Lesson #4: The Carbon Cycle Flashcards
(12 cards)
Carbon
Carbon is a component of ALL organic molecules.
These four unique features of carbon allow it to be the basis of all life on Earth.
Carbon has 4 available binding sites
Carbon can form single, double or triple covalent bonds
Carbon is able to bond covalently with a large number of elements
Carbon can form both long chains and rings of atoms
Carbon Fixation
Carbon is abundant in the atmosphere an inorganic form, carbon dioxide
(CO2).
Autotrophs can convert carbon dioxide into carbohydrates, lipids and other
organic compounds through photosynthesis.
Since carbon dioxide is being converted inside cells there is a concentration
gradient established in which the inside of autotrophs has a lower
concentration than the surrounding environment.
This leads to diffusion of carbon dioxide into autotrophs.
Photosynthesis occurs according to the equation:
6 CO2 + 6 H2O + sunlight 🡪 C6H12O6 + 6 O2
Aquatic Carbon
In aquatic ecosystems, carbon enters the system in two ways:
As dissolved gas in the water
Combined with water to form carbonic acid which can ionize to produce
hydrogen ions and hydrogen carbonate ions, lowering the pH of the water.
Both dissolved carbon dioxide and hydrogen carbonate ions can be absorbed
by aquatic autotrophs through the process of diffusion.
Aerobic Cellular Respiration
Carbon dioxide is returned to the atmosphere or water through the process of cellular
respiration.
Carbon dioxide is a waste product of aerobic cellular respiration carried out by cells.
Carbon dioxide produced by respiration diffuses out of cells and enters the atmosphere or
water.
Organisms that perform cellular respiration are:
Plants
Animals
Saprotrophs
Cellular respiration occurs according to the equation:
6 02 + C6H1206 🡪 6 CO2 + 6 H2O + energy
Anaerobic Respiration
Methane is produced from organic matter in anaerobic conditions.
Three different groups of anaerobic prokaryotes are involved:
Bacteria that convert organic matter into a mixture of organic acids, alcohol,
hydrogen and carbon dioxide
Bacteria that use organic acids and alcohol to produce acetate carbon dioxide and
hydrogen
Archeans that produce methane from carbon dioxide, hydrogen and acetate.
Methane in the atmosphere persists for about 12 years. Methane is then oxidized to
carbon dioxide
Combustion
Carbon dioxide is produced by the combustion of biomass and fossilized
organic matter.
If organic matter is heated to ignition in the presence of oxygen carbon
dioxide and water will be produced.
Natural wildfires, coal, oil and natural gas are all sources of carbon dioxide in
the atmosphere through combustion.
Carbon Sinks
Situations in which carbon is bound up and not available for use by autotrophs.
There are several situations in which this occurs:
Peat
Limestone
Fossilized organic matter
Peat
Saprotrophs obtain oxygen from air spaces in the soil.
In environments where water is unable to drain these air spaces become filled
with water and the saprotrophs cannot thrive.
This leads to incomplete decomposition of organic matter.
Acid conditions tend to develop, which further inhibits decomposition.
Partially decomposed organic matter accumulates in these areas.
This gets compressed to form a dark brown acidic material known as peat.
About 3% of the Earth’s land surface is covered by peat to a depth of about 10
meters.
Limestone
Some animals have hard body parts made of calcium carbonate such as hard corals and
molluscs.
When these animals die, their soft parts are decomposed and in acid conditions the calcium
carbonate dissolves.
In neutral and alkaline conditions, the calcium carbonate deposits on the sea floor.
In some shallow tropical seas carbonate is also deposited by precipitation.
The result of this deposition is limestone rock, where hard parts of animals are often visible
as fossils.
Approximately 10% of all sedimentary rock on Earth is limestone. Since 12% of the mass of
calcium carbonate is carbon.
This binds up a large amount of carbon.
Fossilized Organic Matter
Carbon and some of the compounds it forms are very stable. There are large deposits
of carbon from past geological eras.
These deposits are the result of incomplete decomposition of organic matter on its
burial in sediments that became rock.
Coal – formed when deposits of peat are buried under other sediments. The peat is
compressed and heated, gradually turned into coal.
Large coal deposits were formed during the Carboniferous period.
Oil and natural gas – formed in the mud at the bottom of seas and lakes.
Partially decomposed matter is compressed and heated, chemical changes occur
which produce a complex mixture of liquid carbon compounds or gases.
These are called crude oil and natural gas.
Human Activity and the Carbon Cycle
Humans release excessive amounts of carbon dioxide into the atmosphere
through industrial processes and the burning of fossil fuels.
This excess carbon dioxide and methane in the atmosphere leads to an
increase in the greenhouse effect which is driving climate change.
Excess carbon dioxide in the oceans leads to ocean acidification which affects
ocean life and the ability of the ocean to create limestone as a carbon sink.
The Oxygen Cycle
The cycling of oxygen is
linked to the carbon
cycle.
oxygen is released
during
photosynthesis
oxygen is used
during respiration
