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Carbon cycle represents the movement of carbon in elemental and combined states on earth. Carbon is the basis of all life on earth and is necessary to form everything from elements like graphite to complex molecules such as proteins and DNA.
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Key Terms: Carbon cycle, hydrosphere, oxygen-cycle, food chain, geosphere, minerals, pedosphere, biosphere, atmosphere, Gas
What is Carbon Cycle?
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The carbon cycle can be defined as the process by which carbon compounds are exchanged between the earth's biosphere, geosphere, pedosphere, hydrosphere, and atmosphere. Diamond and graphite are the elemental forms of carbon and are found combined as carbonates in minerals and as carbon dioxide gas in the atmosphere.
Important Steps Of Carbon Cycle
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The following are the most important steps in the carbon cycle process:
- Plants absorb carbon from the atmosphere for photosynthesis.
- These plants are then consumed by animals and the carbon accumulates biologically in their bodies.
- When plants and animals die and decompose, carbon is released back into the atmosphere.
- Some of the carbon that is not released into the atmosphere eventually becomes fossil fuels.
- These fossil fuels are then used in man-made activities that pump more carbon into the atmosphere.
Read More:
| Related Topics | ||
|---|---|---|
| Photosynthetically active radiation | Energy flow in ecosystem | Aquatic Ecosystem |
| Nitrogen Cycle | Phosphorus Cycle | Grazing Food Chain |
| Biomass | Biotic Factors | Marine Biology |
Carbon Cycle on Land
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Carbon in the atmosphere is in the form of carbon dioxide. Carbon enters the atmosphere through natural processes such as respiration and industrial applications such as the burning of fossil fuels. The photosynthesis process involves the absorption of CO2 by plants to produce carbohydrates. The equation is as follows:
CO2 + H2O + energy → CH2O + O2
Carbon compounds pass through the food chain from producer to consumer. Most of the carbon is found in the body in the form of carbon dioxide through respiration. The decomposers' job is to eat up the dead organism and return the carbon from your body to the atmosphere. The equation for this process is:
CH2O + O2 → CO2 + H2O
Ocean Carbon Cycle
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This is essentially a carbon cycle in the ocean. From an ecological point of view, the oceans absorb more carbon than they emit. That is why it is called a "carbon sink". Marine animals convert carbon into carbonate and this forms the raw materials needed to make hard shells, much like those found in clams and oysters.
When carbonate-shelled organisms die, their bodies decompose, leaving behind their hard shells. These accumulate at the bottom of the sea and are eventually broken down by waves and compacted into limestone under enormous pressure.
When these limestone cliffs are exposed to the air, it weathers and the carbon is released into the atmosphere as carbon dioxide.
Read More: Pyramid of Biomass
Importance of the carbon cycle
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Although CO2 is found in small traces in the atmosphere, it plays an important role in energy balance and captures long-wave radiation from the sun. Therefore, it acts like a blanket over the planet. If the carbon cycle is interrupted, it has serious consequences such as climate change and global warming.
Carbon is an integral part of all life on earth. From proteins and lipids to our DNA. Furthermore, all known life on earth is carbon-based. Thus, the carbon cycle, along with the organic process and the oxygen cycle, plays an important role in the existence of life on earth.
Read More:
| Important Chapter Topics | ||
|---|---|---|
| Pelagic Zone | Benthic Zone | Productivity in Ecosystem |
| Biome Vs Ecosystem | Food Chains and Webs | Decomposers |
| Microbes in Human Welfare | Diversity in Living Organisms | Biomes |
Things to Remember
- The carbon cycle leads to the movement of carbon between the earth's biosphere, geosphere, hydrosphere, and atmosphere.
- Carbon is an important element of life.
- Carbon dioxide from the atmosphere is taken up by green plants and other photosynthetic organisms and converted into organic molecules that travel through the food chain. When organisms breathe, carbon atoms are released as CO2.
- The formation of fossil fuels and sedimentary rocks leads to the carbon cycle process over very long periods of time.
- The carbon cycle is also related to the supply of other compounds.
