Final answer:
Mitogens activate Cdc25, a protein that activates cyclin-dependent kinases (Cdk), which are positive regulators of the cell cycle.
Step-by-step explanation:
The presence of mitogens normally results in the activation of Cdc25. Cdc25 is a protein that activates cyclin-dependent kinases (Cdk), which are positive regulators of the cell cycle. When mitogens bind to their receptors on the cell surface, a signaling cascade is initiated, leading to the activation of Cdc25 and subsequent progression of the cell cycle.