Final answer:
Rounds of cell division are triggered by M-cdk/M-cyclin that is only active when Ca2+ is present.
Step-by-step explanation:
Rounds of cell division are triggered by M-cdk/M-cyclin that is only active when Ca2+ is present. M-cdk/M-cyclin is a regulatory complex consisting of cyclin-dependent kinase (cdk) and cyclin subunits. The kinase activity of M-cdk/M-cyclin is regulated by the presence of calcium ions (Ca2+), which activate the complex and initiate cell division.