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Chemical substances move through ecosystems on the Earth in cycles (see carbon cycle).

The source of energy for almost every ecosystem on Earth is the sun.

ecosystem, habitat, environment, biosphere, ecology are all scientific terms that can refer to spaces or systems in which plants and animals (including humans) live in relationship with each other and with the surrounding physical conditions. environment is the most general term. It can refer to a set of surrounding conditions thought of as a whole, as in a desert environment, or it can single out one or more conditions that could exist with a variety of others: This plant thrives in a warm, moist environment. By itself, it usually refers to all the conditions, elements, and living things that humans live among: Armed conflict always harms the environment. A habitat, on the other hand, is a specific area or set of surrounding conditions that is the natural home of a particular animal, plant, or other organism: The polar bear’s habitat is the Arctic sea ice. The word ecosystem refers to all of the organisms and physical conditions within a certain space, interacting with each other to form a complex, balanced web of relationships. It can be of any size: The 3,000-acre marsh is a finely balanced wetland ecosystem. Each aquarium houses a complete ecosystem of rocks and sand, aquatic plants, fish, and other creatures. The largest known ecosystem of all is the biosphere, consisting of the whole earth and all its living inhabitants. ecology is different from all the other words here: like them, it can mean the web of relationships operating within a particular ecosystem, as in a grassland ecology, but more often refers broadly to relationships between organisms and their environments in general, or to the science that studies these relationships.