Theory:

Close your nostrils and mouth while looking at a watch in front of your teacher or parent. Take note of how long you were able to do this and how long you could hold your breath.
 
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A boy is closing his nostrils
 
From this activity, you could know that you cannot hold your breath for a long time. We also notice that when we release our breath, there is difficulty breathing due to the lack of oxygen.
What is breathing?
The process of taking in oxygen-rich air present in the surroundings and giving out the air that lacks oxygen into the surroundings with the help of respiratory organs is known as breathing.
It is a process that occurs continuously in the living organisms as one cannot survive without breathing.
The process of breathing can be broken down into two steps inhalation and exhalation.
  
Inhalation:
The process of taking in the air, which is rich in oxygen is known as inhalation.
 
Exhalation:
The process of giving out the air that is rich in carbon dioxide is known as exhalation.
 
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The process of inhalation and exhalation will be explained clearly in the next theory.
Breathing rate:
Breathing rate is the number of times a person breathes per minute. During the process of breathing, both inhalation and exhalation take place alternately.
An inhalation that is followed by an exhalation is known as breath. In human beings, the breathing rate is not always constant. Instead, this rate increases when there is a high demand for energy by the body.
Activity to explain the breathing rate:
Try counting your breathing rate at various situations such as sitting, while walking and running. You will notice that the breathing rate will vary in all these conditions and will be high during running.

During these conditions, when humans breathe faster, more oxygen is supplied to the cells so that cellular respiration speeds up and more energy is released.

The condition during which a person feels drowsy is an indication of insufficient oxygen supply in the body.
An adult human being breathes 15 to 18 times in a minute. On average, when a person performs heavy exercises, the breathing rate increases up to 25 times per minute to inhale more oxygen.