Final answer:
NADH donates electrons and hydrogen to acetaldehyde during fermentation, converting it into ethanol and regenerating NAD+.
Step-by-step explanation:
The student's question refers to the biochemical process wherein NADH donates its electrons and hydrogen to acetaldehyde. This is a key step in the fermentation process, particularly during the production of ethanol from glucose by yeast. When acetaldehyde receives electrons and hydrogen atoms from NADH, it is reduced to ethanol.
This conversion of acetaldehyde to ethanol also facilitates the regeneration of NAD+ from NADH, allowing glycolysis and fermentation to continue. This overall reaction takes place in the absence of oxygen and is critical for anaerobic organisms to produce ATP. In summary, NADH gives its electrons and hydrogen to acetaldehyde so that acetaldehyde can become ethanol.