Air sacs. Image credit MediaWiki

Air sacs. Image credit MediaWiki

ZIMSEC O Level Combined Science Notes:Exhaled air vs inhaled air

  • Air which enters the lungs (inhaled air) is different in several regards to air that is passed out (exhaled air)
  • Exhaled air contains less oxygen and more carbon dioxide.
  • It is also warmer and more moist.
ComponentInhaled (normal) areaExhaled air
Oxygen2016
Carbon dioxiode0.034
Nitrogen7878
Water vapour approximately6higher
  • Nitrogen is not absorbed by plants or animals.
  • Inhaled air has more oxygen and less carbon dioxide when compared to exhaled air.
An air sac. Image credit wordpress.com

An air sac. Image credit wordpress.com

  • The composition of inhaled air changes in the alveoli.
  • This is where gas exchange takes place.
  • Each alveolus is a microscopic structure with capillaries .
  • The air in the alveoli has more oxygen than the blood around them.
  • The oxygen diffuses into the blood.
  • There is more carbon dioxide in the blood than in the alveoli so it diffuses from the blood into the air sacs.
  • This two way diffusion is called gas exchange.
  • This happens in millions of air sacs every minute of everyday.
  • The breathing process makes sure that there is a higher concentration of oxygen in the air sacs that in the blood.
  • This means that oxygen will always diffuse into the blood and carbon dioxide outside the blood.

To access more topics go to the Combined Science Notes page.


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