Oxygen Cycle

As we all know, the air is a mixture of gases. The air in the atmosphere is composed of different gases, namely nitrogen (78%), oxygen (21%), argon and other trace gases (1%).

According to the earth’s history, oxygen gas was first introduced by cyanobacteria through the process of photosynthesis. Earlier, around 4.6 billion years ago, there was no life on planet earth because the atmosphere was devoid of oxygen. Later, there was a gradual increase in the oxygen levels and by the Carboniferous Period- 299 million years ago, oxygen reached the levels that were similar to today’s estimates.

Today, oxygen is freely available in the air and also dissolved in water. It is the second most abundant gas present in the atmosphere and also the most common element of the human body. It plays an essential role in most life forms on earth and also serves as an essential element in biomolecules like proteins and nucleic acids.

Read on to explore more about oxygen, its uses, production and how it is recycled in a cyclic pattern.

What is Oxygen Cycle?

Oxygen Cycle

A Diagrammatic Representation of the Oxygen Cycle

Oxygen cycle, along with the carbon cycle and nitrogen cycle plays an essential role in the existence of life on the earth. The oxygen cycle is a biological process which helps in maintaining the oxygen level by moving through three main spheres of the earth which are:

  • Atmosphere
  • Lithosphere
  • Biosphere

 This biogeochemical cycle explains the movement of oxygen gas within the atmosphere, the ecosystem, biosphere and the lithosphere. The oxygen cycle is interconnected with the carbon cycle.

The atmosphere is the layer of gases presents above the earth’s surface. The sum of Earth’s ecosystems makes a biosphere. Lithosphere is the solid outer section along with the earth’s crust and it is the largest reservoir of oxygen.

Also Read: Biogeochemical Cycle

Stages of the Oxygen Cycle

The steps involved in the oxygen cycle are:

Stage-1: All green plants during the process of photosynthesis, release oxygen back into the atmosphere as a by-product.

Stage-2: All aerobic organisms use free oxygen for respiration.

Stage-3: Animals exhale Carbon dioxide back into the atmosphere which is again used by the plants during photosynthesis. Now oxygen is balanced within the atmosphere.

Uses of Oxygen

Uses of Oxygen

The  four main processes that use atmospheric oxygen are:

Breathing – It is the physical process, through which all living organisms, including plants, animals and humans inhale oxygen from the outside environment into the cells of an organism and exhale carbon dioxide back into the atmosphere.

Decomposition: It is one of the natural and most important processes in the oxygen cycle and occurs when an organism dies. The dead animal or plants decay into the ground, and the organic matter along with the carbon, oxygen, water and other components are returned into the soil and air. This process is carried out by the invertebrates, including fungi, bacteria and some insects which are collectively called as the decomposers. The entire process requires oxygen and releases carbon dioxide.

Read more: Decomposition

Combustion: It is also one of the most important processes which occur when any of the organic materials, including fossil fuels, plastics and wood, are burned in the presence of oxygen and releases carbon dioxide into the atmosphere.

Rusting: This process also requires oxygen. It is the formation of oxides which is also called oxidation. In this process, metals like iron or alloy rust when they are exposed to moisture and oxygen for an extended period of time and new compounds of oxides are formed by the combination of oxygen with the metal.

Production of Oxygen

Plants: The leading creators of oxygen are plants by the process of photosynthesis. Photosynthesis is a biological process by which all green plants synthesize their food in the presence of sunlight. During photosynthesis, plants use sunlight, water, carbon dioxide to create energy and oxygen gas is liberated as a by-product of this process.

Sunlight: Sunlight also produces oxygen. Some oxygen gas is produced when the sunlight reacts with water vapour in the atmosphere.

Also Refer: Exchange Of Gases

Production of Oxygen

Some Interesting Facts about Oxygen

  • Phytoplankton is one of the most significant producers of oxygen, followed by terrestrial plants and trees.
  • Oxygen is also produced when the sunlight reacts with water vapour present in the atmosphere.
  • A large amount of oxygen is stored in the earth’s crust in the form of oxides, which cannot be used for the respiration process as it is available in the combined state.

Importance of Oxygen Cycle

As we all know, oxygen is one of the most essential components of the earth’s atmosphere. It is mainly required for:

  • Breathing
  • Combustion
  • Supporting aquatic life
  • Decomposition of organic waste.

Oxygen is an important element required for life, however, it can be toxic to some anaerobic bacteria (especially obligate anaerobes).

The oxygen cycle is mainly involved in maintaining the level of oxygen in the atmosphere. The entire cycle can be summarized as, the oxygen cycle begins with the process of photosynthesis in the presence of sunlight, releases oxygen back into the atmosphere, which humans and animals breathe in oxygen and breathe out carbon dioxide, and again linking back to the plants. This also proves that both the oxygen and carbon cycle occur independently and are interconnected to each other.

Also Read: Importance of Air

Frequently Asked Questions

1. What is oxygen cycle?

The oxygen cycle is a biogeochemical cycle involved in the circulation of the oxygen atoms present in the earth through a series of intricate processes.

2. What is a biogeochemical cycle?

A biogeochemical cycle is the process of moving or rotation of matter throughout the biotic and the abiotic spheres of the ecosystem.

3. What are the main reservoirs of oxygen?

The main reservoirs of oxygen are:

  1. Atmosphere
  2. Biosphere
  3. Hydrosphere
  4. Lithosphere

Explore more about the Oxygen cycle or other related topics at BYJU’S Biology



  1. I love you guys your article helped me alot

  2. What is Corrosion?

    1. Corrosion is an irreversible destruction caused to materials or living tissues as a result of an electrochemical reaction. Rusting of iron is the most common example.

  3. Thanks for the best explanation

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  5. Thank you so much for the information!!

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