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Topic: Oxygen cycle

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Carbon cycle

Water cycle

Nitrogen cycle

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	Oxygen - CreationWiki (Site not responding. Last check: 2007-10-14)
		Oxygen is the most widely known element there is. It was discovered by Joseph Priestly in 1774 The name came from the Greek word oxus which means acid and the word gennan which means generate.
		Oxygen is reactive and forms oxides with all elements except neon, helium, argon and krypton.
		Oxygen is the most common component of the Earth's crust and the second most common component of the Earth as a whole as well as being the second most common element of the Earth's atmosphere.
	creationwiki.org /Oxygen (800 words)

	Oxygen cycle - Wikipedia, the free encyclopedia
		The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs: the atmosphere, the biosphere, and the lithosphere.
		The main driving factor of the oxygen cycle is photosynthesis, which is responsible for the modern Earth's atmosphere and life as we know it.
		The main way oxygen is lost from the atmosphere is via respiration and decay mechanisms in which animal life and bacteria consume oxygen and release carbon dioxide.
	en.wikipedia.org /wiki/Oxygen_cycle (751 words)

	The Oxygen Cycle
		This is another form of oxygen cycle - oxygen enters water in rapids and leaves water in pools.
		Oxygen uptake rate (O.U.R.) is the rate at which oxygen is consumed by living organisms in the water.
		Since organisms are constantly using up oxygen in the water and oxygen is constantly reentering the water from the air, the amount of oxygen in water remains relatively constant.
	water.me.vccs.edu /concepts/oxycycle.html (398 words)

	OS411B: M2, U2, P3 : The Oxygen Cycle
		The oxygen cycle is dominated by the process of photosynthesis.
		The graphic of the oxygen cycle shown below is presented in a different format than the carbon cycle discussed on the previous page.
		Oxygen is consumed in the oxidation of rocks and metals.
	www.shodor.org /os411/courses/411b/module02/unit02/page03.html (204 words)

	Oxygen (O) (Site not responding. Last check: 2007-10-14)
		Oxygen is the third most abundant element found in the sun.
		Oxygen is responsible for the bright red and yellow-green colors of the Aurora (a luminous phenomenon that consists of streamers or arches of light appearing in the upper atmosphere of a planet's magnetic polar regions).
		Oxygen is frequently prescribed for patients with respiratory ailments.
	www.bayerus.com /msms/fun/pages/periodic/oxygen/index.html (79 words)

	Botany online: Ecosystems - Nutrient Cycles (Site not responding. Last check: 2007-10-14)
		The water cycle is the first to be introduced as the water supply of the earth's surface is besides the sun and the amount of energy provided by it the most important precondition of vegetation and thus also of the colonization of the earth.
		The oxygen content of the atmosphere increased continuously during earth history since the first occurrence of organisms that were able to split water and perform photosynthesis.
		A main characteristic of the oxygen cycle is its connection with a part of the carbon cycle that plants have a key position in.
	www.biologie.uni-hamburg.de /b-online/e54/54d.htm (2599 words)

	background notes
		Since the number of carbon atoms from the wax (or oxygen atoms from the air) is the same as the number leaving in the CO gas produced, we have a steady state of equilibrium.
		The carbon cycle is a two component cycle: between the atmosphere and lithosphere and between the atmosphere and hydrosphere, with the atmosphere functioning as the common reservoir.
		Oxygen is needed in respiration to break down carbohydrates in which carbon has been stored within the biota, either directly from photosynthesis (plants) or by acquisition from other organisms (animals).
	intro.chem.okstate.edu /ChemSource/BIO/backn.htm (3098 words)

	Biogeochemical cycle Summary
		In ecology, a biogeochemical cycle is a circuit or pathway by which a chemical element or molecule moves through both biotic ("bio-") and abiotic ("geo-") compartments of an ecosystem.
		In addition to being a part of living organisms, these chemical elements also cycle through abiotic factors of ecosystems such as water (hydrosphere), land (lithosphere), and the air (atmosphere); the living factors of the planet can be referred to collectively as the biosphere.
		The most well-known and important biogeochemical cycles, for example, include the carbon cycle, the nitrogen cycle, the oxygen cycle, the phosphorus cycle, and the water cycle.
	www.bookrags.com /Biogeochemical_cycle (2429 words)

	Oxygen and Ozone (Site not responding. Last check: 2007-10-14)
		In the process of producing the oxygen of course, plants absorb CO in the green plant cycle and converted atmospheric nitrogen to plant nitrogen, thereby driving down the atmospheric levels of both of these constituents.
		Oxygen may be chemically combined in these reservoirs whereas in the atmosphere it's free.
		The atmosphere gains oxygen by weathering of rocks, and a comparable amount is lost from the surface by burial, such as marine plant parts and animal skeletons that drift to the bottom of the deep ocean.
	www.iitap.iastate.edu /gccourse/chem/evol/oxygen.html (725 words)

