Membrane Structure and Function

According to the fluid-mosaic model of cell membranes, which of the following is a TRUE statement about membrane phospholipids?
1. They can move laterally along the plane of the membrane.
2. They frequently flip-flop from side of the membrane to the other.
3. They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane.
4. They are free to depart from the membrane and dissolve in the surrounding solution.
5. They have hydrophilic tails in the interior of the membrane.
What are the elevated regions (particles) seen in electron micrographs of split freeze-fractured membranes?
1. peripheral proteins
2. phospholipids
3. carbohydrates
4. intefral proteins
5. cholesterol molecules
What are the membrane structures that function in active transport?
1. peripheral proteins
2. carbohydrates
3. cholesterol
4. cytoskeleton filaments
5. integral proteins
The net movement of uncharged molecules from a lower concentration to a higher concentration is described by which of the following?
1. diffusion
2. active transport
3. osmosis
4. facilitated diffusion
5. exocytosis
What is the voltage across cell membranes called?
1. water potential
2. chemical gradient
3. membrane potential
4. osmotic potential
5. electochemical gradient
All of the following cellular activities require ATP energy EXCEPT
1. Movement of oxygen into the cell.
2. Protein synthesis
3. Sodium ions moving out of the cell.
4. Eytoplasmic streaming.
5. Exocytosis
Of the following functions, the glycoproteins and glycolipids of animal cell membranes are most important for
1. facilitated diffusion of molecules down their concentration gradients.
2. active transport of molecules against their concentration gradients.
3. maintaining the integrity of a fluid-mosaic membrane.
4. maintaining membrane fluidity at low temperatures.
5. the ability of cells to recognize like and different cells.
The U-tube has a membrane that is permeable to water and glucose, but not ot sucrose. The left side is fill with a solution as designated and the right side is filled as designed.

Initially, the solution in the left side, with respect to that in the right side, is
1. hypotonic
2. plasmolyzed
3. isotonic
4. saturated
5. hypertonic
After the system reaches equilibrium, what changes are observed?
1. The molarity of sucrose and glucose are equal on both sides.
2. The molarity of glucose is higher in the left side than in the right side.
3. The molarity of sucrose is increased in the left side.
4. The water level is unchanged.
5. The water level is higher in the left side and in the right side.
Now, suppose the differentially permeable membrane is equally permeable to both sucrose and glucose.

Initially, the solution in the right side, with respect to the left side, is ________.
1. hypotonic
2. plasmolyzed
3. isotonic
4. saturated
5. hypertonic
After the system reaches equilibrium, what changes are observed?
1. Glucose and sucrose no longer cross the membrane.
2. The molarity of sucrose is higher on the right side than on the left side.
3. The molarity of glucose has increased on both sides.
4. The water level is unchanged.
5. The water level is higher on the right side than on the left side.
The sodium-potassium pump is called an electrogenic pump because it
1. pumps equal quantities of sodium and potassium ions across the membrane.
2. pumps hydrogen ions into the cell.
3. contributes to the membrane potential.
4. ionizes sodium and potassium.
5. pumps hydrogen ions out of the cell.
The movement of potassium into or out of an animal cell requires
1. low cellular concentrations of sodium.
2. high cellular concentrations of potassium.
3. an energy source such as ATP or a proton gradient.
4. glucose for binding and releasing ions.
5. plant hormones embedded in the cell membrane.
An organism with a cell wall would have the most difficulty doing which process?
1. diffusion
2. osmosis
3. active transport
4. phagocytosis
5. exocytosis
Which process accounts for the movement of solids into some animal cells?
1. active transport
2. facilitated diffusion
3. diffusion
4. osmosis
5. phagocytosis
All of the following are functions of integral membrane proteins EXCEPT
1. enzyme synthesis
2. active transport
3. hormone reception
4. cell adhesion
5. cytoskeleton attachement
The membrane activity most nearly opposite to exocytosis is
1. plasmolysis
2. osmosis
3. facilitated diffusion
4. phagosytosis
5. active transport
Which of the following statements is CORRECT about diffusion?
1. It is very rapid over long distances.
2. It requires an expenditure of energy by the cell.
3. It is a passive process.
4. It occurs when molecules move from a region of lower concentration to one of higher concentration.
5. It requires integral proteins in the cell membrane
Carrier molecules in the plasma membrane are required for _______.
