Experiment, Plants and Animals

Where Does Oxygen Come From?

Last winter, smog formed in all parts of Poland. And even though it is summer holiday now and there are visibly fewer cars on the streets, we’d still like you to focus attention on this issue. We’ve come to the conclusion that saying ‘Air is polluted; it can harm our health’ to a child is simply not enough. We’ve therefore decided to show you some very easy experiments for children that will help to explain the importance of clean air. So, let’s talk about oxygen and where we get it from. 

The most important properties of oxygen:

  • Oxygen is colourless. 
  • Oxygen is odourless and tasteless. 
  • Oxygen is a non-combustible gas but it supports combustion. 
  • Oxygen has low solubility in water. 


Let’s examine the first three properties of oxygen in our first experiment. 

Experiment 1 – What is oxygen like?

skąd się bierze tlen materiały


  • Three tea light candles
  • Plate
  • Water
  • Pigment (optional, for a better visual effect) 
  • Glass / wine glass
  • Jar

Fire needs oxygen for the candle to burn; when there’s no oxygen left in the glass or jar, the fire goes out. The air inside the glass gets cooler and contracts. And so, it leaves space for the water which gets sucked into the glass and then into the jar. As the jar has a greater volume than the glass, it can contain more oxygen; as a consequence, the candle will burn longer in the jar. 

We need air or, to be more precise, oxygen contained in the air to breathe; without oxygen we would not have the energy that is required for us to live. Without oxygen the candle would not burn, nor would metabolism take place in our bodies – that is, the process of ‘extracting’ energy from the food we’ve eaten. 

The second experiment will help us uncover another property of oxygen. 

Experiment 2 – Where does oxygen come from?

szklany pojemnik, obok liść


  •  A freshly picked leaf 
  • Water
  • Jar / glass / wine glass (depending on the size of the leaf)

The green leaf produces oxygen that we can’t see; however, as oxygen has low solubility in water, after an hour you will be able to observe small bubbles that have gathered on the bottom of the leaf. This indeed is the very oxygen that we breathe. 

The inhaled air that contains oxygen is drawn into the lungs where the oxygen is absorbed into blood through alveoli; blood then delivers oxygen to every cell in our body. When we inhale, we absorb oxygen from air. What we exhale is a gas called carbon dioxide. Plants do the exact opposite. During the day, they produce oxygen and absorb carbon dioxide from the air. Trees are sometimes called the green lungs of our planet because they give us fresh air.