Question

Assertion :

The atmospheric concentration of CO${}_2$ at which photosynthesis just compensates for respiration is referred to as CO${}_2$ compensation point.

Reason: CO${}_2$ compensation point is reached when the amount of CO${}_2$ uptake is less than that generated through respiration because the level of CO${}_2$ is more than that required for achieving CO${}_2$ compensation point.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is C Assertion is correct but Reason is incorrect

CO${}_2$ compensation point: It is that value or point in light intensity and atmospheric CO${}_2$ concentration when the rate of photosynthesis is just equivalent to the rate of respiration in the photosynthetic organs so that there is no net gaseous exchange.

The value of the light compensation point is 2.5 -100 ft. candles for shade plants and 100- 400 ft. candles for solar plants. The value of CO${}_2$ compensation point is very low in C${}_4$ (0-5 ppm), whereas in C${}_3$ plants it is quite high(25-100 ppm).

A plant can not survive for long at compensation point because there is a net loss of organic matter due to respiration of non- green organs and dark respiration.

Hence, the correct answer is 'Assertion is correct but reason is incorrect'.