The topic of Lecture 38 is Ecosystems. Ecosystem designates organisms and the environment they live in, taken together. The first consideration has to do with the flow of energy into and out of ecosystems.
Nutrients also enter and leave ecosystems, but before they leave they are often recycled many times.
Without autotrophs, there can be no ecosystem, because there would be nothing to capture energy. Within an ecosystem, energy is transferred from autotrophs to heterotrophs. All of the energy that enters an ecosystem, however, is ultimately lost to the environment in the form of metabolic heat , a form of energy that autotrophs cannot use. Autotrophs are also referred to as producers , and heterotrophs as consumers . This terminology is often used to describe the feeding, or trophic , relationships within ecosystems.