1. diffusion
2. osmosis
3. facilitated diffusion only
4. active transport only
5. both facilitated diffusion and active transport.
A cell with an internal concentration of 0.02 molar glucose is placed in a test tube containing 0.02 molar glucose solution. Assuming that glucose is not actively transported into the cell, which of the following terms describes the internal concentration of the cell relative to its environment?
1. isotonic
2. hypertonic
3. hypotonic
4. flaccid
5. A or B, depending on the temperature
One of the functions of cholesterol in animal cell membranes is to
1. facilitate transport of ions.
2. store energy.
3. maintain membrane fluidity.
4. speed diffusion.
5. phosphorylate ADP.
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?
1. carbon dioxide
2. an amino acid
3. glucose
4. potassium ion
5. starch
Glucose diffuses slowly through aritficial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from teh glucose-righ food into their glucose-poor cytoplasm. Using this information, which transport mechanism in most probably functioning in the intestianl cells?
1. simple diffusion
2. phagocytosis
3. active transport pumps
4. exocytosis
5. facilitated diffusion
The kind of molecules that pass through a cell membrane most easily are
1. large and hydrophobic.
2. small and hydrophobic.
3. large polar molecules.
4. ionic.
5. monosaccharides such as glucose.
The cotransport protein that allows two different substances to pass through a membrane is the same direction is
1. usually also a uniport.
2. usually also a biport.
3. usually associated with a proton pump.
4. insensitive to temperature.
5. usually associated with an antiport.
Suppose instead that the selective membrane is permeable to both glucose and NaCl in the same way that a plasma membrane of a cell is permeable to both. It takes the system 4 hours to reach equilibrium. In a few minutes,
1. the water level on side A would be higher than on side B.
2. water would no longer move across the membrane.
3. the glucose and NaCl would be at a equilibrium, but osmosis would continue.
4. more glucose than NaCl would have passed through the membrane.
5. more NaCl than glucose would have passed through the membrane.
Now, the solution in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane that permits sodium chloride by not glucose. Both sides are filled with the designated amounts at the same time.

At equilibrium, in side B you would find
1. an increase in NaCl concentration but a decrease in glucose concentration.
2. a decrease inthe molarity of both glucose and NaCl.
3. peripheral proteins
4. cholesterol
5. glycoproteins
What membrane-surface molecules are thought ot be most important as cells recognize each other?
1. phospholipids
2. integral proteins
3. peripheral proteins
4. cholesterol
5. glycoproteins
White blood cells engulf bacteria through what process?
1. exosytosis
2. phagocytosis
3. pinocytosis
4. osmosis
5. receptor-mediated exocytosis
Ions diffuse across membranes down their ___________.
1. chemical gradients
2. concentration gradients
3. electrical gradients
4. electrochemical gradients
5. Both A and B are correct
All of the following situations are consisten with active transport EXCEPT
1. the conversion of ATP to ADP accompanies the movement of molecules.
2. the rate of oxygen consumtion by the cell increases when molecules move.
3. molecules move in or out of a cell against the osmotic gradient.
4. cells accumulate diffusible molecules in greater quantity than was found outside.
5. the rate of movement of molecules across the cell membrane increases in an anaerobic environment.
Of the following, which is the most important role of exocytosis?
1. to move away from danger.
2. to release substances from the cell.
3. to incorporate nutrients.
4. to pump protons.
5. to create new cells.
The presence of cholesterol in the plasma membranes of some animals
1. enables the membrane to stay fluid more easily when cell temperature drops.
2. enables the animal to remove hydrogen atoms from saturated phospholipids.
3. enables the animal to add hydrogen atoms to unsaturated phospholipids.
4. makes the membrane less flexible, so it can sustain greater pressure from within the cell.
5. makes the animals more susceptible to circulatory disorders.
Which of the following would indicate that facilitated diffusion was taking place?
1. Substances were moving against the diffusion gradient.
2. A substance was diffusing much faster than the physical condition indicated it should.
3. ATP was being rapidly consumed as the substance moved
4. A substance was slowing as it moved down its concentration gradient.
5. a substance was moving form a region o flow concentration into a region of higher concentration of the substance.
