Part (a) The cell cycle of a garlic root-tip cell is estimated to be 16 h16\text{ h}16 h.
A root-tip squash preparation from a garlic plant was observed under a light microscope, and a total of 185185185 cells were counted. Out of these, 242424 cells were actively undergoing mitosis.
State why plant root tips are frequently selected to study mitosis.
Calculate the mean length of time each cell spends undergoing mitosis. Give your answer in minutes, correct to 3 significant figures.
Part (b) During the eukaryotic cell cycle, progression is tightly regulated by checkpoints.
Identify the specific phase of interphase during which DNA replication occurs.
Name the checkpoint that directly monitors whether DNA has been completely and accurately replicated before the cell enters mitosis.
If a cell does not satisfy the requirements of a checkpoint, it may enter a resting phase or undergo programmed cell death. State the name of this resting phase and the term for programmed cell death.