Gas Detail View
Oxygen (O₂)
Percentage in air
21%
About one fifth of the air we breathe is oxygen. This is just enough to support life and burning, but not so much that things catch fire too easily.
Role in living things
Cells use oxygen in respiration to release energy from food. Without oxygen, complex animals (including us) cannot survive.
Role in burning
Oxygen supports combustion. Fuels like wood, petrol or gas only burn when oxygen is present.
Where it comes from
- Produced by green plants during photosynthesis.
- Released by algae in the oceans (major source).
- Recycled in the atmosphere through the oxygen cycle.
O
O
Diatomic molecule
Formula: O₂ • Colorless gas • Slightly heavier than air
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What is the main role of oxygen in living things?
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