Final answer:
The abundance and disappearance of the Cdk-cyclin complex in different cell cycle phases suggest its role in triggering transitions between phases.
Step-by-step explanation:
In the cell cycle, the concentrations of cyclin proteins change throughout different phases. The Cdk-cyclin complex plays a crucial role in regulating the cell cycle by activating different checkpoints. When the Cdk-cyclin complex becomes more abundant in G2 phase and disappears before G1, it suggests that this complex is responsible for triggering the transition from G2 to M phase and subsequently degraded to allow cells to progress from M phase to G1 phase.