The carbon cycle
The carbon cycle
- Unlike energy, nutrients are recycled — used again and again.
- In the carbon cycle:
- photosynthesis removes carbon dioxide from the air,
- respiration and combustion (burning) return it,
- feeding passes carbon along the chain,
- decomposition returns carbon to the air and soil.
- Over millions of years, dead organisms can form fossil fuels, which release carbon dioxide when burned.
Practice
Which process removes carbon dioxide from the air?
Photosynthesis takes carbon dioxide out of the air; respiration and combustion return it.
Practice
Which processes return carbon dioxide to the air? (Choose all that apply.)
Respiration, combustion and decomposition all release carbon dioxide; photosynthesis removes it.
Practice
Nutrients like carbon are recycled, while energy flows one way.
Carbon is reused through the carbon cycle; energy is lost as heat and is not recycled.
You've got it
Key idea
- nutrients are recycled (energy is not)
- photosynthesis removes carbon dioxide; respiration + combustion return it
- decomposition recycles carbon; fossil fuels release it when burned