In land plants, the guard cells differ from other epidermal cells in having

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Guard cells are specialized cells present in the epidermis layer of the leaves and stem in plants. Guard cells are always present in pairs with a space between them. The space is called the stomatal pore. The stomatal pore is responsible for the exchange of water and gases in plants.

Apart from the mitochondria, ER, and nucleus, guard cells also contain photosynthetic pigments chloroplasts. Chloroplast is absent in other epidermal cells. Therefore, guard cells also synthesize glucose through photosynthesis. Chloroplasts are light-sensitive photoreceptors and also play an important role in the light-induced stomatal opening.

Usually, most plant species contain about 10–15 chloroplasts per guard cell as compared to 30–70 in the palisade mesophyll cell. The chloroplast in guard cells is less developed, smaller in size, and has less granal stacking as compared to the mesophyll cells.