Which of the following statements regarding the structure and function of cell membranes is correct?

a. The phospholipid bilayer is arranged so that the hydrophilic heads of the phospholipid molecule face the extra- and intracellular fluids.

b. Some proteins integrated into the membrane serve as channels for the passage of nonpolar molecules through the membrane.

c. Peripheral membrane proteins function as channels associated with transport of ions through the membrane.

d. Cholesterol molecules function to transport ions from one side of the plasma membrane to the other.

e. The plasma membrane is a layer of phospholipid molecules with their hyrophilic head groups in contact with the extracellular solution and the hydrophobic tail groups in contact with the intracellular solution.

a. The phospholipid bilayer is arranged so that the hydrophilic heads of the phospholipid molecule face the extra- and intracellular fluids.

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.

d. false, because nonpolar molecules diffuse through more rapidly because much of the bilayer is nonpolar.

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.

c. is affected by differences in electrical charge on the two sides of the membrane.

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.

c. may open in response to binding a ligand.

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

e. Requirement for metabolic energy

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.

a. It depends upon the binding of that substance to a specific site on the membrane protein.

By what transport mechanism does glucose enter most cells?

a. Diffusion through the lipid bilayer

b. Primary active transport

c. Secondary active transport

d. Diffusion through a protein channel

e. Facilitated diffusion

e. Facilitated diffusion

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.

e. It transports Na⁺ and K⁺ in a 1:1 ratio.

What will happen if a normal cell is placed in a hypotonic solution?

a. It will swell in size.

b. It will shrink in size.

c. It will stay the same size.

d. The result can't be predicted.

a. It will swell in size.

What type of cellular transport involves the cytosolic protein clathrin?

a. Exocytosis

b. Receptor-mediated endocytosis

c. Primary active transport

d. Secondary active transport

e. Pinocytosis

b. Receptor-mediated endocytosis

What is the most common transport mechanism by which glucose and other organic solutes cross the luminal membrane of an epithelial cell layer?

a. Secondary active cotransport with Na⁺

b. Glucose ATPase pump

c. Facilitated diffusion

d. Simple diffusion through the paracellular pathway

e. Through an ion channel

a. Secondary active cotransport with Na⁺

A solute, X, is placed in compartment A of a two compartment container and allowed to diffuse to compartment B and attain diffusion equilibrium. At that point in time,

a. there will be no further movement of any solute molecules between compartments.

b. solutes will be moving in both directions equally.

c. solutes will only continue to move from A to B.

d. solutes will only continue to move from B to A.

e. the concentration in compartment B will be much higher than that in compartment A.

b. solutes will be moving in both directions equally.

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.

c. It is characterized by saturable carriers and a maximum velocity of transport.

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.

a. It involves a specific membrane protein that functions as a carrier molecule.

If pure water and a solution containing a nonpenetrating solute are separated by a membrane that is permeable only to water, what would occur?

a. Water will diffuse by osmosis until the water concentrations in the two compartments become equal.

b. Water will diffuse by osmosis until all of the water is on the same side as the solute.

c. Water will diffuse by osmosis toward the side with the solute, until stopped by opposing hydrostatic pressure.

d. No movement will occur between the compartments.

e. Water will diffuse by osmosis away from the side with the solute, until stopped by hydrostatic pressure.

c. Water will diffuse by osmosis toward the side with the solute, until stopped by opposing hydrostatic pressure.

If all other conditions remain the same and the concentration of a nonpenetrating solute increases inside a cell, which is most likely to occur?

a. Water will tend to enter the cell because the interior has an increased osmolarity.

b. Water will tend to leave the cell because the interior has an increased osmolarity.

c. Water will tend to enter the cell because the interior has a decreased osmolarity.

d. Water will tend to leave the cell because the interior has a decreased osmolarity.

e. The solute will diffuse across the membrane until its concentration is equal on both sides of the membrane.

a. Water will tend to enter the cell because the interior has an increased osmolarity.

Regarding the tonicity and osmolarity of solutions, which of the following statements is not true?

a. The term "tonicity" refers to the effect that a solution has on the degree of stretch or shrinking of the cell membrane.

b. The term "osmolarity" refers to the osmotic properties of a solution, regardless of its tonicity.

c. Isotonic solutions are always isoosmotic.

d. Hypoosmotic solutions are always hypotonic.

e. Hypertonic solutions are always hyperosmotic.

c. Isotonic solutions are always isoosmotic.

Substance A, a penetrating solute, crosses the membrane at a rate of 10 molecules per second. When a patient has a fever and body temperature is elevated, we would expect the cell to have a rate of

a. less than 10 molecules per second.

b. 10 molecules per second.

c. more than 10 molecules per second.

c. more than 10 molecules per second.

Substance X is a mostly polar molecule and Substance Y is a mostly non-polar molecule of a similar size. Which will diffuse from the extracellular fluid to the intracellular fluid faster if they are in equal concentrations outside and inside the cell?

a. Substance X will diffuse faster.

b. Substance Y will diffuse faster.

c. Substance X and Substance Y will diffuse at the same rate, as they are of equal size and concentration.

b. Substance Y will diffuse faster.

Red blood cells have a higher proportion of aquaporins on the membrane than skin cells do. Assuming equal osmotic pressures, which is true?

a. The rate of osmosis is faster in skin cells than red blood cells.

b. The rate of osmosis is faster in red blood cells than in skin cells.

c. The rate of diffusion for non-polar molecules is faster in red blood cells than skin cells.

d. The rate of diffusion for non-polar molecules is faster in skin cells than red blood cells.

e. No significant differences in osmosis or diffusion rates between these cells.

b. The rate of osmosis is faster in red blood cells than in skin cells.

You are designing a drug. You’d like to deliver the drug by creating a skin patch that is impregnated with the drug and allowing the drug to diffuse through the layers of the skin to reach the underlying tissues and bloodstream. Which of these chemical changes might you make to increase the number of drug molecules that diffuse through the layers of skin cells?

a. Increasing the number of ionized groups in the drug

b. Increasing the number of nitrogen atoms in the drug

c. Decreasing the number of nonpolar groups in the drug

d. Decreasing the number of polar groups in the drug

e. Increasing the number of oxygen atoms in the drug

d. Decreasing the number of polar groups in the drug

You examine a cell by electron microscopy and find a molecule on the outside of the cell and in vesicles in the cytoplasm. The most likely explanation is that this substance moved into the cell by

a. diffusion.

b. osmosis.

c. facilitated diffusion.

d. endocytosis.

e. apoptosis.

d. endocytosis.

If the ATP-generating mechanisms in a cell are poisoned and the cell depletes its ATP reserves, which would occur first?

a. Primary active transport of molecules would cease.

b. Secondary active transport of molecules would cease.

c. Facilitated diffusion of molecules would cease.

d. Ion concentration gradients would reach equilibrium across the cell membrane.

e. All transport processes would cease immediately when the ATP was depleted.

a. Primary active transport of molecules would cease.

During a lab experiment, you forgot to label your solution containers. You see that red blood cells were placed into an unlabeled solution and they shrunk. What can be concluded about the unknown solution?

a. Its nonpenetrating solute concentration is greater than that of a normal cell.

b. Its nonpenetrating solute concentration is less than that of a normal cell.

c. Its nonpenetrating solute concentration is equal to that of a normal cell.

d. Its penetrating solute concentration is less than that of a normal cell.

e. Its penetrating solute concentration is greater than that of a normal cell.

a. Its nonpenetrating solute concentration is greater than that of a normal cell.