Unit 4.3 - Carbon Cycling

Question 1

Aerobic conditions

Answer 1

Saprotrophic bacteria will break down organic material and return it to the soil
(i.e. decomposition)

Question 2

Anaerobic conditions

Answer 2

• Decomposition is prevented as the saprotrophic bacteria can’t function effectively
• Anaerobic respiration will produce organic acids (⬇ ph)

Question 3

Peat / Coal

Answer 3

• Organic matter that isn’t fully decomposed in anoxic or acidic soils will become peat
• When peat is compressed under layers of sediment, heat and pressure remove moisture to transform it into coal

Question 4

Oil / Natural Gas

Answer 4

When marine organisms are buried under sediment on the ocean floor, compaction and anaerobic conditions transform the organic matter into oil and natural gas

Question 5

Autotrophs

Answer 5

• Convert atmospheric carbon dioxide into organic compounds via the process of photosynthesis
• Equation (balanced):
  6CO2 + 6H2O → C6H12O6 + 6O2

Question 6

Heterotrophs

Answer 6

• Obtain organic compounds via feeding
• The breakdown of organic compounds via cell respiration (to produce ATP) releases carbon dioxide as a by-product
• Equation (balanced):
  C6H12O6 + 6O2 → 6CO2 + 6H2O

Question 7

Hydrocarbons

Answer 7

• Undergo combustion in the presence of O2

* The reaction is exergonic and CO2 and H2O is produced

Question 8

Sources of hydrocarbons

Answer 8

• Fossilised organic matter
  (i. e. coal, oil and gas)
• Biomass
  (e. g. bioethanol and biofuels)

Question 9

Energy produced by combustion reactions

Answer 9

• Typically used to power industrial processes
• The combustion of fossil fuels is responsible for a
  significant increase in atmospheric CO2 concentrations

Question 10

In aquatic ecosystems

Answer 10

Carbon dioxide may remain dissolved in water or alternatively form hydrogen carbonate ions

Question 11

Animals in aquatic conversions

Answer 11

May combine the carbonate ions with calcium to form hard shells (e.g. mollusca) and exoskeletons (e.g. coral)

Question 12

Carbonate ions in aquatic conversions

Answer 12

May also interact with rock and sediment to form limestone

Question 13

Methane (CH4)

Answer 13

• Produced from organic compounds by methanogenic archaeans
• Requires anaerobic conditions (commonly found in wetlands, marine sediments or digestive tract of ruminants)
• Diffuses into the air or forms deposits underground
• In the air, it is oxidised to form CO2 and H2O