Goblet cells dominate in single-membrane-bound secretory vesicles

Steps:

• Define single-membrane-bound structures as organelles like vesicles, ER, Golgi, and lysosomes (excluding double-membrane mitochondria or nucleus).
• Evaluate each cell type's specialization and organelle composition.
• Compare relative volumes: secretory cells prioritize vesicle storage over other components.
• Identify goblet cells as mucus producers with maximal vesicle packing.

Why B is correct:

• Goblet cells specialize in mucus secretion, with mucin granules (single-membrane vesicles) occupying up to 80% of cytoplasmic volume for storage and release.

Why the others are wrong:

• A: Ciliated epithelial cells allocate volume to cilia (non-membrane) and motility structures, with less emphasis on vesicles.
• C: Red blood cells lack organelles, consisting mainly of cytoplasm filled with hemoglobin, so zero single-membrane structures.
• D: Companion cells support phloem transport with balanced organelles like ER and Golgi, but not disproportionately vesicle-filled.

Final answer: B