A System of Cycles, Part 2

A System of Cycles, Part 2

A System of Cycles, Part 2
Reading Level

	edHelper's suggested reading level:	high interest, readability grades 6 to 8
	Flesch-Kincaid grade level:	7.9

Vocabulary

challenging words:

cell-building, methane, phosphorous, reenters, carbonate, geosphere, budget, nitrogen, atmosphere, glucose, maintain, term, excrete, provides, version, responsible

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A System of Cycles, Part 2
By Trista L. Pollard

¹     In System of Cycles, Part 1 you learned about our planet's sources of energy. Now we will discuss how this energy cycles through our planet. Think of our energy cycles as a train making its way on the tracks of our Earth system. Each car stands for a specific cycle; however, all of them together help to maintain our planet's energy budget. This train, the NPCW, stands for the nitrogen cycle, phosphorous cycle, carbon cycle, and water cycle.

²     All of these cycles make their way through reservoirs where energy and matter are stored. The nitrogen cycle provides the nitrogen we need to build up proteins. Since organisms cannot use the nitrogen in our atmosphere, it needs to be converted. A bacterium in our soil "fixes" the nitrogen so that it can be absorbed by plants. Animals eat the plants, so they take in the nitrogen. When animals excrete wastes or die and decay, the nitrogen reenters our atmosphere. This energy exchange happens through a chemical reaction.

³     The phosphorous cycle provides cell-building phosphorous. Rocks provide the phosphorous when they break down in water. It then enters the soil and water. Plants absorb the phosphorous. Animals eat the plants and excrete wastes that contain the phosphorous. Wastes, decaying animals, and decaying plants send the phosphorous back into the soil. The phosphorous does not enter the atmosphere.

Paragraphs 4 to 6:
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