To understand the environment, it is important to understand how organisms interact with their surroundings. Since all organisms use energy, we need to understand how energy can be used and moved between Earth's spheres. We also need to understand how chemicals are moved through an ecosystem.

The movement and changing of compounds and elements in the environment are known as biogeochemical cycles. You started learning about them in quarter 3! The nitrogen, phosphorous, water and carbon cycles are the 4 most important biogeochemical cycles to planet Earth. These cycles involve moving elements and nutrients that help organisms remain healthy and also affect the abiotic factors of the environment. For example, all living things need water to survive. All living things need nitrogen to build proteins and DNA.

Besides being very important for the biosphere (the living parts of earth), water is also an extremely important to the other spheres. When water vapor condenses to form clouds, those clouds reflect sunlight back in to space, helping to cool the climate. On the other hand, water vapor is also an important greenhouse gas in the atmosphere. If there is too much of it, it traps heat and warms the atmosphere.

Water is also involved in other biogeochemical cycles. The water cycle works with almost every other element cycle (such as the carbon cycle or the nitrogen cycle). It also plays an important role in plate tectonics (the geosphere).