Mention the most significant function/role of guard cells in plants.

Explanation

### Step-by-Step Text Solution:

1. **Definition of Guard Cells**: Guard cells are specialized cells located in the epidermis of plant leaves, stems, and other organs. They are responsible for regulating the opening and closing of stomata, which are small pores on the plant surface.

2. **Structure of Guard Cells**: Guard cells are typically found in pairs, with a gap between them that forms a stomatal pore. Each guard cell has a thick cuticle on one side (the pore side) and a thinner cuticle on the opposite side.

3. **Mechanism of Action**: The primary function of guard cells is to control gas exchange. When water enters the guard cells, they swell and change shape, causing the stomatal pore to open. Conversely, when water exits the guard cells, they shrink, leading to the closure of the stomatal pore.

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