Exchange of Gases in Plants!
In plants, oxygen and carbon dioxide diffuse through the stomata and the intercellular spaces of the leaves, and the lenticels of the bark.
In woody plants, the stem is covered with bark.
Lenticels are small openings in the pits of the bark. The exchange of gases takes place through the lenticels also, apart from the exchange through the openings in the leaves.
The direction of exchange of gases between a plant and its surroundings depends upon the time of the day and the usage of the gases by the plant. Plants respire throughout the day, while photosynthesis takes place only in the presence of sunlight. In daytime, carbon dioxide produced in respiration by the plants is used by them in photosynthesis. So, carbon dioxide is not released into the environment.
In fact, plants take in additional carbon dioxide from the air for photosynthesis. Out of the oxygen produced in photosynthesis, some amount is consumed by the plants in respiration.
The rest is released into the air through the stomata. At night, when there is no photosynthesis, no oxygen is released. Also, the carbon dioxide produced in respiration is not used by the plants. So, it is released in the air.
That is why it is advised not to sleep under trees at night. In summary we can say that in daytime, on the whole, the plant releases oxygen and takes in carbon dioxide. And at night the plant releases carbon dioxide and takes in oxygen.
Different parts of the plant respire independently. For example, the root takes in oxygen present in the soil by the process of diffusion. Oxygen diffuses into the root hairs and passes into the other cells of the root. And carbon dioxide released by the root cells diffuses into the soil. Since the root is involved in the exchange of gases, if the root of a land plant remains waterlogged for long, the plant dies.
In certain respects, respiration in plants is different from that in animals. For example, plants produce some of the oxygen used by them for respiration. In plants, respiration occurs at a much slower rate than in animals. Also, there is little transport of gases from one part of the plant to another, unlike in animals.