Question

Why are a large number of stomata present at the lower surface of the dicotyledonous leaves in the terrestrial plants?

Answer 1

Hint: Stomata or stoma which is also called a stomata is a small, pore apparatus present in the epidermis of leaves, stems. Stomata help in controlling the rate of gas exchange during transpiration. There are two guard cells present in stomata which control the opening and closing of stomata.

Complete answer: Leaves are the organs of most plants where photosynthesis occur. They contain small pores called stomata in the leaf which helps in the exchange of oxygen and carbon dioxide as well as the loss of water vapor.
Among different species of plants, the number of stomata on leaf surfaces varies widely. In a leaf, the lower epidermis contains more number of stomata in comparison to the upper surface. Stomata are found on all different types of plants such as the conifer leaf needles as well as on the broad leaves of angiosperms.
The number of stomata on a leaf are affected by several environmental factors. The density of stomata changes in response to changing atmospheric levels of carbon dioxide. Due to global warming progression, because the level of carbon dioxide rises in the atmosphere, the number of stomata per leaf may increase, allowing the plant to absorb more carbon dioxide. Other factors that can increase the density of stomata are an increase in light or the amount of rainfall.
The more number of stomata present at the lower surface of the dicot leaves than the upper surface of the leaves to prevent excess water loss. As the dicot leaves stay horizontally, the upper epidermis of the leaves are directly exposed to sunlight. During the daylight hours, the stomata get opened to let oxygen and carbon dioxide pass through. While the stomata open, they let the gases to pass and water in the form of vapor releases from the epidermis cell of the leaf into the atmosphere by the process of transpiration.
But if the stomata are located on the lower surface of the leaves, they are not directly exposed to the sun, and the stomata will not open like the upper surface and water will evaporate in less amount i.e. the amount of respiration will be reduced. While the stomata are present on the lower surface they are a little more protected from the breeze. These features also help to decrease the amount of transpiration.

Note: Stomata are the pore structures present in both surfaces of the leaf, which is helpful in the exchange of gases and controls the rate of transpiration by its opening and closing features. These features are controlled by the cells present in the stomata, known as the guard cells. Sunlight is a factor in this system. Stomata present in the lower surface are not in direct contact with sunlight, so it opens less, and the rate of transpiration is reduced which prevents the water loss. Thus, a large amount of stomata is present at the lower surface of the dicot leaves.