As you can tell from the question, my science knowledge is lacking. I can see that mammals, reptiles, etc. must eat other living creatures (mammals, insects, plants, etc.) for energy. But do plants, microbes and other types of life forms all depend on eating other life forms? For example, do the nutrients that plants get from the soil contain living organisms and are they essential? In other words, does every organism, simple or complex require eating another living organism for it's energy? If not, is there a term or classification for living organisms that don't eat other organisms for energy? Many thanks for taking the time to answer this question.