a) Sugar provides energy for sustaining all life activities in yeasts.
Yeasts are eukaryotic microorganisms, classified in the kingdom Fungi. Yeasts are chemoorganotrophs and they use organic compounds as a source of energy. Carbon is obtained through various sugars. Yeasts can metabolize sugars as they ferment sugar resulting in the formation of ethanol. So, sugar provides energy to yeasts, which helps to carry out various life processes. Alcoholic fermentation is a complex biochemical process during which yeasts convert sugars to ethanol, carbon dioxide, and other metabolic by products that contribute to the chemical composition and sensorial properties of the fermented foodstuffs.