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Oxygen in Air

Oxygen in air is a gas used by all the human beings and animals to breathe. About one-fifth (1/5) of the air is oxygen. That means there is about 21% of the oxygen in air.


How does the environment get oxygen?

Green plants release (give out) oxygen as a waste product in sunlight when they produce their food.


An experiment to show that the green plants give out oxygen in sunlight.



  • A waterweed
  • A beaker
  • A funnel
  • A test tube
  • Water
  • This experiment should be done on a sunny day.



1) Put a waterweed in a beaker.

2) Put a funnel on the waterweed and a test tube full with water on it.

3) Keep it under the bright sun for about 30 minutes.



1) After 30 minutes you can see water in the test tube has gone down.

Reason: When oxygen is released, it will enter the test tube and the water will go down.

2) When the test tube is filled with oxygen you can insert (put in) a dimmed match.

Reason: If the test tube is really filled with oxygen the dimmed match should take fire again.


Green plants give out oxygen in sunlight.


Ways that people use oxygen in air


  • Humans and other animals need oxygen to breathe.
  • Divers working underwater need oxygen to breathe so they carry oxygen in bottles on their back.
  • Astronauts (A person trained to travel in a spacecraft) take all their oxygen with them.
  • Firefighters carry bottles of oxygen when they put out very smoky fires.
  • When people are very ill, doctors give them oxygen to breathe.
  • Fires need oxygen to burn.
  • Oxygen is mixed with a gas called ‘acetylene’ and this forms a flame called, ‘Oxyacetylene’. The flame Oxyacetylene is used to weld (join) metals such as iron and steel.
  • Oxygen is used to burn the fuel in spacecrafts.

Click here to read more lessons on ‘air’.