Maharashtra Board Class 12 Biology Chapter 8 Respiration and Circulation PDF Download

Respiration And Circulation

Can You Recall?

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.

\[C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + 38 \text{ ATP}\]

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.

Respiration In Animals

As compared to plants, animals show wide variety of respiratory surfaces or organs. The respiratory surfaces differ in various animals. 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. In the higher animals, these respiratory organs are also associated with a transport system.

Gaseous Exchange In Plants

The shape and structure of plants facilitate gaseous exchange by diffusion. A terrestrial flowering plant has many air spaces between the cells of stem, leaf and root. 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. In the aerated soil, the oxygen dissolves in the film of moisture or water around the root tissue and enters it by diffusion.

Woody flowering plants (trees and shrubs) have an external impervious bark. Here, gaseous exchange occurs through small pores in the stem surface, called lenticels.

8.1 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.

Teacher's Note

Plants exchange gases through stomata and lenticels just like we breathe through our nose. If you block a plant's stomata with oil, it will die because it cannot breathe.

Exam Trick

Remember: Respiratory surface needs three things - Large area (like a net), Thin (like paper), and Moist (like wet skin). Think of your lungs - they have millions of tiny air sacs to give large area.

Points To Remember

Gaseous exchange is needed by all living things to get energy.
Plants use stomata and lenticels to breathe.
Animals have different respiratory organs like gills, lungs, and trachea.
Respiratory surfaces must be large, thin, and wet to work properly.
The heart and blood help carry oxygen to all body parts.

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