Yeast is a living organism. Yeast is a type of fungus that belongs to the Kingdom Fungi. It is a unicellular organism, meaning it is made up of a single cell, and it can reproduce asexually by budding. Yeast is commonly used in baking and brewing because it can convert sugar into alcohol and carbon dioxide through a process called fermentation. In addition to being used in food production, yeast is also used in scientific research as a model organism to study genetics and cell biology.