Biogeochemical cycles - Oxygen cycle

THE OXYGEN CYCLE

• Oxygen, one of the main components of the Earth’s atmosphere
• Two oxygen atoms make up one oxygen molecule, and three oxygen atoms together make up the molecule called ozone.
• As a gas, oxygen is odorless, colorless, and highly reactive. 
• Oxygen is essential for the survival of many organisms, and, in the ozone, provides protection to life by filtering out the sun’s ultraviolet rays.
• In the oxygen cycle, oxygen atoms present in the earth circulate through a series of processes.  
• Like the nitrogen, carbon, and water cycles, the oxygen cycle is a biogeochemical cycle.
• A biogeochemical cycle is the movement of matter through the biotic and the abiotic spheres of the ecosystem.

The oxygen cycle begins with plants and photosynthesis.

• Through photosynthesis, plants convert the energy from the sun and water into carbohydrates and oxygen. 
• During the day: plants convert carbon dioxide into oxygen.
• During the night: plants convert oxygen into carbon dioxide to maintain their metabolism.

Oxygen in water

Oxygen in water is known as dissolved oxygen. When water runs over rocks, oxygen enters and creates a lot of high surface area which allows oxygen to transfer from the air into the water very quickly. 

Animals contribution to the oxygen cycle

Animals breathe in oxygen and breathe out carbon dioxide through their processes of metabolism, sparking the process of photosynthesis, once again linking back to the plants’ contribution to the oxygen cycle. 

The Three Main Reservoirs of Oxygen

• Biosphere (living things)
• Lithosphere (Earth’s crust)
• Atmosphere (air)

Within the biosphere and atmosphere, plants begin the oxygen cycle and animals continue it.

Photolysis also donates to a large portion of the oxygen in the atmosphere, where high energy ultraviolet radiation breaks down the atmospheric water and nitrate. 

Figure depicting the interrelationship of Atmosphere, Hydrosphere, Biosphere, Ecosphere and Oxygen

Much of the oxygen present in the atmosphere is used during respiration and decay mechanisms, where animal life and bacteria consume oxygen and release carbon dioxide.

Oxygen is also cycled between the biosphere and lithosphere.

Ecologists fear that there may come a time when the amount of carbon dioxide is very large and there are too few plants to covert it into Oxygen. 

Hence, it is essential that we reduce pollution and protect our environment in order to maintain a well functioning oxygen cycle.