4.3 Carbon cycling Flashcards
Autotrophs absorb CO2 from the atmosphere and convert it into
organic compounds.
Reduces the concentration of CO2 in the atmosphere (approximately 0.039% or 390 micromoles/mole)
Some CO2 will directly dissolve
in water (soluble), but most will combine with water to become carbonic acid.
Carbonic acid can dissociate to
form H+ and HCO3- (bicarbonate/ hydrogen carbonate)
H+ ions explains how carbon dioxide reduces
pH of water.
Both dissolved carbon dioxide and hydrogen carbonate ions are absorbed by
aquatic plants and other autotrophs that live in water.
Photosynthesis uses CO2 keeping the
concentration of CO2 inside the leaf low,
maintains concentration gradient of CO2
CO2 from outside the leaf diffuses down the concentration gradient into
the leaf
CO2 moves through the
stomatal pores in the leaves of land plants
In many aquatic plants diffusion happens directly through the surface tissues.
CO2 is a
waste product of aerobic cell respiration
Methanogens
are archaean microorganisms that produce methane as a metabolic byproduct in anaerobic respiration (methane is produced from carbon dioxide)
Methanogens are found in a variety of anaerobic environments:
Wetlands (paddies, swamps and mangroves)
Digestive tracts of animals (cows, humans, termites)
Marine & freshwater sediments (mud in lakebeds)
Landfill sites (in which organic matter has been buried)
Measurements indicate that the levels of atmospheric methane are
increasing
It is estimated that, on average, methane persists in the atmosphere for
12 years (naturally oxidized in the stratosphere)
The most important process of methane removal is
oxidation by hydroxyl radicals.
methane + hydroxyl radical → carbon dioxide + water
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
it is estimated that the world’s peat contains 550 Gt of carbon
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.
How does peat form?
Organic matter, e.g. dead leaves
Saprotrophs assimilate some carbon for growth and release as carbon dioxide during aerobic respiration.
Waterlogged soils are an anaerobic environment
saprotrophs and methanogens 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
There are _____________– of carbon from past geological eras
large deposits
These deposits of carbon are the result of
incomplete decomposition of organic matter and its burial in sediment that become rock
Coal is formed when
deposits of peat are buried under other sediments.
The peat is compressed and heated over millions of years eventually becoming coal.
Oil and natural gas are formed in the
mud at the bottom of seas and lakes
Anaerobic conditions mean decomposition is incomplete
As mud and sediment are deposited, the partially decomposed organic matter is compressed and heated
Chemical changes produce mixtures of liquid carbon compounds or gases
Methane forms the largest part of natural gas
Deposits are mostly found in porous rocks
Combustion
heated dried biomass or fossilized fuels will burn in the presence of oxygen
Fossil/Biomass fuel + O2 → CO2 + H2O
Natural forest/grass fires occur in some regions (organisms adapted to periodic fires)
Human-caused fires also occur to clear areas for agriculture or as a method of harvesting
Some animals are composed of
calcium carbonate (CaCO3) structures made by secretion:
Mollusc shells
Hard corals exoskeletons
When the animals die the soft body parts decompose, but the calcium carbonate remains to ____________ on the ocean floor (in acidic conditions CaCO3 dissolves)
form deposits
The deposits are buried and eventually
form limestone rock.
Limestone rock is a huge carbon sink
Imprints of the hard body parts remain in rock as
fossils.
The carbon cycle explains the
exchange of carbon between the biosphere, lithosphere, hydrosphere, and atmosphere.
Pool
reserve of C (can be organic or inorganic)
Flux
transfer of C from one pool to another
