Chemotrophs are organisms that obtain energy by the oxidation of reduced compounds. The substrates used by chemotrophs can be organic (organotrophs) or inorganic compounds (lithotrophs). According to the carbon source, chemotrophs can be either chemoautotrophs or chemoheterotrophs. Because chemoheterotrophs use reduced organic compounds as a source of energy and a source of carbon, they are usually called heterotrophs, although the term is misleading because, strictly, it only refers to the carbon source. Chemoautotrophs use inorganic energy sources and are known as chemolithoautotrophs or lithoautotrophs. Chemolithoheterotrophs are a special kind of chemotroph that use inorganic compounds as an energy source and reduced organic compounds as a carbon source. They are known as mixotrophs. Chemotrophs use fermentation and respiration to obtain energy. Fermentation is restricted to organotrophs.