sci_bio
Nutrient Cycles: Carbon & Nitrogen
Chapter summary, hard words and model exam answers for ICSE Class 10 Hindi.
Free online summary and notes (ICSE Class 10 Hindi). Read it here, no PDF download needed.
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Biology · CBSE 10 · ICSE 10 · GCSE (AQA, Edexcel, OCR)
Summary
Carbon, nitrogen and other elements in living things are limited in supply. Decomposers break down dead matter and return these atoms to the soil and air for plants to reuse.
Producers fix carbon dioxide into glucose. When organisms respire, die and decay, or fuels are burned, that carbon returns to the atmosphere as CO2.
Nitrogen-fixing bacteria make ammonia; nitrifying bacteria make nitrates; plants take up nitrates; decomposers recycle protein; denitrifying bacteria return N2 to the air.
Combustion and deforestation raise CO2, driving climate change. Fertiliser run-off causes eutrophication, where algae bloom and starve water of oxygen.
Hard words & meanings
| decomposer | a microorganism (bacterium or fungus) that breaks down dead matter and releases its nutrients |
| nitrogen fixation | conversion of atmospheric N2 into ammonia or ammonium by bacteria such as Rhizobium |
| nitrification | conversion of ammonium into nitrites and then nitrates by nitrifying bacteria |
| denitrification | conversion of nitrates back into nitrogen gas by denitrifying bacteria |
| assimilation | uptake of nitrates by plant roots to build proteins and nucleic acids |
| combustion | burning of fuels, releasing stored carbon as carbon dioxide |
| eutrophication | enrichment of water by fertiliser run-off causing algal blooms that remove oxygen |
| Rhizobium | nitrogen-fixing bacteria living in root nodules of legumes |
Model exam answers, grammar & audio
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