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Matt Wilsonon 11 April 2013
Transcript of Biogeochemical Cycles
Elements continually pass from one environment to the next and from one form to another. This circulation of elements is called a biogeochemical cycle. A biogeochemical cycle is a set of processes through which an element passes from one environment to another, in a giant loop. We are going to examine two important cycles: the carbon cycle and the nitrogen cycle. Carbon is the basic element in the complex molecules that make up our bodies' tissues. There are 9 important stages in the carbon cycle: 1) Photosynthesis: Plants use solar energy to convert carbon dioxide into glucose.
This removes carbon from the overall cycle. 2) Ingestion: To get the carbon they need, animals eat plants or other animals.
This removes carbon from the overall cycle. 3) Respiration: When living organisms breathe, some of the carbon they have ingested returns to the atmosphere as carbon dioxide.
This adds carbon to the overall cycle. 4) Decomposition of Waste: The rest of the carbon is eliminated as waste (urine, feces, etc.) and broken down by decomposers.
This adds carbon to the overall cycle. 5) Forest fires: Release large amounts of carbon by causing the carbon in tree trunks and leaves to be converted into carbon dioxide.
This adds carbon to the overall cycle. 6) Shells & Skeletons: Some carbon is used by marine organisms to form shells & skeletons out of calcium carbonate.
This removes carbon from the overall cycle. 7) Carbonate rock: When these organisms die, their shells break down and form carbonate rock.
This removes carbon from the overall cycle. 8) Volcanic Eruptions: Certain carbonate rocks melt on contact with magma, releasing carbon back into the atmosphere when volcanoes erupt.
This adds carbon to the overall cycle. 9) Fossil Fuels: Some of these carbonate rocks are transformed into oil and coal, which we burn for energy.
This adds carbon to the overall cycle. Nitrogen is needed by living organisms to manufacture proteins and DNA. The problem, though, is that most nitrogen on Earth is found in the air. However, we can only process nitrogen in its molecular forms: NH , NH , NO or NO . 1) Nitrogen fixation: Certain bacteria take the nitrogen from the air can convert it into ammonium and ammonia. 2) Nitrification: Other bacteria oxidize ammonium to form nitrites and nitrates. 3) Absorption: Plants draw ammonium and nitrates from the soil, and animals get nitrites and nitrates from plants. 4) Decomposition of waste: Just as before, organisms expel used nitrogen-rich substances in their waste. 5) Denitrification: Finally, bacteria convert the nitrates in waste back into molecular nitrogen, which returns to the air. 3 4 + 2 - 3 -