4.3 THE CARBON CYCLE

Plants absorb Carbon Dioxide as Carbon and Oxygen are needed for

• Photosynthesis: Make Carbohydrates and Proteins

Animals eat Plants and Carbon is used for

• Growth
• Respiration: Release energy

Flux: Transfer of Carbon

Sink: Method of Carbon Storage in the Ecosystem

Outline the roles of living organisms in the carbon cycle [8]

• Plants use Carbon Dioxide in Photosynthesis
• Carbon compounds are produced in Plants from Photosynthesis
• Carbon compounds in plants are eaten by Primary Consumers
• Carbon compounds in Primary Consumers are eaten by Secondary Consumers/passed along the food chain
• Carbon compounds are digested and absorbed by Consumers
• Carbon Dioxide is released by Plants and Animals
• Plants and Animals die and are decomposed by Saprotrophic bacteria and fungi
• Bacteria and fungi release Carbon Dioxide by Cell Respiration
• Enzymes are released to digest carbon compounds in organic matter
• Combustion releases Carbon Dioxide
• Humans burn Fossil fuels adding to Carbon Dioxide in Atmosphere 

If fully annotated diagram is drawn marks are awarded as well

All Autotrophs convert Carbon Dioxide [from atmosphere / dissolved in water] into Organic Compounds 

• Plants synthesize sugars [Glucose]
• Sugars are convereted into other organic compounds [Carbs, Lipids, Proteins]

Chemoautotrophs fix Carbon by using the energy inside the bonds of Inorganic Compounds [Hydrogen sulpide] 

• Carbon Dioxide disolve/diffuse into Water combining with it

• By CO2 combining with Water Carbonic Acid is formed

• 1 or 2 Hydrogen Ions break away lowering the pH of the Water 

• Dissolved Carbon Dioxide and Hydrogen Carbonate is absorbed by Aquatic Plants and Autotrophs that live in Water 

                                            CO2 + H2O = H2CO3 = H+  HO3-

To photosynthesise Plants must have a continuous supply of Carbon Dioxide 

• CO2 moves through stomatal pores in the leaves of land plants

• Some Aquatic Plants [Lillies] have Stomata but other fully submerged plants diffusion occurs through surface tissues 

• CO2 from outside the leaf diffuses down the concentration gradient into the leaf [H - L]

• Photosynthesis uses the CO2 : concentration of CO2 inside the leaf is low 

Organisms carry out Respiration to release energy [ATP]. Carbon Dioxide is a waste product.

In the Carbon Cycle:

• Autotrophs respire
• Heterotrophs respire
• Saprotrophs and Decomposers respire

Methane is produced by Methanogenic archaeans

Methanogens: Archean organisms microorganisms that produce methane as a metabollic in Anaerobic conditions

Organic Matter is broken down in Anaerobic conditions during ATP production Methane is released as a waste product from Carbon Dioxide

• Swamps
• Bogs
• Wetlands
• Digestive tracts of Animals
• Marine and Freshwater Sediments

Methane can accumulate in the ground or diffuse into the atmosphere

Methane eventually oxcidizes into Carbon Dioxide so actual Methane concentrations remain low

The levels of Methane are increasing in the Atmosphere

Methane released into the Atmosphere can be removed by a few mechanisms but the most important process of methane removal is oxcidization by hydroxyl radicals

Peat forms when organic matter is not fully decomposed because of acidic and/or anaerobic conditions in waterlogged soils

• In soil organic matter [dead leaves] are digested by Saprotrophs 
• Saprotrophs digest some Carbon for growth and release Carbon Dioxide during Aerobic respiration

• BUT water logged soils are an Anaeronic Environment therefore Saprotrophs and Methanogens are inhibited 
• The organic matter is only partially decomposed
• Partial decomposition causes Acidic conditions
• Large quantities of partially decomposed organic matter build up
• The organic matter is compressed to form Peat

Coal is formed when:

• Diposits of peat are buried under other sediments
• Peat is heated and compressed over millions of years eventually becoming coal

• Sea plants and animals died and buried on the ocean floor

• Over time the plants and animals were covered by silt and sand

• In these Anaerobic conditions there is only partial decomposition

• The remains were buried deeper and deeper heat and pressure turned the remains into oil and gas

Different types of oil and gas mix because of complex chemical changes 

Methane is the largest part of Natural Gas

Carbon Dioxide produced by the Combustion of Carbon Compounds is an non-biological process

BUT can happen naturally:

• Lightning sets fire to forest and burns the biomass and releasing Carbon Dioxide

Over time humans learned about Combustion

• Extracts coal oil and natural gas. energy is generated from the Combustion of Fossil Fuels. This releases a lot of Carbon Dioxide into the Atmosphere

If heated  dried biomass or fossil fuels will burn in the presence of Oxygen 

Limestone: Rock made from Calcium Carbonate

Some animals secrete calcium carbonate structures to protect themselves

• Hard shells of Molluscs
• Exoskeletons of hard Coral

When the animals die the body parts decompose but the calcium carbonate remains form deposits on the ocean floor

The deposits are buried and compressed eventually forming limestone

Imprints of the hard body parts remain in the rock as fossils

Limestone is a huge Carbon Sink

Carbon is released when Limestone reacts with acid

Rainwater contains carbonic acid and can cause calcium carbonate to breakdown and release the carbon that it holds inside

It is not possible to measure carbon sinks and fluxes. Estimates are based off of different measurements that are published with large uncertainties.

Impossible to measure globally

Estimates can be made based on Ecosystems and Mescosoms

Global Fluxes estimates are made with Gigatonnes

Keeling Curve and other field stations show a clear upward trend with annual cycles

Historical Data can be collected from Ice Cores - analysing CO2 concentration of air bubbles trapped in the ice and determining the year from estimating the depth of the core