IB Biology 4.3 Carbon cycling

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Which organisms take inorganic carbon dioxide and fit it into organic carbon compounds?
Autotrophs
From where do autotrophs obtain the carbon dioxide?
Carbon dioxide can be obtained from air or from water.
How is inorganic carbon dioxide returned to the ecosystem?
Cell respiration produces carbon dioxide from organic carbon compounds.
Outline the production of methane and how it is converted into carbon dioxide.
1. Methane (CH4) is produced from organic carbon compounds in anaerobic conditions.
2. Anaerobic conditions occur in waterlogged land.
3. Methanogenic archaeans partially break down organic compounds to form methane.
4. Methane can accumulate in the ground or diffuse into the atmosphere.
5. Methane does not build up to high levels in the atmosphere as it is oxidised to form carbon dioxide and water.
Outline the formation of coal.
1. Acidic conditions denature enzymes involved in cell respiration.
2. Partially decomposed plant remains build-up over time and form peat.
3. Over geological eras, peat is converted to coal.
Outline the formation of oil and gas.
1. Silt and organic remains are deposited.
2. Partial decomposition occurs.
3. Over geological eras, silt is converted to shale with the organic carbon compounds being converted to oil or gas that is trapped in the porous rock.
Outline the formation of limestone.
1. The shells of marine molluscs are made of calcium carbonate (CaCO3).
2. Corals build reefs.
3. Their hard outer skeletons are made of calcium carbonate.
4. When marine molluscs and corals die, debris from their shells and skeletons accumulate on the sea floor as sediment.
5. Over geological eras, this sediment forms limestone.
6. The shells of marine molluscs and coral skeletons may become fossilised in limestone.
How can carbon be locked away in biomass and fossil fuels and be released as carbon dioxide into the atmosphere?
Carbon locked away in biomass and fossil fuels can be released by combustion.
How can carbon be locked away in limestone and be released as carbon dioxide into the atmosphere?
- Carbon can be released from limestone by the action of acid.
- Rain is acidic due to the formation of carbonic acid when carbon dioxide reacts with water and this results in the release of carbon dioxide into the atmosphere.