The effects and importance of the carbon and nitrogen cycle

Carbon is the basis of all life. It is the backbone of organic matter whereby other elements can bond to it to form complex specialised polymers used in the functioning of organisms. The two most important features of carbon is that it has a valence of four allowing it to bond to other life essential elements and that the energy input required to make and break bonds is at a level where molecules and complex organic polymers can form. The composition of dietary nutrients like Lipids, proteins and carbohydrates all contain the element of carbon. And so through does the enzymes required to act upon and digest them.

It is because of carbon’s ability to bond to other elements like oxygen, hydrogen and nitrogen that this can happen.

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As each individual carbon atom has the ability to hold eight electrons in its outer shell it can form four other bonds with four other elements. Carbon can also form bonds with itself and as well as single bonds it can also make double bonds with other elements. This allows carbon to form a variety of compounds all differing in sizes and shapes such as cellulose, keratin, chitin and other vital polysaccharides as well as being a fundamental element in all forms of organic matter.

This shows the linkages that relies on carbon

in cellulose, a major component in the structure

of a plant.

Nitrogen is the most abundant element on our planet. It contributes a total of 79% to our atmosphere and as an element is a vital key component to many of the molecules which form the basic building blocks of life.

The four nitrogenous bases adenine, guanine, cytosine and thiamine form part of DNA which is the genetic coding responsible for the stimulation of hormone production, growth and the production of proteins.

There is only a total of 20 amino acids all of which are characterised by the presence of nitrogen (or an amine group) which go on to make up thousands of different proteins or polypeptides which are linked chains of amino acids.

Globular proteins like those of enzymes and haemoglobin are essential to carrying out bodily functions like digestion and respiration.

Therefore proteins are partly composed of nitrogen and that with out it we would be unable to function as organisms.

This shows the composition of the four

nitrogenous bases

in which nitrogen is evidently a key component

in the structures, due to its bonding capacity.

In the absence of nitrogen organisms would be unable to produce any RNA, DNA and in turn any proteins and as a result would cease to exist. Also the nitrogen cycle would fail which would lead to extinction as not only would plants be unable to develop as producers but also herbivores which rely on plants to obtain nitrogen and any other organisms thereafter.

Would it not be for the process of nitrogen fixation this could potentially happen.

The process of nitrogen fixation is needed to convert nitrogen from its natural, inert diatomic form (N2) in to nitrogen compounds so that it can pass through the food chain and the nitrogen cycle.

Nitrogen fixation occurs in three processes which is responsible for nitrogen fixation in the biosphere:

> Biological fixation

> Atmospheric fixation

> Industrial fixation

Plants need nitrogen to make proteins. But they can’t receive nitrogen in the form of gas so organisms are needed to turn them into minerals which the plants can then absorb from the soil.

Any organic waste i.e. rotting plants, dead animals or faeces is broken down by detritus feeders (decomposers) into simple ammonia compounds. This is then acted upon by nitrifying bacteria, which are organisms that convert the nitrogen compounds into nitrates.

Plants then receive these nitrates as minerals from the soil.

This forms part of a delicate balance in the food chain in that animals can’t use nitrogen directly and must eat plants to obtain it, and then of course other animals eat these animals to get their nitrogen to form their proteins.

Atmospheric fixation occurs as a result of lightning. The energy of the lightning provides an imitation of electrolysis which splits diatomic molecules of nitrogen into individual atoms whereby a reaction takes place producing nitrogen compounds, these then dissolve in rain forming nitrates which are then deposited in the earth.

Industrial fixation is what is used to make fertilizers (the haber process) which happens when both nitrogen and hydrogen are put under great stress with factors like temperatures in excess of 450 oC and pressures the equivalent to 200 atmospheres. This process produces ammonia which can be used directly as fertilisers, this can then be acted upon by nitrifying bacteria.

This balance can be disrupted though. Vegetation is the term given to depressions of plant communities and through land clearing and deforestation this can give rise to a disturbance in the nitrogen cycle which in turn can cause further disturbances to biomes.

Deforestation is the process whereby land is cleared of trees to allow for urbanisation and supplies of timber. Subsequently habitats are destroyed which can disrupt the vegetation present in biomes and in turn the organisms present in them.

Further more this can give rise to intense competition between organisms, promoting extinction or at the very least the endangering of species. A deficiency of producers would also result, causing a shortage of mammal compatible nitrates.

