Some nonliving materials, such as water, are used by organisms over and over again. These materials cycle through ecosystems. The word cycle comes from the Greek word that means circle. A cycle is a series of steps that lead back to a starting point.
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The picture shows the water cycle. Because water moves in a cycle, you can begin anywhere in the picture to follow the water's path. You might begin with water that falls from clouds or precipitation. The precipitation might be in the form of rain, snow, sleet, or hail. Water that reaches the earth might move into the soil, or it might fall into bodies of water.
Plants take in water from the soil. some of the water evaporates from their leaves and moves into the air. Animals drink water. They return water to the ecosystem through their wastes. When organisms die, the water in their bodies becomes part of the ecosystem once again.
Notice in the picture that water evaporates from land and from bodies of water. high up in the air, water vapor cools and forms liquid water. Tiny droplets of water gather and form clouds. Eventually, the water falls as precipitation and the water cycle continues.
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