Plants make their own food through the process of photosynthesis. To do this, they need energy from the Sun, carbon dioxide from the air, and water and other nutrients from their roots.

Carbon dioxide enters the plant through tiny openings on the underside of leaves known as stomata. However, whenever the plant opens its stomata to let carbon dioxide in, it also releases water vapor into the atmosphere. This latter process is known as transpiration.

Under which of the following environmental conditions would you expect the stomata to be closed more often than they are open?

One would expect stomata to be closed more often than they are opened under high environmental temperature (like in desert condition), high atmospheric humidity and when the atmospheric condition is windy.

Under high temperature, more water is lost to the environment from the stomata as a result of evaporation. If the rate of water loss is more than the rate at which water is gained through root absorption, the plant will wither off as a result of excessive water loss. Hence, the stomata is closed to minimize water loss in this condition. The guard cells collapse as the turgor pressure on the neighboring cells reduces and the stomata closes.

When the humid condition of the atmosphere is high, evaporation generally becomes low and water loss due to transpiration becomes reduced. The stomata is more inclined to close in this condition as there is little or no water loss due to evapotranspiration.

In windy conditions, more water is lost to the environment as a result of increased evaporation of water. As more water is lost to the surrounding, the turgor pressure of the guard cells decreases and results in their collapse. This leads to the closing of the stomata pores.