Question

A hot, dry summer will reduce crop yields in part because
a)The stomata of plants stay open to help cool the leaves.
b)Too much carbon dioxide enters the plants when stomata are wide open.
c)Carbon dioxide uptake is reduced by the stomata closing to prevent excessive water loss.
d)Oxygen uptake is reduced by the stomata losing to prevent excessive water loss.

Answer 1

The epidermis of leaves has small openings called stomata through which gas exchange. The stomata can be seen as small porese mainly found on the underside of the leaf.

Complete answer:
Stomata are the small openings present on the inner surface of the leaves. They are bounded by the two guard cells. Stomata can be opened or closed depending on the turgidity of guard cells. The closing and opening of the stomata depend upon the concentration of carbon dioxide in the air. It is so because when carbon dioxide levels are below normal, i.e., about 0.03 percent, the guard cells become turgid and the stomata enlarge.

Option a: During hot and dry summer, stomata close to prevent the excessive loss of water, thereby decreasing carbon dioxide uptake. This in turn reduces the crop yield. Therefore, this is an incorrect option.
Option b: In a dry and hot climate, the stomata of leaves close to prevent the loss of excessive water and thereby decrease the uptakes of carbon dioxide. Hence, the crop yield decreases. Therefore, this is an incorrect option.
Option c: During photosynthesis, stomata remain open so that gas exchange takes place. However, when stomata remain open, there is a risk of losing too much water through transpiration. Stomata close when the guard cells lose water and become flaccid. This occurs because potassium ions move back out of the guard cell, followed by water that lowers the pressure in the guard cell. So, during hot and dry summer, stomata close to prevent the excessive loss of water, thereby decreasing carbon dioxide uptake. This in turn reduces the crop yield. Therefore, this is the correct option.
Option d: Through the stomatal opening, carbon dioxide enters while water and oxygen exit through it. It allows the plant to take in carbon dioxide and give out oxygen for photosynthesis. For the process of photosynthesis, carbon dioxide. Therefore, this is an incorrect option.

Thus, option (c) Carbon dioxide uptake is reduced by the stomata closing to prevent excessive water loss is correct.

Note: It is to be noted that depending on the weather conditions, stomata closes or opens its pores to keep the moisture content developed.