Plants respiration is limited by the process of diffusion. Plants take in carbon dioxide through holes, known as stomata, that can open and close on the undersides of their leaves and sometimes other parts of their anatomy. Most plants require some oxygen for catabolic processes. But the quantity of O2 used per hour is small as they are not involved in activities that require high rates of aerobic metabolism. Their requirement for air, however, is very high as they need CO2 for photosynthesis, which constitutes only 0.04% of the environmental air. Thus, to make 1 gm of glucose requires the removal of all the CO2 from at least 18.7 liters of air at sea level. But inefficiencies in the photosynthetic process cause considerably greater volumes of air to be used.
Respiration In Roots
Roots, the underground part of the plants absorb air from the air spaces present between the soil particles. Thus, the oxygen absorbed through roots are used to release energy which is later utilized for the transportation of minerals and salts from the soil.
The process of photosynthesis is so prominent that it sometimes masks the process of respiration in plants. However, we must know that respiration in plants occurs throughout the day while photosynthesis process takes place only in the presence of light. Therefore, at night the respiration in plants becomes prominent. That is why we often hear that people are asked not to sleep under a tree at night. This may cause suffocation due to the excessive presence of carbon dioxide released by trees as a result of respiration.
Respiration In Stems
In the case of the stem, the air gets diffused in the stomata and passes through various parts of the cell for respiration. The carbon dioxide produced during this stage also diffuses through the stomata. In higher plants or woody plants, the gaseous exchange is carried out by lenticels.
Respiration In Leaves
Leaves comprise tiny pores referred to as stomata. The exchange of gases takes place via stomata through the process of diffusion. Each stoma is controlled by Guard Cells. The opening and closing of the stoma help in the exchange of gases between the atmosphere and the interior of leaves.