Final answer:
Positive feedback regulation does not ensure the two-way progression of the cell cycle. Positive regulation promotes the cell cycle, while negative regulation halts the cell cycle. Positive regulators exhibit positive feedback mechanisms.
Step-by-step explanation:
Positive feedback regulation does not ensure the two-way progression of the cell cycle. Positive regulation of the cell cycle is responsible for promoting the progress of the cell through the various checkpoints, while negative regulation can arrest the cell cycle until certain events have occurred.
Positive regulators, such as cyclins and cyclin-dependent kinases (Cdks), show positive feedback mechanisms, whereas negative regulators show negative feedback.