Photochemical smog affects plants by

Options

A. bleaching of leaves and excess production of pigments
B. shedding of foliage and increase of transpiration
C. white patches on leaves and curling
D. degradation of chlorophyll by ozone

Answer

### Step-by-Step Solution:

1. **Understanding Photochemical Smog**:
- Photochemical smog is a type of air pollution that occurs when sunlight reacts with nitrogen oxides and volatile organic compounds in the atmosphere. This reaction produces a brown haze, primarily composed of ozone and other harmful chemicals.

2. **Identifying Effects on Plants**:
- The question asks how photochemical smog affects plants. We need to evaluate the options given to determine the correct answer.

3. **Evaluating the Options**:
- **Option A**: Bleaching of leaves and excess production of pigment.
- These two effects contradict each other. Bleaching implies loss of color, while excess pigments suggest an increase in color. Thus, this option is incorrect.

- **Option B**: Shredding of foliage and increase in transpiration.
- Shredding foliage (leaves) would hinder transpiration, which is primarily conducted by leaves. This contradiction makes this option incorrect as well.

- **Option C**: White patches on the leaves and curling.
- White patches can indicate fungal infections, while curling can be caused by various factors, including environmental stress. However, this option does not directly address the specific effects of photochemical smog.

- **Option D**: Degradation of chlorophyll by ozone.
- Ozone, a component of photochemical smog, can degrade chlorophyll, which is essential for photosynthesis. The degradation of chlorophyll leads to reduced photosynthetic efficiency, affecting the plant's ability to produce food.

4. **Conclusion**:
- Based on the analysis, the correct answer is **Option D: Degradation of chlorophyll by ozone**. This degradation impairs photosynthesis, leading to various negative effects on plant health.