In C3 plants the conservation of water promotes:
photorespiration
photosynthesis
a shift to C4 photosynthesis
the light reactions
the opening of stomata
The Correct Answer and Explanation is:
The correct answer is photorespiration.
Explanation:
C3 plants are named after the three-carbon compound (3-phosphoglycerate) formed during the Calvin cycle in photosynthesis. These plants, such as wheat and rice, are adapted to environments with moderate sunlight and temperature conditions. However, they face a challenge when it comes to water conservation. In hot and dry conditions, C3 plants may experience a decrease in the efficiency of photosynthesis due to a process known as photorespiration.
Photorespiration occurs when the enzyme RuBisCO, which normally fixes carbon dioxide (CO₂) during photosynthesis, binds to oxygen (O₂) instead of CO₂. This happens when the stomata (small pores on leaves) close to conserve water during dry conditions, leading to an increase in the concentration of oxygen inside the leaf. The binding of O₂ to RuBisCO leads to the formation of a two-carbon molecule rather than the normal three-carbon compound, reducing the overall efficiency of photosynthesis. As a result, energy is wasted, and the plant loses fixed carbon atoms that would otherwise contribute to growth and energy production.
In C3 plants, the conservation of water by closing the stomata helps minimize water loss through transpiration, but it also increases the likelihood of photorespiration because it restricts the entry of CO₂ while allowing O₂ to accumulate. This trade-off reduces the overall efficiency of photosynthesis under conditions where water conservation is a priority.
In contrast, C4 plants (like maize and sugarcane) have a mechanism that minimizes photorespiration by spatially separating the initial carbon fixation (in mesophyll cells) from the Calvin cycle (in bundle sheath cells), enabling them to better conserve water while still maintaining high photosynthetic efficiency.
Thus, when water conservation is a priority in C3 plants, photorespiration becomes more prominent, reducing the plant’s overall photosynthetic efficiency.