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Edexcel GCSE Physical Education · 1PE0
Edexcel 1PE0 · 1.2.6 Check the specification (PDF) (opens in a new tab)
Describe the composition of inhaled and exhaled air.
Analyze the impact of physical activity and sport on this composition.
is the air you breathe into your lungs; is the air you breathe out. Neither is pure oxygen or pure carbon dioxide. Nitrogen makes up the largest proportion of both.
The standard approximate percentages to learn are:
| Gas | Inhaled air | Exhaled air |
|---|---|---|
| Nitrogen | 78% | 78% |
| Oxygen | 21% | 16% |
| Carbon dioxide | 0.04% | 4% |
To picture these proportions, imagine 100 equal parts of inhaled air: about 78 parts are nitrogen and 21 are oxygen, while only a tiny fraction is carbon dioxide. In exhaled air, about 16 parts are oxygen and four are carbon dioxide. These three gases do not total 100% because air also contains other gases.
The differences between inhaled and exhaled air reflect what happens inside the body. At the tiny air sacs in the lungs, called alveoli, oxygen passes into the blood and carbon dioxide passes from the blood into the air to be breathed out. This transfer is gas exchange.
Blood carries oxygen to working muscles. Their cells use oxygen in aerobic respiration, which releases energy from nutrients. This energy enables muscles to contract. Because the body takes oxygen from the inhaled air, exhaled air contains a lower proportion of oxygen: approximately 16% rather than 21%.
Carbon dioxide is a by-product of aerobic respiration. It is carried back to the lungs in the blood and breathed out, so exhaled air contains a higher proportion of carbon dioxide: approximately 4% rather than 0.04%.
Nitrogen behaves differently. The body neither uses nitrogen gas for energy production nor produces it as a by-product of respiration. Its proportion therefore remains approximately 78% in both inhaled and exhaled air.
During physical activity, working muscles need more energy than they do at rest. Increased aerobic respiration means that more oxygen is used and more carbon dioxide is produced. The lungs must therefore supply more oxygen and remove more carbon dioxide.
For example, when a footballer moves from standing still to sustained running, their muscles contract more frequently and their energy demand rises. Breathing becomes faster and deeper, increasing ventilation—the movement of air into and out of the lungs. This brings in more oxygen-containing air and allows more carbon dioxide to be breathed out.
Exercise does not itself change the composition of the surrounding air being inhaled. Its impact is on the body's use of oxygen and production of carbon dioxide: oxygen is removed from the air, carbon dioxide is added, and nitrogen remains essentially unchanged. The total amounts exchanged increase during exercise; the standard percentages above are approximate comparison values, not fixed measurements for every exercise intensity.
Oxygen is also needed during recovery after activity. Its use by the body helps explain why exhaled air continues to contain less oxygen than inhaled air.
| Gas | Inhaled | Exhaled |
|---|---|---|
| Nitrogen | 78% | 78% |
| Oxygen | 21% | 16% |
| Carbon dioxide | 0.04% | 4% |
Greater muscle activity → greater energy demand → increased oxygen use and carbon dioxide production.
Faster, deeper breathing increases airflow, supplying more oxygen and removing more carbon dioxide. Inhaled air retains its usual composition; the approximate exhaled percentages are not fixed values for every exercise intensity.
Learn the gas percentages as paired values: inhaled first, then exhaled.
For two reasons why nitrogen stays the same, state that it is neither used in energy production nor produced as a by-product of respiration.
Link sporting activity to increased energy demand, oxygen use and carbon dioxide production. Do not treat the standard exhaled-air percentages as exact values for every breath during exercise.
Exhaled air still contains oxygen: the body does not use all the oxygen breathed in.
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Last updated
Inhaled air
The mixture of gases breathed into the lungs.
Exhaled air
The mixture of gases breathed out of the lungs.
Aerobic respiration
The chemical process in cells that releases energy from nutrients using oxygen and produces carbon dioxide as a by-product.
Ventilation
The movement of air into and out of the lungs through breathing.
Gas exchange
The transfer of oxygen from air in the lungs into the blood, and carbon dioxide from the blood into air in the lungs.
Put your knowledge into practice — try past paper questions for Physical Education
Inhaled air
The mixture of gases breathed into the lungs.
Exhaled air
The mixture of gases breathed out of the lungs.
Aerobic respiration
The chemical process in cells that releases energy from nutrients using oxygen and produces carbon dioxide as a by-product.
Ventilation
The movement of air into and out of the lungs through breathing.
Gas exchange
The transfer of oxygen from air in the lungs into the blood, and carbon dioxide from the blood into air in the lungs.