Which cells in the epidermis help in gas exchange?

Guard cells are specialized cells located in the epidermis of plant leaves and stems that play a crucial role in gas exchange. They are typically found in pairs surrounding the stomata, which are small openings on the surface of leaves. When guard cells swell with water, they curve outward, opening the stomata and allowing carbon dioxide to enter the leaf for photosynthesis. This process also facilitates the release of oxygen and water vapor, contributing to transpiration.

Their ability to regulate the size of the stomatal openings is vital for maintaining the plant's water balance and optimizing gas exchange, especially in response to environmental conditions such as humidity, light intensity, and carbon dioxide concentration. This dynamic control is essential for the overall health and efficiency of plant metabolism.

The other options do not contribute to gas exchange in the same manner. Parenchyma cells primarily serve in storage and tissue repair, while cork cells form protective layers and are not involved in gas exchange. Sieve tube members are part of the phloem and are involved in the transport of sugars and nutrients, not gases.