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17.0 Introduction

All organisms, without exception, require energy for sustaining life activities. Respiration is an energy releasing process. It is defined as biological oxidation in which stored food is broken down step by step to release metabolically usable energy, giving out CO2 and water vapor as by-products. It goes on in all living cells at every moment of their existence as living entities.

Physiologists distinguish respiration into external and internal respiration.

Figure 17.0 Respiration

(1) External respiration or breathing: It involves the exchange of gases between surrounding medium and blood circulating in the respiratory organs. It is a physical process in which free oxygen is acquired by the animal. It neither involves oxidation nor release of energy.

(2) Internal respiration or cellular respiration: It takes place in the cells during which the food is oxidized and energy is released. Biological oxidation is not the process of direct oxidation, but a complex oxidation-reduction process is brought about by a series of respiratory enzymes and coenzymes present in the mitochondria. The overall reaction is as follows:

                          respiratory enzymes
6H12O6 + 6O2------------------> 6CO2+ 6H2O + energy

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Table of Contents

17.0 - Introduction
17.1 - Gaseous Exchange and Transport

Chapter 18


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