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A rapidly dividing human cell finishes its cycle in 24 hours. Which phase takes the least time?
AThe G2 phase, about 4.5 hours
BThe M phase, about half an hour
CThe G1 phase, about nine hours
DThe S phase, about ten hours
Answer & Solution
Correct answer: B. The M phase, about half an hour
1. Set out the four phases with their approximate lengths for a 24 hour cycle.
2. G1 runs about nine hours of growth and stockpiling.
3. S runs about ten hours, the longest stretch, because every chromosome is copied.
4. G2 runs about four and one half hours of final preparation.
5. M runs about one half hour, which is the shortest of the four.
6. Adding nine, ten, four and one half and one half gives 24 hours, so the set is complete.
7. Choosing G2 picks the second shortest and mistakes a few hours for a few minutes.
8. Choosing S picks the longest phase, the exact opposite of what was asked.
_Source: OpenStax Biology 1e (CC BY 4.0), Chs 10 and 11, section 10.3 Control of the Cell Cycle_
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