Topic 4.3 Carbon Cycling

IB Biology

R. Price

v. 1 2015

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#1: Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds

• Autotrophs absorb carbon dioxide from the atmosphere and convert it into carbohydrates, lipids, & other carbon compounds• Reduces the carbon dioxide

concentration in the atmosphere• Lower carbon dioxide

concentrations above parts of the earth where photosynthesis rates are high

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#2: In aquatic habitats, carbon dioxide is present as a dissolved gas and hydrogen carbonate ions

• Carbon dioxide is soluble in water•Can combine with water to form carbonic acid -> hydrogen & hydrogen carbonate ions. (can lower pH of water)•Dissolved carbon dioxide and hydrogen carbonate ions are absorbed by aquatic plants and other autotrophs

#3: Carbon dioxide diffuses from the atmosphere or water into autotrophs

• Autotrophs use carbon dioxide during photosynthesis• Reduces amount of carbon

dioxide inside the cell• Concentration gradient between

cell and atmosphere/water• Carbon dioxide diffuses into the

cell • Stomata / aquatic plant surface

#4: Carbon dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere

• Carbon dioxide is a waste product of aerobic cell respiration• Diffuses out of the cells and into

the atmosphere/water

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#5: Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans and some diffuses into the atmosphere

• Methanogenic archaeans produce methane from carbon dioxide, hydrogen, and acetate.• Found in anaerobic conditions

such as water logged soil, swamps, guts of ruminant animals (cows), human intestines, and landfills

By ms:User:PM Poon (ms:Imej:Arkea.jpg) CC-BY-SA-3.0 via Wikimedia Commons

#6: Methane is oxidized to carbon dioxide and water in the atmosphere

•Methane only lasts about 12 years in the atmosphere•Oxidized in the stratosphere•Reacts with monatomic oxygen (O) & hydroxyl radicals (OH+)•Oxidized -> carbon dioxide & water

#7: Peat forms when organic matter is not fully decomposed because of anaerobic conditions in waterlogged soils

• Saprotrophs normally oxygen in soil air pockets• Can’t thrive in water logged soils• Dead organic matter only

partially decomposed• Acid conditions also develop• Material compresses to make

peat

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#8: Partially decomposed organic matter from past geological eras was converted into oil and gas in porous rocks or into coal

•Oil and natural gas formed in the mud at the bottom of seas & lakes•Coal formed when peat is buried under other sediments•Anaerobic conditions + partially decomposed organic matter + heat & pressure = oil, gas, coal

#9: Carbon dioxide is produced by the combustion of biomass and fossilized organic matter

•Organic matter heated to ignition temperature + oxygen = combustion•Periodic grass fires or forest fires are natural in some ecosystems•Humans clear rainforest or fields•Coal, oil, & natural gas are fossilized organic matter and will also release carbon dioxide when burned

#10: Animals such as reef-building corals and molluscs have hard parts that are composed of calcium carbonate and can become fossilized in limestone

•Mollusc shells and hard corals contain calcium carbonate•Deposits of shells and corals form on the sea bed•Forms sedimentary rock called limestone (fossils may be visible)•Carbon stores locked up in limestone

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Diagram

adapted from U

.S. DO

E, Biological and Environmental Research Inform

ation System. [Public dom

ain], via Wikim

edia Com

mons

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Sources

Content Allott, Andrew, and David Mindorff. Biology: Course Companion. 2014 ed. Oxford: Oxford UP, 2014. Print. Oxford IB Diploma Programme.

Walpole, Brenda. Biology for the IB Diploma. 2nd ed. Cambridge: Cambridge UP, 2014. Print.

ImagesUnless otherwise noted, images are obtained from Pixabay (www.pixabay.com) and used under the CC0 Public Domain license.