Cell division, beginning at the transition from the G2 phase of the cell cycle to mitosis (bottom), and finishing after cytokinesis, when the cells divide (top). The energy related to the input of microtubule-generating pathways are now combined in purple, with chromosome-related processes in yellow and activities related to the cell cortex/membrane in brown. Just before mitosis starts, the cell actively rounds up. Then, during prophase, the microtubules nucleate, the chromosomes condense and are moved within the spindle. As chromosome alignment proceeds from prometaphase to metaphase, microtubules and chromosomes reach a steady state – hence the narrowing of the corresponding shapes. The activity of microtubules dramatically increases early in anaphase, which helps to segregate the chromosomes, which are just 'passive passengers'. By late anaphase, however, the decondensation of the chromosomes begins at the same time as the cortical acto-myosin contractile ring forms and contracts. Finally, cytokinesis itself occurs, requiring a small co-ordinated input from microtubules and the cell cortex. The outer grey shape represents the combined input of each activity described above – therefore corresponding to the overall energy/level of activity of cell division.