Briefly explain why drought stress affects the rate of photosynthesis in plants.
Drought stress affects the rate of photosynthesis in plants primarily due to the reduction in water availability. Water is an essential component of photosynthesis as it is required for the opening and functioning of stomata, which are tiny pores on the surface of leaves that facilitate gas exchange. Stomata allow carbon dioxide to enter the plant and release oxygen, while also enabling the loss of water vapor through transpiration.
However, during drought conditions, plants experience water scarcity, and as a survival mechanism, they tend to limit the opening of stomata. This minimizes water loss through transpiration, but it also restricts the intake of carbon dioxide needed for photosynthesis. With reduced carbon dioxide availability, the rate of photosynthesis decreases.
Moreover, water shortage also hampers the plant's ability to carry out biochemical reactions within the chloroplasts, where photosynthesis occurs. These reactions require water as a solvent and as a reactant in various enzymatic processes. Inadequate water means the plant cannot efficiently perform these reactions, further impairing the rate of photosynthesis.
Overall, drought stress hinders the rate of photosynthesis in plants by restricting carbon dioxide intake and impeding the biochemical reactions necessary for efficient photosynthetic processes.