In a healthy ecosystem, processes and interactions among the nonliving and living parts are well balanced. Organisms have enough food and other resources and exist in appropriate numbers to support one another, unless something disrupts the system.

The diagram shows a healthy, balanced ecosystem. Plants and algae use the Sun’s energy to make their own food. This energy flows through the food web as animals eat the plants or algae and are themselves eaten by other animals. When plants and animals die, they are decomposed and broken down into nutrients by organisms such as fungi and bacteria in the soil or water. A nutrient is a substance that an organism needs to survive, grow, and reproduce. Nutrients and other substances dissolved in water can move from place to place in the ecosystem as the water flows.