The part played by micro-organisms in the nutrient cycles

Micro-organisms although small are a key factor for the Earth’s survival. The Earth needs the biogeochemical cycles to survive; carbon, hydrogen, oxygen, nitrogen, phosphorus and sulphur.(Neff, 2009) Both the carbon and nitrogen cycles use micro-organisms. Without these the cycles would not work and the Earth could not survive.

Earth's atmosphere is approximately 78% nitrogen, much more commen in the atmosphere than either carbon dioxide or oxygen. Nitrogen is essential for many biological processes; it is in all amino acids, is incorporated into proteins, and is present in the bases that make up nucleic acids, such as DNA and RNA. In plants, much of the nitrogen is used in chlorophyll molecules which are essential for photosynthesis and further growth. Therefore it is crucial for any life on earth to exist.(Smil, 2000) The nitrogen cycle is a biogeochemical cycle. It is the circulation of nitrogen; where nitrogen from the atmosphere is turned to nitrates in the soil, which are absorbed by plants, and in turn are eaten by animals that die and decay returning the nitrogen back to the soil, which is then denitrified back to the atmosphere.

Carbon too is a main part of life. Carbon is the fourth most abundant chemical element in the universe by mass after hydrogen, helium, and oxygen. It is present in the oceans, the atmosphere, the biosphere, both the biotic and abiotic, in glucose and water and so in extention the earth can only exist with carbon present. The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere (the sum of all ecosystems), pedosphere (the soil), geosphere (rock and regolith), hydrosphere (the sum of all water), and atmosphere (the layer of gases surrounding the earth), of ...

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Microorganisms are involved in these cycles to keep them flowing. The nitrogen cycle requires many different microorganisms each doing a different job; saphrophytic bacteria and fungi, nitrifying bacteria, nitrogen-fixing bacteria, symbiotic nitrogen-fixing bacteria and denitrifying bacteria. The carbon cycle needs saprophytic bacteria, photsynthetic bacteria, and chemoautotrophic bacteria and just like the nitrogen cycle this is essential for the cycle to work.

Fixation is necessary to convert gaseous nitrogen into forms usable by living organisms. Some fixation occurs in lightning strikes, but most fixation is done by nitrogen-fixing bacteria. These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia, which they then turn into nitrites and nitrates. Some nitrogen fixing bacteria, such as Rhizobium, live in the root nodules of legumes (such as peas or beans), these are called simbiotic nitrogen-fixing bacteria. Symbiosis is where two organisms live and benefit together from a mutual relationship. Symbiotic bacteria gain a habitat and the plant gains nitrates to form amino acids and DNA. Plants can absorb nitrate or ammonium ions from the soil via their root hairs. If nitrate is absorbed, it is first reduced to nitrite ions and then ammonium ions for incorporation into amino acids, nucleic acids, and chlorophyll.(Grech, 2003) In plants which have a symbiotic nitrogen-fixing bacteria, some nitrogen is assimilated in the form of ammonium ions directly from the root nodules. These plants either die and decompose, or are digested and assimilated. When the plants die they are broken down by saprophtic bacteria. A saprophytic bacterium lives on and gets its nourishment from dead organisms or decaying organic material. Saprophytes recycle organic material in the soil, breaking it down into in simpler compounds, like ammonia, that can be taken up by other organisms.(Science dictionary, 2005) Nitrifying bacteria turns this ammonia into nitrates and nitrites which are absorbed back into the soil. By turning ammonia into nitrites and nitrates they in turn benefit by gaining amino acids. If the plant is for example, is eaten by a cow, the plant will be digested and the nutrients absorbed by the cow’s body. After a while the cow excretes faeces and urea which contain undigested proteins and nitrogen. These like the dead plant are broken down to ammonia and turned into nitrates and nitrites by nitrifying bacteria, and absorbed into the soil. The cow will then die and its body too will decompose like the plant and the excretion. Denitrifying bacteria is able to return nitrogen to its abiotic source by converting nitrates in the soil to nitrogen gas, and whilst doing so they gain oxygen for respiration.(S-cool Ltd., 2008)

During the carbon cycle, carbon is released into the atmosphere through the decay of animal and plant matter. Saprophytic bacteria and fungi break down the carbon compounds in dead animals and plants and convert the carbon to carbon dioxide. Much of the carbon in the carbon cycle is carbon dioxide. This form of carbon exists as a gas in the atmosphere and can be dissolved in water. The atmospheric carbon dioxide can be converted to organic material in the process of photosynthesis. Photosynthetic algae are important microorganisms in this regard for keeping the carbon cycle flowing. As well, chemoautotrophs, primarily bacteria and archae are capable of carbon dioxide conversion.(Enotes, 2009)

There are many different types of micro-organisms involved in the carbon and nitrogen cycles. Whilst helping to keep the cycle flowing they also gain benefits that allow them to live. Without any one of the micro-organisms the cycles could not function completely and life on earth would be altered dramatically. Although micro-organisms are the smallest organisms on the planet they prove themselves to be the most important.

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Peer Reviews

Here's what a star student thought of this essay

pictureperfect

3rd of Jul 2012

Quality of writing

This essay is a little jumbled, which makes it confusing to read. The candidate goes form talking about the nitrogen cycle to the carbon cycle then mentions the microorganisms involved in the nitrogen cycle and then discusses how carbon is recycled. The essay would flow better if the candidate had written down all the relevant information on one of the cycles and then gone on to discuss the other. However technical terms are used appropriately and are accurate and there are no real issues with either spelling or grammar.

Level of analysis

Though the candidate has quoted references in brackets, the sources they have used are unclear. It is much more suitable to write up a short bibliography at the end of your essay stating any source used, if this is a webpage you should include a link and if it is a book then you should state the authors name. Finally though the candidate attempts to conclude the essay and ends on a good statement, they should of have summarised their key points as this helps to draw the essay to a close.

Response to question

The candidate gives a suitable introduction, they have introduced the term microorganisms and stated that they are an essential part of nutrient cycles. Though this could be improved by stating what topics they planned to discuss, in this case the specific nutrient cycles they plan to discuss. This gives the essay a clear focus and helps you stay on track, so that you discuss key points. In addition to this the candidate could have defined the term microorganism, definitions make it clear to reader that you understand what you are talking about. If you plan to regularly use a key scientific term within an essay then it can be helpful to include a definition. That said the candidate has given a fairly in depth response, providing information on the different types of microorganisms and how they help recycle important elements.

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