Why does water affect the rate of photosynthesis in plants?

Photosynthesis is a process where plants make their own food using sunlight, carbon dioxide and water. Water is an essential component of photosynthesis as it is required for several biochemical reactions that take place during the process. The availability of water can significantly affect the rate of photosynthesis in plants.

Water and photosynthesis: the relationship

Water is necessary for the functioning of the chloroplasts which are the organelles in plant cells where photosynthesis occurs. Chloroplasts contain pigments like chlorophyll that absorb light and use its energy to produce chemical energy in the form of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH).

During the light-dependent reactions of photosynthesis, water is broken down into oxygen and hydrogen ions. The oxygen is then released into the atmosphere, while the hydrogen ions are carried by NADPH to the stroma of the chloroplasts where they are used in the light-independent reactions to produce sugars and other organic compounds.

In this way, water is necessary for the production of energy-rich compounds that the plant needs for growth and maintenance. Without water, the process of photosynthesis would not be possible, and the plant would eventually die.

Effects of water on photosynthesis rate

The availability of water can affect the rate of photosynthesis in several ways:

Water availability affects stomatal conductance: Stomata are the small openings on the surface of leaves through which gases like carbon dioxide and oxygen enter and exit the plant. The opening and closing of stomata are controlled by specialized cells called guard cells. The opening of stomata also requires the presence of water, and it is controlled by the water potential of the leaf tissue. When there is enough water available, the guard cells swell and open the stomata, allowing for increased uptake of carbon dioxide for photosynthesis. If there is a shortage of water, the stomata close to prevent excess water loss through transpiration, and the rate of photosynthesis decreases.

Water affects enzyme activity: Photosynthesis involves several enzymes that catalyze the various biochemical reactions that take place. Many of these enzymes require water as a substrate or a cofactor. When water is scarce, the activity of these enzymes can be reduced or inhibited, leading to a decrease in the rate of photosynthesis.

Water affects mesophyll cell expansion: The mesophyll cells are the primary site of photosynthesis in leaves. When there is sufficient water available, the mesophyll cells expand, increasing the surface area available for photosynthesis. This, in turn, increases the rate of photosynthesis. However, when water is scarce, the mesophyll cells shrink, reducing the surface area available for photosynthesis and decreasing the rate of photosynthesis.

Conclusion

The availability of water is crucial for the functioning of photosynthesis in plants. Without water, the process of photosynthesis cannot occur, and the plant would eventually die. The availability of water can significantly affect the rate of photosynthesis through various mechanisms like stomatal conductance, enzyme activity, and mesophyll cell expansion. Therefore, it is essential for plants to have adequate access to water to ensure optimal photosynthetic activity and growth.