Organic phosphorous compounds - serve to transform light or chemical fuel into the energy required for cell activities. Cell membrane - isolates a chemical system within the cell and keeps the various components in close proximity so that they can interact. Heterotrophs - The first living things were microscopic in size and unicellular. They would not have evolved a means of manufacturing their own food but rather they would assimilate small aggregates of organic molecules present in the surrounding medium. Fermentation - a process by which organisms are able to disassemble organic molecules, rearrange their parts, and derive energy for life functions.
Yeast is a heterotroph.
Autotrophs - a scarcity of food for heterotrophs favored the evolution of organisms which were able to manufacture their own food from inorganic substances. Sources of inorganic energy included carbon dioxide, hydrogen sulfide, and ammonia. Photoautotrophs - had the capability of dissociating carbon dioxide into carbon and free oxygen. The carbon was then combined with other elements to permit growth. With the multiplication of the photoautotrophs, billions and billions of tiny living oxygen generators began to change the primeval nonoxygenic atmosphere to an oxygenic one.