Question

Which of the following statements are true about C3 type plants ?
(A) Have two CO2 accepter.
(B) First stable product is phosphoglyceric acid.
(C) Optimum temperature for photosynthesis is low as compared to C4
(D) Photosynthesis occurs even when stomata are closed.
(E) Photorespiration rate is very high.
Choose the correct answer from the options given below :

• A. (B), (C) and (E) only.
• B. (A), (B) and (D) only.
• C. (A), (B) and (E) only.
• D. (B), (C) and (D) only.

Hint:

- C3 plants (e.g., wheat, rice, soybean) have Rubisco as their sole carboxylase and suffer from high photorespiration.
- C4 plants (e.g., maize, sugarcane) have evolved PEP carboxylase and Kranz anatomy to completely suppress photorespiration, showing higher water-use efficiency.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Plants are classified into \(C_3\), \(C_4\), and CAM types based on their primary carbon fixation pathway during photosynthesis.
Each type has evolved distinct biochemical adaptations, anatomical structures, and temperature tolerances to optimize carbon assimilation.

Step 2: Detailed Explanation:
Let us analyze each of the given statements regarding \(C_3\) type plants:
- Statement (A): \(C_3\) plants possess only one primary \(CO_2\) acceptor, which is Ribulose 1,5-bisphosphate (RuBP).
\(C_4\) and CAM plants have two acceptors (PEP and RuBP), making this statement false.
- Statement (B): The first stable product formed after carbon fixation in the Calvin cycle of \(C_3\) plants is 3-phosphoglyceric acid (3-PGA), a 3-carbon compound, making this statement true.
- Statement (C): The optimum temperature range for photosynthesis in \(C_3\) plants is lower (typically \(15^{\circ}C\) to \(25^{\circ}C\)) compared to \(C_4\) plants (typically \(30^{\circ}C\) to \(40^{\circ}C\)), making this statement true.
- Statement (D): In \(C_3\) plants, when stomata close (to conserve water), the internal concentration of \(CO_2\) drops rapidly while \(O_2\) rises.
This triggers photorespiration, severely limiting or stopping active photosynthesis, making this statement false.
- Statement (E): \(C_3\) plants have high rates of photorespiration because the enzyme Rubisco can bind with both \(CO_2\) and \(O_2\).
This process wastes nearly 25% of the fixed carbon, making this statement true.
Therefore, statements (B), (C), and (E) are the correct statements about \(C_3\) plants.

Step 3: Final Answer:
The true statements are (B), (C), and (E) only, corresponding to Option A.