What causes the opening and closing of guard cells of stomata during transpiration?

Explanation

### Step-by-Step Solution:

1. **Understanding Transpiration**:
- Transpiration is the process of water loss in the form of water vapor from the leaves of plants. This process is essential for nutrient transport and temperature regulation in plants.

2. **Role of Stomata**:
- Stomata are small openings on the surface of leaves that facilitate gas exchange and transpiration. The opening and closing of these stomata are controlled by guard cells.

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