Which of the following plant's productivity of photosynthesis decreases due to photorespiration ?

Options

A. `C_3` plants
B. `C_4` plants
C. CAM plants
D. Both (A) and (B)

Answer

To solve the question regarding which plant's productivity of photosynthesis decreases due to photorespiration, we can follow these steps:

### Step 1: Understand the Concept of Photorespiration
Photorespiration is a process that occurs in plants when the enzyme RuBisCO reacts with oxygen instead of carbon dioxide. This typically happens under conditions of high oxygen concentration and/or high temperatures, leading to a decrease in the efficiency of photosynthesis.

**Hint:** Remember that photorespiration is a wasteful pathway that can occur when oxygen levels are high and CO2 levels are low.

### Step 2: Identify the Types of Plants
The question provides four options:
1. C3 plants
2. C4 plants
3. CAM plants
4. Both A and B

**Hint:** Familiarize yourself with the characteristics of C3, C4, and CAM plants, especially how they fix carbon dioxide.

### Step 3: Analyze C3 Plants
C3 plants primarily use the Calvin cycle for photosynthesis, where CO2 is fixed in the mesophyll cells. In conditions of high oxygen concentration, RuBisCO can catalyze the reaction with oxygen, leading to photorespiration, which decreases the overall productivity of photosynthesis.

**Hint:** C3 plants are more susceptible to photorespiration because they have a single pathway for CO2 fixation.

### Step 4: Analyze C4 Plants
C4 plants have a different mechanism where CO2 is initially fixed in mesophyll cells to form a four-carbon compound before entering the Calvin cycle in bundle sheath cells. This adaptation minimizes photorespiration by concentrating CO2 around RuBisCO.

**Hint:** C4 plants are more efficient in hot and dry environments and have mechanisms to reduce photorespiration.

### Step 5: Analyze CAM Plants
CAM (Crassulacean Acid Metabolism) plants open their stomata at night to fix CO2, which is stored as malate and used during the day for photosynthesis. This adaptation also helps minimize photorespiration.

**Hint:** CAM plants are adapted to arid conditions and have a unique timing for gas exchange.

### Step 6: Conclusion
Based on the analysis:
- C3 plants experience a decrease in photosynthetic productivity due to photorespiration, especially under high oxygen and temperature conditions.
- C4 and CAM plants have adaptations that significantly reduce the occurrence of photorespiration.

Therefore, the correct answer is **C3 plants**.

**Final Answer:** C3 plants.