Tapeworms derive energy primarily through the catabolism of glucose and glycogen. Glucose is broken down through glycolysis which occurs in both the cytoplasm and mitochondria, generating energy molecules. Some glucose may also pass through the Krebs cycle. Tapeworms have an electron transport chain, using an o-type cytochrome system, that can transfer electrons to either fumarate or oxygen. They are generally facultative anaerobes. Proteins and lipids do not provide significant energy, though some amino acids can be metabolized. Synthetic metabolism allows for protein and nucleic acid production. Compared to trematodes and nematodes, the Krebs cycle and electron transport chain play lesser roles in adult tapeworm