A Levels Biology (9700)•9700/14/M/J/25

Explanation
Protein Secretion Pathway in Eukaryotic Cells Steps:
- Amino acids enter the cell across the cell surface membrane via transport proteins.
- Ribosomes on the rough endoplasmic reticulum assemble amino acids into the polypeptide chain of the digestive enzyme.
- Transport vesicles move the protein from rough ER to the Golgi body for modification and sorting.
- The Golgi body packages the enzyme into secretory vesicles, which fuse with the cell surface membrane for export.
Why B is correct:
- Matches the endomembrane system pathway where proteins for secretion are synthesized in rough ER, processed in Golgi body, stored/transported in secretory vesicles, and released via cell surface membrane exocytosis.
Why the others are wrong:
- A: Places Golgi before rough ER, but protein synthesis must precede Golgi modification.
- C: Positions secretory vesicle before Golgi and rough ER last, reversing the synthesis-to-processing order.
- D: Begins with Golgi, ignoring that amino acid incorporation into protein starts at rough ER.
Final answer: B
Topic: Cells as the basic units of living organisms
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