Read More: Abiotic Factors
Previous Year Questions
- Which of the following aquatic plant does not show pollination by water? … (KCET 2021)
- Aquatic reptiles are … (NEET 1999)
- Upper part of sea/aquatic ecosystem contains … (NEET 1988)
- An ecosystem which can be easily damaged but can recover … (NEET 2004)
- Energy transfer from one trophic level to other...[NEET 1999]
- the rate of production of organic matter by consumers….[NEET 2012]
- About 70% of total global carbon is found in...[NEET 2008]
- An ecosystem which can be easily damaged but can….[NEET 2004]
- The biomass available for consumption by the herbivores...[NEET 2010]
- Both hydrarch and xerarch successions lead to...[NEET 2011]
- During ecological succession...[NEET 2015]
- In a biotic community, the primary consumers are...[NEET 1995]
- In an ecosystem, which one shows one-way passage...[NEET 1988]
- Upper part of sea/aquatic ecosystem contains...[NEET 1988]
- Vertical distribution of different species occupying different...[NEET 2015]
- What is true of ecosystem?...[NEET 1988]
- Which ecosystem has the maximum biomass ?...[NEET 2017]
Sample Questions
Ques. Does the quantity of carbon change? (2 marks)
Ans. Since Earth is a closed system, the amount of carbon on the planet never changes. However, the amount of carbon in a given reservoir can change over time as carbon moves from one reservoir to another. For example, plants could absorb some of the carbon from the atmosphere to make food during photosynthesis. This carbon can then be absorbed and stored by animals that eat the plants. When animals die, they decompose and their remains turn into sediment that encases the carbon stored in layers that eventually turn into rocks or minerals. Some of this sediment could form fossil fuels like coal, oil, or natural gas, which release carbon into the atmosphere when the fuel is burned.
Ques. Explain in detail the type of carbon cycles? (2 marks)
Ans. The carbon cycle can be divided into two types according to the duration of the process:
Short term: this type occurs during a relatively short period of time. It is so named because it only takes days, months, or years for carbon to flow through the various carbon pools.
Long Term: This type takes thousands of years to appear. Excess carbon from the short-term cycle is stored long before release.
Ques. What is the amount of carbon present on the entire planet and where all is it available? (2 marks)
Ans. Carbon constitutes 49% of the dry weight of organisms.
4x1013 kg of carbon is fixed in the biosphere by photosynthesis.
Large amounts of carbon are returned to the atmosphere as carbon dioxide through the respiration of producers and consumers. The decomposers also return carbon dioxide to the reservoir during the decomposition process.
Some of the carbon is lost in the sediments and is removed from the cycle.
Ques. What are the most expansive products made out of carbon? (2 marks)
Ans. The most expensive product made out of carbon is diamond. As diamonds have prestige value so there is actually no limit on the value of diamonds.
The most expensive blue diamond sold was a blue diamond of 14.2 karats, fantastic and animated, which at a price of 57.5 million.
Ques. What is the importance of Carbon? (2 marks)
Ans. Carbon is important to all known living systems and without it, life could not exist. Carbon is available in the form of other hydrocarbons in addition to food and wood, such as fossil fuels, methane gas, and crude oil. Carbon fibre has multiple uses, as it is a strong yet lightweight and durable material. These fibres are used in the manufacture of tennis rackets, fishing rods, even aeroplanes and missiles. Industrial diamonds are used for drilling and cutting rocks.
Ques. Differentiate between the carbon and phosphorus cycle. (2 marks)
Ans.
- Unlike carbon, there is no respiratory release of phosphorus.
- Atmospheric inputs of phosphorus through rainfall are much smaller than carbon inputs.
- Gaseous exchange of phosphorus between organism and environment are negligible.
Ques. How is our atmosphere different from the atmosphere on Venus and Mars? (CBSE 2013) (2 marks)
Ans. Our atmosphere contains a mixture of many gases like nitrogen (78.08%), oxygen (20.95%), carbon dioxide (0.03%) and water vapour (in varying proportions). Whereas the atmosphere on Venus and Mars is mainly comprised of carbon dioxide. This carbon dioxide constitutes up to 95-97% of the atmosphere on Venus and Mars. It is supposed that due to this reason no life is known to exist on these planets.
