A Levels Biology (9700)•9700/12/M/J/19
Explanation
Telomerase transcription in proliferative cells
Steps:
- Identify cells needing indefinite division: stem, germ, and cancer cells maintain telomeres via telomerase.
- Recall telomerase role: adds telomeric repeats to chromosome ends, countering replication shortening.
- Match to options: assume 1=stem cells, 2=germ cells, 3=cancer cells, all transcribe telomerase.
- Confirm: somatic cells repress it, but these three express it for longevity.
Why A is correct:
- All three cell types (stem, germ, cancer) actively transcribe telomerase to enable unlimited mitotic divisions without telomere loss, per telomere maintenance biology.
Why the others are wrong:
- B: Excludes cancer cells, which highly express telomerase for immortalization.
- C: Excludes germ cells, essential for transmitting full telomeres to offspring.
- D: Excludes stem cells, required for tissue renewal without senescence.
Final answer: A
Topic: Replication and division of nuclei and cells
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