Question

Given below are two statements:
Statement (I) : The Photosynthetic Photon Flux Density (PPFD) at which the $\text{CO}_2$ uptake by photosynthesis is exactly equal to $\text{CO}_2$ released through respiratory process is called Light Compensation Point (LCP).
Statement (II) : LCP of sun plants range from $1 - 5\text{ }\mu\text{mol m}^{-2}\text{ s}^{-1}$, whereas the corresponding values for shade plants are $10 - 20\text{ }\mu\text{mol m}^{-2}\text{ s}^{-1}$.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Shade-adapted plants have lower light compensation points ($1-5\text{ }\mu\text{mol m}^{-2}\text{ s}^{-1}$) and lower light saturation points than sun-adapted plants.
This adaptation allows them to maintain a positive carbon balance even in deeply shaded environments.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Light intensity directly influences the rate of photosynthesis in plants.
The relationship between light intensity and carbon exchange is defined by key physiological points, including the Light Compensation Point (LCP).
These thresholds vary significantly between plants adapted to bright sunlight (sun plants) and those adapted to shaded understories (shade plants).

Step 2: Detailed Explanation:
Let us analyze both statements individually:
Statement (I) is correct because the Light Compensation Point (LCP) is defined as the light intensity (measured as Photosynthetic Photon Flux Density, PPFD) where the rate of photosynthetic carbon dioxide assimilation exactly equals the rate of respiratory carbon dioxide release.
At this point, the net gas exchange of the leaf is zero.
Statement (II) is incorrect because the described ranges are reversed.
Shade plants (sciophytes) are adapted to grow under low-light conditions.
To survive in the shade, they maintain lower respiration rates, allowing them to reach their light compensation point at very low light intensities, typically ranging from $1 - 5\text{ }\mu\text{mol m}^{-2}\text{ s}^{-1}$.
Sun plants (heliophytes) are adapted to bright, open environments.
They have higher metabolic rates and higher respiration rates, meaning they require more light to offset respiration, resulting in a higher light compensation point, typically ranging from $10 - 20\text{ }\mu\text{mol m}^{-2}\text{ s}^{-1}$.
Therefore, Statement (I) is correct, and Statement (II) is incorrect.

Step 3: Final Answer:
Statement (I) is correct but Statement (II) is incorrect.
This corresponds to Option (C).