With organised agriculture, urbanisation and intense industrialisation, vegetations and habitats are simply removed. This affects the nitrogen cycle as the number of organisms that can utilise nitrogen which act to provide a viable source of nitrates for other organisms is reduced.

In addition to this, gases which are harmful to the atmosphere are also produced as by products from reactions which take place to provide power and electricity for domestic and industrial processes.

Fossil fuels are used to provide this power and on an industrial level the combustion of either hydrocarbons or organic compounds is at an astronomical level in comparison to the already diminishing finite supply and even more so the gases which are produced.

This is due to the demand for man made products and sources of fuel for domestic needs.

As a result, these gases not only pollute the atmosphere but also damage ecosystems and are harmful to animal species. These gases are also known as green house gases adding to the enhanced green house effect, known as global warming.

The main gases produced are usually those of nitrogen based oxides and of CO2.

This proves to be detrimental to the atmosphere in that nitrogen compounds like that of N2O (nitrous oxide) affect the atmosphere by destroying the ozone layer.

Nitrous oxide is also a major heat trapping gas and so is therefore a green house gas, contributing to global warming.

Carbon dioxide is also a greenhouse gas and traps heat, increasing the surface temperature of the earth.

Traffic is held responsible for one-third of greenhouse gas emissions.

The emissions produced are mainly those of carbon dioxide, carbon monoxide, nitrogen based oxides and volatile organic compounds.

The emissions of pollutants into the atmosphere can cause medical conditions to humans such as asthma, hypoxia, emphysema, bronchitis and other chronic related respiratory illnesses

Gases like carbon monoxide are formed due to incomplete combustion which is readily absorbed by the blood instead of oxygen. This in turn deprives the brain of oxygen and on its own can cause brain damage or even death. Although this is more common in house holds this can occur in any enclosed areas as result of traffic pollution.

Although traffic may be responsible for 1 third of greenhouse gas emissions the other two thirds are complementary to industry and domestic requirements. Other by products also include nitrogen based oxides.

The increase of nitrogen compounds has happened through using nitrogen based fertilizers, disposing of human and animal waste in sewage treatment plants and through exhaust emissions.

Methane is also produced due to the rubbish which lies in land fills.

This increase in both carbon and nitrogen based compounds can disrupt the already delicate balance of both the carbon and nitrogen cycle.

Plants are said to be carbon neutral in that they perform a feedback mechanism by absorbing the carbon dioxide produced by humans for photosynthesis and produce CO2 in the process of respiration (but only at night). This is needed to break down the glucose produced by the plant itself

If levels of CO2 continue to increase this could alter the plant species present and therefore animals which are able to survive. This is of course is referring to biodiversity.

Disregarding the enhanced green house effect, the hypothetical effects of elevated levels of CO2 is that there would be higher concentrations of carbon dioxide present in the atmosphere. According to recent studies this has had a positive impact on the way in which plants have grown in terms of their size, weight and fruit yield-(species dependant) because in this “scenario” carbon dioxide is not a limited factor.

This of course appears to be an advantage and as a result this also promotes abundance for plant life, creating biodiversity. The effect of which, would be on humans and animals alike whereby there’d be an increase in the availability of oxygen.

Nitrogenous oxides which are often unwanted products of industrial reactions would effect the biodiversity in both a biome and ecosystem by producing excess nitrates. Although this may seem indirect and unrelated at first, the presence of nitrogen based oxides in the atmosphere could lead to the formation of a nitrate through nitrogen fixation which was earlier discussed. The effect this could have on organisms is that of eutrophication.

The presence of too many nitrogen compounds can cause eutrophication. Fertilisers used in modern day farming are essential to ensuring crops develop to meet industry requirements and for maximising food yields.

Eutrophication starts when fertilisers are either washed into rivers or streams by rain. This then causes a growth of algae where by neighbouring plants are in competition for light. If the population of algae exceeds that of other primary producers this can cause death of the competing organisms.

Eventually both plants and algae die and due to the increased biomass more microbes/decomposers are introduced. These decomposers then need to be able to respire (aerobically) and consequently consume all oxygen present or at the very least an amount which deprives other organisms of the ability to be able to respire themselves, causing death to all other organisms present in that ecosystem i.e. fish.

This of course is an example of eutrophication in a water based ecosystem.

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