Which of the following statements about a typical plasma membrane is correct?
The two sides of the plasma membrane have different lipid and protein composition.
EXPLANATION:
Because the membrane serves different functions on the cytoplasmic and exterior surfaces, the structure and composition of the surfaces must be different.
Which of the following best describes the structure of a biological membrane?
two layers of phospholipids with proteins either crossing the layers or on the surface of the layers
EXPLANATION:
The membrane proteins can be found either embedded in or attached to the surface of the phospholipid bilayer.
The permeability of a biological membrane to a specific polar solute may depend on which of the following?
the types of transport proteins in the membrane
EXPLANATION:
The lipid bilayer will be impermeable or very poorly permeable to polar or charged solutes. The presence of the correct transport protein will determine the permeability.
Which of the following is least likely to be important in holding the components of a biological membrane together?
covalent interactions between the phospholipid and protein components of the membrane
EXPLANATION:
This is not an important interaction because there are rarely covalent bonds between the phospholipids and integral membrane proteins.
Which of the following statements about osmosis is correct?
The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis.
EXPLANATION:
Aquaporins facilitate water movement across membranes and thus speed up the process of osmosis.
In facilitated diffusion, what is the role of the transport protein?
Transport proteins provide a hydrophilic route for the solute to cross the membrane.
EXPLANATION:
This is the most general description of facilitated diffusion by membrane transport proteins.
If the concentration of phosphate in the cytosol is 2.0 mM and the concentration of phosphate in the surrounding fluid is 0.1 mM, how could the cell increase the concentration of phosphate in the cytosol?
active transport
EXPLANATION:
For the cell to accumulate phosphate, it must move calcium against the concentration gradient. This process requires energy.
The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by which of the following?
cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis
EXPLANATION:
Movement of most solutes against their concentration gradient couples the movement of one solute down its concentration gradient to the movement of another (glucose in this case) against its concentration gradient.
Active and passive transport of solutes across a membrane typically differ in which of the following ways?
Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy.
EXPLANATION:
Active and passive transport can be distinguished by whether or not they use cellular energy.
Which of the following correctly describes some aspect of exocytosis or endocytosis?
Exocytosis and endocytosis change the surface area of the plasma membrane.
EXPLANATION:
The fusion or budding of transport vesicles at the plasma membrane either adds or removes proteins and phospholipids, thus changing the surface area.
A protein that spans the phospholipid bilayer one or more times is
a transmembrane protein.
You are working on a team that is designing a new drug. In order for this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells?
similarity of the drug molecule to other molecules transported by the target cells
The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membrane–more acidic outside the cell than inside the cell. Phosphate transport is an example of
cotransport.
What is the voltage across a membrane called?
membrane potential