Which process does yeast perform when it ferments sugar?

When yeast ferments sugar, the process primarily involves converting sugars into energy, resulting in the production of carbon dioxide and alcohol. This process is known as alcoholic fermentation. During fermentation, yeast organisms consume sugars and, as they metabolize these sugars, they release carbon dioxide gas and ethanol (alcohol) as by-products.

This is particularly important in various food and beverage industries; for example, in baking, the carbon dioxide produced helps dough rise, creating a light and airy texture in bread. In brewing, the alcohol produced is the desired end product that gives beverages like beer and wine their alcoholic content.

The other processes listed in the choices do not accurately describe the fermentation process carried out by yeast. For instance, vinegar is produced through a different process involving acetic acid bacteria, while oxygen and glucose are not outputs of yeast fermentation. Transforming fat and protein is not relevant to the fermentation process initiated by yeast. Thus, the choice that highlights the production of carbon dioxide and alcohol is consistent with the established scientific understanding of yeast fermentation.