Final answer:
The conversion of substances produced during anaerobic respiration back to glucose occurs in the liver, as part of the Cori cycle.
Step-by-step explanation:
The substance produced in anaerobic respiration, often lactic acid in humans, is converted back to glucose in a process known as the Cori cycle. This metabolic pathway takes place in the liver. During intense exercise when oxygen is scarce, muscles produce lactic acid via anaerobic glycolysis. This lactic acid travels through the bloodstream to the liver, where it is converted back into glucose, which can then be used as an energy source or stored as glycogen.