Ques. List any three human activities that you think would lead to air pollution. (CBSE 2013) (3 marks)
Ans. Human activities that would lead to air pollution:
- Excessive use and burning of fossil fuels like coal and petroleum produce different oxides of nitrogen and sulphur. These are not only dangerous to our respiratory system but also leads to acid rain.
- Incomplete combustion of various fuels forms unburnt carbon particles which lower the visibility, especially in cold weather when water also condenses Out of air. This is known as smog and is a visible indication Of air pollution.
- Large usage Of automobiles and improperly tuning of engines leads to the formation of carbon monoxide gas and Other oxides of nitrogen which causes a lot of respiratory problems.
- Forest fires, excessive mining and ore refining, excessive use of chlorofluorocarbons and excessive industrialisation leads to air pollution.
Ques. List any three human activities that would lead to an increase in the carbon dioxide content of the air. (CBSE 2013) (3 marks)
Ans. Three human activities which would lead to an increase in the C02 content of air are :
- Respiration: It is the natural process Of release Of C02 by both plants and animals. But this release is neither dangerous nor has any adverse effect on our environment.
- Combustion of fuels: The various types of fuels are burnt to provide energy for various needs like heating, cooking, transportation and industrial fuels.
- Deforestation: Trees help in the conversion Of C02 into organic compounds such as glucose, starch, etc., by the process of photosynthesis. When these trees are cut non-judiciously, then the level of C02 increases in our environment.
Ques. Why is the atmosphere essential for life? (CBSE 2011) (2 marks)
Ans. The atmosphere is essential for life because of the following masons :
- It keeps the average temperature of the earth fairly steady during the day and even during the course of the whole year.
- It prevents the sudden increase in temperature during the daylight hours.
- It contains all the important gases which are required for sustaining life on earth.
These gases are :
- Oxygen for respiration of living organisms and oxidation.
- Carbon dioxide for photosynthesis in plants and for making food.
- Nitrogen for providing inert atmosphere and making proteins.
- The stratosphere region (16-23 km from the surface of Earth) of the atmosphere contains a thick layer of ozone which filters the harmful UV radiation from the Sun. If these radiations reach the surface of Earth, then they may cause cancer in animals and are also harmful to plants.
Ques. Describe the Carbon cycle. (5 marks)
Ans. Carbon cycle is the most common nutrient or biogeochemical cycle of an ecosystem.
(i) Carbon constitutes 49% of the dry weight of an organism, next to the water.
(ii) About 71% of carbon is found dissolved in oceans, which is responsible for its regulation In the atmosphere.
(iii) Carbon cycle occurs through the atmosphere, the ocean and through living and dead organisms. Fossil fuel also represent a reservoir of carbon
(iv)According to an estimate, 4x 1013 kg of carbon is fixed in the biosphere through photosynthesis annually.
(v) A considerable amount of carbon is returned to the atmosphere as C02, released by the animals and plants during respiration and by the activities of decomposers.
(vi) Some amount of fixed carbon is lost to sediments and removed from circulation.
(vii) The additional sources of carbon for the release in the atmosphere are burning of wood, forest fire and combustion of organic matter, fossil fuel, volcanic activity.
(viii) Human activities like deforestation, massive burning of fossil fuels for energy and transport have increased the rate of release of carbon dioxide into the atmosphere.
Ques. Carbon cycle in nature is a biogeochemical event. Explain. (CBSE 2009) (5 marks)
Ans. Carbon cycle is the most common nutrient or biogeochemical cycle of an ecosystem.
- Carbon constitutes 49% of the dry weight of an organism.
- About 71% of carbon is found dissolved in oceans, which is responsible for its regulation in the atmosphere.
- Carbon cycle occurs through the atmosphere, the ocean and through living and dead organisms.
- According to an estimate, 4 x 1013 kg of carbon is fixed in the biosphere through photosynthesis annually.
- Carbon is returned to the atmosphere as CO2 released by the animals and plants during respiration and by the activities of decomposers.
- Some amount of fixed carbon is lost to sediments and removed from circulation.
- The additional sources of carbon for the release in the atmosphere are burning of wood, forest fire and combustion of organic matter, fossil fuel, volcanic activity.
- Human activities like deforestation, massive burning of fossil fuels for energy and transport have increased the rate of release of carbon dioxide into the atmosphere.
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