Notes on Biogeochemical Cycles and Ecology.pdf

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(autotrophs). In the animal, the carbon also has the same 3 possible fates. Carbon fromplants or animals that is released to the atmosphere through respiration will either betaken up by a plant in photosynthesis or dissolved in the oceans. When an animal or aplant dies, 2 things can happen to the carbon in it. It can either be respired bydecomposers (and released to the atmosphere), or it can be buried intact andultimately form coal, oil, or natural gas (fossil fuels). The fossil fuels can be minedand burned in the future; releasing carbon dioxide to the atmosphere. Otherwise, thecarbon in limestone or other sediments can only be released to the atmosphere whenthey are subducted and brought to volcanoes, or when they are pushed to the surfaceand slowly weathered away. Humans have a great impact on the carbon cycle becausewhen we burn fossil fuels we release excess carbon dioxide into the atmosphere. Thismeans that more carbon dioxide goes into the oceans, and more is present in theatmosphere. The latter condition causes global warming, because the carbon dioxidein the atmosphere allows more energy to reach the Earth from the sun than it allows toescape from the Earth into space.The Oxygen Cycle:If you look back at the carbon cycle, you will see that we have also described theoxygen cycle, since these atoms often are combined. Oxygen is present in the carbondioxide, in the carbohydrates, in water, and as a molecule of two oxygen atoms.Oxygen is released to the atmosphere by autotrophs during photosynthesis and takenup by both autotrophs and heterotrophs during respiration. In fact, all of the oxygen inthe atmosphere is biogenic; that is, it was released from water through photosynthesisby autotrophs. It took about 2 billion years for autotrophs (mostly cyanobacteria) toraise the oxygen content of the atmosphere to the 21% that it is today; this opened thedoor for complex organisms such as multicellular animals, which need a lot ofoxygen.The Nitrogen Cycle:
The nitrogen cycle is one of the most difficult of the cycles to learn, simply becausethere are so many important forms of nitrogen, and because organisms are responsiblefor each of the interconversions. Remember that nitrogen is critically important informing the amino portions of the amino acids which in turn form the proteins of yourbody. Proteins make up skin and muscle, among other important structural portions ofyour body, and all enzymes are proteins. Since enzymes carry out almost all of thechemical reactions in your body, it's easy to see how important nitrogen is. The chiefreservoir of nitrogen is the atmosphere, which is about 78% nitrogen. It is here wereach one of the limits of the hypertext language currently (1995-1996) most in vogueon the WWW. This version does not allow for superscripts or subscripts, so I willhave to stick to the longer chemical names. Nitrogen gas in the atmosphere iscomposed of two nitrogen atoms bound to each other. It is a pretty non-reactive gas; ittakes a lot of energy to get nitrogen gas to break up and combine with other things,such as carbon or oxygen. Nitrogen gas can be taken from the atmosphere (fixed) intwo basic ways. First, lightning provides enough energy to "burn" the nitrogen and fixit in the form of nitrate, which is a nitrogen with three oxygens attached. This processis duplicated in fertilizer factories to produce nitrogen fertilizers. Biology 101 studentswill also recall the experiments of Stanley Miller, who used electrical discharges toshow how nitrogen in the Earth's early atmosphere might have combined to form
Page 1 and 2: Note To Students and Educators:Did
Page 3 and 4: Energy Flow Through the EcosystemTh
Page 5 and 6: classify each as a herbivore, carni
Page 7 and 8: Biological MagnificationBiological
Page 9 and 10: scattered plants. Without food, the
Page 11 and 12: Key Features: In the water cycle, e
Page 13: Once you understand the water cycle
Page 17 and 18: The phosphorous cycle is the simple
Page 19: Thanks to Sharon Baumgard for the p

Notes on Biogeochemical Cycles and Ecology.pdf

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