What is Gas Exchange?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 05 October 2019
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Gas exchange is a process that occurs as part of respiration, allowing an organism to exchange waste gases for gases it needs in order to function. In the case of humans and other mammals, this allows for the expression of carbon dioxide and the intake of oxygen. Gas exchange takes place along the respiratory membrane, such as the lining of the lungs in animals, and the circulatory system of the organism allows the gases to move throughout the body. In unicellular animals, gas exchange allows gases to move freely directly in and out of the cell.

In plants, the leaves act as a respiratory membrane, with small capillary vessels in the leaves acting to transport gases and nutrients throughout the tree. Animals like amphibians may rely on their skins for gas exchange, while gilled animals like fish use the large surface area of the gills to pull dissolved oxygen out of the water and into their bodies.


Every time a person takes a breath, air rich in oxygen and other gases enters the lungs. The air moves from an area of high pressure, the filled lung, to an area of low pressure, one of the alveoli, the tiny sacs lining the lungs. From there, the oxygen passes through a thin membrane into the capillaries supplying the lung, where it binds to hemoglobin for transport throughout the body. As the blood circulates, it also carries away wastes like carbon dioxide, delivering them to the lungs for gas exchange so they can be forced out of the alveoli and exhaled when the person breathes out.

People who have difficulty breathing can start to develop hypoxia, a state where not enough oxygen is reaching the body. This can occur when gas exchange is inhibited by fluid in the lungs, when a lung can't inflate properly, or when the airway is obstructed. A patient who cannot expel carbon dioxide and get oxygen in exchange will start to develop bluing of the extremities and can gasp for air.

In an environment rich with another gas, like nitrogen, that gas can displace oxygen, making it impossible for oxygen to reach the lungs. A patient may be able to breathe normally, but because gas exchange with oxygen is not taking place, the person will become slowly oxygen-starved. Depending on the gas being breathed, patients can develop symptoms like giddiness, confusion, and sleepiness before succumbing to coma and eventual death due to lack of oxygen.


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Post 3

@everetra - I think it’s clear that we live in a symbiotic world, to borrow a big phrase from science. We are all interdependent upon nature.

The gas exchange in plants for example enables them to supply us with the oxygen that we need while we exhale the carbon dioxide that the plants need.

I hope that with this in mind, we can understand how important it is to take environmental concerns seriously, and not treat them as the extremes of fringe elements of our society.

Post 2

@Mammmood - That’s a great point. I have to admit I don’t get out enough. I spend all day working on my computer. About the only time I get out is at night when I take my dog out for a brisk walk. That air is indeed much fresher, and around the winter time it’s also filled with the fresh scent of burning wood.

That doesn’t mean that all outside air will be good for you. For example if you climb mountains you could suffer from hypoxia. That’s because at high altitudes the air gets thin and you may not get the oxygen levels that you need.

Post 1

I think there is something to be said for the advice people give to go outside and “get some fresh air.” I believe that the quality of the air you breathe is just as important as its makeup.

The air we breathe inside can be full of dust and it makes it more difficult for the respiratory system of the body to do its work. It puts an additional load on your lungs. Fresh air is just that – fresh and clean.

I am assuming of course that you are not inhaling smog, which most of the time you would not be. Because the air is cleaner we tend to breathe it in more deeply and thus get more of the oxygen that our body so desperately needs.

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