Question

You remove four fresh tobacco leaves of similar size and age. Leave ‘leaf 1’ as it is, smear ‘leaf 2’ with vaseline on the upper surface, ‘leaf 3’ on the lower surface and ‘leaf 4’ on both the surfaces. Hang the leaves for a few hours and you observe that ‘leaf 1’ wilts the most, ‘leaf 2’ has wilted, ‘leaf 3’ wilted less than ‘leaf 2’ and ‘leaf 4’ remains fresh. Which of the following conclusions is most logical?

(a) Tobacco leaf has more stomata on the upper surface

(b) Tobacco leaf has more stomata on the lower surface

(c) Stomata are equally distributed in upper and lower surfaces

(d) No conclusion on stomatal distribution can be drawn from this experiment

Answer 1

Answer is : (b) Tobacco leaf has more stomata on the lower surface

Tobacco is a dicot plant, thus its leaves have more number of stomata on its lower surface. If you cover the leaves of a healthy plant with vaseline, it will block its stomata and therefore it will not lose water through transpiration, so the upward movement of the water in the plant will stop. This will not allow the plant to wilt quickly.

The leaf ‘2’ is smeared with vaseline on the upper surface, so the plant will lose water from the lower surface and in leaf ‘3’, vaseline is smeared on the lower surface therefore the water is lost from the upper surface. But the number of stomata are more on the lower surface therefore leaf ‘2’ will wilt more quickly than leaf ‘3’.