- Every organism is made up of combinations of chemical elements, such as carbon, oxygen, hydrogen and nitrogen. The chemical elements that are used by organisms to build and openate their bodies are called hutrients.
- The movements of nutuients through the environment are called nutrient cycles.
- Earth is what is called a closed system since there is little or no input of new materials from outside the system.
- When an organism dies, the materials in its body are returned to the environment where they can be used by othe living things.
- With out death and decomposition, there materials would eventually be used and there could be no were new life.

Sustaining Life:
-You know two main factors that sustainlife on earth: energy from the sun, and nutrients.
-In some parts of a nutrient cycle, the nutrients are in the non-living or a biotic part of the environment.
-In some parts of a nutrient cycle, the nutrients are in living organisms, or the biotic part of environment.
-There are three stages of a nutrient cycle.
-In put occurs when nutrients enter a living prganism.
-Through put occurs when nutrients are used by the organisms for growth and function. Output occurs when waste matter and used or unneeded nutrients are returned to the environment, to became arailabic as input for other nutrient sysles.