The strong inhibitor substance for PS II in photosynthesis is

Options

A. Ethylene
B. Chloroform
C. Dichlorophenyl dimethyl urea
D. Yellow light.

Answer

To answer the question regarding the strong inhibitor substance for PS II in photosynthesis, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Inhibitor Options**: The question provides several options: ethylene, chloroform, dichlorophenyl dimethylurea (DCMU), and yellow light.

2. **Understand the Role of PS II**: Photosystem II (PS II) is a crucial component of the photosynthetic process, responsible for the photolysis of water and the initial steps of electron transport.

3. **Research the Inhibitors**: Among the given options, we need to determine which substance is known to inhibit the function of PS II.

4. **Recognize DCMU**: DCMU, or dichlorophenyl dimethylurea, is a well-known herbicide that specifically inhibits PS II. It does this by blocking the binding site of plastoquinone (PQ), which is the primary electron acceptor in PS II.

5. **Explain the Mechanism**: By blocking the binding site of plastoquinone, DCMU interrupts the electron transfer process that is essential for photosynthesis, thereby hindering the overall process.

6. **Conclude the Answer**: Based on the information gathered, the strong inhibitor substance for PS II in photosynthesis is DCMU (dichlorophenyl dimethylurea).

### Final Answer:
The strong inhibitor substance for PS II in photosynthesis is **Dichlorophenyl Dimethylurea (DCMU)**.

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