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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.



  • Put a waterweed in a beaker.
  • Put a funnel on the waterweed and a test tube full with water on it.
  • Keep it under the bright sun for about 30 minutes.



  • 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.

  • 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.

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