What is oxygen cycle

The Oxygen cycle is closely related to carbon dioxide (CO2) - and the water (H2O) circuit connected. Molecular Oxygen (O2) is a strong cell poison for living organisms. A stable oxygen content of approx. 21% by volume has established itself in the air.

The transport of oxygen in the ecosystems takes place mainly with oxygen, which is bound in compounds such as carbon dioxide, water and carbohydrates.

In principle, oxygen plays a decisive role in all oxidation and reduction processes in all material cycles.

The oxygen cycle, as shown in the following scheme, consists mainly of O2-consuming and O2-generating processes:

- O2 is released molecularly in the atmosphere (by green plants) and in the hydrosphere (by algae) through photosynthesis.

- O2-Consumers are land (humans, animals) and aquatic organisms (phytoplankton)

- since the processes of photosynthesis take place the other way around in green plants at night, these also count to the O2- consumers

- Carbon monoxide (CO) released by volcanoes reacts with oxygen in the air to form carbon dioxide (CO2).

- Oxygen-forming and oxygen-consuming processes also take place in the ozone layer, an example of this are the reactions:

Ozone formation: O2 + Light energy -> O * + O * (radical formation)

O * + O2 -> O3

Oxygen formation: O3 + Light energy -> O2 + O *


Fig .: Schematic representation of the oxygen cycle

[Source: dtv-Atlas Ökologie, Deutscher Taschenbuch Verlag, 4th edition, 1998]