4.3 Carbon Cycling Flashcards
What is the carbon cycle?
The carbon cycle is a biogeochemical cycle whereby carbon is exchanged between the different spheres of the Earth
What are the four spheres?
The four spheres are the atmosphere (air), lithosphere (ground), hydrosphere (water / oceans) and biosphere (living things)
In what 4 forms can carbon be exchanged?
atmospheric gases
oceanic carbonates
organic materials
non-living remains
In what form can carbon be found in atmospheric gases?
mainly carbon dioxide (CO2), but also methane (CH4)
In what form can carbon be found in atmospheric gases?
mainly carbon dioxide (CO2), but also methane (CH4)
In what form can carbon be found in oceanic carbonates?
including bicarbonates dissolved in the water and calcium carbonate in corals and shells
In what form can carbon be found in organic materials?
including the carbohydrates, lipids and proteins found in all living things
In what form can carbon be found in living remains?
as detritus and fossil fuels
How do autotrophs convert inorganic compounds?
Autotrophs, such as all plants and algae, convert inorganic carbon dioxide into organic compounds via photosynthesis
What organic compounds is CO2 converted into via photosynthesis?
These organic compounds include the carbohydrates, lipids and proteins required by the organism for survival
What levels of CO2 should autotrophs have?
Since autotrophs use carbon dioxide for photosynthesis, the levels of carbon dioxide within the organism should always be low
In which sphere should there be a higher conc of CO2?
In other words, carbon dioxide should always be at a higher concentration in the atmosphere (or water)
What does the differing concentration of CO2 ensure?
This concentration gradient ensures that carbon dioxide will passively diffuse into the autotrophic organism as required
How does diffusion of CO2 differ in aquatic and terrestrial autotrophs?
In aquatic producers, CO2 can usually diffuse directly into the autotroph; whereas in terrestrial plants, diffusion occurs at stomata
What do all organisms produce to survive?
All organisms may produce the chemical energy (ATP) required to power metabolic processes via the process of cell respiration
What does cell respiration involve?
Cell respiration involves the breakdown of organic molecules (e.g. sugars) and produces carbon dioxide as a by-product
What is a result of respiration? How is this useful?
The build up of CO2 in respiring tissues creates a concentration gradient, allowing it to be removed by passive diffusion
In autotrophs, what may happen in relation to these two processes?
In autotrophs, the uptake of CO2 by photosynthesis may at times be balanced by the production of CO2 by respiration
What is it called when rate of photosynthesis=rate of respiration?
This is known as the compensation point, at which the net carbon dioxide assimilation is zero (intake = output)
What determines the level of carbon dioxide in the environment? (2 relating to net ___)
If there is more net photosynthesis than cell respiration occuring in the biosphere, atmospheric carbon dioxide levels should drop
If there is more net respiration than overall photosynthesis occuring, atmospheric carbon dioxide levels should increase
What happens when Co2 dissolves in water?
Carbon dioxide dissolves in water and some of it will remain as a dissolved gas, however the remainder will combine with water to form carbonic acid
Give equation for CO2 dissolving in water
CO2 + H2O ⇄ H2CO3
What happens to carbonic acid + equation?
Carbonic acid will then dissociate to form hydrogen carbonate ions (H2CO3 ⇄ HCO3– + H+)
What causes the change in pH of the ocean?
This conversion (H2CO3) also releases hydrogen ions (H+), which is why pH changes when CO2 is dissolved in water (> acidic)
What do autotrophs absorb in relation to ocean CO2?
Autotrophs absorb both dissolved carbon dioxide and hydrogen carbonate ions and use them to produce organic compounds
What can hydrogen carbonate ions come into contact with in the ocean?
When the hydrogen carbonate ions come into contact with the rocks and sediments on the ocean floor, they acquire metal ions
What can the contact between HCO3- ions with rocks and sediments form?
This commonly results in the formation of calcium carbonate and the subsequent development of limestone
How can CaCO3 be formed in oceans?
Living animals may also combine the hydrogen carbonate ions with calcium to form calcium carbonate
What is the use of calcium carbonate in aquatic environments?
This calcium carbonate forms the hardened exoskeleton of coral, as well as forming the main component of mollusca shells
What happens to the calcium carbonate when an organism dies?
When the organism dies and settles to the sea floor, these hard components may become fossilised in the limestone
What are methanogens?
Methanogens are archaean microorganisms that produce methane (CH4) as a metabolic by-product in anaerobic conditions
Where can methanogens be found?
