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.
