4.3 - Carbon Cycling Flashcards
Essential idea:
Continued availability of carbon in ecosystems depends on carbon cycling.
4.3.U1 Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds.
All autotrophs however convert carbon dioxide (from the atmosphere or dissolved in water) or into organic compounds.
Plant initially synthesis sugars (e.g. glucose) which are then converted into other organic compounds such as:
complex carbohydrates e.g. starch, cellulose
lipids
amino acids
4.3.U2 In aquatic ecosystems carbon is present as dissolved carbon dioxide and hydrogen carbonate ions.
Some CO2 will directly dissolve in water, but most will combine with water to become carbonic acid.
Both dissolved carbon dioxide and hydrogen carbonate ions are absorbed by aquatic plants and other autotrophs that live in water.
Free H+ ions explains how carbon dioxide reduces the pH of water.
CO2 + H2O → H2CO3 → H+ + HCO3–
4.3.U3 Carbon dioxide diffuses from the atmosphere or water into autotrophs
Plants must have a constant supply of carbon dioxide (CO2) to continually photosynthesize
CO2 from outside the leaf diffuses down the concentration gradient into the leaf
Photosynthesis uses CO2 keeping the concentration of CO2 inside the leaf low
*Some aquatic plants, e.g. water lilies have stomata, but in many fully submerged plants diffusion happens directly through the surface tissues.
4.3.U4 Carbon dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere.
Organisms carry out respiration to release energy in the form of ATP. Carbon dioxide is a waste product of cell respiration
terms of the carbon cycle three main categories of organisms carry out respiration:
autotrophs, e.g. plants
heterotrophs, e.g. animals
saprotrophs and decomposers, e.g. fungi and bacter
Describe peat
Partially decomposed organic matter can be compressed to form brown soil-like peat
Peat is a highly effective carbon sink,
it is estimated that the world’s peat contains 550 Gt of carbon
Once dried peat burns easily and can be used as a fuel.
In soils organic matter, e.g. dead leaves, are digested by saprotrophic bacteria and fungi.
Saprotrophs assimilate some carbon for growth and release as carbon dioxide during aerobic respiration.
Aerobic respiration requires oxygen
Waterlogged soils are an anaerobic environment
saprotrophs and methanogens [4.3.U5] are inhibited
Organic matter is only partially decomposed
Partial decomposition causes acidic conditions
Large quantities of (partially decomposed) organic matter build up.
The organic matter is compressed to form peat
formation of coal
Coal is formed when deposits of peat are buried under other sediments.
The peat is compressed and heated over millions years eventually becoming coal.
The cycle of sea-level changes that happened during the Carboniferous period caused costal swamps to be buried promoting the formation of coal.
oil and gas formation
oil and gas formation occurred in ancient oceans
300-400 million years ago, tiny sea plants and animals died and were buried on the ocean floor. Overtime, they were covered by layers of silt and sand. Conditions are anaerobic so decomposition i sonly partial.
over millions of years, the remains were buried deeper and deeper. Th e enormous heat and pressure turned them into oil and gas.
The mixture of different types of oil and gas is the result of complex chemical changes.
Methane forms the largest part of natural gas.
limestone formation
Some animals secrete calcium carbonate (CaCO3) structures to protect themselves:
Shells of molluscs
Hard corals exoskeletons
When the animals die the soft body parts decompose, but the calcium carbonate remains to form deposits on the ocean floor.
The deposits are buried and compressed and eventually form limestone rock.
Imprints of the hard body parts remain in the rock as fossils.
Limestone rock is a huge carbon sink.
4.3.U9 Carbon dioxide is produced by the combustion of biomass and fossilized organic matter.
If heated dried biomass or fossilized fuels will burn in the presence of oxygen
Fossil/Biomass fuel + O2 → CO2 + H2O
Methanogens
Methanogens are archaean microorganisms that produce methane as a metabolic byproduct in anoxic conditions.
Typically during ATP production methane is produced from carbon dioxide.
Methanogens are found in a variety of anoxic (low oxygen) environments:
Wetlands (e.g. paddies, swamps and mangroves)
Digestive tracts of animals (e.g. cows, humans and termites)
Marine and freshwater sediments (e.g. mud in the beds of lakes)
Landfill sites (in which organic matter has been buried)
4.3.U6 Methane is oxidized to carbon dioxide and water in the atmosphere.
Measurements indicate that the levels of atmospheric methane are increasing
It is estimated that, on average, methane persists in the atmosphere for 8.4 years.
Methane released into the atmosphere can be removed by a number of mechanisms.
The most important process of methane removal is oxidation by hydroxyl radicals.
methane+ hydroxyl radical → carbon dioxide + water
4.3.A1 Estimation of carbon fluxes due to processes in the carbon cycle.
It is not possible to measure the size of carbon sinks and the fluxes between them. Estimates are based on many different measurements are often published with large uncertainties as a result.
What is the evidance for increasing levels of CO2 in the atmosphere?
Recent data has been easy to collect experimentally
Over 40 years, charles keeling measured atmospheric co2 from his observatory in Mauna Loa, and the keeling curve has become an icon of climate science
my field stations globally use the same standardized method. All stations show a clear upward trend with annual cycles.
Historical data takes more effort to collect and is more variable in the reliability of the results produced.
Ice cores are a good source of co2 data, where researchers can analyse the co2 concentration of air bubbles trapped in the ice and estimate year based on depth of the core.
