DCMU, (3,4-dichlorophenyl , 1-dimethyl urea, also called diuron) a potent herbicide , inhibits
(a) `O_(2)` evolution
(b) Photophosphorylation
(c) Both a and b
(d) oxidative phosphorylation

Options

A. `O_(2)` evolution
B. Photophosphorylation
C. Both (1) amd (2)
D. oxidative phosphorylation

Answer

To solve the question regarding the effects of DCMU (3,4-dichlorophenyl, 1-dimethyl urea) on photosynthesis, we will analyze the options provided and the mechanism of action of DCMU.

### Step-by-Step Solution:

1. **Understanding DCMU**:
- DCMU is a potent herbicide and algaecide that inhibits photosynthesis. It belongs to the class of compounds known as aryl ureas.

2. **Mechanism of Action**:
- DCMU inhibits photosynthesis by blocking the electron transport chain in the light-dependent reactions of photosynthesis. This inhibition affects the production of ATP and the evolution of oxygen.

3. **Identifying the Processes Affected**:
- **Oxygen Evolution**: This process occurs during the light reactions of photosynthesis when water is split, releasing oxygen. Since DCMU inhibits the light reactions, oxygen evolution is also inhibited.
- **Photophosphorylation**: This is the process of ATP synthesis during the light reactions, which is also inhibited by DCMU as it disrupts the electron transport chain.

4. **Evaluating the Options**:
- (a) O₂ evolution - Inhibited by DCMU.
- (b) Photophosphorylation - Inhibited by DCMU.
- (c) Both a and b - Since both processes are inhibited, this option is correct.
- (d) Oxidative phosphorylation - This process occurs in cellular respiration, not photosynthesis, and is not affected by DCMU.

5. **Conclusion**:
- The correct answer is (c) Both a and b, as DCMU inhibits both oxygen evolution and photophosphorylation.

### Final Answer:
(c) Both a and b