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Carbon Cycle – cycling of the Matter

Class 7
May 31, 2023


You may have heard about how people recycle paper, plastics, or aluminum. But have you ever heard about how the Earth recycles?

All the matter (rocks, water, air, plants, and animals) that we see on Earth results from the continuous cycling of Earth’s materials. Very little new matter enters the Earth’s system.

Water, carbon, nitrogen, phosphorus, and even rocks pass through cycles continuously in order to support life on this planet.


What happens to the leaves that fall from trees in a forest? Does anyone sweep them, or do they pile up? Where do these leaves go?

Dead organisms break down matter and make materials available for new life. Leaves, plants, and other living organisms gradually break down after dying.


These dead organisms contain certain chemicals that may become a part of the organic matter in the soil or go into the air as gases. In this way, carbon, nitrogen, and all other elements become available to support new life.

Cycling of the Matter:

The amount of matter on Earth never changes, and the elements that form matter keep cycling between the living and non-living environment.

We know that Earth’s water supply is not increasing or decreasing. This happens as a result of the water cycle. Water cycles from land to sea to air and again back to the land. Water is taken up by plants and animals and is then released back into the environment.

Like energy, water, and rocks, elements are not created or destroyed. In some instances, these elements become part of the cells of living organisms as nutrients.

At other times these nutrients exist as abiotic factors of the environment. Let us learn about these cycles that deal with the cycling of matter in both biotic and abiotic factors of the environment. These are as follows:

  • Nitrogen cycle
  • Phosphorus cycle
  • Carbon cycle

Nitrogen Cycle:

Nitrogen is an important nutrient for all living organisms. The cycling of nitrogen among Earth’s spheres is called the nitrogen cycle. The atmosphere contains 78% nitrogen but still remains unavailable to plants.

A certain type of bacteria present in the soil, called nitrifying bacteria, changes this atmospheric nitrogen, N2, into other forms so that it becomes available to plants.

Plants then take up this nitrogen through their roots and accumulate it in their tissues as they grow. This nitrogen then passes through the food chain as one organism eats another.

When living organisms die, decomposers feed on them and release the nitrogen back into the soil. Some bacteria present in the soil again change this nitrogen into atmospheric nitrogen, which is released into the air.

In this way, nitrogen passes from the atmosphere to the soil, to living organisms, and then back into the atmosphere.

Nitrogen cycle
Nitrogen cycle

Phosphorus Cycle:

Phosphorus is also an essential element found in living organisms. Unlike nitrogen, it does not occur as a gas in the Earth’s atmosphere. Phosphorus occurs in soil and water due to weathering of rocks.

Similar to nitrogen, phosphorus in the soil is also absorbed by plants with the help of roots.

This phosphorus moves from plants to animals when herbivores feed on plants and carnivores feed on herbivores. Phosphorus is returned to the soil through animal wastes and decomposition when plants and animals die.

Phosphorus cycle
Phosphorus cycle

Carbon Cycle:

Carbon is the chemical foundation of all life on Earth. Carbon compounds regulate the Earth’s temperature, provide food for us to eat, and provide energy to power our global economy.

The majority of the carbon on Earth is stored in rocks and sediments. The remainder is found in the ocean, atmosphere, and living organisms. These are the reserves where carbon cycles.

The carbon cycle explains how carbon moves between the biotic and abiotic environment. Life on Earth would not exist without carbon as it is the key element in the sugars, proteins, starches, and other compounds present in living organisms.

But carbon is also present in non-living factors like the atmosphere, the land, the water, and the remains of living things. The cycling of carbon takes place through both short-term and long-term processes.

Short-term Cycling of Carbon:

Short-term processes are relatively rapid.  Plants use energy from the sun, carbon-di-oxide, and water in order to grow. Carbon is absorbed in the form of CO2 from the air during photosynthesis by plants.

Producers combine carbon dioxide from the air and water from the soil to make sugars and other compounds. When herbivores eat plants, and then carnivores eat herbivores, energy transfer takes place. Carbon is also circulated by this energy transfer.

During cellular respiration, animals break down food to release energy, and carbon is released back into the atmosphere as CO2.

This CO2 is again used by plants for photosynthesis. When organisms die and then decompose, the carbon is released back into the soil, which continues the cycling of matter between living and nonliving forms.

The amounts of carbon, hydrogen, and oxygen in the ecosystem never change. They simply transfer from air, water, and nutrients into the living parts of the ecosystem.

Photosynthesis and cellular respiration
Photosynthesis and cellular respiration
Photosynthesis and cellular respiration
Photosynthesis and cellular respiration

Long-term Cycling of Carbon:

The long-term process of the carbon cycle is much slower. When dead organisms are buried before they decompose, they remain compacted over millions of years.

During this process, their bodies undergo certain chemical changes. This process, over time, leads to the formation of rocks such as limestones, or fossil fuels, such as coal, gas, and oil.

When humans utilize these resources by burning them, carbon is released back into the atmosphere as CO2. This process of burning fuels is called combustion.

Carbon cycle
Carbon cycle

Human Impact on Carbon Cycle

Human activity has a huge effect on the carbon cycle. The use of fossil fuels, changes in land use, and the use of limestone to form concrete all emit significant amounts of carbon into the atmosphere.

As a result, the amount of CO2 in the atmosphere is rapidly increasing; it is already higher than it has been in the last 3.6 million years.

The ocean absorbs a large portion of the carbon dioxide produced by the combustion of fossil fuels. This extra carbon dioxide is reducing the pH of the ocean, a process known as ocean acidification. Ocean acidification impairs marine organisms’ capacity to create shells and skeletons.

Carbon Cycle


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