4.3: Carbon Cycling
*Define "flux" as related to the carbon cycle.* Application: Estimation of carbon fluxes due to processes in the carbon cycle.
A carbon flux is the exchange of carbon between Earth's carbon pools.
*State the molecular formula for the hydrogen carbonate ion.* Understanding: In aquatic ecosystems carbon is present as dissolved carbon dioxide and hydrogen carbonate ions.
Hydrogen carbonate ion= Bicarbonate= HCO₃⁻.
*Define "fossilization."* Understanding: Partially decomposed organic matter from past geological eras was converted either into coal or into oil and gas that accumulate in porous rocks.
If conditions are not favourable for the process of decomposition, dead organisms decay slowly or not at all. These organisms build up and, if compressed over millions of years, can form fossil fuels (coal, oil or gas).
*State the formula for the oxidation of methane to carbon dioxide that occurs in the atmosphere.* Understanding: Methane is oxidized to carbon dioxide and water in the atmosphere.
In the atmosphere, methane (CH₄) is oxidized (gains oxygen and loses hydrogens) when it reacts with atmospheric oxygen (O₂). The result is carbon dioxide and water vapor. CH₄ + 2O₂ → CO₂ + 2H₂O
*List flux processes in the carbon cycle.* Application: Estimation of carbon fluxes due to processes in the carbon cycle.
Photosynthesis Respiration Decomposition Diffusion Lithification Combustion Fossilization Feeding
*Explain the reduction of the pH in water when carbon dioxide is added.* Understanding: In aquatic ecosystems carbon is present as dissolved carbon dioxide and hydrogen carbonate ions.
When CO₂ combines with H₂O, hydrogen and hydrogen carbonate ions (H⁺ and HCO₃⁻) are formed. The increased [H⁺] will cause a reduction in the pH of the solution. Reduced pH = more acidic
*State the role of respiration in the carbon cycle.* Understanding: Carbon dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere.
All living things respire, the metabolic process of converting biochemical energy from nutrients into adenosine triphosphate (ATP) for cellular work. CO₂ is a waste product of respiration. Respiration converts organic carbon molecules into inorganic carbon molecules which then diffuse into water or the atmosphere.
*Outline formation of oil and natural gas.* Understanding: Partially decomposed organic matter from past geological eras was converted either into coal or into oil and gas that accumulate in porous rocks.
All of the oil and gas available today began as microscopic plants and animals living in the ocean millions of years ago. As these microscopic plants and animals lived, they stored carbon molecules in their bodies. When they died, they sank to the bottom of the sea. Over millions of years, layer after layer of sediment were formed. As they became buried ever deeper, heat and pressure began to rise. The amount of pressure and the degree of heat, along with the type of biomass, determines if the material becomes oil or natural gas. The gas or oil then accumulates in tiny pores in the surrounding rock.
*Define "autotroph."* Understanding: Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds.
An autotroph is *an organism capable of making energy-containing organic molecules from inorganic sources* via photosynthesis (involving light energy) or chemosynthesis (involving chemical energy).
*State the role of photosynthesis in the carbon cycle.* Understanding: Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds.
Autotrophs take in carbon from the atmosphere in the form of CO₂. They then use the carbon atoms from the CO₂ in the process of photosynthesis to make sugars, proteins and lipids for their growth. Photosynthesis *converts inorganic carbon molecules into organic carbon molecules.*
*List pools of carbon in the carbon cycle.* Application: Estimation of carbon fluxes due to processes in the carbon cycle.
Biosphere (living things, terrestrial and aquatic) Pedosphere (soil) Geosphere (rocks and Earth's crust) Hydrosphere (water, mostly ocean) Atmosphere Fossil fuels
*Outline the role of diffusion in the carbon cycle.* Understanding: Carbon dioxide diffuses from the atmosphere or water into autotrophs.
CO₂ diffuses into autotrophs from the atmosphere or water. Without diffusion of CO₂, autotrophs would not have a carbon source for performing photosynthesis. A waste product of cellular respiration, CO₂ diffuses out of living things to the atmosphere or water.
