Why do people and animals need to breathe? A biologist explains why you need a constant source of oxygen
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Why do humans and animals have to breathe? – Tennessee, age 7, Hartford, Kentucky
You need to breathe for the same reason you need to eat: It helps you make the energy your body requires.
You probably already know that food is fuel for your body. When you eat, food gets broken down in your stomach and enters your bloodstream.
From there, it gets delivered to your cells. Inside your cells are even tinier structures called mitochondria, which are the engines that power your entire body. Your mitochondria use the nutrients from food as fuel. But to turn it into energy, they need one more ingredient – oxygen.
One reason is that air on Earth is only 21% oxygen – the rest is mostly nitrogen. That means you need to take five breaths just to get the equivalent of one complete lungful of oxygen.
Also, when you take a breath, only some of the oxygen makes it into your bloodstream. Even though people and many animals make specialized proteins to grab and carry oxygen, there’s a limit to how much they can hold at once. To keep your body’s oxygen levels high enough to power all your cells, you need to keep breathing.
Of course, once you breathe in, you also have to breathe out. The gas you breathe out is called carbon dioxide. You can think of it as the exhaust from your mitochondria engines, the leftovers once the mitochondria burn oxygen and nutrients to release energy.