Question

Statement a. Photorespiration decreases photosynthetic output.
Statement b. In the photorespiratory pathway, neither ATP nor NADPH is produced.
A) Both the statements a and b are correct.
B) Both the statements a and b are wrong
C) Statement a is correct and b is wrong
D) Statement b is correct and a is wrong

Answer 1

The photorespiration is also known as the oxidative photosynthetic carbon cycle. It refers to a process in which plant metabolism where the enzyme RuBisCO oxygenates RuBP, wasting some of the energy produced by photosynthesis. The photorespiration also incurs a direct cost of one ATP and one NADPH.

Complete answer:
The photorespiration is a process which involves loss of fixed carbon as carbon dioxide in the plants in the presence of a light.
• It is initiated in the chloroplasts.
• This process does not produce ATP or NADPH and is the wasteful process. The photo-respiratory reactions are operated in the chloroplasts, mitochondria, and in the peroxisomes.
• The loss of carbon dioxide​ occurs in the mitochondria. The photorespiration occurs usually when there is a high concentration of oxygen. Under such circumstances, RuBisCO, the enzyme that catalyzes the carboxylation of RuBP during the first step of the Calvin cycle, functions as an oxygenase.
• Some dioxides do not bind to RuBisCO and hence the carbon dioxide fixation is decreased. The RuBP binds with dioxide to form one molecule of PGA and the phosphoglycolate in the pathway of the photorespiration.
• In Spite of this, it results in the release of carbon dioxide with the utilization of ATP. It leads to around twenty five percent loss of the fixed carbon dioxide​. Dioxide ​is first utilized in chloroplasts and then in peroxisomes. It decreases the photosynthetic output.

Hence, the correct answer is option (A).

Note: The biochemical studies indicate that the photorespiration consumes ATP and NADPH, the high-energy molecules made by the light reactions. Therefore, photorespiration is a wasteful process because it prevents plants from using their ATP and NADPH to synthesize carbohydrates.