Plant Hormone Signalling and How a Plant Decides · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How plants decide without nerves

Science · Organisms & Life Processes · ages 19-20
Name ______________________   Date ____________

  1. A dry seed waits because abscisic acid says wait. Which hormone tips the balance toward germination when water arrives?

    • Ethylene
    • Cytokinins
    • Gibberellins

  2. How does a shoot bend toward light?

    • Auxin collecting on the shaded side, speeding growth there
    • Roots pushing the shoot toward the light
    • Leaves sensing light and pulling the stem

  3. What does ethylene do in a plant?

    • Ripening fruit and ageing leaves
    • Closing stomata in drought
    • Growing roots in tissue culture

  4. Why does pruning the tip make a bush grow bushy?

    • Pruning the tip lowers auxin, freeing side buds to grow
    • Pruning the tip raises auxin, slowing all growth
    • Side buds grow only when auxin rises

  5. In tissue culture, a cell lump grows roots when auxin dominates and shoots when cytokinin dominates, with both present throughout. True or false?

    Circle one:   True   False

  6. How does a hormone signal change what a plant cell does?

    • Travel to the roots and stop there
    • Reach the nucleus and switch growth genes on or off
    • Dissolve the cell wall directly

  7. How does a plant with no nerves coordinate a whole-body response?

    • Binds a receptor, signals to the nucleus, and flips gene switches
    • Carries an electric pulse along nerves to the leaves
    • Pumps water directly into the responding cells

  8. Sam predicts roots from a high auxin level alone, ignoring cytokinin. What is wrong with that?

    • Auxin level alone decides everything
    • Cytokinin is irrelevant once auxin is high
    • Only the balance of the two decides the outcome
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Answer key

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

How plants decide without nerves W1-mt_Zg2xpsb-p_-s1

  1. Gibberellins · Gibberellins wake seeds and stretch stems, opposing the dormancy signal.
  2. Auxin collecting on the shaded side, speeding growth there · Faster growth on the shaded side bends the shoot toward the light.
  3. Ripening fruit and ageing leaves · Ethylene is the gas that ripens fruit and triggers the controlled ageing of leaves.
  4. Pruning the tip lowers auxin, freeing side buds to grow · Auxin streaming from the tip suppresses side buds, so removing the tip lifts the suppression.
  5. True · Both hormones present means only their relative strength decides: auxin dominance grows roots.
  6. Reach the nucleus and switch growth genes on or off · A hormone binds a receptor, the signal travels inward, and transcription factors flip growth genes.
  7. Binds a receptor, signals to the nucleus, and flips gene switches · Plants coordinate with chemistry: receptors, relays, and transcription, with no nerves involved.
  8. Only the balance of the two decides the outcome · Two hormones push opposite switches on one promoter, so only relative strength decides.
Worksheet · LightMySky