Because you need a lot of oxygen, your lungs need a lot of surface area to do their job. They achieve this by having millions of little air sacs lined with tiny blood vessels called capillaries.
If breathing is kind of like eating, why can’t you just take three breaths a day?
Your blood can carry only so much oxygen.
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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.
Other animals and plants
Most living things get oxygen without lungs.
Many aquatic animals use gills, which are sort of like lungs turned inside out. Instead of a bunch of capillaries wrapped around air sacs, gills are a bunch of capillaries sticking out into the water. Just like in your lungs, the blood vessels take in oxygen from the water and release carbon dioxide.
Insects take in oxygen through a network of little air tubes just under their skin , sort of like the chimneys of a building. This system works because insects are small, so the tubes are already close enough to their cells to give them oxygen. When large insects need extra energy, they pump air through the tubes with their muscles.
A close-up look at the underside of this tomato leaf shows where the air goes in and out.
Vojtěch Dostál , CC BY-ND
Plants have little holes in their leaves called stomata . They open and close to let in air when plants need it. Plant roots need oxygen, too, which they usually get from the soil.
You may have heard that plants are the opposite of people: They breathe in carbon dioxide and breathe out oxygen . That’s true because carbon dioxide is a crucial ingredient in photosynthesis – the process plants use to make their own sugar fuel – and oxygen is a byproduct. But plants’ mitochondria also need oxygen to make energy, just like yours do.
Even though most animals and plants don’t breathe in and out the way people do, they all have ways of getting enough oxygen. Learning how organisms solve the same problem in different ways is one of my favorite things about biology.
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Christina S. Baer does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
Source: The Conversation