1. Removal of CO2 from the atmosphere by plants and bacteria.
2. Generation of organic molecules, and building of biological mass in plants.
3. Consumption of plants by animals.
4. Respiration of animals restoring the CO2 in the atmosphere.
5. Dead and decaying organic matter getting decomposed.
6. Burning of organic matter releasing CO2 in the environment.
7. Fossil fuel combustion, volcanic eruptions and erosion returning CO2 in the atmosphere.

Nitrogen is an essential component of biological molecules like amino and nucleic acids, but most living organisms cannot use the element in its pure form and need a derivative component, NH3(ammonia) to be able to synthesize organic components.

1. Nitrogen (N2) is converted in ammonia (NH3) by bacteria in water and soil, and subsequently converted into nitrite and its derivatives.
2. Plants get nitrogen from the soil through the roots, producing organic compounds.
3. Animals absorb nitrogen by eating the plants.
4. Decomposed plants and animals, along with the solid waste return nitrogen into the soil.
5. Bacteria convert ammonia into nitrite and nitrate.
6. These compounds are then converted into pure nitrogen by nitrifying bacteria, taking it back into the atmosphere.

Photosynthesis in plants takes care of the production of most of the oxygen.

Plants make use of sunlight, water and carbon dioxide to produce glucose and oxygen, which is used by animals(respiration and consumption of plants). Oxygen is then removed from the atmosphere by the process of decomposition.

A component of certain biological molecules like phospholipids, DNA and adenosine triphosphate (ATP), phosphorus is circulated in the environment through the soil, water rocks and living organisms.

It is found organically as phosphate ion and is added to the soil and water through natural weathering of rocks. It is absorbed from the soil by plants, which are in turn consumed by animals, getting back into the soil by the process of decomposition.