The Cycling of Chemical Elements In The Ecosystem

Essay by haejineeHigh School, 10th grade May 2004

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In the water cycle, energy is supplied by the sun, which drives evaporation either from ocean surfaces or from treetops. Wind moves the clouds to different places, otherwise it would only rain at the ocean. Precipitation occurs when water condenses from a gaseous state in the atmosphere and falls to earth. Once water condenses, gravity takes over and the water is pulled to the ground. Gravity continues to operate, either pulling the water underground or across the surface. In either event, gravity continues to pull water lower and lower until it reaches the oceans. Frozen water may be trapped in cooler regions of the Earth (the poles, glaciers on mountaintops, etc.) as snow or ice, and may remain as such for very long periods of time. Lakes, ponds, and wetlands form where water is temporarily trapped. The oceans are salty because any weathering of minerals that occurs as the water runs to the ocean will add to the mineral content of the water, but water cannot leave the oceans except by evaporation, and evaporation leaves the minerals behind.

Organisms play an important role in the water cycle, Most organisms contain a significant amount of water (up to 90% of their body weight). This water is not held for any length of time and moves out of the organism rather quickly in most cases. Animals and plants lose water through cellular respiration(C H O +6O 6CO +6H O + Energy (ATP + Heat)). In plants, water is drawn in at the roots and moves to the gas exchange organs, the leaves, where it evaporates quickly. This special case is called transpiration because it is responsible for so much of the water that enters the atmosphere. In both plants and animals, the breakdown of...