What is the reason for the drop in the photosynthetic rate when plants do not receive enough water?

The drop in the photosynthetic rate when plants do not receive enough water is primarily because water is a raw material for the light reactions in photosynthesis. During these light-dependent reactions, water molecules are split through a process called photolysis, providing electrons needed for the conversion of solar energy into chemical energy. This process also releases oxygen as a byproduct. If water is scarce, the plant cannot perform this crucial step efficiently, leading to a reduced capacity for photosynthesis and ultimately affecting the plant's energy production and growth.

While water does play various roles in plant health, such as being involved in nutrient transport, cellular processes, and maintaining cell turgor, its direct involvement in the photosynthetic process, specifically in the light reactions, is fundamental for sustaining the overall photosynthetic activity.