S4.3.5 For the adult
The carbon and nitrogen cycles
The carbon in your body was once in the air. How did it get from there into you, and where will it go next?
What this chapter teaches
Carbon moves from the air into plants by photosynthesis, passes along food chains, and returns to the air by respiration, decay and burning. Fossil fuels are stored carbon. Plants take nitrates from the soil, and bacteria fix nitrogen, make ammonium, make nitrates and return nitrogen gas to the air.
Three questions to ask
There is no one right wording. Listen for the idea.
- What are two ways that carbon dioxide gets back into the air?
- Why can plants not use the nitrogen gas that makes up most of the air?
- Why do farmers sometimes grow beans or peas in a field?
After the chapter, the learner can
- Draw the carbon cycle with photosynthesis, respiration, decay and burning
- Explain how bacteria in the nitrogen cycle help plants grow
What they copy into their notebook
Photosynthesis takes carbon dioxide in. Respiration, decay and burning give it out. Roots take in nitrates. Fixing bacteria add nitrogen compounds, nitrifying bacteria make nitrates, and denitrifying bacteria return nitrogen gas to the air.