O Levels Biology (5090)•5090/12/M/J/19
Explanation
DNA Content in Binary Fission Stages
Steps:
- Identify starting cell V in G1 phase with unreplicated DNA (1 unit).
- Note cell W before S phase, still with 1 unit of DNA.
- Recognize cell X after DNA replication in G2 phase, with 2 units.
- Observe cells Y and Z as daughter cells post-division, each with 1 unit after cytokinesis.
Why C is correct:
- Matches binary fission where DNA doubles from 1 to 2 during S phase before splitting equally into two 1-unit cells.
Why the others are wrong:
- A: Shows premature doubling in later cells without replication sequence.
- B: Places doubling too early, before S phase.
- D: Starts with 2 units, inconsistent with G1 starting point.
Final answer: C
Topic: Asexual and sexual reproduction
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