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Lungs Trade Oxygen for Carbon Dioxide

with Medi

Medi stands beside a giant glowing model of the lungs inside a colorful science lab, blowing gently into a clear tube to watch tiny oxygen and carbon dioxide bubbles travel back and forth through branching airways.

Explain that the respiratory system brings oxygen into the body from the air.
Identify carbon dioxide as the waste gas the body breathes out.
Describe how the lungs act like a trading post, swapping oxygen for carbon dioxide.
Compare what is in the air you breathe in with what is in the air you breathe out.
Predict what would happen to your body if your lungs could not get oxygen from the air.

Key terms

oxygen: the gas your body needs for energy
carbon dioxide: the waste gas your body breathes out
lungs: two air bags inside your chest
alveoli: tiny air sacs deep inside your lungs
gas exchange: trading oxygen for carbon dioxide gas

Air Goes In

When you breathe in, air goes down your throat and into two big tubes called bronchi. Then the air fills your lungs. Inside each lung are millions of tiny air sacs called alveoli. They look like a bunch of grapes. The air sacs are wrapped in very thin blood tubes, ready to do an important trade with your blood.

The Great Trade

Inside the tiny air sacs, a trade happens with every breath. Oxygen from the air moves into your blood. At the same time, carbon dioxide moves out of your blood and into the air sacs. Then you breathe out and push the carbon dioxide away. Your lungs do this trade about twenty thousand times every single day.

Worked examples

What does your body do with one breath?

You breathe in air full of oxygen.
Oxygen moves from the air sacs into your blood.
Carbon dioxide moves from your blood into the air sacs.
You breathe out and push the carbon dioxide away.

Answer: Oxygen goes in to your blood and carbon dioxide goes out.

Hey there, I am Medi, and today we are going inside your chest to see one of the coolest trades in your whole body! Every cell in your body needs oxygen to work — think of oxygen like the spark that lets your cells burn their food for energy. When you breathe in, air travels down your throat, through two big tubes called bronchi, and into your lungs. Inside each lung are millions of tiny air sacs called alveoli — they look like a bunch of grapes. These little sacs are surrounded by super-thin blood vessels. Here is where the trade happens: oxygen from the air sacs crosses into the blood, and at the same time, carbon dioxide — a waste gas your cells produce as a by-product of making energy — moves from the blood back into the air sacs. Then when you breathe OUT, your lungs push that carbon dioxide right out of your body. So every single breath is a two-way deal: oxygen IN, carbon dioxide OUT. Your lungs do this trade about 20,000 times every single day without you even thinking about it! Here is your hint: think of your lungs like a busy swap shop. Things only move the right way because one side has too much of what the other side needs. And remember — most of the air around us is actually a gas called nitrogen, which we breathe in and breathe back out without using it at all.

Activity

Sort each gas bubble into the correct basket — breathe IN or breathe OUT.

Practice

What gas do your lungs bring into your body?

What waste gas do you breathe out of your body?

Common mistakes to avoid

We breathe in carbon dioxideWe breathe in oxygen and breathe out carbon dioxide waste.
We use up all the oxygenOur lungs only take some oxygen; the rest is breathed out.

Check your understanding

What does the respiratory system bring INTO your body with every breath?

A student says, 'When we breathe out, we breathe out all of the air, so there is no oxygen left in the air at all.' Is this correct?

Where inside the lungs does the swap between oxygen and carbon dioxide actually take place?

Recap

Your lungs bring oxygen into your body and push carbon dioxide out. The trade happens in tiny air sacs called alveoli, where oxygen and carbon dioxide swap places.

Reflect

Take a slow breath and feel oxygen come in!