Which is a form of cellular transport that involves the movement of molecules into cells without passing through the plasma membrane's structural matrix?
A. diffusion
B. osmosis
C. facilitated diffusion
D. endocytosis
E. apoptosis
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Question 2) What is the best description of a secondary active transport process that cotransports an amino acid with Na+?
A. Both Na+ and the amino acid bind on the side of the membrane where the Na+ concentration is lowest, and undergo net movement to the other side of the membrane.
B. Na+ and the amino acid bind to opposite sides of the membrane, and Na+ undergoes net transport from the side of the membrane with higher Na+ concentration toward the side with lower concentration, while the amino acid moves in the opposite direction.
C. Both Na+ and the amino acid bind on the side of the membrane where the Na+ concentration is higher, and both are transported to the side of the membrane where the Na+ concentration is lower.
D. Both Na+ and the amino acid bind to the side of the membrane where the amino acid concentration is highest and are transported toward the side of the membrane where the amino acid concentration is lower.
E. Na+ and the amino acid bind to opposite sides of the membrane, and the amino acid undergoes net transport from the side of the membrane with lower Na+ concentration to the side of the membrane where the Na+ concentration is higher.
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Question 3) Which of the following statements about the Na+-K+ ATPase pump is false?
A. It transports Na+ out of cells and K+ into cells.
B. It binds to, and hydrolyzes, ATP.
C. It is constantly active in all cells.
D. Its activity requires the expenditure of metabolic energy.
E. It transports Na+ and K+ in a 1:1 ratio.
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Question 4) Which is true about mediated transport of substances across cell membranes?
A. It involves a specific membrane protein that functions as a carrier molecule.
B. It always involves the movement of substances against a concentration gradient.
C. It is always directly coupled to the splitting of ATP molecules.
D. There is no limit to how fast it can occur as the concentration gradient becomes larger.
E. It is the main mechanism for transporting hydrophobic molecules across membranes.
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Question 5) Which is true about mediated transport across cell membranes?
A. It refers to the movement of ions through protein channels.
B. It refers both to simple diffusion and to the active transport of molecules.
C. It is characterized by saturable carriers and a maximum velocity of transport.
D. As the concentration gradient across a membrane increases, the transport rate always increases.
E. It is nonspecific; any transporter can transport any molecule across the cell membrane.
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Question 6) Which of the following is a feature that distinguishes active transport from facilitated diffusion?
A. saturation of transport rate
B. requirement for a carrier molecule
C. carrier molecules have specificity
D. presence of a transport maximum
E. requirement for metabolic energy
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Question 7) Which is true regarding the mediated transport of a substance across a plasma membrane?
A. It depends upon the binding of that substance to a specific site on the membrane protein.
B. It depends upon movement of proteins from one side of the membrane to the other.
C. It always increases in direct proportion to the increasing concentration of the substance on one side of the membrane.
D. Both depends upon the binding of that substance to a specific site on the membrane protein and depends upon movement of proteins from one side of the membrane to the other are correct.
E. All of the choices are correct.
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Question 8) Ion channels in cell membranes:
A. are nonspecific.
B. are not affected by differences in electrical potential across the membrane.
C. may open in response to binding a ligand.
D. only allow ions to move from the extracellular fluid into the cell.
E. only allow ions to move from the intracellular fluid out of the cell.
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Question 9) The permeability of the plasma membrane to mineral ions:
A. is not influenced by channels formed by proteins.
B. is the same in all cell types.
C. is affected by differences in electrical charge on the two sides of the membrane.
D. is zero in all living cells.
E. is only possible because of the hydrophobic interior of the lipid bilayer.
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Question 10) In general, polar molecules diffuse more rapidly through the lipid bilayer part of cell membranes than do nonpolar molecules. This statement is:
A. true.
B. false, because polar molecules diffuse through less rapidly because the bilayer is polar throughout its width.
C. false, because polar molecules diffuse through less rapidly because the bilayer is nonpolar throughout its width.
D. false, because nonpolar molecules diffuse through more rapidly because much of the bilayer is nonpolar.
E. false, because the rate of diffusion of nonpolar and polar molecules through the bilayer is essentially the same as long as the molecules are the same size.
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