Question:
Given below are two statements:
Statement I: \(C_3\) plants are more efficient than \(C_4\) plants in terms of carbon dioxide fixation
Statement II: \(C_4\) plants are less water efficient and consume more amount of water than \(C_3\) plants for same amount of \(CO_2\) fixed.
In light of the above statements, choose the correct answer from the options given below
Given below are two statements:
Statement I: \(C_3\) plants are more efficient than \(C_4\) plants in terms of carbon dioxide fixation
Statement II: \(C_4\) plants are less water efficient and consume more amount of water than \(C_3\) plants for same amount of \(CO_2\) fixed.
In light of the above statements, choose the correct answer from the options given below
Statement I: \(C_3\) plants are more efficient than \(C_4\) plants in terms of carbon dioxide fixation
Statement II: \(C_4\) plants are less water efficient and consume more amount of water than \(C_3\) plants for same amount of \(CO_2\) fixed.
In light of the above statements, choose the correct answer from the options given below
Show Hint
\(C_4\) plants (like maize, sorghum, and sugarcane) are highly efficient "super-plants" compared to \(C_3\) plants. They have higher rates of carbon fixation, higher water-use efficiency, and zero photorespiration.
Updated On: Aug 5, 2026
- Both Statement I and Statement II are true
- Both Statement I and Statement II are false
- Statement I is true but Statement II is false
- Statement I is false but Statement II is true
Show Solution
Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Plants are classified into \(C_3\) and \(C_4\) groups based on the biochemical pathways they use to fix carbon dioxide.
This classification determines their photosynthetic efficiency, water-use efficiency, and adaptation to different environmental conditions.
Step 2: Detailed Explanation:
Let us analyze both statements in detail:
- Statement I: "\(C_3\) plants are more efficient than \(C_4\) plants in terms of carbon dioxide fixation."
This statement is incorrect.
In \(C_3\) plants, the enzyme Rubisco can bind with both \(CO_2\) and \(O_2\). When temperatures are high, Rubisco binds with oxygen instead of carbon dioxide in a wasteful process called photorespiration, which can lose up to 25% of the fixed carbon.
In contrast, \(C_4\) plants have a specialized anatomy (Kranz anatomy) and use the enzyme PEP carboxylase to concentrate \(CO_2\) in the bundle sheath cells. This suppresses photorespiration, making \(C_4\) plants significantly more efficient than \(C_3\) plants in terms of carbon dioxide fixation, especially under high temperature and light conditions.
- Statement II: "\(C_4\) plants are less water efficient and consume more amount of water than \(C_3\) plants for same amount of \(CO_2\) fixed."
This statement is incorrect.
Because PEP carboxylase has a very high affinity for \(CO_2\), \(C_4\) plants can keep their stomata partially closed during hot days while maintaining high rates of photosynthesis.
Consequently, \(C_4\) plants lose only about 250 to 300 grams of water per gram of \(CO_2\) fixed, compared to \(C_3\) plants which lose 400 to 500 grams of water.
This makes \(C_4\) plants twice as water-efficient as \(C_3\) plants.
Therefore, both Statement I and Statement II are false.
Step 3: Final Answer:
The correct option is (B).
Plants are classified into \(C_3\) and \(C_4\) groups based on the biochemical pathways they use to fix carbon dioxide.
This classification determines their photosynthetic efficiency, water-use efficiency, and adaptation to different environmental conditions.
Step 2: Detailed Explanation:
Let us analyze both statements in detail:
- Statement I: "\(C_3\) plants are more efficient than \(C_4\) plants in terms of carbon dioxide fixation."
This statement is incorrect.
In \(C_3\) plants, the enzyme Rubisco can bind with both \(CO_2\) and \(O_2\). When temperatures are high, Rubisco binds with oxygen instead of carbon dioxide in a wasteful process called photorespiration, which can lose up to 25% of the fixed carbon.
In contrast, \(C_4\) plants have a specialized anatomy (Kranz anatomy) and use the enzyme PEP carboxylase to concentrate \(CO_2\) in the bundle sheath cells. This suppresses photorespiration, making \(C_4\) plants significantly more efficient than \(C_3\) plants in terms of carbon dioxide fixation, especially under high temperature and light conditions.
- Statement II: "\(C_4\) plants are less water efficient and consume more amount of water than \(C_3\) plants for same amount of \(CO_2\) fixed."
This statement is incorrect.
Because PEP carboxylase has a very high affinity for \(CO_2\), \(C_4\) plants can keep their stomata partially closed during hot days while maintaining high rates of photosynthesis.
Consequently, \(C_4\) plants lose only about 250 to 300 grams of water per gram of \(CO_2\) fixed, compared to \(C_3\) plants which lose 400 to 500 grams of water.
This makes \(C_4\) plants twice as water-efficient as \(C_3\) plants.
Therefore, both Statement I and Statement II are false.
Step 3: Final Answer:
The correct option is (B).
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