NUR 4909 Membrane Transport Review

NUR 4909 Membrane Transport Review Questions

• 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

• 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

• Name three functions of the sodium potassium ATPase pump.

Answer

• Maintain ionic gradients (important to resting potential)
• Provides gradients for secondary active transporters
• Maintains cell volume by keeping ionic concentrations constant
• 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

• / 2

Decrease in plasma proteins results in a decrease in osmotic pressure within the vessels. This results in fluid moving from the vessels into the ECF and increases the volume of the ECF causing cerebral edema

• In simple diffusion,
• the rate of movement of molecules is controlled by temperature and mole- cular size.
• the movement of individual molecules is random.
• the movement of molecules of one substance is independent of the move- ment of any other

substance.

• the net movement is away from the region of highest concentration.
• all of these

Answer

• all of these

• Oxygen, carbon dioxide, and other small molecules cross the plasma mem- brane through the

process(es) of

• osmosis
• diffusion
• endocytosis and exocytosis
• active transport
• facilitated diffusion

Answer

• diffusion

• The sodium-potassium pump is an example of
• simple diffusion
• facilitated diffusion.
• osmosis.

• active transport

Answer

• active transport
• / 2