(a) Respiration in roots: The roots of a plant take the oxygen required for respiration from the air present in between the soil particles by the process of diffusion. The roots have extensions of epidermal cells of a root called root hair which are in contact with the air in the soil. Oxygen diffuses from root hairs and reaches all the other cells of the root for respiration. Carbon dioxide gas produced in the cells of the root during respiration moves out through the root hairs by the process of diffusion. Thus, the respiration in roots occurs by diffusion of respiratory gases through the root hairs.

(b) Respiration in stems: The stems of herbaceous plants takes place through stomata. The oxygen from the air diffuses into the stem of a herbaceous plant through stomata and reaches all the cells for respiration. The carbon dioxide produced diffuses out through stomata. In woody stems, the bark has lenticels for the exchange of gases.

(c) Respiration in leaves: The leaves of a plant has tiny pores called stomata through which the exchange of respiratory gases takes place by diffusion. Oxygen from air diffuses into a leaf through stomata and reaches all the cells, where it is used for respiration and the carbon dioxide produced diffuses out from the leaf into the air through stomata.