The Web of Life

Energy flows from the Sun to the Earth in a one-way direction. Green plants play a role in this flow as producers when they absorb the Sun’s radiant energy and convert inorganic nutrients and carbon dioxide to organic compounds. Thus plants produce forms of energy and matter that can be used by animals. Those animals that eat plants for energy and nutrients are called consumers, specifically, they are primary consumers because they are the first step in energy exchange from plant life to animal life. Some

Since human life began on Earth, species have disappeared for reasons other than natural causes. In the Earth’s history, however, many species, such as dinosaurs, have become extinct owing to natural causes.

consumers feed on living prey—a large fish ingesting a smaller fish—and others feed on matter that is no longer living—a human eating a steak dinner. These animals represent secondary, tertiary, or quaternary consumers. In biology most consumers are also called heterotrophs, organisms that depend on a wide variety of substances for their nutrition.