Question

Normally, a dorsiventral leaf contains more stomata on its lower epidermis than on its upper epidermis. Which of the following explanation(s) is/are true in this regard?
a. Such an arrangement permits water vapour to come out of the leaf more easily under the influence of gravity.
b. The molecular weight of $C{O}_2$ and $O_2$ are $44$ and $32$ respectively. At night there is no photosynthesis to remove the respiratory $C{O}_2$, which due to its greater density comes out more easily through the stomata at the lower surface of the leaves.
c. This reduces the chances of excessive water loss through the stomata because the lower surface is shaded away from the direct illumination of sunlight.
Select the correct answer using the codes given.

• A. $1$ alone
• B. $2$ alone
• C. $3$ alone
• D. $2$ and $3$

Answer 1

The correct option is C $3$ alone

All surfaces of the leaf have some amount of stomata for regulating gas exchange for photosynthesis. However, the lower epidermis (the underside of the leaf) has more, because it is more often in the shade and so it is cooler, which means evaporation won't take place as much. Evaporation would mean the plant loses water, vital for life. So, the correct answer is '3 alone'