I have this question that I cannot seem to figure out. Here it goes: If you add yeast to a sweet grape juice mixture and allo the yeast to grow, then wait several days and find that the sugar levels in the grape juice have dropped and there is no alcohol in the mixture, the most likely explanation would be:

1. The mixture needs more oxygen, yeast need oxygen to break down sugar and get enough energy to produc alcohol.
2. the mixture needs less oxygen, yeast only produce alcohol in the absence of oxygen.
3. the mixture needs more sugar because yeast need lots of energy before they can produce alcohol.
4. the mixture needs less sugar because high concentrations of sugar stimulate cellular respiration and alcohol is not a by product of cellular respiration.

5. no answer

I think the answer is number two, but I am not 100% sure. thanks

I believe it's 2, too. Since alcohol is produced by anaerobic cellular respiration, which means, no oxygen.