All living organisms require energy to carry out various life processes. The energy that is stored in the body in the form of complex organic compounds (potential energy) is however not usable by the organisms unless it is converted into usable form. This conversion is achieved through the process of respiration.
Respiration: It is a biochemical process of oxidation of organic compounds in an orderly manner for the liberation of chemical energy in the form of ATP.
For this, the process of gaseous exchange takes place between the organism and the environment. The site of gaseous exchange is called the respiratory surface.
Organs of Respiratory Exchange:
Respiratory exchange is a simple physical process. For efficient gaseous exchange, the respiratory surface should have the following features: -
a. It should have a large surface area.
b. It should be thin, highly vascular and permeable to allow exchange of gases.
c. It should be moist.
Gaseous exchange in plants:
1. The shape and structure of plants facilitate gaseous exchange by diffusion.
2. A terrestrial flowering plant has many air spaces between the cells of stem, leaf and root.
3. These air spaces are continuous. Oxygen diffuses into the air space through stomata (the pores on leaves and young stems), carbon dioxide and water vapour diffuse out.
4. In the aerated soil, the oxygen dissolves in the film of moisture or water around the root tissue and enters it by diffusion.
5. Woody flowering plants (trees and shrubs) have an external impervious bark. Here, gaseous exchange occurs through small pores in the stem surface, called lenticels.
Respiration in Animals:
1. As compared to plants, animals show wide variety of respiratory surfaces or organs.
2. The respiratory surfaces differ in various animals.
3. In animals, depending upon the complexity of organization and the surrounding medium, certain parts of the body have become specialized into different types of respiratory organs.
4. In the higher animals, these respiratory organs are also associated with a transport system.
