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Question Video: Explaining the Relationship between Light Intensity and the Rate of Transpiration Biology

Which of the following best explains the relationship between light intensity and the rate of transpiration? [A] As light intensity increases, the rate of transpiration decreases because stomata are open in the dark. [B] As light intensity decreases, the rate of transpiration increases because stomata are closed in the dark. [C] As light intensity increases, the rate of transpiration increases because stomata are open in the light. [D] As light intensity decreases, the rate of transpiration increases because stomata are open in the light.

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Video Transcript

Which of the following best explains the relationship between light intensity and the rate of transpiration? (A) As light intensity increases, the rate of transpiration decreases because stomata are open in the dark. (B) As light intensity decreases, the rate of transpiration increases because stomata are closed in the dark. (C) As light intensity increases, the rate of transpiration increases because stomata are open in the light. Or (D) as light intensity decreases, the rate of transpiration increases because stomata are open in the light.

You may recall that transpiration is the loss of water vapor from the leaves of a plant through tiny pores known as stomata. Stomata open and close in response to environmental conditions, one of which is light intensity. Let’s have a look at how light intensity affects the opening and closing of stomata and hence the rate of transpiration.

In the light, the stomata are open. This is because plants can carry out lots of photosynthesis in the light, converting carbon dioxide and water into glucose and oxygen. The stomata therefore need to open to allow carbon dioxide to diffuse from the atmosphere into the leaves. As a consequence of the stomata being open, there is also a high rate of transpiration, as lots of water vapor diffuses out of the leaves.

By contrast, in the dark, photosynthesis cannot take place. The stomata are therefore closed because carbon dioxide is not required. This closing of stomata also limits water loss by preventing transpiration.

We can therefore deduce that the correct answer to the question is (C). As light intensity increases, the rate of transpiration increases because stomata are open in the light.

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