Stomata are usually open
(a) at night, when the plant requires a supply of oxygen
(b) during the day, when the plant requires a supply of carbon dioxide
(c) during the day, when transpiration occurs
(d) both (b) and (c )

Options

A. at night, when the plant requires a supply of oxygen
B. during the day, when the plant requires a supply of carbon dioxide
C. during the day, when transpiration occurs
D. both (b) and (c )

Answer

**Step-by-Step Solution:**

1. **Understanding Stomata**: Stomata are small openings on the surface of leaves that allow for gas exchange. They are surrounded by guard cells that regulate their opening and closing.

2. **Function of Stomata**: The primary function of stomata is to facilitate the exchange of gases. During photosynthesis, plants take in carbon dioxide (CO2) and release oxygen (O2).

3. **Stomata Opening During Day**: Stomata typically open during the day. This is when photosynthesis occurs, and the plant requires a supply of carbon dioxide to produce glucose.

4. **Transpiration**: When stomata are open, water vapor can also escape from the plant in a process called transpiration. This occurs during the day when stomata are open for gas exchange.

5. **Evaluating Options**:
- **Option (a)**: Stomata are usually open at night. This is incorrect because stomata generally close at night to conserve water and reduce oxygen loss.
- **Option (b)**: Stomata are open during the day for carbon dioxide intake. This is correct.
- **Option (c)**: Stomata are open during the day when transpiration occurs. This is also correct.
- **Option (d)**: Both (b) and (c) are correct.

6. **Conclusion**: The correct answer is (d) both (b) and (c) since stomata are open during the day for both carbon dioxide intake and transpiration.

**Final Answer**: (d) both (b) and (c)

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