*Outline the process that converts carbon dioxide to hydrogen carbonate ion in water.* Understanding: In aquatic ecosystems carbon is present as dissolved carbon dioxide and hydrogen carbonate ions.
CO₂ diffuses into water. Some will remain as a dissolved gas. The remainder will combine with water to form carbonic acid (CO₂ + H₂O ⇄ H₂CO₃) which dissociates to form hydrogen and hydrogen carbonate ions (H⁺ and HCO₃⁻).
*Draw a diagram of the terrestrial carbon cycle.* Skill: Construct a diagram of the carbon cycle.
CO₂ in atmosphere linked to producer (plant) with an arrow labeled photosynthesis; Producer linked to consumer (animal) with an arrow labeled feeding; Producer and consumer linked to CO₂ in the atmosphere with an arrow labeled (cell) respiration; Producer and consumer linked to decomposers (bacteria or fungi) with an arrow labeled decomposition; Decomposers linked to CO₂ in the atmosphere with an arrow labeled cell respiration; Producer linked to CO₂ in the atmosphere with an arrow labeled combustion; Producers, consumers and decomposers linked to fossil fuels (coal, oil, natural gas) with arrow labeled fossilization; Fossil fuels linked to CO₂ in the atmosphere with an arrow labeled combustion; Methanogenic bacteria linked to methane in the atmosphere with an arrow labeled anaerobic respiration; Methane linked CO₂ in the atmosphere with an arrow labeled oxidization;
*State the molecular formula for carbon dioxide.* Understanding: Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds.
Carbon dioxide = *CO₂* One carbon atom with double bonds to two oxygen atoms.
*Define "pool" as related to the carbon cycle."* Application: Estimation of carbon fluxes due to processes in the carbon cycle.
Carbon pools are locations or systems that have the capacity to both take in and release carbon.
*Outline formation of coal.* Understanding: Partially decomposed organic matter from past geological eras was converted either into coal or into oil and gas that accumulate in porous rocks.
Coal forms from peat over long periods of time. Heat and pressure produce chemical and physical changes in the peat layers which force out oxygen and leave rich carbon deposits called coal.
*State the products of a combustion reaction.* Understanding: Carbon dioxide is produced by combustion of biomass and fossilized organic matter.
Combustion occurs when a organic molecule reacts with oxygen to produce carbon dioxide and water.
*Outline the role of combustion in the carbon cycle.* Understanding: Carbon dioxide is produced by combustion of biomass and fossilized organic matter.
Combustion occurs when any organic material is reacted (burned) in the presence of oxygen to give off the products of carbon dioxide and water. In the carbon cycle, combustion converts carbon stored in organic molecules (biomass, coal, gas and oil) to atmospheric CO₂.
*State sources of fuel for a combustion reaction.* Understanding: Carbon dioxide is produced by combustion of biomass and fossilized organic matter.
Combustion reactions are commonly referred to as "burning." Biomass (such as wood), coal, gas and oil are common fuel sources in combustion reactions.
*Define "decomposition."* Understanding: Peat forms when organic matter is not fully decomposed because of acidic and/or anaerobic conditions in waterlogged soils.
Decomposition is the process of complex, carbon compounds in dead organisms, urine and faeces being broken down into simpler carbon compounds by bacteria or fungi.
*Define "diffusion."* Understanding: Carbon dioxide diffuses from the atmosphere or water into autotrophs.
Diffusion is the net movement of particles down their concentration gradient (from areas of higher concentration to areas of lower concentration).
*State the unit of measure for carbon flux values.* Application: Estimation of carbon fluxes due to processes in the carbon cycle.
Global carbon fluxes are estimated in gigatonnes (1 gigatonne = 1 billion metric tonnes).
*State that hard shells, such as in mollusk and coral, are made of calcium carbonate.* Understanding: Animals such as reef-building corals and Mollusca have hard parts that are composed of calcium carbonate and can become fossilized in limestone.
Hard shells are the exoskeletons of corals and mollusks such as snails, clams and oysters. The shells are composed mostly of calcium carbonate, CaCO₃.
