Oxygen cycle: Definition, properties, and significance

Oxygen cycle


Earth is the home of various plants and organisms. A relationship has developed between the organisms and the natural environment through mutual interaction. The plant receives the essential nutrients from the soil i.e. inert environment. Nutrients are transferred through various processes. After the death of plants and animals, that element is re-entered in the physical environment. In this way, the cyclical flow of nutrients continues. The oxygen cycle is one such natural cycle and is described below.

A few basic substances or elements are especially needed to sustain life. These 6 elements are carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. These elements are found in large quantities in the human body.

Organisms use them in almost every aspect of life. As a result of continuous use from the earliest times of creation, they do not end at once. Because there is a cyclical flow of all these substances between the environment and the organism. This cyclical flow results in the formation of various natural cycles (1).

What is an oxygen cycle?

Oxygen is the primary and most essential element for the survival of an organism. The oxygen cycle refers to the transformation of oxygen in various forms through nature.

Oxygen, an essential element of life, circulates from the environment to the organism and from the organism to the environment to form the oxygen cycle. Just as this element helps the organisms to survive, it also originates from the organism.

The oxygen cycle is one of the most important biogeochemical cycles. This cycle causes an endless cyclical flow of oxygen in the atmosphere. It is not possible for an organism to survive without oxygen. Therefore, the oxygen cycle is the vital cycle for the survival of all species (2) & (4).


The controlled cyclic process by which the oxygen in the atmosphere rotates from the environment to the organism’s body and from the organism’s body to the environment and maintains the balance of oxygen in the environment is called the oxygen cycle. The oxygen cycle is a gaseous biogeochemical cycle (3).

Sources of oxygen

Oxygen is the third most abundant element in the universe. It exists in the form of various compounds on earth. The atmosphere, biosphere, and hydrosphere are the primary place, where this element is found. The various sources of oxygen are as follows.

  • At least half of the amount of oxygen in the world comes from the oceans. Scientists estimate that about 60- 80% of the oxygen produced on earth comes from the oceans.
  • The atmosphere is the main source of oxygen. The total amount of oxygen in the atmosphere is about 21%. Other forms of oxygen present in the atmosphere are water vapor (H₂O), ozone (O₃), and carbon dioxide (CO₂).
  • Green plants release oxygen into the environment through photosynthesis. Plants absorb water and carbon dioxide in photosynthesis and produce glucose and oxygen.
  • The liquid outer layer of the earth’s core contains other elements, including oxygen.
  • Every year some amount of oxygen is added to the atmosphere as a result of the release of carbon dioxide and water from volcanic substances.
  • The reduction of various mineral oxides also produces some oxygen.
  • Various phytoplankton present in marine ecosystems produces large amounts of oxygen in photosynthesis processes. One of the largest sources of oxygen on earth is the phytoplankton, located near the surface of the ocean. Phytoplankton is small plants. They are abundant in the oceans and they produce a lot of oxygen (5) & (6).

Properties of the oxygen cycle

Oxygen is a vital non-metallic element for living organisms. This oxygen rotates in a circular way from the atmosphere to the organism’s body and from the organism’s body to the atmosphere to form an oxygen cycle. The symbol of this element is O and the atomic number is 8. There are some characteristics of the oxygen cycle.

1. The oxygen cycle is the most significant biogeochemical cycle that is constantly moving

2. This cycle is the movement of oxygen between the four main reservoirs: the atmosphere, the biosphere, the hydrosphere, and the lithosphere.

3. The oxygen cycle maintains the balance of oxygen (O₂) in the atmosphere.

4. An essential element in the human body, water contains one molecule of oxygen.

5. The oxygen in the oxygen cycle helps to control the various physiological and metabolic activities of the organism.

6. Oxygen acts as an essential component of proteins and nucleic acids in the human body.

7. It makes up about 30% of the earth and 20% of the atmosphere by this oxygen cycle.

8. The rotation of oxygen in the oxygen cycle helps in the rotation of other elements in the biosphere.

9. Chemically, oxygen is a highly active gas because it combines with most of the elements in the biosphere.

10. Oxygen makes up about 70% of living substances.

11. The oxygen cycle in the biosphere is very complex because it contains many chemical forms of oxygen (2) & (3).

Explain oxygen cycle

The oxygen cycle is considered to be the complex biogeochemical cycle. This cycle is completed in two steps.

