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 seed treatment uses gibberellic acid to favour germination by opposing ABA's dormancy-promoting effects. Which hormone class is being applied?

    • Abscisic acid
    • Cytokinins
    • Gibberellins

  2. A young shoot is lit from one side. How does it bend toward the light?

    • Auxin on the shaded side promotes faster elongation there
    • Auxin on the lit side promotes faster elongation there, bending the shoot toward light
    • Roots push the shoot upward while leaves pull it sideways toward the light

  3. Which pair of responses can ethylene promote?

    • Ripening in some fruits and leaf senescence
    • Seed dormancy and drought-related stomatal closure
    • Cell division in cultures and release of side-bud growth

  4. How can removing a growing shoot tip encourage side buds to grow?

    • Removing the tip adds auxin to every bud, forcing all of them to grow at once
    • Removing the tip reduces its auxin signal, which can release side buds
    • Removing the tip eliminates every hormone, so all side buds grow without signals

  5. In many responsive tissue cultures, increasing auxin relative to cytokinin can favour root formation over shoot formation. True or false?

    Circle one:   True   False

  6. Which sequence links hormone detection by a receptor to a change in target-gene transcription?

    • Receptor binding changes ion channels, producing a response without changing target-gene transcription
    • Receptor binding changes signalling proteins, which alter transcription-factor activity and transcription
    • The hormone first changes target-gene transcription; newly made proteins then activate its receptor and relay

  7. ABA reaches two tissues at the same concentration. One responds, but the other does not. Which interpretation is justified?

    • Receptor or downstream differences could explain the result; it does not locate the cause
    • The result locates the difference at ABA receptors, so downstream signalling need not be tested
    • Equal ABA concentrations establish equal receptor activity, so the difference must be downstream

  8. Two cultures of the same tissue have the same auxin-to-cytokinin ratio but different total hormone doses. Sam predicts identical root formation. Which claim is justified?

    • The shared ratio guarantees identical root formation in both cultures, even if the absolute doses differ
    • The higher total dose guarantees shoot formation, while the lower total dose guarantees root formation
    • The ratio alone is insufficient; the different absolute doses may affect root formation
LightMySky · lightmysky.comW1-mt_Zg2xpsb-p_-s1

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 · Gibberellic acid belongs to the gibberellins. Gibberellins can favour germination and oppose ABA's dormancy effects; water and suitable conditions are still needed.
  2. Auxin on the shaded side promotes faster elongation there · The shaded side elongates faster. Unequal growth bends the young shoot toward the light.
  3. Ripening in some fruits and leaf senescence · Ethylene can promote ripening in some fruits and leaf senescence, the ageing process in leaves.
  4. Removing the tip reduces its auxin signal, which can release side buds · Tip-produced auxin helps limit side-bud growth indirectly, through interacting signals. Removing the tip can lift this limitation.
  5. True · Relatively more auxin often favours roots in responsive cultures. The words 'many' and 'can' leave room for dose, species and culture effects.
  6. Receptor binding changes signalling proteins, which alter transcription-factor activity and transcription · The transcriptional route runs from receptor binding through intracellular signalling to altered transcription-factor activity. An ion-channel response without changed transcription is a different response.
  7. Receptor or downstream differences could explain the result; it does not locate the cause · Equal hormone concentrations do not establish equal receptor activity or identify a downstream difference. Receptor and downstream explanations remain possible; further tests are needed.
  8. The ratio alone is insufficient; the different absolute doses may affect root formation · The same ratio can occur at different absolute doses. Dose also affects responses, so the ratio alone cannot establish identical root formation.
Worksheet · LightMySky