[Biology Class Notes] on Carbon Cycle Pdf [2024]

Carbon cycle represents the movement of carbon in elemental and combined states on earth. Diamond and graphite are the elemental forms of carbon and in a combined state, it is found as carbonates in minerals and as carbon dioxide gas in the atmosphere.

Carbon Cycle Definition

Carbon cycle can be defined as the process where carbon compounds are interchanged among the biosphere, geosphere, pedosphere, hydrosphere, and atmosphere of the earth.

Carbon Cycle Steps

Following are the main steps that are involved in the process of the carbon cycle:

Carbon present in the atmosphere is absorbed by plants for photosynthesis.
These plants are then consumed by animals, and carbon gets bio accumulated into their bodies.
When the plants and animals die and they are decomposed, carbon is released back into the atmosphere.
Some of the carbon that’s not released back to the atmosphere eventually becomes fossil fuels.
These fossil fuels are then used for man-made activities, which pumps more carbon back to the atmosphere.

Carbon Cycle Diagram

The carbon cycle diagram below explains well the flow of carbon along different paths –

The global carbon cycle is divided into various parts which act as the reservoirs of carbon, which are interconnected by some pathways of exchange. The major division of the global carbon cycle are –

The Atmosphere: The carbon present in the atmosphere of earth in the form of CO₂.
The Terrestrial Biosphere: Carbon incorporated in the surface of the earth, by the living beings like plants and animals living on the earth’s surface are all included in this section.
Oceanic Carbon Cycle: the creatures living in the oceans reserves a certain amount of carbon, and also the inorganic carbon dissolved in the waters and the carbon present at the surface of the oceans.
Geosphere: The excessive carbon is trapped deep within the earth’s crust in the form of various sediments of minerals and fossil fuels. Sediments of limestone had stored a vast amount of carbon in them.
A vast amount of the carbon is also trapped in the inner parts of the planet earth. The mantle and core of the earth have a grave quantity of carbon present in there, carbon from the lower mantle often leaks into the atmosphere by the volcanic activities.

Carbon Cycle in the Atmosphere of the Earth

In the atmosphere of the earth, the major quantity of carbon is present in the form of carbon dioxide(CO₂) and methane (CH4). Both of these gases are major contributors of global warming as these are both greenhouse gases and hence absorb and retain heat, hence causing the atmospheric heating of the planet earth. Both these two gases, carbon dioxide(CO₂) and methane (CH₄), are gradually removed from the atmosphere by the natural process of carbon cycle.

The major quantity of carbon dioxide (CO₂) is absorbed by the terrestrial and oceanic biospheres with the help of photosynthesis performed by various creatures in them like Plants in the terrestrial biosphere and cyanobacteria and algaes in the oceanic biospheres. Some of the carbon dioxide and other compounds of carbon, also falls down with the pouring of the rain.

Carbon cycle of the earths atmosphere is also the worst affected part of the global carbon cycle due to human activities, mainly in the form of carbon dioxide.

Carbon Cycle on Land

The carbon cycle on the land is called the terrestrial biosphere, all it includes all the living creatures living on the surface of the planet earth. Around 500 gigatons of carbon are stored in this biosphere above ground in the form of plants and other living organisms.

Carbon in the atmosphere is present in the form of carbon dioxide. Carbon enters the atmosphere through natural processes like respiration and industrial applications like burning fossil fuels. The process of photosynthesis involves the absorption of CO₂ by plants to produce carbohydrates. The equation is as follows:

[CO_{2} + H_{2}O + text{energy} rightarrow CH_{2}O + O_{2} ]

Carbon compounds are passed along the food chain from the producers to consumers. The majority of the carbon exists in the body in the form of carbon dioxide through respiration. The role of decomposers is to eat the dead organism and return the carbon from their body back into the atmosphere. The equation for this process is:

[CH_{2}O + O_{2} rightarrow CO_{2} + H_{2}O ]

Oceanic Carbon Cycle

This is essentially a carbon cycle but within the sea. Ecologically, oceans absorb more carbon than it gives out. Hence, it’s called a “carbon sink.” Marine animals convert carbon to carbonate and this forms the raw building materials required to make hard shells, almost like the ones found in clams and oysters.

When organisms with carbonate shells die, their body decomposes, leaving their hard shells. These accumulate on the seafloor and are eventually broken down by the waves and compacted under enormous pressure, forming limestone.

When these limestone rocks are exposed to air, they get weathered and the carbon is released back into the atmosphere as carbon dioxide.

Importance of Carbon Cycle

Even though CO₂ is found in small traces within the atmosphere, it plays an important role in balancing the energy and traps the long-wave radiations from the sun. Therefore, it acts like a blanket over the planet. If the carbon cycle is disturbed it’ll end in serious consequences like climatic changes and heating .

Carbon is an integral component of every life form on earth. From proteins and lipids to even our DNA. Furthermore, all known life on earth is predicated on carbon. Hence, the carbon cycle, alongside the organic process and oxygen cycle, plays an important role within the existence of life on earth.

Key Points on Carbon Cycle

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 in the atmosphere is taken up by the green plants and other photosynthetic organisms and is converted into organic molecules that travel through the food chain. Carbon atoms are then released as CO₂ when organisms respire.
The formation of fossil fuels and sedimentary rocks lead to the process of carbon cycle for very long periods.
The carbon cycle is related to the supply of other compounds also.