How does water availability affect photosynthesis in leaves?

How does water availability affect photosynthesis in leaves?

• A. Water limitation closes stomata, reducing CO2 uptake and photosynthesis; prolonged drought reduces leaf growth and chlorophyll content, affecting the rate.
• B. Water limitation increases stomatal conductance, increasing CO2 uptake.
• C. Water availability has no effect on photosynthesis.
• D. Only roots are affected, not leaves.

Answer: (A)

Water availability controls how open the stomata are, which governs how much carbon dioxide can enter the leaf for photosynthesis. When water is scarce, stomata close to conserve water, so CO2 uptake drops and the rate of photosynthesis falls. In addition, extended drought slows leaf growth and can reduce chlorophyll content, meaning the leaf absorbs less light and the photosynthetic machinery becomes less effective, further lowering the rate. This explains why the best answer notes both the immediate effect on gas exchange and the longer-term impact on leaf development and pigment levels. The other ideas contradict how stomata respond to water stress or ignore the role of water in photosynthesis.

Water availability controls how open the stomata are, which governs how much carbon dioxide can enter the leaf for photosynthesis. When water is scarce, stomata close to conserve water, so CO2 uptake drops and the rate of photosynthesis falls. In addition, extended drought slows leaf growth and can reduce chlorophyll content, meaning the leaf absorbs less light and the photosynthetic machinery becomes less effective, further lowering the rate.

This explains why the best answer notes both the immediate effect on gas exchange and the longer-term impact on leaf development and pigment levels. The other ideas contradict how stomata respond to water stress or ignore the role of water in photosynthesis.