A Levels Biology (9700)•9700/13/O/N/22
Explanation
Organelles lacking internal ribosomes
Steps:
- Identify ribosomes' locations: free in cytoplasm, attached to rough ER surface, or inside certain organelles.
- Examine endoplasmic reticulum (1): Ribosomes bind externally to rough ER membrane, not enclosed within its lumen.
- Examine Golgi body (2): Lacks ribosomes entirely; functions in protein modification without protein synthesis machinery.
- Examine chloroplast (3): Houses 70S ribosomes in stroma for synthesizing chloroplast proteins.
- Examine mitochondrion (4): Contains 70S ribosomes in matrix for mitochondrial protein synthesis.
Why C is correct:
- C identifies 1 and 2 only, matching the definition that ER and Golgi lack internal or enclosed ribosomes, unlike semi-autonomous organelles.
Why the others are wrong:
- A includes 4, but mitochondria contain their own ribosomes per endosymbiotic theory.
- B includes 3, but chloroplasts contain 70S ribosomes for organelle-specific synthesis.
- D lists 3 and 4, both containing ribosomes as self-replicating structures.
Final answer: C
Topic: Cells as the basic units of living organisms
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