Final answer:
The final electron acceptor in anaerobic respiration that is not used is pyruvate, as it is associated with fermentation, which uses organic molecules as electron acceptors. Sulfur, iron, and nitrate are typical inorganic acceptors involved in anaerobic respiration.
Step-by-step explanation:
The final electron acceptor that is not used in anaerobic respiration is pyruvate. Anaerobic respiration is a type of respiration that does not require oxygen and uses an inorganic molecule other than oxygen as a final electron acceptor to derive energy. In contrast, fermentation involves the use of an organic molecule, such as pyruvate, as the final electron acceptor, which is used to regenerate NAD+ from NADH. Therefore, the correct answer is E) pyruvate, as it is associated with fermentation rather than anaerobic respiration.
Components like sulfur, iron, and nitrate are typical inorganic final electron acceptors in various types of anaerobic respiration. For example, sulfur bacteria use sulfate as a final electron acceptor, while denitrifiers use nitrate to produce nitrogen gas.