118
Chapter 4
Chapter 4 Test Questions
4. Which is (are) true of epithelial cells?
a. They can only move uncharged molecules across their surfaces.
b. They may have segregated functions on luminal and
basolateral surfaces.
c. They cannot form tight junctions.
d. They depend upon the activity of Na
+
/K
+
-ATPase pumps
for much of their transport functions.
e. Both b and d are correct.
5. Which is
incorrect?
a. Diffusion of a solute through a membrane is considerably
quicker than diffusion of the same solute through a water
layer of equal thickness.
b. A single ion, such as K
+
, can diffuse through more than one
type of channel.
c. Lipid-soluble solutes diffuse more readily through the
phospholipid bilayer of a plasma membrane than do water-
soluble ones.
d. The rate of facilitated diffusion of a solute is limited by the
number of transporters in the membrane at any given time.
e. A common example of cotransport is that of an ion and an
organic molecule.
6. In considering diffusion of ions through an ion channel, which
driving force(s) must be considered?
a. the ion concentration gradient
b. the electrical gradient
c. osmosis
d. facilitated diffusion
e. both a and b
(Answers appear in Appendix A.)
1. Which properties are characteristic of ion channels?
a. They are usually lipids.
b. They exist on one side of the plasma membrane, usually the
intracellular side.
c. They can open and close depending on the presence of any
of three types of “gates.”
d. They permit movement of ions against concentration
gradients.
e. They mediate facilitated diffusion.
2. Which of the following does not directly or indirectly require
an energy source?
a. primary active transport
b. operation of the sodium/potassium pump
c. the mechanism used by cells to produce a calcium ion
gradient across the plasma membrane
d. facilitated transport of glucose across a plasma membrane
e. secondary active transport
3. If a small amount of urea were added to an isoosmotic saline
solution containing cells, what would be the result?
a. The cells would shrink and remain that way.
b. The cells would fi rst shrink, but then be restored to normal
volume after a brief period of time.
c. The cells would swell and remain that way.
d. The cells would fi rst swell, but then be restored to normal
volume after a brief period of time.
e. The urea would have no effect, even transiently.
Chapter 4 Quantitative and Thought Questions
(Answers appear in Appendix A.)
1. In two cases (A and B), the concentrations of solute X in two
1-L compartments separated by a membrane through which X
can diffuse are:
Concentration of X, mM
Case
Compartment 1
Compartment 2
A
3
5
B
32
30
a. In what direction will the net fl
ux of
X
take place in case A
and in case B?
b. When diffusion equilibrium is reached, what will the
concentration of solute in each compartment be in case A
and in case B?
c. Will A reach diffusion equilibrium faster, slower, or at the
same rate as B?
2. When the extracellular concentration of the amino acid alanine
is increased, the net fl ux of the amino acid leucine into a cell is
decreased. How might this observation be explained?
3. If a transporter that mediates active transport of a substance
has a lower affi nity for the transported substance on the
extracellular surface of the plasma membrane than on the
intracellular surface, in what direction will there be a net
transport of the substance across the membrane? (Assume that
the rate of transporter conformational change is the same in
both directions.)
4. Why will inhibition of ATP synthesis by a cell lead eventually
to a decrease and, ultimately, cessation in secondary active
transport?
5. Given the following solutions, which has the lowest water
concentration? Which two have the same osmolarity?
Concentration, mM
Solution
Glucose
Urea
NaCl
CaCl
2
A
20
30
150
10
B
10
100
20
50
C
100
200
10
20
D
30
10
60
100
6. Assume that a membrane separating two compartments is
permeable to urea but not permeable to NaCl. If compartment
1 contains 200 mmol/L of NaCl and 100 mmol/L of urea,
and compartment 2 contains 100 mmol/L of NaCl and 300
mmol/L of urea, which compartment will have increased in
volume when osmotic equilibrium is reached?
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