1. Removal of oxygen from the environment

Oxygen is released from the environment by various processes.

1. All the animals present in the environment receive oxygen from the atmosphere for respiration. The result is a lack of oxygen in the atmosphere and environment.

2. During the combustion of fossil fuels (wood, coal, petroleum, diesel, kerosene, paper, etc.) the oxygen in the atmosphere is absorbed and the amount of oxygen decreases.

3. Oxygen is absorbed from the atmosphere during the formation of oxides of various minerals like copper, iron, lead, etc.

4. Large amounts of oxygen are removed from the atmosphere during volcanic eruptions or emission of heated igneous substances (4) & (5).

2. Re-entry of oxygen into the environment

Oxygen re-enters the environment through certain methods.

1. In the process of photosynthesis, water is dissolved in chlorophyll-containing space in the presence of sunlight and turns into hydrogen and hydroxyl ions. Water and oxygen molecules are formed again from those hydroxyl ions. And re-entry of oxygen into the atmosphere. As a result, oxygen balance is maintained in the atmosphere.

H₂O → H⁺ + OH⁻

4OH → 2H₂O + O₂ ↑

2. At high levels of the atmosphere, the sun’s ultraviolet rays cause water vapor to dissolve into water and oxygen molecules and marge into the atmosphere.

3. A small amount of oxygen is produced from the ozone gas off the coast and re-enters the atmosphere.

4. Animals take in oxygen from the air during respiration. It is mixed with soil during excretion. The plant absorbed that oxygen mixed water from the soil with the help of roots. And during photosynthesis, it dissolves in the atmosphere in the form of oxygen.

Atmosphere → animal body → excretory substances in soil → plant → atmosphere (3) & (7).

Relationship between oxygen cycle and carbon cycle

The oxygen cycle and the carbon cycle are intimately involved in the environment. In the oxygen cycle, the oxygen produced by the carbon cycle is used for the respiration of plants and animals and the carbon dioxide is released into the atmosphere.

On the other hand, green plants present in the carbon cycle using the carbon dioxide produced by the oxygen cycle during the process of photosynthesis, and oxygen (O₂)  is released into the environment.

After all, the cycle of oxygen and carbon continues uninterrupted at the same time. So the amount of oxygen and carbon dioxide in the environment is balanced (1) & (4).

Significance of oxygen cycle

It is an ever-moving process. It is completed by the inflow of oxygen from the physical environment or atmosphere to the biosphere or living environment and the outflow of oxygen from the biosphere or living environment to the physical environment or atmosphere. This is a very important cycle in the whole of the biosphere, hydrosphere, and atmosphere.

1. It helps to maintain the balance of oxygen between the physical environment and the biosphere.

2. The energy required to regulate the metabolism of an organism is mainly due to respiration. The respiratory function requires a constant supply of oxygen to every living cell.

As a result of the constant oxygen uptake by the organism, the oxygen gas (O₂) would be depleted. But the supply of oxygen in the environment never ends through the oxygen cycle. Thus maintaining the balance of oxygen in the environment is the main significance of the oxygen cycle.

3. The oxygen cycle also balances the carbon cycle. The presence of oxygen is essential for the combustion and decomposition of organic matter. This element oxidizes organic matter to produce carbon dioxide gas. As a result, the balance of carbon dioxide in the environment is never-ending.

4. Oxygen is converted to ozone gas through certain chemical processes. This ozone gas creates a layer of coating called the ozone layer on the surface of the atmosphere. This layer protects the living world from destruction by absorbing various harmful cosmic rays and ultraviolet rays of the sun.

5. The oxygen cycle maintains an uninterrupted supply of oxygen, which is an essential element for all plants and animals (3) & (7).

The oxygen (O₂)  cycle is a biological process that helps maintain oxygen levels through the earth’s three main regions, such as the atmosphere, lithosphere, and biosphere. It has a significant impact on the environment and fauna.

This cycle also plays a vital role in the ecosystem. These biochemical substances explain the movement of oxygen gases in the atmosphere, ecosystems, fauna, and the lithosphere. The sum of the earth’s ecosystems creates a living world. This oxygen cycle is the main basis of the existence of the whole organism.

Written By: Manisha Bharati

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