Which of the following statements regarding the structure and function of cell membranes is correct?

• The phospholipid bilayer is arranged so that the hydrophilic heads of the phospholipid molecule face the extra- and intracellular fluids.

• Some proteins integrated into the membrane serve as channels for the passage of nonpolar molecules through the membrane.

• Peripheral membrane proteins function as channels associated with transport of ions through the

  membrane.

• Cholesterol molecules function to transport ions from one side of the plasma membrane to the other.

• The plasma membrane is a layer of phospholipid molecules with their hyrophilic head groups in contact with the extracellular solution and the hydrophobic tail groups in contact with the intracellular solution.

Which is TRUE regarding diffusion?

• It depends upon the random motion of molecules.

• It results in net movement of molecules from regions of low concentration to regions of high concentration.

• It is the principle mechanism by which molecules are moved over large distances in the body.

• It requires energy in the form of ATP.

• It requires integral membrane proteins to occur.

A solute, X, is placed in compartment A of a two compartment container and allowed to diffuse to

compartment B and attain diffusion equilibrium. At that point in time,

• There will be no further movement of any solute molecules between compartments.

• Solutes will be moving in both directions equally.

• Solutes will only continue to move from A to B.

• Solutes will only continue to move from B to A.

• The concentration in compartment B will be much higher than that in compartment A.

Which of the following statements regarding the diffusion of a nonpolar solute X across a cell membrane is correct?

• At equilibrium the net flux of X across the cell membrane is zero

• At equilibrium, X will cease moving across the cell membrane

• Solute X will be unable to reach equilibrium because it is nonpolar

• Solute X will reach equilibrium, but the concentration will be much higher on the inside of the cell because of the smaller volume

• Which of the following would decrease the net flux of a penetrating solute into a cell?

Which of the following would decrease the net flux of a penetrating solute into a cell?

• Increasing the permeability constant for that solute

• Decreasing the temperature

• Increasing the concentration of the solute in the extracellular fluid

• Increasing the area of the cell membrane

• Decreasing the thickness of the membrane

Equal amounts of two solutes, A and B, are placed into the same beaker of water at the same time.

Solute A reaches diffusion equilibrium faster than solute B. What is the most likely explanation for this

observation?

• The temperature was greater for solute A than solute B

• The concentration gradient for A was greater than B

• Solute A is smaller than solute B

• Solute A traveled a shorter distance than solute B

• Solute B is more soluble in water than solute A

In general, polar molecules diffuse more rapidly through the lipid bilayer part of cell membranes than do

nonpolar molecules. This statement is:

• True

• False, because polar molecules diffuse through less rapidly because the bilayer is polar throughout its

  width.

• False, because polar molecules diffuse through less rapidly because the bilayer is nonpolar throughout

  its width.

• False, because nonpolar molecules diffuse through more rapidly because much of the bilayer is

  nonpolar.

• False, because the rate of diffusion of nonpolar and polar molecules through the bilayer is essentially the

  same as long as the molecules are the same size.

The permeability of the plasma membrane to mineral ions:

• Is not influenced by channels formed by proteins

• Is the same in all cell types

• Is affected by differences in electrical charge on the two sides of the membrane

• Is zero in all living cells

• Is only possible because of the hydrophobic interior of the lipid bilayer

Ion channels in cell membranes:

• Are nonspecific.

• Are not affected by differences in electrical potential across the membrane.

• May open in response to binding a ligand.

• Only allow ions to move from the extracellular fluid into the cell.

• Only allow ions to move from the intracellular fluid out of the cell.

Which is TRUE about mediated transport across cell membranes?

• It refers to the movement of ions through protein channels

• It refers both to simple diffusion and to the active transport of molecules

• It is characterized by saturable carriers and a maximum velocity of transport

• As the concentration gradient across a membrane increases, the transport rate always increases

• It is nonspecific; any transporter can transport any molecule across the cell membrane.