Ecosystems are the basic units of ecology, comprising living organisms (biotic components) and their physical environment (abiotic components). Ecosystems can be terrestrial (e.g., forests, grasslands) or aquatic (e.g., rivers, oceans). In an ecosystem, energy flows through the food chain, from producers (plants, algae) to consumers (animals) and decomposers (microorganisms). Nutrients are cycled through the ecosystem, with each component playing a vital role in maintaining the balance of nature.