Plants need the energy to grow, reproduce, and carry out other metabolic activities. They oxidise glucose into carbon dioxide, water, and energy in presence of oxygen. Plants take in oxygen and give out carbon dioxide in the atmosphere by the process of respiration. Stomata are tiny pores present on the epidermal layer of the leaves. These structures help in exchange for gases during respiration as well as photosynthesis.

In woody trees, the bark has numerous minute openings called lenticels. It helps them in the exchange of gases from the internal tissue and atmosphere whereas, in small green herbs, the exchange of gases takes place through stomata present on the epidermal layer of the leaves.