Oxygen Cycle

Oxygen Cycle The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs: the atmosphere (air), the biosphere (living things), and the lithosphere (Earth's crust).

Factor The main driving factor of the oxygen cycle is photosynthesis, which is responsible for the modern Earth's atmosphere and life.

Billions of years ago, it is believed that there was virtually no oxygen found in the atmosphere at all. What caused an increase in oxygen levels? Most of the oxygen now found in our atmosphere was released by plants, as a bi-product of photosynthesis. Over millions of years, as plants around the globe released oxygen, the levels continued to rise, until they reached a balance around 1 billion years ago. For the last billion years, the amount of oxygen has remained relatively constant. At the same time that plants continue adding oxygen to the atmosphere, it is also being removed by various processes. Oxygen is highly reactive. As the oxygen in our atmosphere interacts with other substances, it often bonds to them, becoming trapped. Many life forms also remove oxygen from the atmosphere, as they breathe. This oxygen is used by these life forms to carry out the functions of life.

Detailed Mechanism Almost all living things need oxygen. They use this oxygen during the process of creating energy in living cells. Just as water moves from the sky to the earth and back in the hydrologic cycle, oxygen is also cycled through the environment. Plants mark the beginning of the oxygen cycle. Plants are able to use the energy of sunlight to convert carbon dioxide and water into carbohydrates and oxygen in a process called photosynthesis.

This means that plants "breathe" in carbon dioxide and "breathe" out oxygen. Animals form the other half of the oxygen cycle. We breathe in oxygen which we use to break carbohydrates down into energy in a process called respiration.

Carbon dioxide produced during respiration is breathed out by animals into the air. So oxygen is created in plants and used up by animals, as is shown in the picture above. But the oxygen cycle is not actually quite that simple. Plants must break carbohydrates down into energy just as animals do. During the day, plants hold onto a bit of the oxygen which they produced in photosynthesis and use that oxygen to break down carbohydrates. But in order to maintain their metabolism and continue respiration at night, the plants must absorb oxygen from the air and give off carbon dioxide just as animals do. Even though plants produce approximately ten times as much oxygen during the day as they consume at night, the night-time consumption of oxygen by plants can create low oxygen conditions in some water habitats.

Phosphorous Cycle Definition The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere.

 The Cycle The phosphorus cycle is long and slow, but it is an important part of the environment. It helps plants grow, and is used by farmers to fertilize them. When animals eat the plants, they absorb phosphates.

When the animals die, their body decays and the phosphorus is absorbed into the soil, where it re-enters plants. What isn’t absorbed by plants ends up in rock, and may stay there for millions of years, slowly being released as the rocks weather.

 Atmosphere The Phosphorus cycle has no involvement in the atmosphere, because it does not naturally form in gaseous forms.

 Hydrosphere  Phosphorous usually enters the hydrosphere by the phosphate salt rocks found on the ocean floor. As the water erodes them away, the phosphorous escapes.  Marine organisms take some of the phosphorus particles in order to live and grow.

 Lithosphere  Phosphorous is presented in the form of rocks and soil.  Phosphates go down to the bottom of the ocean and forms rocks over millions of years.  Phosphates enter the soil when plant and animal matter decompose, the cycle repeats.

 Biosphere  Phosphorous is used for organisms to build DNA, RNA, and ATP.  Phosphate is in plants, which the herbivores eat, which the herbivores are eaten by the carnivores. Than phosphorus is released back into the soil by the herbivores and carnivores waste.