Roots, shoots and gravity — questions

1. describe

Which statement describes gravitropism?

Circle one answer.

• A response in which parts of a plant grow towards or away from gravity.
• A part of a plant being pulled downwards by its own weight.
• A response in which the roots of a plant grow towards water in the soil.
• A response in which parts of a plant grow towards or away from the direction of the light source.

Nudge (only if you are stuck): Which response happens even in complete darkness?

2. identify

Match each seedling part with how it grows over a day.

Write the number of the matching option.

1. curves upwards, away from gravity
2. curves towards the light
3. curves away from the light
4. curves downwards, towards gravity

• a root lying on its side in the dark: ______
• a shoot lying on its side in the dark: ______
• an upright shoot lit from one side: ______
• an upright mustard root lit from one side: ______

Nudge (only if you are stuck): Two are responses to gravity and two to light. Do roots and shoots respond in the same direction?

3. identify

A student turns a dish of seedlings on its side to investigate gravitropism. Where should the dish spend the next day?

Circle one answer.

• In a dark cupboard at room temperature.
• Under a lamp shining from one side, so the seedlings can photosynthesise.
• Beside a warm radiator, so that the seedlings grow faster.
• On a windowsill, with the window on one side of the dish.

Nudge (only if you are stuck): Which other stimulus could make a shoot curve, and how do you take it away?

4. identify

Seedlings are pinned on their sides to a clinostat that turns slowly in the dark. Which statement explains why their roots grow straight out sideways?

Circle one answer.

• The turning damages the root tips, so the roots stop growing.
• Gravity stops acting on the seedlings while the disc turns.
• The pins hold the growing roots flat against the turning disc.
• Gravity acts on every side of the root in turn, for the same time.

Nudge (only if you are stuck): Gravity cannot be switched off. What does the turning change?

5. predict / explain

A broad bean seedling with a 2 cm root pointing straight down is pinned upside down in a dark box, so that its root now points straight up. Predict what the root does over the next two days, and explain why.

Nudge (only if you are stuck): Which way does a root grow in response to gravity, and how can it change direction?

6. identify

A dish of mustard seedlings stands upright in a dark room with a lamp on its left. Which row shows how the shoots and the roots respond after a day?

Circle one answer.

• A
• B
• C
• D

Nudge (only if you are stuck): Do the shoots and the roots of mustard respond to light in the same direction?

7. explain

Potatoes stored in a closed dark sack grow long white shoots that point upwards. Explain which response this is, and how you can tell that it is not phototropism.

Nudge (only if you are stuck): What stimulus is there inside a dark sack?

8. explain / suggest

A student compares two sets of seedlings lying on their sides in the dark: set 1 on a turning clinostat in a warm room, set 2 on a still clinostat in a cold room. Set 2 hardly curves. Explain why the student cannot draw a conclusion about gravity, and suggest how to improve the experiment.

Nudge (only if you are stuck): How many things differ between the two sets?

9. calculate

After a dish of seedlings was turned on its side, the angle between one root tip and the straight-down direction was measured every 2 hours. Calculate the mean rate at which this angle decreased between 2 hours and 6 hours, in degrees per hour.

Mean rate of decrease of the angle: ______________ unit ________

Nudge (only if you are stuck): Find the decrease in angle between the two times, then divide by the time taken.

10. predict

A dish of seedlings is turned through 90° and left in the dark for a day. Then it is turned back to its starting position and left in the dark for another day. Predict the shape of the roots at the end.

Nudge (only if you are stuck): Which part of a root is still growing, and so can still change its shape?

11. predict / explain

Seeds germinated in the dark on a space station, where things float and gravity has almost no effect. Predict how their roots and shoots grew, and explain your prediction.

Nudge (only if you are stuck): Which two stimuli give a seedling a direction, and is either of them there?

12. explain

Trees on a steep hillside grow vertically upwards, not at right angles to the slope. Explain this.

Nudge (only if you are stuck): Does gravity act at right angles to the ground, or straight down?