Why can’t I breathe underwater?

Why can’t I breathe underwater?

Human beings have a very important system in their body responsible for respiration or breathing. It is known as the respiratory system.



  • Breathing basically refers to the gaseous exchange that takes place in the body as air is inhaled into the lungs through the nose and carbon dioxide is expelled out from the lungs through the nose.
  • This process is also known as respiration. Respiration is also carried out by organisms other than humans such as animals and plants.
  • For respiration, we take oxygen from environment and release carbon dioxide in environment.
  • We require this oxygen to carry out the metabolic processes of cellular metabolism in our cells. In this process, CO2 or carbon dioxide is produced and released out of the body.


  • The process of respiration takes place in the lungs. Our lungs are designed to utilise oxygen in its molecular state or as O2.
  • The molecular formula of water is H2O and the water molecule is held together through very strong resilient covalent bonds.
  • A huge amount of energy would be required to break a water molecule to obtain the oxygen atom and the lungs do not have the resources or energy necessary to carry out this reaction. At the same time, the oxygen extracted from H2O would be in its atomic form as O, not O2 which also cannot be utilised by humans.
  • This is why humans can’t breathe water.
  • Fishes on the other hand have specialized structures called gills that help them breathe in water. However, they also do not break up the water molecule to obtain oxygen; they simply utilize the oxygen that is dissolved in water.

A human being has lungs for the exchange of gases to take place. Till the time our lungs collect oxygen from water after a tough process, we will be already out of oxygen that can lead to serious issues. That’s why we cannot breathe in water.

The human respiratory system can work only with air however some people can dive in water by holding their breath for few seconds.

Fun Facts:

  1. Unlike us, horses can only breathe through their nose. But we can breathe through our mouth as well as our nose.
  2. Elephants have a unique respiratory system that allows them to withstand both air and water.
  3. On average, we can hold our breath from 30-60 sec or more.

Additional Questions:

  1. Which animals breathe through gills?
  2. Explain the respiratory system.
  3. Explain the importance of oxygen in the human body.

True or False:

  1. Humans can easily breathe underwater.
  2. Our lungs are capable of breathing in water.
  3. There is a system called the respiratory system present in our body responsible for respiration and its related functions.
  4. Fish have gills for their breathing.
  5. We can stay underwater for a few seconds by holding our breath.

Objective Quiz:

  1. We have a system called _________ for the breathing process and its related function.
    1. Respiratory system.
    2. Digestive system.
    3. Nervous system.
    4. Urinary system.
  2. We take _______ in through our nose and expel carbon dioxide.
    1. Oxygen.
    2. Nitrogen.
    3. Carbon dioxide.
    4. Water.
  3. We cannot breathe under _______.
    1. Water.
    2. Air.
    3. Both 1) and 2).
    4. None of the above.
  4. The molecular formula for oxygen is _______.
    1. H2
    2. O2.
    3. O3.
    4. H3
  5. Fish have __________ for breathing underwater.
    1. Gills.
    2. Kidney.
    3. Liver.
    4. Pancrease.

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