4.3 Carbon cycling

Outline formation of oil and natural gas.

Oil and natural gas are formed in the mud at the bottom of seas and lakes. Conditions are usually aerobic and so decomposition is often incomplete. As more mud or other sediments are deposited the partially decomposed matter is compressed and heated. Chemical changes occur, which produce complex mixtures of liquid carbon compounds or gases. We call these mixtures crude oil and natural gas.

Define combustion.

Organic matter being heated to its ignition temperature in the presence of oxygen causing it to set light and burn.

Explain why accurate measurements of CO2 and methane in the atmosphere are important.

Reliable data are an essential perquisite for evaluating hypothesis and predictions about CO2 and methane in the atmosphere. Reliable measurements of atmospheric carbon dioxide and methane concentration are needed over as long a period as possible before we can evaluate the past and possible future consequences of human activity.

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

Some animals such as mollusc shells and hard corals have hard body parts composed of calcium carbonate.

State that carbon dioxide diffuses out of cells into the atmosphere or water.

carbon dioxide diffuses out of cells into the atmosphere or water.

State that carbon dioxide is a waste product of aerobic cellular respiration.

carbon dioxide is a waste product of aerobic cellular respiration.

Define peat.

A dark brown acidic material (which is compressed partially decomposed organic matter which has accumulated)

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

All stations show a clear upward trend with annual cycles.

State the role of photosynthesis in the carbon cycle.

Autotrophs absorb carbon dioxide from the atmosphere and convert it into carbohydrates, lipids and all other carbon compounds that they require. This has the effect of reducing the carbon dioxide concentration of the atmosphere. The mean concentration of CO2 in the atmosphere is currently approximately 0.039% but it is lower above parts of the Earth's atmosphere where photosynthesis rates have been high.

Outline the process that converts CO2 to hydrogen carbonate ion in water, leading to a reduction of the pH in the water.

CO2 can combine with water to form carbonic acid. Carbonic acid can dissociate to form hydrogen and hydrogen carbonate ions. Hydrogen ions explains how carbon dioxide reduces the pH of water.

State the products of a combustion reaction.

Carbon dioxide and water

State that in diffusion, molecules move from an area of higher concentration to an area of lower concentration.

Carbon dioxide diffuses from the atmosphere or water into autotrophs because there is a lower concentration of carbon dioxides inside autotrophs as a result of them using it to produce carbon compounds by photosynthesis.

List seven flux processes in the carbon cycle.

Cell respiration Combustion Death Egestion Feeding Photosynthesis Incomplete decomposition and fossilisation Ocean uptake Ocean loss Deforestation and land use changes Burial in marine sediments

Outline formation of coal.

Coal is formed when deposits of peat are buried under other sediments. The peat is compressed and heated, gradually turning into coal.

State sources of fuel for a combustion reaction.

Coal, oil and natural gas.

Outline how data on concentration of atmospheric CO2 and methane are collected.

Data on concentrations of gases in the atmosphere is collected by the Global Atmosphere Watch programme of the World Meteorological Organization. Research stations in various parts of the world now monitor the atmosphere, but Mauna Loa Observatory on Hawaii has records from the longest period. Carbon dioxide concentrations have been measured from 1959 onwards and methane from 1984.

State the unit of measure for carbon flux values.

Gigatonnes (which is equivalent to 1x1015 grams)

Outline formation of peat.

In many soils all organic matter such as dead leaves from plants is eventually digested by saprotrophic bacteria and fungi. However, in acidic or waterlogged conditions the break down of organic matter is inhibited. Large quantities of partially decomposed organic matter have accumulated in some ecosystems and become compressed to form a dark brown acidic material called peat. About 3% of the Earth's land surface is covered by peat.

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

Methane is produced widely in anaerobic environments, as it is a waste product of a type of anaerobic respiration Archeans produce methane from carbon dioxide, hydrogen and acetate. They do this by two chemical reactions: CO2 + 4H2 ---> CH4 + 2H2O CH3COOH ----> CH4 + CO2

define pool

a reserve of the element. (eg. Carbon dioxide in the atmosphere is an inorganic pool of carbon. The biomass of producers in an ecosystem is an organic pool.)

State that methane is oxidized to carbon dioxide in the atmosphere.

methane is oxidized to carbon dioxide in the atmosphere.

define flux

the transfer of the element from one pool to another (eg. Absorption of carbon dioxide from the atmosphere and its conversion by photosynthesis to plant biomass)