Biol 131
Question Bank
Membranes
You are expected to bring completed study questions to the evening study session. Answer
these study questions by referencing the relevant sections of the textbook. The written
explanations are the most important part of your answers and key to learning of concepts.
1. During the process of diffusion, molecules:
A. move from areas of high concentration to areas of lesser concentration until an equilibrium
is reached.
B. move from areas of low concentration to areas of higher concentration until an equilibrium
is reached.
C. remain stationary as water molecules move around them until an equilibrium is reached.
D. must use membrane transport proteins to move from areas of high concentration to areas of
lesser concentration.
2. The diagram to the right shows an osmosis tube containing different
concentration of solutes (black circles) in water.
A. Identify the solutions as either hypertonic or hypotonic.
Left side = _______________ Right side = ________________
B. Redraw the diagram below showing its appearance after osmosis occurs
and equilibrium is reached.
C. How will the tube appear after the same period of time if the membrane is
also permeable to the solute?
B.
C.
D. Let’s start the experiment again with fresh solutions. If the surface of the liquid on the
hypertonic side were covered with a flexible rubber seal, what would happen? How does this
explain the formation of “turgor” pressure in plant cells?
3. The center group (B) of red blood cells in the diagram to
the right are in an isotonic solution. What must the
relative solute concentrations be of the solutions in which
the other cells exist?
A: ________________
C: ________________
Biol 131
Question Bank
A
B
Membranes
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C
Membrane
4. For each of the situations shown to the right,
label the sides of the membranes as being
either isotonic, hypotonic or hypertonic.
0.2 M NaCl
0.4 M NaCl
________________
_______________
0.2 M Fructose
0.2 M Glucose
________________
_______________
0.3 M Sucrose +
0.2 M Fructose
0.1M Sucrose +
0.3M Fructose
________________
_______________
0.5 M NaCl
0.3 M KCl
________________
_______________
Distilled water
Blood serum
________________
_______________
A.
B.
C.
5. The bacterium Vibrio cholerae causes the
disease cholera. The main symptom of this
disease is severe diarrhea that if not treated
rapidly causes death. If a person drinks water
that is contaminated with this bacterium, the
bacteria can colonize the intestine and then
start to produce a toxin. The toxin causes
cells lining the small intestine to release
chloride (Cl-) and sodium (Na+) ions into the
intestine.
D.
E.
Explain how the release of these ions from the cells would result in severe dehydration.
6. In this diagram of a cell membrane, identify
and label the features listed below.
A.
B.
C.
D.
E.
F.
G.
membrane protein
cytosolic & cell exterior sides
cytoskeletal proteins
membrane hydrophobic region
membrane hydrophilic regions
glycoprotein
cholesterol
Explain how you can tell which is the extracellular and cytosolic side of the membrane:
Biol 131
Question Bank
Membranes
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7. A small vesicle in the cell cytoplasm containing a transmembrane protein is shown below, and a
section of the cell membrane is shown above it. The cell membrane is shown as a double solid
line. The C and N termini of the protein are labeled, and the outer layer of the vesicle membrane
is shown as a solid line, the inner as a dashed line.
A. Sketch the plasma membrane after the vesicle has fused
with the plasma membrane and become a concave region
like this:
Show how each layer of the vesicle has joined with the
corresponding layer of the membrane. Show the
orientation of the protein according to the position of the
C-terminus and N-terminus.
B. The transmembrane proteins of a secretory vesicle are
initially inserted into the membrane of the Endoplasmic
Reticulum (ER). In the ER, would the protein’s N or C
terminus face the cytoplasm?
Will the protein’s N or C terminus ultimately face the cell
exterior?
8. At this point you should be able to, from memory, draw an accurate
schematic representation of a phospholipid molecule. Do so again in
the space provided and label all of the constituent parts.
Phospholipid
9. A bacterium is suddenly expelled from a warm human intestine into
the cold world outside.
