Question

What proportion of photosynthetically fixed CO2 goes back to the atmosphere, in C4 plants by photorespiration?

• A. 1/6
• B. 2/3
• C. 1/4
• D. 5/6

Hint:

In C4 plants, photorespiration releases approximately 1/4 of the fixed CO2 back to the atmosphere.

Answer 1

The Correct Option is C

Step 1: Understanding photorespiration in C4 plants.
In C4 plants, photorespiration involves the loss of some fixed carbon dioxide due to the process in which oxygen competes with carbon dioxide in the Calvin cycle. Typically, about one-quarter of the photosynthetically fixed CO2 is released back to the atmosphere.
Step 2: Analyzing the options.
(A) 1/6: Incorrect. This is a lower value and does not match the proportion observed in C4 plants.
(B) 2/3: Incorrect. C4 plants lose less CO2 compared to this value.
(C) 1/4: Correct. In C4 plants, approximately 1/4 of the fixed CO2 is lost to photorespiration.
(D) 5/6: Incorrect. This is too high of a value compared to the actual photorespiration rate in C4 plants.
Step 3: Conclusion.
The correct answer is (C) 1/4, as this is the proportion of CO2 released back to the atmosphere due to photorespiration in C4 plants.