A Levels Biology (9700)•9700/11/O/N/19

Explanation
Telomerase Activity in Specific Cell Types
Steps:
- Telomerase extends telomeres to allow repeated cell divisions without shortening.
- In most somatic cells, telomerase is inactive, leading to telomere loss and eventual senescence.
- Germ-line cells require high telomerase to preserve telomeres across generations.
- Differentiated or cultured somatic cells lack sustained telomerase expression.
Why D is correct:
- Germ-line cells (3) express high telomerase to maintain reproductive cell immortality, per telomere maintenance theory.
Why the others are wrong:
- A and B include 1 or 2, but somatic cells (1) and cultured cells (2) have low telomerase to limit proliferation.
- C includes only 1, but somatic cells suppress telomerase to prevent uncontrolled division.
Final answer: D
Topic: Structure of nucleic acids and replication of DNA
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