Solution: The G1 phase is the longest in the cell cycle. It’s the beginning of the interphase. The cell prepares for division during the G1 phase. During the G1 phase, cells are extremely metabolically active. During this phase, the associated proteins in DNA replication, as well as the energy required for DNA replication, are synthesized. The interphase’s G1 phase is followed by the S phase. Hence, Interphase is the longest phase of cell division. In a 24-hour cell cycle, 23 hours are for the Interphase -phase and 1 hour for the Mitosis phase.