4.3 Carbon Cycling

Question 1

What is carbon cycling?

Answer 1

Biogeochemical cycle whereby carbon is exchanged between the different spheres of the Earth

Question 2

What are the four spheres of the Earth?

Answer 2

Atmosphere, lithosphere(ground), hydrosphere, biosphere

Question 3

What forms is carbon exchanged? (4 ways)

Answer 3

Atmospheric gases - CO2, CH4 (methane)
Oceanic carbonates - bicarbonates dissolved in water, calcium carbonate in corals and shells
Organic material - carbohydrates, lipids, proteins
Non-living remains - detritus, fossil fuels

Question 4

Why should carbon dioxide in the air always be at a higher concentration in the atmosphere than in the plant?

Answer 4

Autotrophs use CO2 for photosynthesis (so should be low)

Question 5

What are compensation points?

Answer 5

When the uptake of CO2 is balanced by the production of CO2 by respiration
(The net carbon dioxide assimilation is zero)

Question 6

What 2 things can carbon dioxide do when it dissolve in water? (Plus equation)

Answer 6

• remain as dissolved gas
• combine with water to form carbonic acid
  CO2 + H2O <-> H2CO3

Question 7

What happens to carbonic acid after? and equation and effect? (2)

Answer 7

• Disassociates to form hydrogen carbonate ions (H2CO3 <-> HCO3- +H+)
• releases hydrogen ions and pH changes

Question 8

What occurs when hydrogen carbonate ions come into contact with rocks and sediments on the ocean floor? (3)

Answer 8

• They acquire metal ions
• Resulting in the formation of calcium carbonate
• Then the development of limestone

Question 9

What occurs when living organisms combine hydrogen carbonate ions and calcium? (1)
what do the organisms use it for?? (2)

Answer 9

• It forms calcium carbonate
• forms hardened exoskeletons of coral (and main component of Mollusca shells)
• Wen organism dies and settles to sea floor, the hardened components may become fossilized in the limestone

Question 10

What is the summary of Carbon conversion (equations) in aquatic environments? (5 steps)

Answer 10

1. CO2 (atmosph) <-> CO2 (dissolved)
2. CO2 (dissolved) + H2O <-> H2CO3 (carbonic acid)
3. H2CO3 <-> HCO3- (bicarbonate ions) + H+
4. HCO3- <-> CO3^2- (carbonate ions) + H+
5. CO3^2- + Ca^2+ <-> CaCO3 (calcium carbonate)

Question 11

What are methanogens?

Answer 11

Archean microorganisms that produce methane (CH4) as a metabolical byproduct in anaerobic conditions

Question 12

What anaerobic conditions can methanogens can be found? (3)

Answer 12

• wetlands
• marine sediments
• digestive tract of ruminant animals

Question 13

What do methanogens have two byproducts of anaerobic digestion? (2) (Equations)

Answer 13

• acetic acid = Acetic acid-> methane and carbon dioxide (CH3COO- + H+ -> CH4 + CO2)
• CO2 = Carbon dioxide and hydrogen -> methane and water (CO2 + 4H2 -> CH4 + 2H2O)

Question 14

How can methane accumulate under the ground or diffuse into the atmosphere? (2)

Answer 14

-organic matter is buried in anoxic conditions, deposits of methane may form underground
-rising global number of domesticated cattle may be increasing levels of methane by releasing into atmosphere

Question 15

How long does methane persist in the atmosphere for and what happens afterwards?

