4.3 carbon cycle

State the role of photosynthesis in the carbon cycle

State the role of photosynthesis in the carbon cycle

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.

Outline the process that

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⁻).

Explain the reduction of the pH in water when carbon

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

Define diffusion

Diffusion is the net movement of particles down their concentration gradient (from areas of higher concentration to areas of lower concentration(.

Outline the role of diffusion in the carbon cycle

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.

State the role of respiration in the carbon cycle.

Respiration converts organic carbon molecules into inorganic carbon molecules which then diffuse into water or the atmosphere.

Outline the role of methanogenic archaea in the transformation of organic material into methane.

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.

State the formula for the oxidation of methane to carbon dioxide that occurs in the atmosphere.

CH₄ + 2O₂ → CO₂ + 2H₂O

Define decomposition.

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 peat.

Peat is a brown deposit resembling soil, formed by the partial decomposition of organic matter in wet acidic conditions (such as in bogs).

Outline the formation of peat.

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 fossilisation

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).

Outline the formation of coal.

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.

Outline the formation of oil and natural gas.

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.

Outline the role of combustion in the carbon cycle

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 that hard shells, such as in mollusk and coral, are made of calcium carbonate.

Hard shells are the exoskeletons of corals and mollusks such as snails, clams and oysters. The shells are composed mostly of calcium carbonate, CaCO₃.

Outline the role of lithification in the carbon cycle.

Lithification is the compaction of sediments into rocks through compaction and cementation. In the carbon cycle, lithification creates limestone.

Outline the formation of 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.

Define 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.

Explain the annual fluctuation in atmospheric carbon dioxide concentration in the northern hemisphere.

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.

Outline how data on concentration of atmospheric carbon dioxide and methane are collected.

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.

List pools of carbon 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

Define “carbon pool”

Carbon pools are locations or systems that have the capacity to both take in and release carbon.

Define “carbon flux”

A carbon flux is the exchange of carbon between Earth's carbon pools.

List the flux processes in the carbon cycle

Photosynthesis
Respiration
Decomposition
Diffusion
Lithification
Combustion
Fossilization
Feeding