Question

why is that there is differential number of stomata on the leaf surface in betel leaf?​

Answer 1

Answer:

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

Answer 2

Answer:

Transpiration is the loss of water through stomata, so, more stomata are found on the lower surface to prevent excessive loss of water.