Relating to or denoting the cycle in which chemical elements and simple substances are
transferred between living systems and the environment.
• Carbon cycle.
• Nitrogen cycle.
• Nutrient cycle.
• Oxygen cycle.
• Phosphorus cycle.
• Sulfur cycle.
• Rock cycle.
• Water cycle.
• A colourless, odourless reactive gas, the chemical element of atomic number 8 and
the life-supporting component of the air.
• Oxygen is the chemical element with the symbol O and atomic number 8, meaning its
nucleus has 8 protons.
Oxygen is used by animals and plants in the respiration (breathing) process. Tanks
of oxygen are used in medicine to treat people with breathing problems. They are also used
as life support for astronauts and scuba divers.
• The oxygen cycle is a biogeochemical cycle that describes the movement of oxygen within the
earth's three main reservoirs which are the atmosphere (air), the hydrosphere (water), and the
• Oxygen is constantly used and generated by different processes on Earth and all these processes
together make up the oxygen cycle.
8. HOW OXYGEN IS PRODUCED
• The oxygen is produced by plants via photosynthesis. Plants are the
main creator of oxygen in the atmosphere.
• Some oxygen is produced when sunlight reacts with water vapour in the
9. OXYGEN IS USED UP IN…..
• Oxygen is used up in :
• Respiration – All organisms use oxygen for respiration.
• Decomposing – When plants and animals die, they decompose. This process uses up
oxygen and releases carbon dioxide into the air.
• Rusting – Also called oxidation, this process causes metals to rust. Also a process which
uses up oxygen.
• Combustion – The process by which fire is generated also requires oxygen, along with
heat and fuel. This process also uses up oxygen and releases carbon dioxide into the
10. HOW THE OXYGEN CYCLE TAKES PLACE
• It starts, of course, with plants and photosynthesis.
• 1. Photosynthesis :–
• During the day, plants take energy from the sun, carbon dioxide from the air,
and water from the soil to make their food. Their food is simple – glucose.
This process is called photosynthesis. Oxygen is released into the air as a
by-product of photosynthesis.
• During the night, plants take in oxygen and release carbon dioxide, to
maintain their metabolism. Which is why it is not a good idea to sleep under
trees at night.
2. Respiration :–
The oxygen that is released by plants is used by humans, animals, and
other organisms for respiration, i.e. breathing. We use oxygen to break down
simple sugars and generate energy to sustain ourselves. During respiration,
organisms take in oxygen and release carbon dioxide into the air.
3. Repeat :–
This carbon dioxide is again, taken up by plants, for photosynthesis.
Thus, we see that our life force is generated chiefly by plants. Which is why it is
super important to preserve plant life on earth.