Auxin: the message from the tip — questions

1. identify

Supplement: where in a shoot is auxin made?

Circle one answer.

• In the shoot tip.
• In the roots.
• In the region below the tip, where the curve forms.
• In the leaves, by photosynthesis.

Nudge (only if you are stuck): Which part did Went stand on the agar?

2. identify

Supplement: what does auxin do to the cells in the region below a shoot tip?

Circle one answer.

• It makes them photosynthesise faster.
• It makes them divide faster.
• It makes the cells on the lit side shrink.
• It stimulates them to elongate.

Nudge (only if you are stuck): Think of Went's stump: did it end up with more cells, or with longer cells, under the block?

3. identify

Supplement: a seedling grows in a box whose only opening is a hole in its north wall. On which side of the shoot does most of the auxin end up?

Circle one answer.

• In the tip only; none of it moves down.
• The north side, facing the hole.
• Evenly on every side of the shoot.
• The south side, away from the hole.

Nudge (only if you are stuck): Which side of the shoot is in the shade?

4. identify

Supplement: a bean shoot is lit only through a gap on one side. Put the steps of its response in order.

Write the number of each step in order.

1. The shaded cells elongate more than the lit cells.
2. The shoot curves towards the light.
3. Light reaches the tip from one side, and the tip detects its direction.
4. The cells on the shaded side receive more auxin than those on the lit side.
5. Auxin made in the tip moves to the shaded side as it diffuses down.

• Step 1: ______
• Step 2: ______
• Step 3: ______
• Step 4: ______
• Step 5: ______

Nudge (only if you are stuck): Which changes cause the later changes?

5. explain

Supplement: why are phototropism and gravitropism of a shoot called examples of the chemical control of plant growth?

Circle one answer.

• A hormone made in one part of the shoot travels to another part and changes how much its cells grow.
• The plant takes up chemicals from the soil that steer the shoot towards light or away from gravity.
• Nerve impulses carry a message from the shoot tip to the cells in the region below it.
• Light and gravity are chemicals that act directly on the cells of the shoot.

Nudge (only if you are stuck): What carries the message from the tip to the region below?

6. identify

Supplement: a shoot is laid on its side in the dark. Which row shows where most of the auxin collects, which side elongates more and which way the shoot curves?

Circle one answer.

• A
• B
• C
• D

Nudge (only if you are stuck): Start with gravity: where does the auxin go? Then follow it.

7. predict / explain

Supplement: an oat seedling grows upright on a table in a room lit evenly from every side. Predict how it grows, and explain this in terms of auxin.

Nudge (only if you are stuck): Is any side of the shoot shaded more than another?

8. identify

Supplement: the figure shows three cut oat stumps X, Y and Z in the dark. Match each stump with how it grows over the next few hours.

Write the number of the matching option.

1. grows very little and does not curve
2. curves to the left
3. curves to the right
4. grows straight up, getting longer

• X: tip agar on the right side: ______
• Y: tip agar over the whole cut top: ______
• Z: plain agar on the right side: ______

Nudge (only if you are stuck): Which blocks carry auxin? Then: on which side do the cells get more of it?

9. identify

Supplement: which statements about auxin in shoots are correct?

Tick every correct statement.

• It makes the cells on one side divide faster.
• Gravity makes it collect on the upper side of a shoot lying on its side.
• It diffuses from the shoot tip into the region below.
• It is made in the shoot tip.
• Light from one side makes more of it move to the shaded side.

Nudge (only if you are stuck): Check each statement against the four facts about auxin in the reading.

10. explain

Supplement: in an old experiment, oat tips were cut off and put back on their stumps, either with a thin layer of gelatin between the tip and the stump, or with a thin sheet of mica, which chemicals cannot pass through. Lit from one side, the shoots with gelatin bent towards the light; the shoots with mica did not. Explain what this shows about auxin.

Nudge (only if you are stuck): What can pass through gelatin but not through mica?

11. explain

Supplement: a shoot has a light-proof band round the region just below its tip, and its tip is lit from the right. It still curves to the right. Explain why light does not need to reach the region that curves.

Nudge (only if you are stuck): Which part detects the light, and what carries the message to the part that curves?