Harder to understand, anyway. It's cellular respiration time!
Cellular respiration is what we do with the oxygen we breathe in and the food we eat. It happens on a level that's beyond microscopic, and it happens about a kazillion times per second. Most importantly, it's going to be on my final exam, so let's poke at it a little.
The oxygen we breathe is produced by plants through the process of photosynthesis. We know from elementary school that plants use the power of sunlight (kind of like the power of friendship, only with fewer cupcakes) to turn carbon dioxide and water into oxygen. And that's true! But it's also an incomplete equation. It doesn't account for all of the molecules in play or the actual sunlight energy that activates photosynthesis. Besides oxygen, plants also create pure glucose (sugar), which they find delicious. (I do too. I've been known to eat brown sugar right out of the bag.)
Before I go on, let me explain something real quick about atoms. Atoms are the most basic unit of everything. An atom consists of a core surrounded by electrons, which are energized particles buzzing around the core in an orbit. (Picture Saturn.) These electrons are always in motion, though their energy levels can fluctuate. When atoms link up to form bigger substances, like a molecule of sugar or your keyboard, it generally means that they're sharing or swapping electrons around somehow and linking their orbits up with one another.
What did that have to do with anything? Well, the sunlight energy that kicks off photosynthesis also gives those electrons within that reaction a bit of a boost. The oxygen is released as a convenient byproduct, and the glucose that's formed as a result is linked together with high-energy chemical bonds. This becomes important when we start harvesting those turnips or bamboo shoots or kale or whatever, because those chemical bonds are what we're really after.
Yes, we eat chemical bonds. Bear with me.
So we eat our tempura. Once that glucose hits our system, we start doing a bunch of things to it. First, we have to break it down a little in a process called glycolysis (literally, breaking down glucose). This requires a teensy bit of an energy investment on our part, which is why you can hear stuff like "celery takes more energy to digest than you get out of it." That energy is added to the chemical bonds in the glucose, exciting them and making them unstable, which makes the glucose easier to break apart. We take that complex glucose molecule and break it down into two simpler halves. We add some other stuff, and so from one molecule of glucose we get two molecules of something called pyruvic acid. We also get a little return on our energy investment, but it's not much compared with what we're in for.
All that I just described--glycolysis--will happen no matter what as long as there's glucose and energy to spend. What follows is the part we need oxygen for, and the only reason we have to breathe.
Each of our cells has a structure called the mitochondria. The mitochondria are teensy energy factories, each one housing a process called the Krebs cycle. Pyruvic acid is the raw material for our mitochondria to work with. Through a long series of chemical reactions, helped along by vitamins (take 'em!), the pyruvic acid is shuffled around and systematically dismantled. There are a lot of steps to the Krebs cycle, and I won't go into them all, but the reason for it is so that we can squeeze every last atom out of the equation to use in our bodies.
And what exactly are we squeezing out? Believe it or not, hydrogen! It's the smallest, most basic element on the whole periodic table, but we're totally screwed without it. Throughout the Krebs cycle, a couple of different vitamins snatch up hydrogen, taking with them that energy we saw infused into the sugar when it was first made by photosynthesis. At the end of the process, all that's left is the carbon and oxygen parts of the equation, and we release that as carbon dioxide, which we breathe out. But you knew that.
What happens next is a little weird and a little hard to describe, so you'll have to bear with me. All that hydrogen that the vitamins picked up is whisked away to something called the electron transport system, which is also in the mitochondria. This is a four-stage process facilitated by--guess what--more vitamins! (Seriously, take them.) The first three parts are full of things called Coenzyme Q and Cytochrome C, which doesn't sound arbitrary at all (it totally is), but at the end of the chain is oxygen. Remember from all that antioxidant talk how greedy oxygen is? That makes it an excellent magnet to stick at the end of this electron transport system. It draws that hydrogen all the way through this little system, and the hydrogen gives up a little more of that photosynthesis energy in each stage. By the time it gets to the oxygen, it's totally depleted and perfectly content to shut up and make water. All that energy goes out into the universe that is our body, and we can use it to do important things, like eating more tempura. Mmm, tempura.
Honestly, this was a tough concept for me to grasp, because it's totally invisible and a little metaphysical and full of concepts that aren't in my area of expertise. I'm hoping that by the time I'm a big, grown-up scientist, I'll be better able to grasp the concept of energy being a tangible product that we can consume, manipulate and produce. Maybe that's more of a physics thing. I was never very good at physics.
Anyway, be good to your body. It does a lot of really cool stuff without even thinking about it. (If I had to think about cellular respiration a persquillion times a day, my brain would explode.) And take your vitamins. Just not too many. That's bad.
