Oxygen cycle - SS2 Biology Lesson Note
The oxygen cycle is a biogeochemical cycle that describes the movement of oxygen within the Earth's atmosphere, biosphere, and lithosphere. It is an essential cycle for sustaining life on our planet.
The oxygen cycle begins with photosynthesis, which occurs primarily in plants, algae, and some bacteria. During photosynthesis, these organisms use sunlight, water, and carbon dioxide to produce glucose (a form of stored energy) and release oxygen as a byproduct. The equation for photosynthesis is:
6CO2 + 6H2O + sunlight → C6H12O6 (glucose) + 6O2
The released oxygen enters the atmosphere and is available for consumption by other organisms, including animals and humans. Oxygen is necessary for respiration, where organisms use it to break down glucose and produce energy in a process called cellular respiration. The equation for cellular respiration is essentially the reverse of photosynthesis:
C6H12O6 (glucose) + 6O2 → 6CO2 + 6H2O + energy
During respiration, oxygen combines with carbon compounds to form carbon dioxide, which is released back into the atmosphere.
In addition to photosynthesis and respiration, other processes contribute to the oxygen cycle. Combustion, both natural (such as forest fires) and human-induced (burning fossil fuels), consumes oxygen and releases carbon dioxide. Decomposition of organic matter by bacteria and fungi also consumes oxygen and produces carbon dioxide.
The exchange of oxygen between the atmosphere and the oceans is another important aspect of the oxygen cycle. Oceans act as a large oxygen reservoir, as oxygen dissolves in water and is used by marine organisms for respiration. Additionally, oceanic photosynthesis by phytoplankton contributes to the production of oxygen.
Overall, the oxygen cycle is a complex interplay between photosynthesis, respiration, combustion, and other natural processes. It ensures a continuous supply of oxygen in the atmosphere, allowing for the survival and functioning of aerobic organisms.