*Explain why accurate measurements of carbon dioxide and methane in the atmosphere are important.* Nature of Science: Making accurate, quantitative measurements-it is important to obtain reliable data on the concentrations of carbon dioxide and methane in the atmosphere.
It is important to make observations and collect data regarding greenhouse gas levels (such as CO₂ and methane). The information helps scientists understand trends and test whether actions to reduce greenhouse gases are working.
*Outline the formation of limestone.* Understanding: Animals such as reef-building corals and Mollusca have hard parts that are composed of calcium carbonate and can become fossilized in limestone.
Limestone is primarily composed of calcium carbonate (CaCO₃). It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal, and fecal debris in shallow, calm, warm marine waters.
*Outline the role of lithification in the carbon cycle.* Understanding: Animals such as reef-building corals and Mollusca have hard parts that are composed of calcium carbonate and can become fossilized in limestone.
Lithification is the compaction of sediments into rocks through compaction and cementation. In the carbon cycle, lithification creates limestone.
*State the molecular formula for methane.* Understanding: Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans and some diffuses into the atmosphere or accumulates in the ground.
Methane= CH₄.
*Outline the role of methanogenic archaea in the transformation of organic material into methane.* Understanding: Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans and some diffuses into the atmosphere or accumulates in the ground.
Methanogenic archaeans are microorganisms that produce methane as a metabolic byproduct in anaerobic conditions. The methane produced will either accumulate underground (forming natural gas) or diffuse into the atmosphere.
*Define "oxidation."* Understanding: Methane is oxidized to carbon dioxide and water in the atmosphere.
Oxidation is the gain of oxygen or loss of a hydrogen in a "redox" reaction.
*Outline formation of peat.* Understanding: Peat forms when organic matter is not fully decomposed because of acidic and/or anaerobic conditions in waterlogged soils.
Peat forms when organic material (mostly plants/Sphagnum moss) does not fully decompose. Peat forms in in acidic, waterlogged and/or anaerobic conditions where decomposers (such as bacteria, fungi and other saprotrophs) are inhibited.
*Define "peat."* Understanding: Peat forms when organic matter is not fully decomposed because of acidic and/or anaerobic conditions in waterlogged soils.
Peat is a brown deposit resembling soil, formed by the partial decomposition of organic matter in wet acidic conditions (such as in bogs).
*Outline how data on concentration of atmospheric carbon dioxide and methane are collected.* Nature of Science: Making accurate, quantitative measurements-it is important to obtain reliable data on the concentrations of carbon dioxide and methane in the atmosphere.
Scientists measure the amount of greenhouse gases in the atmosphere in several ways. They use satellites and other instruments to measure the amount of greenhouse gases in the air all around the world. They also collect samples of air from specific places and then analyze these samples in a laboratory. We also have clues about the levels of greenhouse gases that existed in the past. For example, ancient air bubbles trapped deep in the ice of Greenland and Antarctica reveal how much atmospheric CO₂ was present long ago.
*Sketch a graph of the annual fluctuation in atmospheric carbon dioxide concentration.* Application: Analysis of data from air monitoring stations to explain annual fluctuations.
Sinusoidal shape with a peak in May and a trough in October. Axis labeled: X axis = month Y axis = Atmospheric CO₂ level (ppm)
*Explain the annual fluctuation in atmospheric carbon dioxide concentration in the northern hemisphere.* Application: Analysis of data from air monitoring stations to explain annual fluctuations.
The annual, seasonal fluctuations of CO₂ levels are caused by increased photosynthesis during Northern hemisphere spring/summer. Photosynthesis uses CO₂; lowering carbon dioxide level in atmosphere during the spring and summer months.
*State the molecular formula for calcium carbonate.* Understanding: Animals such as reef-building corals and Mollusca have hard parts that are composed of calcium carbonate and can become fossilized in limestone.
The calcium carbonate chemical formula is CaCO₃.
*Define "carbon cycle."* Application: Estimation of carbon fluxes due to processes in the carbon cycle.
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere (living things), pedosphere (soil), geosphere (rocks), hydrosphere (water), and atmosphere of the Earth.