GCSE Biology · Edexcel 1BI0 · Topic 9C
Material cycles
Key points
- Materials such as carbon, water and nitrogen are recycled through living and non-living parts of the ecosystem.
- Carbon cycle: photosynthesis takes CO₂ from the air; respiration, combustion and decomposition return it; carbon passes along food chains.
- Water cycle: evaporation, condensation and precipitation. In dry places, desalination can produce drinking water.
- Nitrogen cycle: nitrogen-fixing bacteria (in soil and root nodules of legumes) turn N₂ into nitrogen compounds; nitrifying bacteria make nitrates; denitrifying bacteria return N₂ to the air. Crop rotation and fertilisers add nitrates.
- Separate science: decomposition rate depends on temperature, water and oxygen. Core practical: measure decay of milk using pH change with lipase at different temperatures.
- Rate of decay = change ÷ time.
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The atoms that make up living things have been used many times before. This sub-topic shows how carbon, water and nitrogen are recycled between organisms and the environment, the vital role of decomposers, and the core practical on how…
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