	[No title] (Site not responding. Last check: 2007-10-14)
		The Krebs cycle is an enzymatic cycle that occurs in the matrix of the mitochondrion.
		The carbon and oxygens of the carbon dioxide are from the carboxyl group of pyruvic acid.
		Normally in the presence of oxygen the concentrations of NADH are low because of their use in the electron transport system and the breakdown of pyruvate in the Krebs cycle is favored over fermentation.
	www.towson.edu /~hull/Courses/CGB/Discuss/Respire.html (2711 words)

	Environmental Biology Sequence - Ecosystems
		Oxygen is present in the carbon dioxide, in the carbohydrates, in water, and as a molecule of two oxygen atoms.
		Oxygen is released to the atmosphere by autotrophs during photosynthesis and taken up by both autotrophs and heterotrophs during respiration.
		The nitrogen cycle is one of the most difficult of the cycles to learn, simply because there are so many important forms of nitrogen, and because organisms are responsible for each of the interconversions.
	www.hobart.k12.in.us /jkousen/Biology/ecosystem.html (5391 words)

	Oxygen Radicals, Pro-oxidants and Antioxidant Nutrients
		What caught my interest was that the chronic damage from oxygen toxicity was not a direct concentration effect like that of a poison, but that the damage was greater than what one would expect from just the number of oxygen molecules involved.
		Occasionally an extra electron is added to the oxygen to make it into a free radical; then there are intermediate steps in the reduction of oxygen that eventually may lead back to producing water, but along the way we form some potentially dangerous species.
		When oxygen absorbs photons of energy and is transformed to the first electronic state, it can then fairly readily decay into its lowest excited electronic state, which for oxygen is the singlet state.
	www.drpasswater.com /nutrition_library/packer_interview1.html (4316 words)

	Bio200 Homework #4 KEY
		In the presence of oxygen, the pyruvate produced by glycolysis is modified and enters the Citric Acid Cycle, where more energy is extracted from the chemical bonds and more electron acceptors are reduced (energy is also produced in the modification of pyruvate (pyruvate dehydrogenation)).
		Oxygen oxidizes these reduced forms so that they are again able to accept electrons; the ability of the electron carriers to be reduced and then re-oxidized is essential to powering the citric acid cycle and electron transport chain.
		Oxygen molecules are steadily supplied by respiration; respiration's continuous input of oxygen molecules allows organisms to survive in defiance of the natural tendency to entropy.
	www.lclark.edu /~bkbaxter/200lecture/homework/homework4key.htm (1362 words)

	Atlantic Green Lane - Element Cycles
		Biogeochemical cycles (bio meaning 'life', geo for 'earth' and chemical for the changing of matter from one form to another) are natural processes that recycle elements in various chemical forms from the environment, to organisms, and then back to the environment.
		The water cycle (or hydrological cycle) is the circulation of the waters of the Earth between land, freshwater lakes and rivers, the salt seas and oceans, and the atmosphere.
		It regulates the life cycles of plants and animals, affects their growth and vitality, and is a principal factor in determining how they distribute themselves around the globe.
	www.p2pays.org /ref/03/02426/primer3.html (3863 words)

	BioGeochemical Cycling
		The cycle is controlled by large fluxes that equilibrate pools such as the atmosphere and the ocean, and chemical fluxes driven by biology that drive the H
		The largest oxygen pool is found in the sedimentary rocks that contain >96% of earths oxygen.
		Biogeochemical Cycles A journal called Global Biogeochemical Cycles is available that has a wealth of information on this fascinating research topic is available from American Geophysical Union.
	www.rsbs.anu.edu.au /ResearchGroups/PBE/Oxygen/O2_2_GeoCycling.htm (708 words)

	Environment - the O cycle
		The advent of oxygen, made by the photochemical splitting of water during photosynthesis, led to the precipitation of iron oxides to the sea floor, forming banded iron formations in rocks that can be dated to 3.8 billion years ago (3.8 GA bp).
		The release of free oxygen established the oxidation state of the earth's surface, inhibited anaerobic respiration, promoted eukaryotic metabolism, formed ozone in the stratosphere and led to chemoautotrophy (S-oxidation; N-oxidation which is nitrification).
		The concentration of oxygen in the oceans is influenced horizontally and vertically by physical features such as the thermocline, which isolates deep water from exchange with the atmosphere and can be a zone of significant decomposition causing an oxygen minimum.
	www.lifesciences.napier.ac.uk /teaching/Env/Ocycle.html (817 words)

	nucleosynthesis. The Columbia Encyclopedia, Sixth Edition. 2001-05
		There are two chains of reactions by which the conversion of hydrogen to helium is effected: the proton-proton cycle and the carbon-nitrogen-oxygen cycle (sometimes referred to simply as the carbon cycle).
		The proton-proton cycle operates in less massive and luminous stars like the sun, while the carbon-nitrogen-oxygen cycle (which speeds up dramatically at higher temperatures) dominates in more massive and luminous stars.
		In the proton-proton cycle, two hydrogen nuclei (protons) are fused and one of these protons is converted to a neutron by beta decay (see radioactivity) to make a deuterium nucleus (one proton and one neutron).
	www.bartleby.com /65/nu/nucleosy.html (608 words)

