DCMU also called DIURON' is a potent non selective herbicide. It kills plant by -

Options

A. Inhibiting light reaction-I
B. Inhibiting light reaction - II
C. Inhibiting dark reaction/Calvin cycle
D. Inhibiting respiration/Kreb's cycle

Answer

### Step-by-Step Solution:

1. **Identify the Compound**: DCMU, also known as Diuron, is a non-selective herbicide that affects plants.

2. **Understand the Mechanism of Action**: DCMU acts by inhibiting a specific process in photosynthesis. It blocks the electron transport chain, which is crucial for the light-dependent reactions of photosynthesis.

3. **Locate the Target in Photosynthesis**: The primary target of DCMU is the electron flow between P680 (a pigment in Photosystem II) and Plastoquinone. P680 is responsible for capturing light energy and initiating the electron transport process.

4. **Explain the Consequence of Inhibition**: By blocking the electron transport from P680 to Plastoquinone, DCMU prevents the transfer of electrons necessary for the formation of ATP and NADPH, which are essential for the Calvin cycle (the light-independent reactions of photosynthesis).

5. **Resulting Effect on the Plant**: The inhibition of photosynthesis leads to a lack of food production in the plant. Without the energy and reducing power generated from the light reactions, the plant cannot synthesize glucose and other organic compounds, ultimately leading to its death.

6. **Conclusion**: Therefore, DCMU kills plants by inhibiting the light reactions of photosynthesis, specifically by blocking the electron transport chain between P680 and Plastoquinone.