In which of the following plants metabolism would be hindered if leaves are coated with vaseline on their upper surface ?

Options

A. Pistia
B. Vallisneria
C. Lotus
D. Mango

Answer

To determine which plant's metabolism would be hindered if the leaves are coated with Vaseline on their upper surface, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding the Role of Stomata**:
- Stomata are small openings on the leaf surface that allow for gas exchange (CO2 in, O2 out) and transpiration. The functioning of stomata is crucial for photosynthesis and respiration in plants.

2. **Analyzing Each Plant**:
- **Pistia**:
- Pistia is a monocot with stomata on both the upper and lower surfaces of its leaves. If the upper surface is coated with Vaseline, only the upper stomata would stop functioning. However, since there are stomata on the lower surface as well, gas exchange can still occur, albeit at a reduced rate. Therefore, metabolism would not be severely hindered.

- **Valisneria**:
- Valisneria is a submerged hydrophyte that does not rely on stomata for gas exchange. Instead, it absorbs gases directly from the water. Coating the upper surface with Vaseline would have no effect on its metabolism because it does not depend on stomatal function for gaseous exchange.

- **Lotus**:
- Lotus is a partially submerged hydrophyte. Its stomata are located only on the upper surface of the leaves, which are exposed to air. If the upper surface is coated with Vaseline, the stomata will be blocked, preventing gas exchange. This would significantly hinder the plant's metabolism since it relies solely on the upper stomata for gaseous exchange.

- **Mango**:
- Mango is a dicot with stomata present on both upper and lower surfaces, but more concentrated on the lower surface. If the upper stomata are coated with Vaseline, the lower stomata can still function, allowing for some gas exchange. Thus, while there may be a slight reduction in metabolic activity, it would not be severely affected.

3. **Conclusion**:
- Based on the analysis, the plant whose metabolism would be most hindered by coating the upper surface of its leaves with Vaseline is the **Lotus**. This is because it relies exclusively on the upper stomata for gas exchange.

### Final Answer:
**Lotus** (Option 3) is the correct answer.