Question

when making wine, yeast is added to grape juice in a sealed container. as time passes, the yeast uses up all of the oxygen in the container, but continues to thrive and produce alcohol. this process is not a fast process; it takes considerable time. explain how this happens.
a. the grapes undergo aerobic respiration until there is no more oxygen, then they ferment, creating alcohol.
b. yeast can undergo both aerobic and anaerobic respiration, since both produce carbon dioxide as a by - product, alcohol can be produced over long periods of time.
c. yeast can undergo aerobic or anaerobic respiration. when the food source is plentiful, it will undergo fermentation, producing alcohol and atp.
d. yeast is a facultative anaerobe, meaning it can use oxygen for respiration, but then switch to anaerobic respiration when o₂ is not present, undergoing fermentation, producing alcohol as a byproduct.

Explanation:

Yeast is a facultative anaerobe. In the presence of oxygen, it first undergoes aerobic respiration to produce ATP, carbon - dioxide and water. Once the oxygen in the sealed container is used up, due to the limited oxygen supply, yeast switches to anaerobic respiration (fermentation) to produce alcohol and carbon dioxide. This allows yeast to continue living and metabolizing even when oxygen is scarce.

Answer:

D. Yeast is a facultative anaerobe, meaning it can use oxygen for respiration, but then switch to anaerobic respiration when O₂ is not present, undergoing fermentation, producing alcohol as a by - product.