A unicellular or non-mycelial, either spherical or oval in shape and the size is very small is known as yeast. The colonies in yeast may appear white, creamy, brown, red, or yellow. The individual cells are colourless. The types of reproduction that are possible in the case of yeast are vegetative, sexual, or asexual. Yeast is most commonly used while preparing food as the presence of carbon dioxide in it rises the baked food.