Most yeast species’ reproductive growth is very rapid, especially in certain substances like sugar. Certain yeast cells reproduce by fission, or splitting in two. But most yeasts reproduce by budding, in which the cell wall of the yeast swells, then forms a growth called a bud. The bud then breaks off, forming a new independent yeast cell, with each bud that separates from its mother yeast cell having the ability to grow into a new yeast cell.