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What Cycles Are Molecules Passed Around In Again & Again Within the Biosphere?

Cycles that move molecules throughout the world and into living things again and again are called biogeochemical cycles. Only atoms that can exist, both as building blocks of living organisms and of nonliving matter, are part of these cycles. Although biogeochemical cycles are self-sustaining, changes to the environment, such as deforestation or burning fossil fuels, can upset their delicate balance. Upsetting the balance of these cycles can cause global warming.

The Nitrogen Cycle
- Nitrogen is a key component of DNA and protein.
  
  Nitrogen molecules, N2, are important to both living and inanimate matter. Earth's atmosphere is made up of 80 percent N2. However, nitrogen is found in soil and water because when living things die, and nitrogen is released during decomposition. Nitrogen in the air is broken up into usable nitrogen by bacteria or fires, and plants take the nitrogen from the soil or the air to maintain their functioning. In turn, animals eat plants to obtain their nitrogen requirements.
The Carbon Cycle
- All plants and animals are carbon based.
  
  Carbon molecules cycle through the earth primarily through respiration. Plants take in carbon dioxide, CO2, during their respiration process and separate the carbon from the oxygen during photosynthesis. The carbon is used to help build the plants' tissue. Carbon is replenished into the atmosphere by the waste product of human respiration in the form of CO2. When living things die, carbon is absorbed into the earth as they decompose. Water also receives carbon directly from the air when carbon atoms dissolve into the water and from decaying marine matter. It is used by marine life to build tissue and shells.
The Oxygen Cycle
- Waterfalls provide a lot of exposed water surface.
  
  The oxygen cycle works much like the carbon cycle in that oxygen molecules are cycled through respiration. Plants release O2 as a waste product of their respiration and animals take it in during their respiration process. Oxygen enters water usually by being directly dissolved into it from the air. When water has a large surface area exposed to the air, such as when it moves over rocks and creates rapids, more oxygen can be dissolved into the water.
The Hydrologic Cycle
- Clouds are condensed water vapor.
  
  The hydrologic, or water, cycle moves water, H2O molecules, through the planet. Water evaporates from standing water sources and is pulled into the air. The molecules are then transported by wind, moving from high energy systems into low energy systems where the water is released in the form of precipitation. Water that hits the ground is absorbed into the soil and used by plant life, while water that collects in reservoirs may be consumed by animal life.

Nature