Question

Photorespiration is favoured by

• A. high $O_2$ and low $CO_2$
• B. low light and high $O_2$
• C. low temperature and high $O_2$
• D. low $O_2$ and high $CO_2$

Answer 1

The Correct Option is A

Photorespiration refers to a process in plant metabolism where the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) oxygenates RuBP, leading to the release of carbon dioxide. This process is considered wasteful because it results in a net loss of carbon and energy for the plant. Let's analyze and understand the conditions under which photorespiration is favored:

1. RuBisCO Enzyme: The enzyme RuBisCO plays a crucial role in both photosynthesis and photorespiration. It can act on either carbon dioxide or oxygen due to its dual catalytic activity, which is affected by the concentrations of these gases.
   • CO_2 fixation results in glucose production (photosynthesis).
   • O_2 fixation leads to photorespiration.
2. High Oxygen and Low Carbon Dioxide: Photorespiration is favored under conditions of high oxygen (O_2) and low carbon dioxide (CO_2):
   • With higher O_2 concentration, RuBisCO tends to oxygenate RuBP more frequently, initiating photorespiration.
   • A lower CO_2 concentration reduces competition for RuBisCO, allowing more oxygenation.
3. Incorrect Options Analysis:
   • Low light and high O_2: Low light reduces photosynthesis, but high O_2 alone isn’t sufficient to favor photorespiration if CO_2 isn't low.
   • Low temperature and high O_2: Temperature impacts enzyme activity; however, without low CO_2, photorespiration isn't directly favored.
   • Low O_2 and high CO_2: These conditions favor photosynthesis and reduce photorespiration.

In conclusion, the correct option is: high \, O_2 and low \, CO_2, which creates an environment favoring photorespiration over photosynthesis due to the increased likelihood of RuBisCO catalyzing oxygenation rather than carbon fixation.