Question 1

When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that

Accepted Answer

A)  the integral membrane proteins are not strong enough to hold the bilayer together. 
B)  water that is present in the middle of the bilayer freezes and is easily fractured. 
C)  hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing. 
D)  the carbon-carbon bonds of the phospholipid tails are easily broken. 
E)  the hydrophobic interactions that hold the membrane together are weakest at this point.

Question 2

In what way do the membranes of a eukaryotic cell vary?

Accepted Answer

A)  Phospholipids are found only in certain membranes. 
B)  Certain proteins are unique to each membrane. 
C)  Only certain membranes of the cell are selectively permeable. 
D)  Only certain membranes are constructed from amphipathic molecules. 
E)  Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm.

Question 3

For the following questions, match the labeled component of the cell membrane in the figure with its description.
 
-Which component is a glycolipid?

Accepted Answer

A)  A 
B)  B 
C)  C 
D)  D 
E)  E

Question 4

Cystic fibrosis is a genetic disease in humans in which the CFTR protein, which functions as a chloride ion channel, is missing or nonfunctional in cell membranes.
-The CFTR protein belongs to what category of membrane proteins?

Accepted Answer

A)  gap junctions 
B)  aquaporins 
C)  electrogenic ion pumps 
D)  cotransporters 
E)  hydrophilic channels

Question 5

Why are lipids and proteins free to move laterally in membranes?

Accepted Answer

A)  The interior of the membrane is filled with liquid water. 
B)  Lipids and proteins repulse each other in the membrane. 
C)  Hydrophilic portions of the lipids are in the interior of the membrane. 
D)  There are only weak hydrophobic interactions in the interior of the membrane. 
E)  Molecules such as cellulose can pull them in various directions.

Question 6

Cystic fibrosis is a genetic disease in humans in which the CFTR protein, which functions as a chloride ion channel, is missing or nonfunctional in cell membranes.
-If the sodium ion concentration outside the cell increases, and the CFTR channel is open, in what direction will chloride ions and water move across the cell membrane?

Accepted Answer

A)  Chloride ions will move out of the cell, and water will move into the cell. 
B)  Both chloride ions and water will move out of the cell. 
C)  Chloride ions will move into the cell, and water will move out of the cell. 
D)  Both chloride ions and water will move into the cell. 
E)  The movement of chloride ions and water molecules will not be affected by changes in sodium ion concentration outside the cell.

Question 7

Which of the following statements is correct about diffusion?

Accepted Answer

A)  It is very rapid over long distances. 
B)  It requires an expenditure of energy by the cell. 
C)  It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration. 
D)  It is an active process in which molecules move from a region of lower concentration to one of higher concentration. 
E)  It requires integral proteins in the cell membrane.

Question 8

Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a 0.15 M salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are

Accepted Answer

A)  hypotonic to both fresh water and the salt solution. 
B)  hypertonic to both fresh water and the salt solution. 
C)  hypertonic to fresh water but hypotonic to the salt solution. 
D)  hypotonic to fresh water but hypertonic to the salt solution. 
E)  isotonic with fresh water but hypotonic to the salt solution.

Question 9

Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean?

Accepted Answer

A)  Proton pumps must have evolved before any living organisms were present on Earth. 
B)  Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life. 
C)  The high concentration of protons in the ancient atmosphere must have necessitated a pump mechanism. 
D)  Cells of each domain evolved proton pumps independently when oceans became more acidic. 
E)  Proton pumps are necessary to all cell membranes.

Question 10

Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells?

Accepted Answer

A)  simple diffusion 
B)  phagocytosis 
C)  active transport pumps 
D)  exocytosis 
E)  facilitated diffusion

Question 11

Who was/were the first to propose that cell membranes are phospholipid bilayers?

Accepted Answer

A)  H. Davson and J. Danielli 
B)  I. Langmuir 
C)  C. Overton 
D)  S. Singer and G. Nicolson 
E)  E. Gorter and F. Grendel

Question 12

What kinds of molecules pass through a cell membrane most easily?

Accepted Answer

A)  large and hydrophobic 
B)  small and hydrophobic 
C)  large polar 
D)  ionic 
E)  monosaccharides such as glucose

Question 13

The solutions in the two arms of this U-tube are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose. Side B is half-filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels on both sides are equal.
 
-Initially, in terms of tonicity, the solution in side A with respect to that in side B is

Accepted Answer

A)  hypotonic. 
B)  plasmolyzed. 
C)  isotonic. 
D)  saturated. 
E)  hypertonic.

Question 14

According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?

Accepted Answer

A)  They can move laterally along the plane of the membrane. 
B)  They frequently flip-flop from one side of the membrane to the other. 
C)  They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane. 
D)  They are free to depart from the membrane and dissolve in the surrounding solution. 
E)  They have hydrophilic tails in the interior of the membrane.

Question 15

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

Accepted Answer

A)  It is a peripheral membrane protein. 
B)  It exhibits a specificity for a particular type of molecule. 
C)  It requires the expenditure of cellular energy to function. 
D)  It works against diffusion. 
E)  It has few, if any, hydrophobic amino acids.

Question 16

Several epidemic microbial diseases of earlier centuries incurred high death rates because they resulted in severe dehydration due to vomiting and diarrhea. Today they are usually not fatal because we have developed which of the following?

Accepted Answer

A)  antiviral medications that are efficient and work well with all viruses 
B)  antibiotics against the viruses in question 
C)  intravenous feeding techniques 
D)  medication to prevent blood loss 
E)  hydrating drinks that include high concentrations of salts and glucose

Question 17

Which of the following would increase the electrochemical potential across a membrane?

Accepted Answer

A)  a chloride channel 
B)  a sucrose-proton cotransporter 
C)  a proton pump 
D)  a potassium channel 
E)  both a proton pump and a potassium channel

Question 18

In the small airways of the lung, a thin layer of liquid is needed between the epithelial cells and the mucus layer in order for cilia to beat and move the mucus and trapped particles out of the lung. One hypothesis is that the volume of this airway surface liquid is regulated osmotically by transport of sodium and chloride ions across the epithelial cell membrane. How would the lack of a functional chloride channel in cystic fibrosis patients affect sodium ion transport and the volume of the airway surface liquid?

Accepted Answer

A)  Sodium ion transport will increase; higher osmotic potential will increase airway surface liquid volume. 
B)  Sodium ion transport will increase; higher osmotic potential will decrease airway surface liquid volume. 
C)  Sodium ion transport will decrease; lower osmotic potential will decrease airway surface liquid volume. 
D)  Sodium ion transport will decrease; lower osmotic potential will increase the airway surface liquid volume. 
E)  Sodium ion transport will be unaffected; lack of chloride transport still reduces osmotic potential and decreases the airway surface liquid volume.

Question 19

The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. Refer to the figure to answer the following questions.
 
-At the beginning of the experiment,

Accepted Answer

A)  side A is hypertonic to side B. 
B)  side A is hypotonic to side B. 
C)  side A is isotonic to side B. 
D)  side A is hypertonic to side B with respect to glucose. 
E)  side A is hypotonic to side B with respect to sodium chloride.

Question 20

A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in

Accepted Answer

A)  peroxisomes. 
B)  lysosomes. 
C)  Golgi vesicles. 
D)  vacuoles. 
E)  secretory vesicles.

Exam 7: Membrane Structure and Function