CARBON CYCLE

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Carbon is the element that anchors all other organic substances or compounds in the ecosystem. It is the building block of life; and the atomic number of carbon in the periodic table is 6. Carbon is the major chemical constituent of most living matter on earth including man, microorganisms, animals and plants. Carbon is among the major elements (inclusive of oxygen, calcium, phosphorus, nitrogen and hydrogen) that living organisms are made up of. Carbon combines with other elements or molecules to form important compounds such as sugar (glucose), fats, proteins and starches that are vital for sustenance of life on earth. Carbon cycle is defined as the cyclical interconversion of carbon compounds in the ecosystem. It is the biogeochemical cycle by which carbon is exchanged between the biosphere, lithosphere, atmosphere and hydrosphere components of the earth. Carbon is stored or reserved in each of these earth components in varying amounts; and the various chemical, physical, geological, and biological processes occurring in them lead to the continual cycling of carbon in the ecosystem through the carbon cycle.

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The carbon cycle is important because like the oxygen and hydrogen cycles, it is a critical biogeochemical cycle of life that contributes significantly to the sustenance of life on earth. Carbondioxide (CO2) is a major metabolite in the carbon cycle; and it is fixed by autotrophic organisms including microbes/microorganisms and plants through several metabolic pathways. The energy required for the fixation of carbondioxide is usually from chemical reactions or from light energy as is applicable in photosynthesis. Life is the oxidation of carbon because the oxidation of carbon is the source of the vast biodiversity which we have on our planet earth today. In the carbon cycle, plants absorb carbondioxide from the atmosphere and use it (combining it with water they get from the soil) to make their own food needed for growth and development through the process of photosynthesis. The plants use the carbon atoms from carbondioxide in the atmosphere (Figure 1) to make simple sugars such as glucose.

Figure 1. Carbon cycle. Carbon continuously moves between the atmosphere, plants, soils and animals; and through the processes of respiration, photosynthesis and decomposition. Carbon is returned to the atmosphere by respiration, bush burning and decomposition; and it is taken up by green plants through the process of photosynthesis in the presence of sunlight and water. Carbon is later transferred to animals and man through feeding and later to the soil through decomposition of organic matter including dead plants, animals and man. Source: https://www.sciencefacts.net/carbon-cycle.html

Carbon cycle is the circulation of carbon on earth in which atmospheric carbon dioxide is converted to organic nutrients through photosynthesis and is again converted back to the inorganic state by respiration, decay, or combustion (Figure 1). The atmosphere, the oceans, vegetation, rocks, and soil forms the major carbon reserve of our planet. Herbivorous animals and man feed on the plants and use the carbon derived from them to build their own tissues while carnivorous animals eat the herbivores and use the carbon derived from them for their own growth and development (Figure 1). When these animals including man respire, they return carbon to the atmosphere through their respiration process; and when they die, they also return carbon to the atmosphere through their decomposition in the soil after death. As these processes are occurring as nature directs it, the carbon atoms from the atmosphere and in the soil are then used to build new plants and microorganisms, and the carbon atoms continue to be recycled from one organism to another and from one place to another without being lost. The carbondioxide in the atmosphere diffuses into and out of water; and this dissolved CO2 is taken up by other aquatic plants or organisms to support aquatic life. And when aquatic organisms die and decompose, they also transfer carbon to the sediments of the water body.

Human activities including but not limited to bush burning, deforestation, burning of fossil fuels and industrialization have greatly affected the carbon cycle and caused many problems such as global warming and climate change. Climate change is the long-term fluctuations in temperature, precipitation, wind, and other aspects of the earth’s climate. These activities have resulted in increase in the amount of carbondioxide in the atmosphere. And the carbon footprints of man, as well as other human activities (e.g., bush burning, gas flaring etc) have also contributed to several damages to the environment (e.g., global warming, climate change etc) over many years. The carbon cycle has a large effect on the function and well being of the planet. It plays a key role in regulating the climate of the earth by controlling the concentration of CO2 in the atmosphere. CO2 is important because it contributes to the greenhouse effect, in which heat generated from sunlight at the earth’s surface is trapped by certain gasses and prevented from escaping through the atmosphere.

The earth would be much colder without the greenhouse effect, but unnatural buildup of greenhouse gasses in the atmosphere can lead to a planet that gets unnaturally hot. Because CO2 is a greenhouse gas, the increase of carbondioxide in the atmosphere is believed to be causing a rise in global temperatures (i.e., global warming of the earth’s climate); and this is the primary cause of climate change. Global warming is the term used to describe the unusual increase in average global temperatures of the earth’s climate due to the greenhouse effect. The term global warming is often used interchangeably with the term climate change. Greenhouse gases are those gases, such as water vapor, carbon dioxide, ozone, nitrous oxide, and methane, which allow solar radiation to pass through to the earth, but block outgoing long wave radiation. The effect of these gases in keeping the earth’s climate warmer than normal is generally described as greenhouse effect.   

Further reading

Jee C and Shagufta (2007). Environmental Biotechnology. APH Publishing Corporation, Darya Ganj, New Delhi, India.

Latha C.D.S and Rao D.B (2007). Microbial Biotechnology. First edition. Discovery Publishing House (DPH), Darya Ganj, New Delhi, India.

Maier R.M, Pepper I.L. and Gerba C.P (2000). Environmental Microbiology. Academic Press, San Diego.

Mishra B.B, Nanda D.R and Dave S.R (2009). Environmental Microbiology. First edition. APH Publishing Corporation, Ansari Road, Darya Ganj, New Delhi, India.

Paul E.A (2007). Soil Microbiology, ecology and biochemistry. 3rd edition. Oxford: Elsevier Publications, New York.

Pelczar M.J., Chan E.C.S. and Krieg N.R. (2003). Microbiology of Soil.  Microbiology, 5th Edition. Tata McGraw-Hill Publishing Company Limited, New Delhi, India.

Pepper I.L and Gerba C.P (2005). Environmental Microbiology: A Laboratory Manual. Second Edition. Elsevier Academic Press, New York, USA. 

Roberto P. Anitori (2012). Extremophiles: Microbiology and Biotechnology. First edition. Caister Academic Press, Norfolk, England.

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