Possible size and shape changes of yeast cells during the reproductive phase of life. (a) The spherical cell with a regular shape. Cell size increases gradually, but its shape does not change during the reproductive phase of life. Depending on the rate of cell size increase per generation, spherical cells may reach the size that is critical only for further reproduction (no cell lysis occurs) (1) or that is also critical for the strength of the cell wall (cell lysis generally occurs) (2). (b) The ellipsoidal cell. Cell size increases gradually during each subsequent reproductive cycle. At the end of the reproductive phase, a cell may change its shape from elliptical to spherical (cell lysis may occur) (3) or maintain the elliptical shape (no cell lysis occurs) (4).