Answer 15

For 12 years
- methane will be naturally oxidised to form carbon dioxide and water (CH4 +2O2 -> CO2 + 2H2O)

Question 16

What is partial decomposition?(3)

Answer 16

• When saprotrophs bacteria and fungi which decompose matter lack oxygen (anaerobic conditions)
• The anaerobic respiration by organisms produces organic acids (acidic conditions)
• The bacteria and fungi can’t function effectively in anaerobic/acidic conditions preventing decomposition

Question 17

How is coal formed? (3)

Answer 17

• Organic mater does not fully decompose in waterlogged solid, carbon rich molecules remain in the soil and form peat
• the deposits of peat are compressed under sediments, the heat and pressure force out impurities and remove moisture
• the remaining material has high carbon concentration and undergoes a chemical transformation to produce coal

Question 18

How is oil/natural gas formed? (5) (takes place over millions of years)

Answer 18

As a result of decay of marine organisms on ocean floor
- sediments are deposited on top of the organic matter
- creating anoxic condition preventing decomposition
- result of burial and compaction, organic matter becomes heated and hydrocarbons are formed
- hydrocarbons form oil and gas which are forced out of the rock and accumulate in porous rock

Question 19

What occurs when compounds rich in hydrocarbons are heated in the presence of oxygen?

Answer 19

Undergo combustion reaction

Question 20

What are the characteristic of combustion? And where does it go usually? (2)

Answer 20

-Exergonic and releases water and carbon dioxide as by-product
-carbon dioxide is released into atmosphere increasing concentration of gas in the air

Question 21

Why is the combustion of fossil fuels non-renewable energy source?

Answer 21

Geological process takes millions of years

Question 22

Why is combustion of biomass a renewable energy source? (3 steps)

Answer 22

• Living organisms produce hydrocarbons as a part of their biomass (either for use or as waste produ)
• Hydrocarbons can be extracted and purified to produce fuel source (eg. bioethanol/diesel)
• As long as new raw materials are provided and waste products are removed it is renewable

Question 23

What are carbon fluxes?

Answer 23

The rate of exchange of carbon between carbon sinks/reservoirs

Question 24

What are the four carbon sinks?

Answer 24

Lithosphere, hydrosphere, atmosphere, biosphere

Question 25

What are the conversion processes involved between carbon reservoirs? (6)

Answer 25

• Photosynthesis - removes CO2 from atmsp & fixes in producers as organic compounds
• Respiration - releases CO2 into atmsp when digested in living organism
• Decomposition - release carbon products into air/sediment when organic matter is recycled after death of organism
• Gaseous dissolution - exchange of carbon gases between ocean and atmosp
• Lithification - compaction of carbon containing sediment when organic matter is recycled after death
• Combustion - releases carbon gases when organic hydrocarbon are burned as fuel source

Question 26

What is made as it is not possible to measure the size of carbon sinks or fluxes?

Answer 26

Estimated are made

Question 27

What are carbon fluxes measuring in?

Answer 27

Gigatonnes (1 billion metric tonnes)

Question 28

What are the three main causes of flux change?

Answer 28

Climate conditions
Natural events
Human activity

Question 29

Why do climate conditions cause carbon fluxes? (4)

Answer 29

• rate of photosynthesis higher in summer seasons,more direct sunlight and longer days
• oceanic temps determine by how much carbon is stored as dissolved CO2 or as hydrogen bicarbonate ions
• el Nino and La Niña change the rate of carbon flux between ocean and atmosp
• melting polar caps - decomposition of frozen detritus

Question 30

Why do natural events cause carbon fluxes? (2)

Answer 30

-Forest fires can release high levels of CO2 (+ loss of trees to photosynthesise)
-volcanic eruptions can release carbon compounds from Earth’s crust into atmph

Question 31

Why does human activity cause carbon fluxes? (3)

Answer 31

-clearing trees for agricultural purposes (deforestation) reduce the removal of atmospheric (CO2)
-increased number of ruminant livestock will produce higher levels of methane
-burning fossil fuels will release CO2 into atmosph

Question 32

Atmospheric CO2 at Mauna Loa observatory data graph description) (4)

Answer 32

-CO2 levels fluctuate annually (summer long days, more light increase photosynthesis)
-CO2 trends will conform to northern hemisphere pattens (contains more land mass)
-CO2 levels are steadily increasing every year since industrial revolution
-atmosp CO2 lvl are at highest lvl recorded