Question

If in a green plant, the rates of respiration and photosynthesis are equal, the plant will be?
A. Taking in carbon dioxide
B. Giving out oxygen
C. Taking in carbon dioxide and giving out oxygen
D. giving out water vapour

Answer 1

$CO_2$ intake in photosynthesis balanced with $CO_2$ released in respiration = compensation point.

Complete Answer:
In case of respiration, plants take $O_2$ in and $CO_2$ out. This $O_2$ is used up by the plant and in result, $CO_2$ is produced in the environment. As the light intensity increases the release of $CO_2$ is reduced because this $CO_2$ is used up by photosynthesis and in result $O_2$ is released as a byproduct. The rate of photosynthesis increases with the increase in the light intensity. Eventually a point is reached where rate of respiration is equal to rate of photosynthesis. This point is called a compensation point. Thus, the amount of $O_2$ released is equal to the amount of $CO_2$ taken in. Consequently, the taking in $CO_2$ and giving out$O_2$ . Both processes occur.

Hence the correct answer is option C.

Note: Photosynthesis is just reverse of Respiration. $O_2$ is the inhibitor of photosynthesis. That's why high $O_2$ conc. decrease the rate of photosynthesis and favours the photorespiration.