Check Your Knowledge: Self-Test

1. Why is it advantageous for the cell membrane to be fluid in nature?
2. Why do phospholipids tend to spontaneously orient themselves into something resembling a membrane?
3.  Discuss why the following affect the rate of diffusion: molecular size, temperature, solution concentration, and the distance that must be traveled.
4. Why does water move through a membrane?
5. Both of the regular intravenous solutions administered in medicine, normal saline and lactated Ringer’s solution, are isotonic. Why is this important?
6. Describe two ways that decreasing temperature would affect the rate of diffusion of molecules across a cell’s plasma membrane.
7. Where does the cell get energy for active transport processes?

8. Why is it important that there are different types of proteins in plasma membranes for the transport of materials into and out of a cell?

9. Why do ions have a difficult time getting through plasma membranes despite their small size?

10. What happens to the membrane of a vesicle after exocytosis?

  1. It leaves the cell.
  2. It is disassembled by the cell.
  3. It fuses with and becomes part of the plasma membrane.
  4. It is used again in another exocytosis event.

11. Which transport mechanism can bring whole cells into a cell?

  1. pinocytosis
  2. phagocytosis
  3. facilitated transport
  4. primary active transport

12. In what important way does receptor-mediated endocytosis differ from phagocytosis?

  1. It transports only small amounts of fluid.
  2. It does not involve the pinching off of membrane.
  3. It brings in only a specifically targeted substance.
  4. It brings substances into the cell, while phagocytosis removes substances.

13. Many viruses enter host cells through receptor-mediated endocytosis. What is an advantage of this entry strategy?

  1. The virus directly enters the cytoplasm of the cell.
  2. The virus is protected from recognition by white blood cells.
  3. The virus only enters its target host cell type.
  4. The virus can directly inject its genome into the cell’s nucleus.

14. Which of the following organelles relies on exocytosis to complete its function?

  1. Golgi apparatus
  2. vacuole
  3. mitochondria
  4. endoplasmic reticulum

15. Imagine a cell can perform exocytosis, but only minimal endocytosis. What would happen to the cell?

  1. The cell would secrete all its intracellular proteins.
  2. The plasma membrane would increase in size over time.
  3. The cell would stop expressing integral receptor proteins in its plasma membrane.
  4. The cell would lyse.

16.  Which plasma membrane component can be either found on its surface or embedded in the membrane structure?

  1. protein
  2. cholesterol
  3. carbohydrate
  4. phospholipid

17.  Which characteristic of a phospholipid contributes to the fluidity of the membrane?

  1. its head
  2. cholesterol
  3. a saturated fatty acid tail
  4. double bonds in the fatty acid tail

18. Water moves via osmosis _________.

  1. throughout the cytoplasm
  2. from an area with a high concentration of other solutes to a lower one
  3. from an area with a high concentration of water to one of lower concentration
  4. from an area with a low concentration of water to higher concentration

19. The principal force driving movement in diffusion is the __________.

  1. temperature
  2. particle size
  3. concentration gradient
  4. membrane surface area

20. Active transport must function continuously because __________.

  1. plasma membranes wear out
  2. not all membranes are amphiphilic
  3. facilitated transport opposes active transport
  4. diffusion is constantly moving solutes in opposite directions