• Question: How do we breathe in oxygen only and not carbon dioxide?

    Asked by to Aimee, Chris, Dave, Greig, Laurence on 23 Jun 2014. This question was also asked by .
    • Photo: Aimee Hopper

      Aimee Hopper answered on 23 Jun 2014:

      We breath in everything in the air, but only the oxygen diffuses into our bloodstream. This is because of diffusion in the alveoli in the lungs (as they make a HUGE surface area!), and a very thin membrane separating the gas in the lungs from the blood.

      Because the blood has less oxygen than the air you breathe, oxygen crosses this membrane into the bloodstream. On the other hand, there is more CO2 in the blood than in the air, so that diffuses IN to the lungs, and gets breathed out.

    • Photo: Greig Cowan

      Greig Cowan answered on 23 Jun 2014:

      Aimee already answered this one. The reason that we need to breath oxygen is that our cells need this in order to metabolise and produce energy which is then used to power our other bodily functions. Oxygen is a basic requirement for metabolism – you can’t convert glucose into energy that the cells use with with carbon dioxide.

    • Photo: Laurence Perreault Levasseur

      Laurence Perreault Levasseur answered on 23 Jun 2014:

      Just like Aimee explained, it’d because of something called diffusion. Diffusion is when molecules move from a high concentration region to a low concentration region. It’s explained pretty well here (with drawings!! 😀 )

      The part that is relevant here is just simple diffusion (through the rest is pretty interesting too!!). The membrane is the surface of the alveolus (the little pockets where the air you breath in goes. Like Aimee said, there is a HUGE amount of them. If you were to flatten them they’d cover the area of a full tennis court!!!!) in the lungs, and the air you breath is on one side, while the blood is on the other side. The air has high concentration in O2, while the blood has high concentration in CO2. They will move across the membrane until there is the same concentration of O2 and CO2 on both sides.

      That means there is always some CO2 left in the blood, and we never get all the O2 form the air!

    • Photo: Dave Jones

      Dave Jones answered on 24 Jun 2014:

      Question has already been answered, but thought I’d add something interesting. Our red blood cells are the ones that carry the oxygen or carbon dioxide around the body, to and from the lungs. They also can make the same bond with carbon monoxide, carrying it around the body. The reason carbon monoxide is so dangerous is that it while it makes the same bond as the others it makes it much more strongly, meaning it is difficult to break the bond and swap it out of the blood for oxygen that we need. So, if you breathe in carbon monoxide (like from a faulty fireplace) it doesn’t poison you directly it just occupies too many of your red blood cells for you to get the oxygen you need to survive, kind of like suffocating!

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