<P> Detritivores are heterotrophs which obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). Saprotrophs (also called lysotrophs) are chemoheterotrophs that use extracellular digestion in processing decayed organic matter . It is a term most often associated with fungi . The process is most often facilitated through the active transport of such materials through endocytosis within the internal mycelium and its constituent hyphae . </P> <P> Heterotrophs can be organotrophs or lithotrophs . Organotrophs exploit reduced carbon compounds as electron sources, like carbohydrates, fats, and proteins from plants and animals . On the other hand, lithotrophs use inorganic compounds, such as ammonium, nitrite, and sulfur to obtain electron sources . Another way of classifying different heterotrophs is by assigning them as chemotrophs or phototrophs . Phototrophs utilize light to obtain energy and carry out metabolic processes, whereas chemotrophs use the energy obtained by the oxidation of chemicals from their environment . </P> <P> Photoorganoheterotrophs, such as Rhodospirillaceae and purple non-sulfur bacteria synthesize organic compounds using sunlight coupled with oxidation of inorganic substances, including hydrogen sulfide, elemental sulfur, thiosulfate, and molecular hydrogen . They use organic compounds to build structures . They do not fix carbon dioxide and apparently do not have the Calvin cycle . Chemolithoheterotrophs like the Oceanithermus profundus obtain energy from the oxidation of inorganic compounds . Mixotrophs (or facultative chemolithotroph) can use either carbon dioxide or organic carbon as the carbon source, meaning that mixotrophs have the ability to use both heterotrophic methods as well as autotrophic methods . Although mixotrophs have the ability to grow both under both heterotrophic and autotrophic conditions, C. vulgaris have higher biomass and lipid productivity when growing under heterotrophic conditions compared to autotrophic conditions . </P> <P> Heterotrophs, by consuming reduced carbon compounds, are able to use all the energy that they obtain from food for growth and reproduction, unlike autotrophs, which must use some of their energy for carbon fixation . Both heterotrophs and autotrophs alike are usually dependent on the metabolic activities of other organisms for nutrients other than carbon, including nitrogen, phosphorus, and sulfur, and can die from lack of food that supplies these nutrients . This applies not only to animals and fungi but also to bacteria . </P>

Part 2 energy conversion in animals and other heterotrophs