Anaerobic conditions where methanogens may be found include:
Wetlands (e.g. swamps and marshes)
Marine sediments (e.g. in the mud of lake beds)
Digestive tract of ruminant animals (e.g. cows, sheep, goats)
What do methanogens produce and how?
Methanogens produce methane from the by-products of anaerobic digestion, principally acetic acid and carbon dioxide:
How is acetic acid used in methanogens? give equation
Acetic acid → Methane and Carbon Dioxide (CH3COO– + H+ → CH4 + CO2)
How is CO2 and H2O used by methanogens? Give equation
Carbon Dioxide and Hydrogen → Methane and Water (CO2 + 4 H2 → CH4 + 2 H2O)
What happens to released methane?
Methane may either accumulate under the ground or diffuse into the atmosphere
How may natural gas be formed?
When organic matter is buried in anoxic conditions (e.g. sea beds), deposits of methane (natural gas) may form underground
What may be increasing global levels of methane?
Rising global numbers of domesticated cattle may be increasing the levels of methane being released into the atmosphere
How long does methane persist in the atmosphere?
When methane is released into the atmosphere as a result of anaerobic reactions, it only persists for ~12 years
Why are methane levels in the atmosphere are not very large, even though significant quantities are being produced ?
Methane will be naturally oxidised to form carbon dioxide and water (CH4 + 2 O2 → CO2 + 2 H2O)
What is methane oxidised to? Give equation
Methane will be naturally oxidised to form carbon dioxide and water (CH4 + 2 O2 → CO2 + 2 H2O)
How are nutrients recycled in soil?
In many soils, saprotrophic bacteria and fungi will decompose dead organisms and return nutrients to the soil for cycling
What does the process of decomposition require?
This decomposition process requires oxygen (cell respiration is required to fuel digestive reactions)
Where is aerobic decomposition not possible?
Waterlogged regions may lack oxygenated air spaces within the soil and thus possess anaerobic conditions
What does anaerobic respiration form?
Anaerobic respiration by organisms in these regions produces organic acids (e.g. acetate), resulting in acidic conditions
What do the acidic conditions (in soils) prevent?
Saprotrophic bacteria and fungi cannot function effectively in anaerobic / acidic conditions, preventing decomposition
What is formed due to the incomplete decomposition of organic matter?
Since the organic matter is not fully decomposed in waterlogged soils, carbon-rich molecules remain in the soil and form peat
What happens when peat is compressed?
When deposits of peat are compressed under sediments, the heat and pressure force out impurities and remove moisture
How is coal produced from peat?
The remaining material has a high carbon concentration and undergoes a chemical transformation to produce coal
In general, how is oil and natural gas formed?
Oil (i.e. petroleum) and natural gas form as the result of the decay of marine organisms on the ocean floor
In aquatic ecosystems, what is deposited upon organic matter to start the formation of oil/natural gas?
Sediments (e.g. clay and mud) are deposited on top of the organic matter, creating anoxic conditions that prevent decomposition
What is a result of the material compaction in aquatic ecosystems?
As a result of the burial and compaction, the organic material becomes heated and hydrocarbons are formed
What do the hydrocarbons form? (aquatic ecosystem)
The hydrocarbons form oil and gas, which are forced out of the source rock and accumulate in porous rocks (e.g. sandstone)
How long does it take for various fossil fuels to be formed?
The formation of fossil fuels (coal, oil and gas) takes place over millions of years, making them a non-renewable energy source
What is a combustion reaction? (conditions)
When organic compounds rich in hydrocarbons are heated in the presence of oxygen, they undergo a combustion reaction
What type of reaction is combustion?
This reaction is exergonic (produces energy) and releases carbon dioxide and water as by-products
What happens to the carbon dioxide produced by combustion?
The carbon dioxide is typically released into the atmosphere, increasing the concentration of the gas in the air
What happens to organic compounds when they’re compacted for millions of years?
Organic compounds can become rich in hydrocarbons when compacted underground for millions of years
What does compaction trigger in order to make organic matter rich in hydrocarbons?
The heat and pressure over time triggers a chemical transformation that results in the compaction of the organic matter
What is produced by the compaction of organic matter?
The resulting products of this process are fossil fuels (coal, oil and natural gas)
Why are fossil fuels considered non-renewable?
Because this geological process takes millions of years to occur, fossil fuels are a non-renewable energy source
What is another way to manufacture fuels, reducing dependence on fossil fuels?
An alternative to relying on fuels produced by geological processes is to manufacture fuels from biological processes
What do living organisms produce which are useful for fuels?
