(a) Respiration in living organisms:
Respiration: It is a process whereby living things-
1. Use oxygen from the air to oxidize food substances mainly glucose, in their body cells.
2. Release energy in the form of heat.
3. Carbon dioxide and water vapour are also produced and released in the exhaled air. (refer the below reaction)
Process-
1. Inhaled air- oxygen from inhaled air dissolves in the bloodstream in the lungs. It is carried to the cells where the food materials i.e, glucose is oxidized by the oxygen.
2. Exhaled air- Carbon dioxide, water vapour and heat energy diffuse out of the lungs as exhaled air.
3. Energy liberated- The energy liberated is utilised for metabolic activities and maintains the body temperature.