Final answer:
Acetaldehyde acts as the last electron acceptor in ethanolic fermentation because it promotes the synthesis of ethanol, hence the correct response is B) It promotes ethanol synthesis. The process converts NADH back to NAD+, allowing glycolysis to continue.
Step-by-step explanation:
The question 'Why is acetaldehyde the last electron acceptor in ethanolic fermentation?' relates to the metabolic processes of yeast during fermentation. The correct answer is B) It promotes ethanol synthesis. During the process of ethanolic fermentation, pyruvate decarboxylase catalyzes the conversion of pyruvic acid to acetaldehyde by removing a carboxyl group and releasing CO2. This acetaldehyde then serves as the electron acceptor for the electrons from NADH, a process catalyzed by alcohol dehydrogenase, which results in the reduction of acetaldehyde to ethanol and the oxidation of NADH to NAD+. This step is crucial for regenerating NAD+ which is necessary for glycolysis to continue, allowing for ongoing ATP production in the absence of oxygen.