A Levels Biology (9700)•9700/13/M/J/23
Explanation
Telomeres cap linear eukaryotic chromosomes
Steps:
- Recall telomeres are repetitive DNA sequences at ends of linear chromosomes in eukaryotes.
- Identify listed structures: nucleus (linear nuclear DNA), mitochondrion (circular mtDNA), chloroplast (circular cpDNA), rough ER (no DNA).
- Determine only nucleus contains linear DNA with telomeres.
- Count structures: one qualifies.
Why A is correct:
- Telomeres define ends of linear chromosomes; only nuclear DNA in eukaryotes is linear and telomeric per eukaryotic cell biology.
Why the others are wrong:
- B overcounts by including circular DNAs without telomeres.
- C further overcounts non-DNA structures.
- D counts all, ignoring telomere absence in organelles and ER.
Final answer: A
Topic: Structure of nucleic acids and replication of DNA
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