DCMN kills the herbs by

Options

A. inhibiting photoreactionII of Photosynthesis
B. checking electron transport system in photo-synthesis from is PS-II to is PS-I
C. inhibiting photoreaction-I of Photosynthesis
D. all of the above

Answer

**Step-by-Step Solution:**

1. **Identify the Compound**: The question refers to DCMU, which stands for Di-chloro-phenyl-dimethyl-urea.

2. **Mechanism of Action**: DCMU acts as a specific inhibitor of photosynthesis in plants, particularly targeting Photosystem II (PSII).

3. **Binding Specificity**: DCMU shows specific binding towards the plastoquinone (PQ) site in Photosystem II. It does not bind to plastoquinone itself but inhibits the electron transport chain associated with it.

4. **Inhibition of CO2 Fixation**: By inhibiting Photosystem II, DCMU disrupts the light-dependent reactions of photosynthesis, leading to a decrease in the production of ATP and NADPH, which are essential for the Calvin cycle (CO2 fixation).

5. **Conclusion**: DCMU kills weeds by inhibiting the light-dependent reactions of photosynthesis, specifically by blocking the electron transport chain in Photosystem II, which ultimately inhibits CO2 fixation.

6. **Correct Answer**: The correct answer to the question is that DCMU kills the herbs by inhibiting the photoreaction of Photosystem II.

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