NUR 4909 Membrane Transport Review
Questions
1. Lipid bilayers are differentially permeable to different types of molecules.
- Which types of molecules can readily cross such bilayers without the help of transport
proteins?
- Name some of the physical properties of molecules that prevent them from freely diffusing
across lipid bilayers.
Answer
- Small uncharged lipid soluble molecules cross bilayers easily.
- Large molecules, charged molecules and hydrophilic molecules do not diffuse readily across
the membrane
2. The opening of membrane channels can be controlled by "gates".
What factors can cause these gates to open?
Answer
- Mechanical stimulation
- Ligand binding
- Change in membrane voltage
3. Name three functions of the sodium potassium ATPase pump.
Answer
1. Maintain ionic gradients (important to resting potential)
2. Provides gradients for secondary active transporters
3. Maintains cell volume by keeping ionic concentrations constant
4. If the vessels of the brain have a reduced amount of plasma proteins, what effect would you
expect this to have on the volume of extracellular fluid surrounding the brain neurons?
Answer
, Decrease in plasma proteins results in a decrease in osmotic pressure within the vessels. This
results in fluid moving from the vessels intothe ECF and increases the volume of the ECF causing
cerebral edema
5. In simple diffusion,
a. the rate of movement of molecules is controlled by temperature and mole- cular size.
b. the movement of individual molecules is random.
c. the movement of molecules of one substance is independent of the move- ment of any other
substance.
d. the net movement is away from the region of highest concentration.
e. all of these
Answer
e. all of these
6. Oxygen, carbon dioxide, and other small molecules cross the plasma mem- brane through the
process(es) of
a. osmosis
b. diffusion
c. endocytosis and exocytosis
d. active transport
e. facilitated diffusion
Answer
b. diffusion
7. The sodium-potassium pump is an example of
a. simple diffusion
b. facilitated diffusion.
c. osmosis.
d. active transport
Answer
d. active transport
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