All of the following statements about membrane structure and function are true EXCEPT:
1. Diffusion of gases is faster in air than across membranes.
2. Diffusion, osmosis, and facilitated diffusion do not require any energy input from the cell.
3. Both sides of a membrane are identical in structure and function.
4. Voltage across teh membrane depends on an unequal distribution of ions across the plasma membrane.
5. Special membrane proteins can cotransport two solutes by coupling diffusion with active transport.
Two similar-sized animal cells are placed in a 0.5% sucrose solution. Cell A enlarges in size for a while, then stops; cell B continues to enlarge and finally ruptures. Which of the following was true at the beginning of the experiment?
1. Cell A was hypotonic to th esolution and cell B was hypertonic.
2. Cell A was hypertonic to th esolution and cell B was hypotonic
3. Cell A was hpertonic to cell B
4. Cell B was hypertonic to cell A
5. Cells A and B were isotonic to each other.
Which of the following characterizes the sodium-potasium pump?
1. All of the below characterize the sodium-potassium pump.
2. Sodium ions are pumped out of a cell against their gradient.
3. Potassium ions are pumped into a cell against their gradient.
4. Each exchange costs the cell one ATP
5. A carrier protein undergoes conformational change.
Which of the following is a characteristic feature of a carrier protein in a plasma membrane?
1. It is a peripheral membrane protein.
2. It exhibits a specificity for a particular type of molecule.
3. It requires energy to function.
4. It works against diffusion.
5. It has few, if any, hydrophobic amino acids.
Which molecule is NOT part of the cell membrane?
1. lipid
2. nucleic acid
3. protein
4. phosphate group
5. steroid
A cell lacking oligosaccharides on the external surface of its plasma membrane would likely be inefficient in
1. transporting ions against an electrochemical gradient.
2. cell-cell recognition.
3. maintaining fluidity of the phospholipid bilayer.
4. attaching to the cytoskeleton.
5. establishing the diffusion barrier to charged molecules.
Which of the following adheres to the extracellular surface of an animal cell plasma membrane?
1. fibers of the extracellular matrix
2. fibers of the cytoskeleton
3. the phospholipid bilayer
4. cholesterol
5. carrier proteins
You are conducting research on nerve cells. During an experiment, you administer an electrical stimulation to the cells. The probable result of this stimulation will be to
1. start the membrane water pump
2. cause increased saturation of phospholipid tails.
3. result in increased membrane fluidity and asymmetry
4. activiate the acitve transport system.
5. open gated channels
The most abundant lipid in most membranes are
1. sterols
2. glycolipids
3. cholesterol
4. phospholipids
The ability of phospholipids to form membranes
1. is important to animal cells but not bacterial cells.
2. is related to their amphipathic properties.
3. was discovered by Singer dn Nicolson.
4. depends on their secondary structure.
Of the following, a cell lacking motor proteins would most likely
1. lack movement of membrane proteins directed by cytoskeletal fibers.
2. be unable to incorporate cholesterol in the membranes.
3. be inhibited in teh fip-flop fluidity of the bilayer.
4. be unable to carry out active transport
Integral proteins
1. lack tertiary structure.
2. are loosely bound to the bilayer
3. are usually transmembrane proteins.
4. are not mobile within the bilayer
5. have no known functions in membranes
A membrane protein with hydrophobic regions
1. would be more fluid than those lacking hydrophobic regions.
2. would contain nonpolar amino acids in the hydrophobic region
3. could not span the lipid bilayer.
4. would be considered a peripheral protein
5. would be highly soluble in water.
Water passes quickly through cell membranes because
1. the bilayer is hydrophilic
2. it moves through protein channels
3. water movement is tied to ATP hydrolysis
4. it is a small, polar, unchanged molecule
5. None of the above
Which of the following best characterizes membrane structure
1. rigidity and water repellance.
2. asymmetry and fluidity.
3. streaming and unorganized.
4. passive and active.
5. enzymes and ATP.
Mutant cells lacking coated pits would most likely
1. be deficient in receptor-mediated endosytosis.
2. be unable to adapt to the cold.
3. be characterized by a smooth surface on both sides of the bilayer.
4. be unable to actively transport ions into the cell.
5. be a cell involved in steroid synthesis.