What are the final electron acceptor in electron transport chain?

In aerobic respiration, the final electron acceptor in the electron transport chain  is oxygen.  It accepts two electrons and a molecule of water is formed as a by product.

In anaerobic respiration, the final electron acceptor in the electron transport chain is pyruvate.  Anaerobic respiration  commonly occurs in the muscle tissue of animals as  a result of intense activity or exertion. Pyruvate is used as makeshift electron acceptor in place of oxygen and is reduced or converted to lactic acid.

before it leaves the nucleus of a eukaryotic cell, mrna is altered in the following ways: - a cap is added to the 5' end of the mrna molecule; - a poly a tail is added to the 3' end; - introns are removed and exons are spliced together.