Final answer:
Inhibition of phosphate group removal from MPF would result in MPF remaining in its active state, allowing the cell to enter mitosis, but possibly preventing proper cell cycle progression later on.
Step-by-step explanation:
If a drug is injected into a cell that inhibits the removal of phosphate groups from Mitosis-promoting factor (MPF), the impact on the cell cycle would be significant. MPF is a complex of cyclin and cyclin-dependent kinase and is essential for a cell to transition from the G2 phase into mitosis. The removal of phosphate groups from MPF is crucial for its deactivation. Therefore, inhibition of this dephosphorylation would mean that MPF would remain in its active state. This sustained activity would allow the cell to enter mitosis but could prevent the cell from exiting mitosis properly since the inactivation of MPF is necessary for the cell to progress through the later stages of the cell cycle and eventually divide.
The levels of Cyclin B, which is a part of MPF, would not be directly affected by this inhibitor, thus, C is incorrect. Since MPF activity is concerned with the G2/M transition, the G1/S checkpoint would not be influenced in this scenario, so D is not correct. Cyclin D, involved in the G1 phase, operates independently of the G2/M transition regulation by MPF, so E would also be incorrect.
The correct answer to the student's question is B. MPF would remain in its active state.