(a) The epidermal cells of a root have extensions which are known as root hairs. These root hairs are in contact with the soil and the air present in between the soil particles diffuses through these root hairs to reach all other cells of the root for respiration. Carbon dioxide produced by the cells during the respiration reaches the root hairs and moves out through the process of diffusion. Hence, respiration in roots happens by diffusion of respiratory gases through root hairs.

(b) The stems of herbaceous plants have stomata through which oxygen diffuses into the stem and reaches all the cells for respiration. The carbon dioxide produced during respiration diffuses out the stomata. In woody stems, respiration happens through lenticels present in the bark.

(c) Leaves of a plant have tiny pores called stomata. Oxygen, present in the air, diffuses through these stomata and reaches other cells for respiration. Carbon dioxide produced in the cells during respiration also diffuses out through these stomata.