Of the nine planets in the solar system, Earth is the only planet that has life on it. Life is in a variety of forms. Life forms include: plants, animals including man, and microorganisms. Living things cannot exist by themselves. They live in an environment. The environment has other life forms. It also has sunlight, soil, air, water, and minerals. These are non-living elements and are called abiotic factors. Life forms interact with other life forms and the abiotic factors. It is these interactions that help maintain life as we have it on earth. This unique interaction between a set of life forms interacting with one another and with non-living elements is called an ecosystem.

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