1What is in the air?
Dry air is mostly nitrogen (78%) and oxygen (21%), with almost 1% argon. Carbon dioxide is only about 0.04%.
nitrogenoxygen
Lesson 26.3 notes
The atmosphere and the carbon cycle
What the air is made of, and how carbon moves between the air, living things, the sea and the rocks.
2A tiny but vital gas
Only about 4 in every 10,000 molecules in the air are carbon dioxide. Plants need it for photosynthesis, and it traps heat.
carbon dioxide
3Photosynthesis
Plants take carbon dioxide from the air and use light energy to make glucose, giving out oxygen. This is photosynthesis.
photosynthesis
4Eating and respiration
Animals get carbon by eating plants. Living things release energy from glucose by respiration, giving out carbon dioxide.
respiration
5Decay
When living things die, microbes feed on them. The microbes respire, so the carbon goes back into the air as carbon dioxide.
decaymicrobes
6Fossil fuels and combustion
Plants and plankton buried for millions of years became coal, oil and gas. Burning them, combustion, releases their carbon as carbon dioxide.
fossil fuelcombustion
7The carbon cycle
Carbon moves round and round between the air, living things, the oceans and the rocks. This is the carbon cycle.
carbon cycle
Explore: Follow a carbon atom
Start with a carbon atom in a molecule of carbon dioxide. Choose what happens to it next and follow it round the carbon cycle.
Common mistake: The air is not mostly oxygen
Only about a fifth of the air is oxygen. Almost four-fifths is nitrogen, which we breathe in and out without using it.
Remember
- Dry air is about 78% nitrogen, 21% oxygen, 0.9% argon and 0.04% carbon dioxide. Air also contains some water vapour.
- Photosynthesis takes carbon dioxide out of the air. Respiration, decay and combustion put it back.
- Carbon is stored in living things, fossil fuels, the oceans and rocks such as limestone.
Going further at GCSE
GCSE: The air and the early Earth → GCSE: The carbon cycle →