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Oxygen Cycle (Replacement of Oxygen in Air)

Last updated date: 09th Apr 2024
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Atmosphere: An Introduction

The Atmosphere is the term referring to the gaseous encirclement of the Earth. The atmosphere rises many kilometres above the surface of the Earth. We occupy the Earth's atmosphere. For life to exist on Earth, the atmosphere is required. This is so that we, and all other living things, may breathe oxygen, which is provided by the atmosphere. The amount of air decreases as we ascend higher in the atmosphere. On very high mountain summits, the air is so thin that there is not enough oxygen for people to breathe normally.

As a result, those who scale high mountains do so with the aid of oxygen gas cylinders. To remain alive in these high mountains, they breathe oxygen from these cylinders. Due to differences in temperature and pressure at various altitudes, the atmosphere is separated into several concentric shells or spheres. The troposphere, stratosphere, mesosphere and thermosphere are the four layers of the atmosphere.

Chemical Composition of Air

Nitrogen gas is the major component of air. About 99% of the elements that make up air are nitrogen, oxygen, water vapour, argon and carbon dioxide. Neon, methane, helium, krypton, hydrogen, xenon, ozone and several more substances are examples of trace gases. From one location to the next, and even depending on whether it is day or night, the makeup of the air differs.

Elements and Compounds in Air









Carbon dioxide
















Nitrogen dioxide




Carbon monoxide




Water Vapour Content in Air

Air can contain up to 5% water vapour; however, it usually only contains 1-3%. Water vapour is the third most prevalent gas in the 1% to 5% range (which alters the other percentages accordingly). Depending on the temperature of the air, water content changes. Humid air is less dense than dry air. In contrast, humid air that just includes water vapour occasionally contains actual water droplets, which can increase its density.

Replacement of Oxygen Element in Atmosphere

Living things constantly use the oxygen in the air to breathe. Fuels are also burned with oxygen. Plants constantly replace the oxygen that is exhaled and burned by humans and animals during photosynthesis. The words "photo" and "synthesis" both refer to the use of light. Green plants use carbon dioxide and water to manufacture their own food during the process of photosynthesis, which occurs in the presence of sunshine. Carbohydrates are processed as food while gaseous oxygen is released.

For photosynthesis, plants use water from the soil and carbon dioxide from the atmosphere. Only green plants can carry out this process because they have chlorophyll, a green pigment that can absorb solar energy. As a result, it only occurs during the day, in contrast to breathing, which happens both during the day and at night. Although it is created during photosynthesis, glucose is preserved in plants as starch.

With the assistance of ambient oxygen, food is broken down during the respiration of plants and animals to produce carbon dioxide, water and energy. The respiration of living beings releases carbon dioxide back into the atmosphere whereas the photosynthesis of green plants removes it. Together, these two diametrically opposed processes maintain the same composition of the air. In other words, it maintains the necessary level of oxygen in the air by mixing with it and making it fresher during photosynthesis. Additionally, plants continuously consume carbon dioxide to maintain the necessary level in the atmosphere.

Importance of Oxygen Cycle

One of the most crucial elements of the earth's atmosphere is oxygen. It is primarily needed for:

  • Breathing - It is the physiological process by which all living things, including plants, animals and people, take in oxygen from their surroundings and release carbon dioxide back into the atmosphere.

  • Combustion - It is also one of the most significant processes that take place when any organic substance, such as wood, plastic and fossil fuels, burns when oxygen is present and releases carbon dioxide into the atmosphere.

  • The Breakdown of Organic Waste - It takes place when an organism dies and is one of the most crucial natural processes in the oxygen cycle. The organic matter, which includes carbon, oxygen, water and other elements, returns to the soil and air as the deceased animal or plant decomposes into the earth. The invertebrates, sometimes known as the "decomposers," which include fungi, bacteria and some insects, carry out this activity. Carbon dioxide is released and oxygen is needed during the entire process.

Although oxygen is a vital component of life, some anaerobic bacteria may be poisonous to it (especially obligate anaerobes).

The oxygen cycle primarily works to keep the atmosphere's oxygen content stable. The complete process can be summed up as follows: the oxygen cycle starts with the process of photosynthesis in the presence of sunlight, releases oxygen back into the atmosphere and then links back to the plants. Humans and other animals then breathe in oxygen and exhale carbon dioxide. This further demonstrates the independence and interdependence of the oxygen and carbon cycles.



Interesting Facts

  • 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.

  • Aurora borealis, or northern lights, is produced by solar wind particles colliding with oxygen elements in the earth’s atmosphere.

Key Features

  • About 99% of the elements that make up air are nitrogen, oxygen, water vapour, argon and carbon.

  • Neon, methane, helium, krypton, hydrogen, xenon, ozone and several more substances are examples of trace gases.

  • Living things constantly use the oxygen in the air to breathe. Fuels are also burned with oxygen.

  • It is primarily needed for Breathing/Combustion, keeping aquatic life alive, and the breakdown of organic waste.

Competitive Exams after 12th Science

FAQs on Oxygen Cycle (Replacement of Oxygen in Air)

1. What is a biogeochemical cycle?

The flow of nutrients and other elements between biotic and abiotic forces is referred to as "biogeochemical cycles." The words "bio" and "geo," which refer to the biosphere, "geo" and "chemical," which refer to the elements that flow through a cycle, are the roots of the term "biogeochemical.

2. Which is the hottest layer of the atmosphere?

The thermosphere is the hottest layer of the atmosphere because it contains the fewest molecules and atoms, making it possible for even modest amounts of solar energy to considerably raise the air's temperature.

3. Why is oxygen considered an element?

Since it cannot be decomposed further, oxygen is regarded as an element. Elements are unadulterated materials that combine to form an atom. The simplest building components into which matter may be divided using only chemical processes are the elements. On the periodic table, oxygen is represented by the atomic number eight. Air is a mixture of primarily oxygen and nitrogen, which makes it a substance. Even though oxygen gas molecules are formed of two oxygen atoms covalently bound together, oxygen is still regarded as an element.