Living organisms produce hydrocarbons as part of their total biomass (either for use or as a waste product)
What can be done with the hydrocarbons produced by organisms?
These hydrocarbons can be extracted and purified to produce an alternative fuel source (e.g. bioethanol and biodiesel)
Why is biomass considered a “better” fuel source?
Provided new raw materials are provided and waste products are removed, this source of energy is renewable
What are carbon fluxes?
Carbon fluxes describe the rate of exchange of carbon between the various carbon sinks / reservoirs
What are the 4 main carbon sinks?
There are four main carbon sinks – lithosphere (earth crust), hydrosphere (oceans), atmosphere (air), biosphere (organisms)
What does the rate of carbon exchange depend on?
The rate at which carbon is exchanged between these reservoirs depends on the conversion processes involved
What is the role of photosynthesis in the carbon cycle?
removes carbon dioxide from the atmosphere and fixes it in producers as organic compounds
What is the role of respiration in the carbon cycle?
releases carbon dioxide into the atmosphere when organic compounds are digested in living organisms
What is the role of decomposition in the carbon cycle?
releases carbon products into the air or sediment when organic matter is recycled after death of an organism
What is the role of gaseous disolution in the carbon cycle?
the exchange of carbon gases between the ocean and atmosphere
What is the role of lithification in the carbon cycle?
the compaction of carbon-containing sediments into fossils and rocks within the Earth’s crust (e.g. limestone)
What is the role of combustion in the carbon cycle?
releases carbon gases when organic hydrocarbons (coal, oil and gas) are burned as a fuel source
Is it possible to measure the size of carbon sinks?
NO
It is not possible to directly measure the size of the carbon sinks or the fluxes between them – instead estimates are made
How are global carbon fluxes measured?
Global carbon fluxes are very large and are therefore measured in gigatonnes (1 gigatonne of carbon = 1 billion metric tonnes)
Are carbon flux calculations accurate?
Because carbon fluxes are large and based on measurements from many different sources, estimates have large uncertainties
What does estimating carbon fluxes require?
estimating carbon fluxes requires an understanding of the factors that can affect the exchange of carbon between different sinks
What are some of the main causes for flux changes?
Some of the main causes for flux change include climate conditions, natural events and human activity
Climate conditions
When will rates of photosynthesis be higher?
Rates of photosynthesis will likely by higher in summer seasons, as there is more direct sunlight and longer days
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how do oceanic temepratures affect co2?
Oceanic temperatures also determine how much carbon is stored as dissolved CO2 or as hydrogen bicarbonate ions
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how do climate events change carbon flux?
Climate events like El Nino and La Nina will change the rate of carbon flux between ocean and atmosphere
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how does the melting of polar ice caps affect carbon fluxes?
Melting of polar ice caps will result in the decomposition of frozen detritus
what two natural events can affect co2 concentrations?
forest fires
volcanic eruptions
How do forest fires affect co2 conc?
Forest fires can release high levels of carbon dioxide when plants burn (loss of trees also reduces photosynthetic carbon uptake)
How do volcanic eruptions affect carbon dioxide concentration?
Volcanic eruptions can release carbon compounds from the Earth’s crust into the atmosphere
What 3 human activities affect carbon dioxide concentration?
clearing of trees
ruminant livestock
fossil fuels
How does clearing of trees affect co2 conc?
Clearing of trees for agricultural purposes (deforestation) will reduce the removal of atmospheric CO2 via photosynthesis
How does increased number of ruminant livestock affect co2 conc?
Increased numbers of ruminant livestock (e.g. cows) will produce higher levels of methane
Who has measured atmospheric co2 concs and where?
Atmospheric CO2 concentrations have been measured at the Mauna Loa Observatory (in Hawaii) since 1958 by Charles Keeling
(findings from Charles Keeling)
how often do co2 levels flc=uctuate?
CO2 levels fluctuate annually (lower in the summer months when long days and more light increase photosynthetic rates)
(findings from Charles Keeling)
WHat will global co2 patterns conform to and why?
Global CO2 trends will conform to northern hemisphere patterns as it contains more of the planet’s land mass (i.e. more trees)
(findings from Charles Keeling)
How are CO2 levels changing?
CO2 levels are steadily increasing year on year since the industrial revolution (due to increased burning of fossil fuels)
(findings from Charles Keeling)
How are CO2 levels now?
Atmospheric CO2 levels are currently at the highest levels recorded since measurements began
Why may different monitoring stations have different trends in CO2?
Different monitoring stations may have slightly different trends due to seasonal variations and the distribution of local vegetation
