Why do hot and dry conditions favor photorespiration in plants?

• A. Because high temperatures increase the solubility of CO\(_2\) in the leaf, enhancing the carboxylase activity of Rubisco.
• B. Because stomata close to conserve water, leading to decreased CO\(_2\) and increased O\(_2\) concentrations inside the leaf, which promotes Rubisco's oxygenase activity.
• C. Because Rubisco becomes inactive at low temperatures, so photorespiration only occurs when it is hot.
• D. Because plants increase their rate of photosynthesis under hot and dry conditions, resulting in more photorespiration as a byproduct.

Answer: (B)

Verified step by step guidance

1. Understand the role of Rubisco: Rubisco is an enzyme involved in the Calvin cycle of photosynthesis. It can act as either a carboxylase (fixing CO\(_2\)) or an oxygenase (fixing O\(_2\)). Photorespiration occurs when Rubisco fixes O\(_2\) instead of CO\(_2\), which is less efficient for the plant.
2. Recognize the impact of stomatal closure: In hot and dry conditions, plants close their stomata to conserve water. This reduces the exchange of gases, leading to lower CO\(_2\) levels and higher O\(_2\) levels inside the leaf.
3. Analyze the effect of gas concentrations: When CO\(_2\) levels decrease and O\(_2\) levels increase, Rubisco is more likely to act as an oxygenase, initiating photorespiration. This is because Rubisco has a dual affinity for both CO\(_2\) and O\(_2\), and the relative concentrations of these gases influence its activity.
4. Clarify why photorespiration is favored: Photorespiration is favored under hot and dry conditions because the closed stomata create an environment with reduced CO\(_2\) availability and increased O\(_2\) concentration, promoting Rubisco's oxygenase activity.
5. Debunk incorrect options: High temperatures do not increase CO\(_2\) solubility in the leaf, nor does Rubisco become inactive at low temperatures. Additionally, increased photosynthesis does not directly lead to more photorespiration; rather, it is the altered gas concentrations due to stomatal closure that drive photorespiration.