	Geography4Kids.com: BGC Cycles: Oxygen Cycle (Site not responding. Last check: 2007-10-14)
		Oxygen is one of the major compounds found in the atmosphere of the Earth.
		There is a large amount of oxygen dissolved in the water of oceans, lakes, and streams.
		Oxygen bonds with silicon (silicates), iron, and carbon (carbonates) to form many of the compounds in rock.
	www.geography4kids.com /files/cycles_oxygen.html (341 words)

	Environmental Decision Making, Science, and Technology
		Early in the evolution of the Earth, oxygen is believed to have been released from water vapor by UV radiation and accumulated in the atmosphere as the hydrogen escaped into the earth's gravity.
		The role of oxygen in life is describe in the unit on Biological Systems.
		If enough oxygen is not available for these bacteria, for example, because of enormous quantities of wastes in a body of water, they die and anaerobic bacteria that do not need oxygen take over.
	telstar.ote.cmu.edu /environ/m3/s4/cycleOxygen.shtml (362 words)

	Chemical Cycles - Cycles - Themepark
		But this oxygen is fed again and again through the world's living systems in a never-ending circle called the oxygen cycle.
		The cycle involves a continual exchange of gases between the air and animals and plants.
		Enormous quantities of oxygen are taken in by plants and animals every day, and huge quantities of oxygen are returned to the air by plants.
	www.uen.org /themepark/cycles/chemical.shtml (1461 words)

	Amazon Life - Ecology - Matter Cycle
		Water cycle takes place under a rigorous balance, related to many factors, as the amount of vegetation that covers the soil, wind regime and presence of water bodies, like rivers and lakes.
		Carbon and oxygen cycles are deeply related because they are directly associated to photosynthesis respiration process.
		Ammonia can returns to the cycle by the action of nitrifying bacteria or can be transformed in gaseous nitrogen by denitrifying bacteria, coming back to the air, closing the cycle.
	library.thinkquest.org /20248/cm.html (768 words)

	Econet
		This free oxygen, which constitutes nearly a fifth of our atmosphere by volume, is a product of photosynthesis, carried out over more than 3 billion years of earth history.
		In the process of respiration, free oxygen reacts rapidly with reduced organic material; most processes of this sort are now catalyzed by organisms.
		In the absence of photosynthesis, respiration would consume all organic material containing oxygen in about 50 years, but a large pool of oxygen would still remain in the atmosphere.
	www.owc.org.mn /econet/html/oxygen_cycle.htm (97 words)

	Lecture 17 Answers
		This cycle generates a number of reduced cofactors (3 molecules of NADH and one of FADH2) per molecule of acetate that goes through this pathway.
		Oxygen is reduced to the oxide ion driven by the energy of the reduced cofactors.
		The utilization and regeneration of oxaloacetate is the "cycle" part of the TCA cycle.
	www.uic.edu /depts/mcam/mcbc/531leq17ans.html (1087 words)

	[Regents Prep Living Environment] Ecology: Material Cycles (Site not responding. Last check: 2007-10-14)
		Oxygen is required by many living things to release the energy in their food in the process of aerobic cellular respiration.
		Oxygen is released to the environment as a waste product of the process of photosynthesis.
		Carrying capacity is limited by the available energy, water, oxygen, and minerals, and by the ability of ecosystems to recycle the remains of dead organisms through the activities of decomposers such as bacteria and fungi.
	regentsprep.org /Regents/biology/units/ecology/material.cfm (278 words)

	Lepton Oxygen Italian electric motor scooter
		With quick and quiet acceleration to a top speed of 28 mph and a range of up to 31 miles on a 5-hour charge, the Oxygen is approved for legal street use by the US Department of Transportation (DOT) and the European Union Transportation Agency.
		The Italian-built Oxygen scooter has a level of quality and more importantly, a standard of safety that can't be matched by other, cheaper Asian imports currently on the market.
		All our Oxygen electric scooters are DMV-friendly and come fully-loaded with DOT approved components, full instrumentation, plus mirrors and turn signals to complete the package.
	www.greenspeed.us /lepton_oxygen_electric_scooter.htm (486 words)

	Chem4Kids.com: Oxygen: Say It
		Oxygen is the eighth element of the periodic table and found in the second row (period).
		Alone, oxygen is a colorless and odorless compound that is a gas at room temperature.
		Oxygen molecules are not the only form of oxygen in the atmosphere; you will also find oxygen as ozone and carbon dioxide.
	www.chem4kids.com /files/elements/008_speak.html (198 words)

	oxygen — FactMonster.com
		The existence and properties of oxygen had been noted by many scientists before the announcement of its isolation by Priestley in 1774.
		Scheele had also succeeded in preparing oxygen from a number of substances, but publication of his findings was delayed until after that of Priestley's.
		oxygen: Uses - Uses Oxygen is of great importance in the chemical and the iron and steel industries.
	www.factmonster.com /ce6/sci/A0837189.html (196 words)

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