Biology 4.3 Flashcards
Carbon Cycle
biological cycle whereby carbon is exchanged between the different species of the earth
- atmosphere
- litosphere
- hydrosphere
- bioshpere
Carbon is exchanges in variety of forms
- atmospheric gases
- organic materials
- non-living remains
draw the carbon cycle
transferance of carbon compounds on land
autotrophs convert inorganic compounds via photosynthesis
- includes carbs, lipds and proteins
as autotrophs use CO2 for photosynthesis, the level of CO2 withing organisms should always be low
- CO2 conc should alwayds be higher in atmosphere
- this conc gradient ensures that CO2 will passively diffuse into autotrophic organisms
heterotrophs cannot synthesise their own organic molecules - so they obtain it through feeding
All organisms may produce ATP via cell respiration
In autotrophs the uptake of CO2 by photosynthesis may at times be balanced by the production of CO2
Aquatic conversion of Carbon compounds
CO2 dissolves in H2O and some of it will remain as dissolved gas, however the remainder will combine with water to form carbonic acid –> H2O+CO2⇌H2CO3
- H2CO3 will then dissociate to form hydrogen carbonate ions
- also releases H+ ions, that lead to change in pH
- autotrophs absorb both dissolved CO2 and HCO3- and use them to produce organic compounds
Fossilization of Limestone
when HCO3- come into contact with the rocks and sediments on the ocean floor, they acquire metal ions
- commonly result in the formation of CaCO3 and the formation of LIMESTONE
living animals may also combine the hydrogen carbonate ions with calcium to form CaCO3
- this forms the hardened exoskeleton of coral, and mollusca shells
- when the organism dies, and settles on the ocean floor, hard components may become fossilised in the limestone
methane production
methanogens are archean microorganisms that produce methane as a metabolic by-product in anaerobic conditionds
found in:
- wetlands
- marine sediments
- digestive trat of ruminant animals
acetic acid –> methane + CO2
or
CO2 + H2 –> methane + water
methane may either accumulate under ground or diffuse into the atmosphere
- when organic matter burried in anoxic conditiond, deposits of methane may form underground
- rising global numbers of domestic cattle may include levels of methane
when methane is released into the atmosphere as a result of anaerobic reactions, it only persists for 12 yrs, and will naturally oxidise to form CO2 and H2O
Partial decomposition
In many soils, saprotrophic bacteria and fungi will decompose dead organisms and return nutrients to the soil for cycling
- This decomposition process requires oxygen (cell respiration is required to fuel digestive reactions)
Waterlogged regions may lack oxygenated air spaces within the soil and thus possess anaerobic conditions
- Anaerobic respiration by organisms in these regions produces organic acids (e.g. acetate), resulting in acidic conditions
- Saprotrophic bacteria and fungi cannot function effectively in anaerobic / acidic conditions, preventing decomposition
Coal formation
Since the organic matter is not fully decomposed in waterlogged soils, carbon-rich molecules remain in the soil and form peat
- When deposits of peat are compressed under sediments, the heat and pressure force out impurities and remove moisture
- The remaining material has a high carbon concentration and undergoes a chemical transformation to produce coal
Oil/natural gas formation
Oil (i.e. petroleum) and natural gas form as the result of the decay of marine organisms on the ocean floor
- Sediments (e.g. clay and mud) are deposited on top of the organic matter, creating anoxic conditions that prevent decomposition
- As a result of the burial and compaction, the organic material becomes heated and hydrocarbons are formed
- The hydrocarbons form oil and gas, which are forced out of the source rock and accumulate in porous rocks (e.g. sandstone)
combustion of biomass and fossilised organic matter
When organic compounds rich in hydrocarbons are heated in the presence of oxygen, they undergo a combustion reaction
- This reaction is exergonic (produces energy) and releases carbon dioxide and water as by-products
- The carbon dioxide is typically released into the atmosphere, increasing the concentration of the gas in the air
Combustion sources : Fossil Fuels
Organic compounds can become rich in hydrocarbons when compacted underground for millions of years
- The heat and pressure over time triggers a chemical transformation that results in the compaction of the organic matter
- The resulting products of this process are fossil fuels (coal, oil and natural gas)
- Because this geological process takes millions of years to occur, fossil fuels are a non-renewable energy source
Combustion sources: Biomass
An alternative to relying on fuels produced by geological processes is to manufacture fuels from biological processes
- Living organisms produce hydrocarbons as part of their total biomass (either for use or as a waste product)
- These hydrocarbons can be extracted and purified to produce an alternative fuel source (e.g. bioethanol and biodiesel)
- Provided new raw materials are provided and waste products are removed, this source of energy is renewable
carbon fluxes
rate of exchange of carbon between carbon sinks
- lithosphere
- hydrosphere
- atmosphere
- biosphere
what does the rate of carbon exchange depend on?
conversion processes
- Photosynthesis – removes carbon dioxide from the atmosphere and fixes it in producers as organic compounds
- Respiration – releases carbon dioxide into the atmosphere when organic compounds are digested in living organisms
- Decomposition – releases carbon products into the air or sediment when organic matter is recycled after death of an organism
- Gaseous dissolution – the exchange of carbon gases between the ocean and atmosphere
- Lithification – the compaction of carbon-containing sediments into fossils and rocks within the Earth’s crust (e.g. limestone)
- Combustion – releases carbon gases when organic hydrocarbons (coal, oil and gas) are burned as a fuel source
What factors affec thte exchange of carbon between different sinks?
Climate conditions
Natural events
Human activity
