Introduction

Every living organism needs a continuous supply of energy to carry out its everyday life processes. That energy starts out stored inside the body as potential energy, locked away in the chemical bonds of complex organic compounds -- but an organism cannot use this stored energy directly; it first has to be converted into a form the cell can actually put to work. This conversion is achieved through 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.

C6H12O6 + 6O2 --> 6CO2 + 6H2O + 38 ATP

Because respiration uses up oxygen and gives off carbon dioxide, every respiring organism needs a continuous exchange of these gases with its surroundings. The site of this gaseous exchange is called the respiratory surface. MSBSHSE's HSC Biology syllabus for this chapter draws on the same ground as the NCERT/CBSE Class 11 chapters on breathing and exchange of gases and on body fluids and circulation, so the vocabulary used here serves Maharashtra board and CBSE students alike.