Question

The amount of water taken up by a plant can be investigated experimentally using a potometer. Refer to the following diagram showing a potometer to answer the following question.

What is expected to occur after the leafy shoot, together with the potometer, is placed in a dark, cool cupboard for one hour?

• A. The air bubble in the capillary tube moves towards the leafy shoot at a faster rate
• B. The air bubble in the capillary tube moves towards the leafy shoot at a slower rate
• C. The air bubble in the capillary tube moves away from the leafy shoot
• D. There is no observable change in the set-up

Answer 1

The correct option is D

There is no observable change in the set-up

The correct option is D.

Explanation of the correct option:

1. Potometer is an apparatus used to measure the rate of transpiration by a plant.
2. The given potometer is used to determine how much water the plant's shoot takes in.
3. The movement of the air bubble in the potometer corresponds to the plant's intake of water, and the distance covered by the bubble in a given period determines the transpiration rate.
4. As the whole apparatus is kept in dark and the transpiration rate is regulated by temperature, in the given case, the plant transpiration is lowered, causing the air bubble to move less.
5. So, there will be no observable change in the setup.

Explanation of the incorrect options:

Option A:

• The air bubble in the capillary tube moves towards the leafy shoot at a faster rate when there is more sunlight (high temperature) or the plant is placed in a windy environment (in front of a fan).
• It is because, due to high temperature or fast wind, the transpiration rate of plants increases.

Option B:

• The air bubble in the capillary tube moves towards the leafy shoot at a slower rate when the light in which the apparatus is placed is dim or there is not enough wind around the apparatus.
• Because dim light or slow air decreases a plant's transpiration rate.

Option C:

• The air bubble in the capillary tube will never move away from the leafy shoot.
• Because it intends that water is moving outside the root which does not happen.

Final answer: There is not a significant change in the movement of the air bubble when the potometer is placed in the dark.