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 determine which plant's productivity of photosynthesis decreases due to photorespiration, we need to analyze the different types of plants and their photosynthetic pathways.

### Step-by-Step Solution:

1. **Understanding Photorespiration**:
- Photorespiration is a process that occurs in plants when the enzyme RuBisCO reacts with oxygen instead of carbon dioxide. This leads to a decrease in the efficiency of photosynthesis because it results in the production of a compound that cannot be used for energy production.

2. **Identifying Plant Types**:
- There are three main types of plants based on their photosynthetic pathways: C3 plants, C4 plants, and CAM (Crassulacean Acid Metabolism) plants.

3. **C3 Plants**:
- In C3 plants, carbon dioxide fixation occurs only once during the Calvin cycle. The primary enzyme involved is RuBisCO. These plants are more susceptible to photorespiration, especially under high oxygen conditions or low carbon dioxide concentrations. This results in a decrease in photosynthetic productivity.

4. **C4 Plants**:
- C4 plants have a different mechanism where carbon dioxide is fixed twice. The initial fixation occurs in the mesophyll cells, and the subsequent reactions occur in the bundle sheath cells. This adaptation minimizes photorespiration and allows for higher productivity in conditions where C3 plants would suffer.

5. **CAM Plants**:
- CAM plants also have a unique adaptation for arid conditions. They fix carbon dioxide at night and store it as malate, which is then used during the day for photosynthesis. This method also reduces the occurrence of photorespiration.

6. **Conclusion**:
- Based on the analysis, C3 plants are the ones whose productivity of photosynthesis decreases due to photorespiration. Therefore, the correct answer is C3 plants.

### Final Answer:
- The productivity of photosynthesis decreases due to photorespiration in **C3 plants**.