Gaseous Exchange in Plants
Plants have no organs or systems for the exchange of gases with the environment. Every cell of the plant body exchanges gases With the environment by its own. Following structures help exchange of gases between the plant cells and atmosphere.
1. Stomata
The leaves and young stems have stomata (pores surrounded by guard cells) in their epidermis. The gaseous exchange occurs through these stomata. The inner cells of leaves (mesophyll) and stems also have air spaces among them, which help in the exchange of gases. Figure 10.1.
Leaf cells face two situations. During the daytime when the mesophyll cell of leaves are carrying out photosynthesis and respiration side by side, the oxygen produced in photosynthesis is utilized in cellular respiration. Similarly the carbon dioxide produced during cellular respiration is utilized in photosynthesis However, during night when there is no photosynthesis occurring, the leaf cells get oxygen from the environment and release carbon dioxide through stomata.
2. Lenticels
In woody stems and mature roots, the entire surface is covered by bark which is impervious to gases or water. However, there are certain pores in the layer of bark. These are called the lenticels. The lenticels allow air to pass through them. The lenticles are not surrounded by guard cells, while stomata are guarded by guard cells and are present in epidermis of plant leaf. Figure 10.2. .
3. DIFFUSION
Gases diffuse in and out of the general surface of the young roots. The gases are present in the soil surrounding roots.
The aquatic plants get the oxygen dissolved in water and release carbon dioxid in the water.
4. Cuticle
In young stems and leaves, some gaseous exchange also occurs through the cuticle which is present over their epidermis.