(b) Based on the data for the groups of cells cultured with 0.1% serum (groups 3 to 7), identify the groups(s) most likely to include cells undergoing mitosis.
AP Biology FRQ

Groups 4 to 7 are most likely to be undergoing the mitotic phase of the cell cycle.

Explanation:

Since the four proteins used p16,  p18,  p21, and  p27 are inhibitors of cyclin-dependent kinases (CDK), their absence indicates that the cell is undergoing mitosis - the cell cycle is regulated by CDKs. In the absence of these inhibitors, the cell cycle moves on forward. Because the bar for DNA replication is longer in the case for groups 4 to 7, it is indicative of the fact that these cells have gone through the mitotic phase.

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the answer is d. chordata