What are the openings on the underside of leaves that facilitate gas exchange?

The openings on the underside of leaves that facilitate gas exchange are known as stomata. Stomata are tiny pores that allow gases such as carbon dioxide, oxygen, and water vapor to move in and out of the leaf. This gas exchange is crucial for photosynthesis, as plants take in carbon dioxide and release oxygen. Each stoma is surrounded by a pair of guard cells that regulate its opening and closing, ensuring that the plant can manage water loss while still allowing for the necessary gas exchange during the day and night.

In contrast, lenticels are openings found in the bark of some woody plants that facilitate gas exchange in stems, not leaves. Guard cells are specialized cells that control the opening and closing of the stomata but are not the openings themselves. The cuticle is a waxy protective layer covering the leaf surface that helps reduce water loss but does not function in gas exchange. Thus, stomata are the key structures for this vital process in leaves.