A Levels Biology (9700)•9700/13/M/J/21
Explanation
Eukaryotic cells contain organelle-specific structures
Steps:
- Recall that eukaryotic nuclear DNA is linear, but mitochondrial DNA is circular.
- Note that eukaryotic cytoplasm contains 80S ribosomes for protein synthesis.
- Identify that mitochondria (and chloroplasts in plants) contain 70S ribosomes, similar to prokaryotes.
- Conclude that all three features—circular DNA, 70S ribosomes, and 80S ribosomes—are present in eukaryotic cells.
Why A is correct:
- Eukaryotic cells have circular DNA and 70S ribosomes in mitochondria, plus 80S ribosomes in the cytoplasm, per standard cell biology definitions.
Why the others are wrong:
- B: 70S ribosomes are present in mitochondrial organelles.
- C: Both 70S (mitochondrial) and 80S (cytoplasmic) ribosomes are present.
- D: Circular DNA is present in mitochondria, and 80S ribosomes are in the cytoplasm.
Final answer: A
Topic: Cells as the basic units of living organisms
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