An ecosystem is a community of organisms interacting with each other and with the non-living (abiotic) environment in which they live. It includes both the living (biotic) parts and the physical and chemical conditions, such as light, temperature, water and soil.Ecosystems can be any size. A rock pool, a pond, a rotting log, an oak wood and an ocean are all ecosystems. Their boundaries are not always sharp, and organisms and materials move between neighbouring ecosystems.Two key processes happen in every ecosystem:
• Energy flow. Energy enters mainly as light, which producers convert into chemical energy in organic molecules by photosynthesis. It passes along food chains to consumers and decomposers, and at each stage some is lost, mostly as heat from respiration. Energy flows through an ecosystem; it is not recycled.
• Nutrient cycling. Elements such as carbon and nitrogen are taken up from the environment, passed between organisms and returned to the environment by decomposers, so they are recycled.Ecosystems are dynamic. Population sizes rise and fall, and the community can change over time, but a mature ecosystem tends to stay fairly stable because of the many interactions within it.Ecologists study ecosystems at several levels. The key terms, each covered in its own lesson, are habitat (where an organism lives), community (all the populations in an area), abiotic and biotic factors, and the biosphere.
• Energy flow. Energy enters mainly as light, which producers convert into chemical energy in organic molecules by photosynthesis. It passes along food chains to consumers and decomposers, and at each stage some is lost, mostly as heat from respiration. Energy flows through an ecosystem; it is not recycled.
• Nutrient cycling. Elements such as carbon and nitrogen are taken up from the environment, passed between organisms and returned to the environment by decomposers, so they are recycled.Ecosystems are dynamic. Population sizes rise and fall, and the community can change over time, but a mature ecosystem tends to stay fairly stable because of the many interactions within it.Ecologists study ecosystems at several levels. The key terms, each covered in its own lesson, are habitat (where an organism lives), community (all the populations in an area), abiotic and biotic factors, and the biosphere.