Enzyme secretion via vesicular transport

Steps:

• Enzymes are synthesized in the pancreas cells and packaged into vesicles.
• Vesicles move to the cell membrane when secretion is triggered.
• Vesicle membrane fuses with the plasma membrane.
• Contents are released outside the cell.

Why D is correct:

• Exocytosis is defined as the fusion of intracellular vesicles with the plasma membrane to expel large molecules like enzymes into the extracellular space.

Why the others are wrong:

• A: Active transport uses energy to move small ions or molecules across the membrane, not to secrete bulk proteins.
• B: Facilitated diffusion passively transports specific molecules through channels, unsuitable for directed enzyme release.
• C: Endocytosis imports substances into the cell, the opposite of secretion.

Final answer: D