Theory:

Introduction
At certain times when we are running late to catch a bus or train, we run fast to catch that bus or train. Once when we stop, we notice that we will be breathing heavily. Have you ever wondered that why are we breathing heavily at times like these? To know this first, we have to know that why do we breathe. Breathing is part of the process of respiration. In this topic, we shall discuss about the process of respiration.
What is respiration?
Respiration is a process through which all the living organisms derive their energy from food. The air we breathe contains oxygen, and the air we breathe out contains carbon dioxide. The oxygen we breathe is transported to all the cells found in the body.
The process in which the oxygen in the air helps in the breakdown of food to release energy is known as cellular respiration.
The process of cellular respiration takes place in the mitochondria of the cells. Hence they are known as the power houses of the cell.
 
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Need for respiration
All the living organisms are made up of cells which are small microscopic units.
The smallest structural and functional unit of an organism is known as a cell.
The cells are considered as the functional units as they perform various functions such as nutrition, transport, excretion and reproduction. The cells perform these functions with the help of energy. We require energy to eat, sleep, to read and listen.
Have you ever wondered that from where do we get this energy?
The food we eat contains stored energy. That's why our parents insist us to eat well. This stored energy is released by the process of respiration.