We inhale O2 and exhale CO2, so does that mean we just add carbon and exhale the same oxygen we just inhaled? Why cant we just exhale carbon?

Question

We inhale O2 and exhale CO2, so does that mean we just add carbon and exhale the same oxygen we just inhaled? Why cant we just exhale carbon?

In: Biology

Answer 1

So, let’s use an example to give another viewpoint.

When you have a lovely campfire of burning wood, it releases a lot of heat: This is energy of the wood being released by reactions with oxygen. In fact, a lot of the reactions with oxygen are pretty much the same, just at different speeds.

Now, we also need energy to do things, but we can’t exactly put a campfire inside us to do that. That’s why we ‘slow-burn’ various chemical compounds to give us energy. Oxygen happens to be abundant and very reactive, so it’s available and pretty good at what it does. Just as a campfire is not just adding carbon to oxygen (well it is, but there’s more to it), we are basically burning something like sugar to give us the energy.

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A bit more detailed explanation involving entropy:
Imagine you have a bunch of perfectly organized rocks in a line. Then you shake up whatever your rocks are on, and they’re not organized anymore. To organize the rocks again, you need to spend energy.

So, what’s very organized in chemical terms? Well, oxygen for one, and the sugar we burn for food. So, something has spent energy to organize these things, and then we combine them to recover that energy. Simple, right?
(This is a gross oversimplification that only helps explain the process and there’s a lot of details I’ve left out so please don’t quote that for anything but ELI5 purposes)