Carbon cycling PDF

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Summary

Biology SL
Topic 4.3
carbon, role of autotrophs, carbon dioxide, aquatic ecosystems, methane, peat, fossil fuels, biomass, limestone...

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Carbon cycling

Topic 4.3

Biology SL

Carbon ➢ Life on Earth is referred to as carbon-based life ➢ The biosphere refers to all the places where life is found and the lithosphere refers to all the places where rocks are found ➢ Cycling involves how the carbon atoms are incorporated into dierent molecules

Role of autotrophs ➢ Photosynthetic autotrophs take carbon dioxide from the atmosphere and convert it into carbohydrates In its inorganic form, carbon isn’t usable as a food source by the autotrophs

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or by any consumer, but sugars (organic form of carbon) are ■

Fructose, galactose, starch, cellulose are all made by glucose

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Other organic compounds, like lipids and amino acids, are also made of glucose ●

Glucose is the starting point in this case, since other elements, such as nitrogen, must be added to it

Carbon dioxide ➢ Absorbed by photosynthetic autotrophs and is turned into organic compounds ➢ Consumers eat the producers and use the carbon compounds ➢ Consumers and decomposers respire and release carbon dioxide back into the environment

Carbon in aquatic ecosystems ➢ Carbon dioxide can be absorbed by water ➢ Organisms that live in the water produce cc through cell respiration ➢ As the carbon dioxide is dissolved in the water, it forms and acid The pH of water decreases and carbon dioxide increases

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CO2 + H2O ⇒ H2CO3 (carbonic acid) -

➢ HCO3 is an inorganic molecule which participates in the carbon cycle +

H2CO3 + H ⇒ HCO3 ○

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(hydrogen carbonate ion)

Carbon can be absorbed in this form by organisms

➢ Carbon by carbon sequestration can turn into: ○

Methane, limestone, peat, fossil fuels

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Carbon cycling

Topic 4.3

Biology SL

Methane ➢ Some organisms are capable of living in anaerobic conditions, such as methanogenic archaeans ➢ When these methanogenic archaeans metabolise food, they produce methane instead of carbon dioxide, as a waste gas ➢ They’re also common in wetlands where they produce marsh gas, which can sometimes glow at night ➢ Methane forms slowly and large quantities can be trapped in the ground ➢ Methane is a very potent greenhouse gas ➢ It can be burnt in oxygen to form carbon dioxide CH4 + 2O2 ⇒ 2H2O + CO2 ➢ Methane is the main ingredient in the fossil fuel we call natural gas ➢ The carbon found in methane was borrowed from a carbon dioxide molecule that was removed from the atmosphere millions of years ago during photosynthesis ○

Methane formed and accumulated underground

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Through burning, the carbon is returned to the atmosphere as carbon dioxide ■

The problem is that the burning is very fast, but the formation very slow

Peat

➢ Peat is an organic substance that consists of partially decomposed plant material ○

It’s a heterogeneous mixture of many things

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At least 30% of its dry mass has to be composed of dead organic material

➢ Used as fossil fuel ➢ It’s a kind of waterlogged soil found in certain types of wetlands ➢ The low pH hinders decomposition ○

Anaerobic conditions are created

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Certain types of microorganisms grow, but microorganisms that would help in the decomposition of plant material are prevented from growing

➢ It takes a long time to form and it isn’t considered to be a renewable source of energy ➢ Wetlands are an important part of the ecosystem and a habitat for unique species ➢ Pollen trapped in deep layers of the bogs can provide evidence of what the climate was like in the past

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Carbon cycling

Topic 4.3

Biology SL

➢ When left in the correct conditions, partially decomposed peat can be further transformed into coal

Fossil fuels ➢ When organic compounds are trapped under sediments over a long time, fossil fuels can form ○

Sediments are layers of dead organisms that weren’t fully decomposed usually formed at the sea bottom

➢ The carbon-rich deposits are under huge pressure and exposed to high temperatures ○

These 2 factors cause chemical transformations associated with lithification ■

Lithification is the transformation of sediments into solid rock

➢ The term fossil fuel refers to the fact that the source of energy in the fuel comes from partially decayed once-living organisms that died millions or hundreds of millions years ago ○

Theyäre considered to be a non-renewable source of energy

➢ Such ideal conditions have existed in a few parts of the world ○

If favourable geological changes occur the compounds can be trapped and later extracted

Biomass ➢ The dried dung of domesticated animals can be burnt and used for various purposes ➢ Fresh, wet dung can be mixed with other refuse from a farm and put into a large container where methane-producing microorganisms will decompose and ferment he material to produce flammable methane gas ➢ Plant material is fed to microorganisms that ferment it and in the process release ethanol ○

Ethanol is added to gasoline for vehicles and contributes to a reduction in gasoline use

➢ The burning of any biomass still releases carbon dioxide into the atmosphere but unlike fossil fuels, the carbon dioxide from biofuels was removed from the atmosphere by plants just a few months/years before the biofuel was used

Limestone ➢ The organisms that build coral reefs are called coral polyps and they absorb 2 ions from seawater to build the reef: 3

Carbon cycling

Topic 4.3

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Hydrogen carbonate ions

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Calcium ions

Biology SL

➢ When combined, molecules of calcium carbonate are formed -

2+ Ca + 2HCO3 ⇒ CaCO3 + CO2 + H2O

➢ As these organisms die, their shells are deposited on the bottom of the sea and they accumulate in sediments ○

When the sediments go through the process of lithification, they form limestone

➢ The process of taking carbon out of the environment and “locking it up” in a substance for an extended period of time is called carbon sequestration ○

When it happens naturally, it is called biosequestration ■

This is one way in which balance is maintained in the carbon cycle

➢ When limestone is used, some of the carbon is released back into the atmosphere as carbon dioxide cancelling out the biosequestration

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