Endocytosis and exocytosis Knowledge-Based Practice

Questions

1. 1.

   When a secretory vesicle carrying membrane-bound glycoproteins fuses with the plasma membrane during exocytosis, what happens to the luminal surface of the vesicle membrane?

   • A) It becomes integrated into the outer leaflet of the plasma membrane, exposing attached carbohydrate groups to the extracellular space.
   • B) It becomes integrated into the inner leaflet of the plasma membrane, exposing attached carbohydrate groups to the cytosol.
   • C) It is broken down into free fatty acids, releasing membrane proteins directly into the extracellular fluid.
   • D) It inverts its molecular orientation via flippases, sequestering attached carbohydrate groups within the hydrophobic core of the bilayer.
2. 2.

   Which of the following best describes the mechanism of receptor-mediated endocytosis in eukaryotic cells?

   • A) Nonspecific droplets of extracellular fluid are trapped by non-selective membrane invaginations.
   • B) Dynamic pseudopodia extend outward to engulf large solid targets into an internal phagosome.
   • C) Intracellular secretory vesicles fuse with the outer lipid bilayer to discharge receptors into the extracellular fluid.
   • D) Target ligands specifically bind to membrane receptors, triggering coated pits to invaginate and pinch off as intracellular vesicles.
3. 3.

   Which of the following statements correctly describes a characteristic shared by both endocytosis and exocytosis?

   • A) They transport small nonpolar molecules down their concentration gradient without vesicular involvement.
   • B) They allow solutes to cross the lipid bilayer passively through specialized channel proteins.
   • C) They occur exclusively across the cell wall in plant cells without altering the plasma membrane.
   • D) They require metabolic energy in the form of ATP to transport large substances packaged within vesicles.
4. 4.

   Which of the following statements accurately distinguishes pinocytosis from phagocytosis?

   • A) Pinocytosis transports large solid aggregates using pseudopodia, whereas phagocytosis is restricted to small dissolved solutes.
   • B) Pinocytosis is a passive transport mechanism that operates down a concentration gradient, whereas phagocytosis requires metabolic energy.
   • C) Pinocytosis involves the non-specific uptake of extracellular fluid and dissolved solutes, whereas phagocytosis is the engulfment of large solid particles.
   • D) Pinocytosis adds membrane material to expand the cell surface, whereas phagocytosis pinches off vesicles to reduce it.
5. 5.

   Which of the following correctly describes a cellular event that specifically occurs during exocytosis rather than endocytosis?

   • A) Solutes are moved strictly down their concentration gradients without the expenditure of metabolic energy.
   • B) The total surface area of the plasma membrane decreases as portions of the bilayer pinch inward.
   • C) Extracellular materials are engulfed into the cell via the formation of newly pinched intracellular vesicles.
   • D) Vesicle membranes fuse with the plasma membrane, releasing their contents externally and expanding membrane surface area.

Answers and step-by-step solutions appear after you finish the test.