; blind search plus capture does it
    • Chromosomes repel all fibres
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Answer key

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

How the spindle finds every chromosome W1-mt_RWhMJxOmUu-s1

  1. A change at the growing tip · The tip state decides which mode the tube is in.
  2. Switching between growth and rapid shrinking · Ends switch modes suddenly instead of growing smoothly.
  3. It is captured and held · Capture holds the hit while misses shrink away.
  4. None form, because the search stopped · Frozen ends cannot grow out, so nothing new gets captured.
  5. It searches blindly and captures hits · Blind repeated growth plus capture covers space with no aiming.
  6. True · Only a few hits lock on; the rest withdraw and regrow.
  7. False · Without switching there is no search, so division stalls.
  8. There is no aiming; blind search plus capture does it · The spindle finds targets with undirected trials, not guidance.
Worksheet · LightMySky