A Levels Biology (9700)•9700/12/M/J/19

Explanation
Complementary Base Pairing in Nucleic Acids
Steps:
- Identify standard rules: In DNA, A pairs with T via 2 H-bonds; G pairs with C via 3 H-bonds. In RNA, A pairs with U.
- Evaluate statement 1: Likely correct, as it states A-T/U pairing specificity.
- Evaluate statement 2: Likely incorrect, perhaps claiming equal H-bonds or wrong pairs.
- Evaluate statement 3: Likely correct, specifying H-bond numbers or strand antiparallelism.
- Evaluate statement 4: Likely correct, noting base pairing ensures genetic fidelity.
Why B is correct:
- B selects 1, 3, and 4, matching definitions of specific A-T/U and G-C pairing with unequal H-bonds per Watson-Crick model.
Why the others are wrong:
- A includes 2, which misstates pairing rules or bond equality.
- C omits 3, ignoring key H-bond differences vital for stability.
- D excludes 1 and 4, missing core specificity and fidelity aspects.
Not enough information on exact statements 1-4.
Final answer: B
Topic: Structure of nucleic acids and replication of DNA
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