Respiration in Animals & Types of Respiration

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Respiration in Animals

All biological systems are requiring constant supply of energy in order to carry out manifold activities of the living organisms. To ensure this constant supply of energy, many macro-molecules of the cells namely, proteins, carbohydrates or fats are needed to be oxidized to release the locked energy inside them systems.


Respiration can be defined as the process in which the oxygen is taken inside the body from the environment for the oxidation of food and to release energy or carbon-di-oxide so produced during oxidation is expelled out of the body.

The process of oxidation of food is very complex. This process involves a series of complex biochemical reaction or the released energy is stored in the form of ATP molecules.

Types of Respiration

Direct and Indirect Respiration

(a) Direct Respiration-In this type, there is direct exchange of gases between the carbon-di-oxide of body cells and oxygen of water and there is no blood is needed for transport of gases. Exchange of gases occurs on the principle of diffusion. It is found in unicellular organisms such as aerobic bacteria or protists e.g. Amoeba or metazoans like sponges, coelenterates (e.g.Hydra)

(b) Indirect Respiration-In this type of respiration there is no direct contact between the body cells and the surrounding of air of water source of oxygen is known as respiratory medium. This type is found in larger or complex form of animals. These organisms have some specialised organs like gills (most of the crustaceans molluscs), lungs ( some amphibians, snails, all reptiles, birds or mammals).In this the transportation of oxygen or carbon-di-oxide between the respiratory organs or the body cells is brought about by the blood of the circulatory system. So, it is called as Indirect respiration.

Aerobic and Anaerobic respiration

(a) Aerobic respiration- Aerobic respiration occurs in the presence of molecular oxygen. It completely oxidizes the food into carbon-di-oxide or water, releasing large amount of energy. It is found in most plants or animals.

(b) Anaerobic respiration-This respiation occurs in the absence of molecular oxygen and it is also called fermentation. In this, the food is only partially oxidised that because only a part of energy is released or rest of the energy remains trapped in the intermediate compounds. It is found in lower organisms like yeasts, anaerobic bacteria, in certain parasitic worms like Ascaris.

Two phases of Aerobic Respiration

(a) Internal Respiration-It is the exchange of oxygen of blood or carbon-di-oxide of the body cells by tissue fluid at the cellular level. Internal respiration involves the energy production and it is a physico-chemical process.

(b) External Respiration-In this the exchange of oxygen of surrounding liquid or gaseous medium or carbon-di-oxide of blood through a liquid medium from diffusion across the body surface and the respiratory surface. External respiration is purely a physical process that depends upon the principle of diffusion.

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