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 2. Elements essential for life also cycle through ecosystems

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PostSubject: 2. Elements essential for life also cycle through ecosystems   03/03/09, 11:31 pm

o Biogeochemical cycle- the movement of a particular chemical through the biological and geological, or living and non living, parts of an ecosystem.
o Substances may change shape as they move through their cycles.
OXYGEN CYCLE
o Plants release oxygen as a waste product of photosynthesis
o Humans and other organisms take this in and release carbon dioxide during respiration
o Plants use carbon dioxide
CARBON CYCLE
o Plants use energy from the sun to convert carbon dioxide from the air into organic material that becomes a part of the plant’s structure
o Carbon moves through biotic world as one organism eats another
o Carbon is returned to the atmosphere as carbon dioxide from respiration or through the decomposition of dead organisms. The burning of fossil fuels and wood also contributes to this.
o Areas that store carbon over a long period of time are called carbon sinks. One example is forest land, where large amounts of carbon are stored in the cellulose of wood
NITROGEN CYCLE
o Nitrogen fixation- process where certain types of bacteria convert gaseous nitrogen into ammonia
o These bacteria release ammonia that is transformed into ammonium by the addition of hydrogen ions found in acidic soil
o Some ammonium is taken up by plats, but most is used by nitrifying bacteria for energy
o These bacteria change ammonium into nitrate
o Nitrates released by soil bacteria are taken up by plants, which turn them into amino acids and proteins
o When decomposers break down dead animals or plants, nitrogen is returned to the soil as ammonium (called ammonification)
o Denitrifying bacteria use nitrate as an oxygen source, releasing nitrogen gas into the atmosphere as a waste product
o Some also enters soil from atmospheric fixation by lightning, which breaks apart nitrogen molecules in the atmosphere
o Nitrogen combines with oxygen in the air, forming nitrogen oxide
o Nitrogen oxide + rain water = nitrates, which are absorbed by the soil
PHOSPHORUS CYCLE
o Does not include an atmospheric portion
o Phosphates are released from weathering rocks
o Plants take in some of the phosphates
o Animals eat the plants
o Decomposers break down the dead animal
o Phosphates is released back into soil
o Some phosphates may leach into groundwater, which can go into a lake or other body of water
o Phosphorus becomes locked in sediments at the bottom
o Thousands of years pass, sediment becomes rock again
o Rocks begin to weather

o Mining and agriculture add to the amount of phosphates being produced
o This causes problems because it disrupts the ecosystem
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