Nothing. It just breathes it out. It’s too hard to break apart to use. Other stuff can use atmospheric nitrogen and turn it into useful chemicals, but we can’t. So we don’t.
It’s like asking “what does a deer do with a dead moose it found”, nothing. It’s too hard to eat, so it just doesn’t. Other things can do stuff to it, and turn it into things the deer can use. But by itself, the deer doesn’t do anything to it.
Our bodies cannot use nitrogen directly.
Oxygen is combined with compounds such as carbohydrates to make CO2, water, and other waste products and give up energy. Nitrogen cannot be used for this purpose because nitrogen combining with other substances does not generally generate energy.
Our bodies do need nitrogen, but they need it in compounds, mostly proteins and amino acids. Instead of using the nitrogen in the air to make these compounds, we get them from eating plants, which make them, and animals, which convert them from plants to make up their own bodies.
Nothing. Nitrogen in the air is inert. Our bodies don’t do anything with it, we just inhale it and exhale it again. The only time nitrogen in the air is important is when a person moves between environments with very different air pressures, like when scuba diving.
Note that nitrogen is present in many molecules that we need to survive, but we don’t get it from breathing, we get it from our food.
Nothing. None of the nitrogen from the air actually enters your body . You breathe in and the air enters your lungs (the space in your lungs is still external to your body). Oxygen from the air goes into your blood, carbon dioxide from the blood leaves into your lungs, and then you breathe out. The nitrogen doesn’t do anything. It just…doesn’t get absorbed, and then leaves again.
Our feeble little bodies can’t handle nitrogen as it exists in the atmosphere. The reason we utilize oxygen is because our cells are capable of breaking O2s bond and reacting the oxygen with fats and sugars in our bodies to keep us going. While nitrogen is an important building block for the proteins in our body, the triple bond between diatomic nitrogen is too strong for anything in our body to break, so it passes through us without interacting with us at all.
We get the nitrogen in our bodies from bacteria (and maybe other things, I’m not 100% sure) that ARE capable of breaking the triple bond. It’s a process called “nitrogen fixing”. They often live on the roots of certain plants and have a symbiotic relationship with them, providing the necessary ammonia for the plants to grow.
There’s a common misconception that we inhale only the oxygen and exhale only carbon dioxide. Or that we completely deplete the oxygen from what we breathe. The truth is that the composition of the air barely changes during our respiratory process. It goes from 21% O2 and 0.04% CO2 to 16% and 4.4% respectively. That’s why you can breathe into a bag and reinhale the same air again and not suffocating.
The corollary to this is if we don’t even process all the oxygen, we sure as hell aren’t processing anything else in the air. We ignore all of the other gases and breath them back out
Nothing. It just gets breathed straight back out.
Nitrogen gas comprised two nitrogen atoms bonded together and it is an extremely stable molecule. Our bodies have no way of braking it down, it needs something like a lightning strike or the conditions (temperature and pressure) found in an internal combustion engine or power plant to force the nitrogen to react with oxygen.
So everyone has said nothing, and that’s true, but: our bodies are *used* to it being there. It’s like saying you don’t need a pillow and blanket to sleep, but it’s comfortable and we’re used to it so we want it. Our bodies want air with nitrogen in it because it’s easier to breathe. Oxygen is actually a pretty harsh gas and so it’s much easier on our bodies to just get a little at a time.
If life on Earth evolved with a much higher Oxygen content, we would have developed a *much* different set of lungs.
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