9.3 Biogeochemical Cycles
Notes
Energy flows through ecosystems, but matter is recycled through biogeochemical cycles.
- Water cycle: evaporation, transpiration (from plants), condensation, precipitation, runoff.
- Carbon cycle: photosynthesis removes $\text{CO}_2$ from air; respiration, decomposition and burning fossil fuels add it back.
- Nitrogen cycle: plants and animals cannot use nitrogen gas ($\text{N}_2$) directly. Nitrogen-fixing bacteria in soil and root nodules turn it into usable forms like ammonia and nitrates.
- Phosphorus cycle: phosphorus moves through rocks, soil, water and organisms; it has no gas phase.
Practice
Which process removes carbon dioxide from the atmosphere?
Plants take in CO2 to make glucose.
Why are nitrogen-fixing bacteria important?
Plants need nitrogen compounds, not N2 gas, to build proteins and DNA.
Water released from the leaves of plants into the air is called:
Transpiration is evaporation of water from plant leaves.
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