4.3 Carbon cycling

Question 1

What are the spheres on Earth? What form of CO2 is taken up?

Answer 1

atmosphere (CO2), lithosphere (ground - detritus, fossil fuels), hydrosphere (bicarbonates and CaCO3 in shells, corals) and biosphere (living things - carbohydrates, proteins, lipids)

Question 2

Give and example of a carbon cycle

Answer 2

Question 3

Which processes determine the level of CO2?

Answer 3

• Photosynthesis
• Respiration
• Decomposition – releases carbon products into the air or sediment when organic matter is recycled after death of an organism
• Gaseous dissolution – the exchange of carbon gases between the ocean and atmosphere
• Lithification – the compaction of carbon-containing sediments into fossils and rocks within the Earth’s crust (e.g. limestone)
• Combustion

Question 4

Explain how CO2 is converted into CaCO3 in oceans?

Answer 4

Question 5

Define methanogens, where can they be found?

Answer 5

Methanogens are archaean microorganisms that produce methane (CH4) as a metabolic by-product in anaerobic conditions

• 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)

Question 6

Chemical equations of methane production by methanogens

Answer 6

Anaerobic digestion

• Acetic acid → Methane and Carbon Dioxide (CH3COO– + H+ → CH4 + CO2)
• Carbon Dioxide and Hydrogen → Methane and Water (CO2 + 4 H2 → CH4 + 2 H2O)

Question 7

Whta happens to methane in atmospeher?

Answer 7

Its is oxidised to CO2

Question 8

How are coal, fossil fuels and natural gas formed?

Answer 8

• Decomposition: by saprotrophs (if oxygenated env) - in anaerobic conditions decomposition does not occur => peat (acidic) - compressed with heat and pressure -> impurities removed -> high C conc -> coal
• Oil and natural gas - decay of amrine organisms - anoxic conditions prevent decomposition - _hydrocarbons forme_d - over million years into gas and oil - non-renewable

Question 9

Sources of combustion

Answer 9

1. Fossil fuels: human activity
2. Biomass: organisms produce hydrocarbons as their mass - can be used to produce laternative fuel

Question 10

Example of carbon cycle

Answer 10