A. If the composition of the bacterial membrane were to remain
unchanged, would its fluidity increase or decrease in its cooler
environment? (circle one)
B. Which of the following adjustments might the bacterium make
to maintain the same level of membrane fluidity?
a. Increase the length of the hydrocarbon tails of its
membrane phospholipids.
b. Increase the proportion of unsaturated fatty acids of its
membrane phospholipids.
c. Increase the proportion of saturated fatty acids of its membrane phospholipids.
d. Decrease the amount of cholesterol in the membrane.
Explain your selection:
Biol 131
Question Bank
Membranes
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10. The illustration below show proteins serving different functions in cells. Identify each as either a
Transport protein, Anchor protein, Enzyme or Receptor
________________
________________
________________
________________
11. Why is it not possible for a membrane transport protein to transport large molecules such as
another protein across the membrane?
12. The diagram to the right shows the part of a transmembrane
protein that spans the membrane (the edges of the membrane are
shown as dashed lines).
A. What type of protein secondary structure does this protein
display? ____________________
B. Label on the diagram the regions of the protein that you would
expect to be hydrophobic and the regions you would expect to
be hydrophilic.
13. While on a trip to the desert, a friend of yours was bitten by a rattlesnake. He nearly died from
hemolysis, or breakage of many of his red blood cells. You have analyzed the snake venom and
found three enzymes: phospholipase, which degrades phospholipids; neuraminidase, which
removes cell surface carbohydrates; and protease, which degrades proteins. Which of these
enzymes do you think was responsible for his near fatal red blood cell hemolysis? (Question
adapted from http://www.biology.arizona.edu/default.html)
A. The neuraminidase; by removing carbohydrates from glycoproteins which are responsible
for strengthening of the cell membrane.
B. The protease; by degrading transmembrane proteins which would lead to cell lysis.
C. The phospholipase; by degrading the phospholipid component of the membrane.
Why?
Biol 131
Question Bank
Membranes
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14. The diagrams below show the structure of the detergent SDS as ‘lollipop’ icons associated with a
solubilized membrane protein.
A. In the diagram of the detergent SDS shown to the right, circle and label the hydrophobic and
hydrophilic regions of the molecule.
B. Label the hydrophilic and hydrophobic regions of the SDS icon.
C. Label the hydrophilic and hydrophobic regions of the protein.
protein with SDS
SDS icon
D. How does the association of SDS with the protein explain why the
protein becomes soluble in water.
E. Extend this to explain how detergents (and soaps) help to clean dirt particles from surfaces.
15. Cells use facilitated transport to allow movement of molecules into and out of the cell. Identify
the three statements below that are incorrect and explain why they are wrong.
A. _____ Protein transporters are not specific to the molecule that is transported.
B. _____ A protein transporter can transport molecules only into or out of the cell, but not both
directions.
C. _____ The net direction of movement is always down the concentration gradient, never
against the gradient.
D. _____ A protein transporter can either transport the molecule passively down a gradient or,
if ATP is present, against the gradient.
Biol 131
Question Bank
Membranes
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16. Consider the transport of lactose into a cell via the Na/lactose symport shown here.
A. Would you expect that lactose is being moved up or down a gradient? (circle one)
Explain:
B. Thus, lactose transport must be classified as active / passive
(circle).
C. What energy source is utilized directly by the Na/lactose symport?
_______________________________ (it’s not ATP).
D. If ATP is not used directly by the Na/lactose symport, explain why a sudden deficiency in
ATP would stop lactose import:
17. The diagrams to the right show three mechanisms of bulk
transport across membranes. Different cell types typically use
these transport processes to serve specific functions.
A. Label which diagram depicts pinocytosis, receptormediated endocytosis, and phagocytosis
B. Which transport process would you expect to occur in each
of the following cell types?
a. Macrophages of the immune system that attack and
destroy microorganisms. ______________________
b. Liver cells that must selectively take up specific types of
proteins from the blood. ____________________
c. Protozoa that use a variety of organic molecules as nutrient
sources. ____________________________
C. What type of protein binds to the cytoplasmic side of the
vesicle as it forms? (see arrow in bottom diagram)
D. Redraw the center diagram below to show the process of
exocytosis.
Biol 131
Question Bank
Membranes
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