23. What's the main function of the guard cells? (1) regulate the rate of gas exchange (3) undergo mitotic cell division (2) store food for winter dormancy (4) give support to the veins in the leaf

The correct answer is (1) regulate the rate of gas exchange.<br /><br />Guard cells are specialized cells surrounding the stomata (pores) on the surface of leaves. They control the opening and closing of these stomata, thus regulating the exchange of gases (like carbon dioxide and oxygen) and water vapor between the plant and the atmosphere.<br />