Ecosystems are open systems through which energy flows and materials are cycled. B. Structure of Ecosystems 1. Decomposers feed on organisms from all levels. Interconnected food chains comprise food webs in which the same food resource is often part of more than one food chain. A. Primary Productivity 1.
Primary productivity is the rate of photosynthesis for the ecosystem during a specified interval.
Net primary productivity is the rate of energy storage in plant tissues in excess of the rate of respiration by the plants themselves. B. Major Pathways of Energy Flow 1. Energy flows into ecosystems from the sun. In detrital food webs it flows mainly from plants through decomposers and detritivores. Energy leaves ecosystems through heat losses generated by metabolism.