Final answer:
M-cyclin levels peak during the Mitotic Phase of cell division, allowing cells to pass the mitosis checkpoint and ensuring proper cell division.
Step-by-step explanation:
In cell division, M-cyclin accumulation reaches its highest level during the Mitotic Phase (M phase). This is associated with the cell's preparation for mitosis, which is a crucial part of the cell cycle for the division of the mother cell into two daughter cells. M-cyclin molecules help regulate the progression of the cell cycle and their concentration peaks allow cells to pass the mitosis checkpoint, ensuring that mitosis is properly completed before division.