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Air to breathe

Air and fluids · level 1, lesson 5 of 6

A question to start

You breathe in and out all day and all night, without even thinking about it. What does your body take from the air?

The idea

Air is a mix of different gases. The one your body needs is oxygen. About one fifth of the air on Earth is oxygen.

When you breathe in, your lungs take oxygen from the air. When you breathe out, you give out a gas called carbon dioxide. Plants do the opposite in daylight: they take in carbon dioxide and give out oxygen.

Earth's airMars's air blue: oxygen, 1 part in 5grey: carbon dioxideoxygen: 1 part in 600
What the air is made of Mars Earth
Oxygen about 1 part in every 600 about 1 part in every 5
Carbon dioxide almost all of it a tiny bit

So Mars's air is mostly carbon dioxide, the gas you breathe out. People there would need to bring air with them, or make oxygen.

Worked examples

1. Holding your breath. You can only do it for a short time, because your body keeps needing new oxygen.

2. Out of breath. After running, you breathe faster, to take in more oxygen.

3. On Mars. NASA's Perseverance rover carried a machine called MOXIE that made oxygen from Mars's carbon dioxide air.

Try it

  1. Which gas in the air does your body need?
  2. What gas do you breathe out?
  3. What is most of Mars's air made of?
  4. Could you breathe Mars's air?
Answers
  1. Oxygen.
  2. Carbon dioxide.
  3. Carbon dioxide.
  4. No. It has hardly any oxygen, and there is far too little of it.

Common mistake

"Air is all oxygen." Only about one fifth of Earth's air is oxygen. Most of the rest is a gas called nitrogen.

Where it leads