Biology (NTSE/Olympiad)  

2. Respiration

Respiration In Plants

Respiration In Plants
By young roots : Air occurs in soil interspaces. Root hairs as well as epiblema cells of the young roots are in contact with them. They are also permeable to metabolic gases. Oxygen of the soil air diffuses through root hair-epiblema cells and reaches all internal cells of the young root. Carbon dioxide produced by root cells diffuses in the opposite direction.

By Leaves : Leaves and Young Stems. Leaves and young stems are ideally suited to quick exchange of gases. The organs have a covering of nearly impermeable epidermis for reducing loss of water. The epidermis of leaves bears a number of aerating pores called stomata (singular stoma or stomata, Gk. stoma-mouth). Each aerating or stomatal pore is bordered a pair of guard cells. In most of the plants, the guard cells are kidney or bean shaped with inner walls being thicker and less elastic than the outer walls.
When the stomata are open, gases diffuse into and out of the leaf as per their concentration gradient. A gas which has come from outside first reaches substomatal chambers. From here, it diffuses to all the intercellular air spaces present in between the mesophyll cells. If the stomata are open during night, oxygen from outside will diffuse into the leaves and young stems while carbon dioxide will diffuse out. It is due to respiratory gas exchange.

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