chapter 6

Which of the following processes includes all others? A) osmosis B) diffusion of a solute across a membrane C) facilitated diffusion D) passive transport E) transport of an ion down its electrochemical gradient

D

3) Cooking oil and gasoline (a hydrocarbon) are NOT amphipathic molecules because they ________. A) do not have a polar or charged region B) do not have a nonpolar region C) have hydrophobic and hydrophilic regions D) are highly reduced molecules

A

A membrane protein that spans the phospholipid bilayer one or more times is ________. A) a transmembrane protein B) an associated protein C) a peripheral protein D) an integrin E) a glycoprotein

A

A phospholipid is a ________. A) nonpolar lipid molecule that is made polar by the addition of a phosphate B) nonpolar lipid molecule that is made amphipathic by the addition of a phosphate C) polar lipid molecule that fully interacts with water D) polar lipid molecule that fully repels water

A

In some cells, there are many ion electrochemical gradients across the plasma membrane even though there are usually only one or two proton pumps present in the membrane. The gradients of the other ions are most likely accounted for by ________. A) cotransport proteins B) ion channels C) pores in the plasma membrane D) passive diffusion across the plasma membrane E) cellular metabolic reactions that create or destroy ions

A

The membranes of winter wheat are able to remain fluid when it is extremely cold by ________. A) increasing the percentage of unsaturated phospholipids in the membrane B) increasing the percentage of cholesterol molecules in the membrane C) decreasing the number of hydrophobic proteins in the membrane D) cotransport of glucose and hydrogen E) using active transport

A

The presence of cholesterol in the plasma membranes of some animal cells ________. A) enables the membranes to stay fluid when cell temperature drops B) enables the cell to remove hydrogen atoms from saturated phospholipids C) enables the cell to add hydrogen atoms to unsaturated phospholipids D) makes the cell membrane less flexible, allowing it to sustain greater intracellular pressure E) reduces mutations to genetic material inside the cell

A

The text states that ribonucleotides can diffuse through some types of liposomes. It is likely that the lipids present early in chemical evolution had short chains. Would liposomes formed from these types of lipids be more or less permeable to ribonucleotides than if early cells formed from long-chained lipids? A) more permeable B) less permeable C) same permeability

A

What is the most important factor in explaining why osmosis occurs spontaneously? A) It leads to an increase in entropy. B) It leads to a decrease in entropy. C) The process is exothermic. D) The process is endothermic.

A

Which aspect of phospholipids is most important to the formation of bilayers? A) They are amphipathic. B) Their polar heads can interact with water. C) The length of their hydrocarbon tails can be altered to modulate membrane fluidity. D) Their hydrocarbon tails can consist of fatty acids or isoprene subunits.

A

Which of the following crosses lipid bilayers the slowest? A) a sodium ion B) a small, polar molecule like water C) a large, polar molecule like glucose D) a small, nonpolar molecule like oxygen (O2)

A

Which of the following factors would tend to increase membrane fluidity? A) a greater proportion of unsaturated phospholipids B) a greater proportion of saturated phospholipids C) a lower temperature D) a relatively high protein content in the membrane E) a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses

A

Which of the following is a large organic molecule that is NOT assembled by polymerization of a few kinds of simple subunits? A) a steroid B) cellulose C) DNA D) an enzyme E) a contractile protein

A

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly? A) CO2 B) an amino acid C) glucose D) K+

A

You have a planar bilayer with equal amounts of saturated and unsaturated phospholipids. After testing the permeability of this membrane to glucose, you increase the proportion of unsaturated phospholipids in the bilayer. What will happen to the membrane's permeability to glucose? A) Permeability to glucose will increase. B) Permeability to glucose will decrease. C) Permeability to glucose will stay the same. D) You cannot predict the outcome; you simply have to make the measurement.

A

2) What region of a steroid is hydrophilic? A) the methyl (—CH3) groups B) the terminal hydroxyl group C) the ring structures D) the long hydrocarbon chain

B

If you mechanically shook a mixture of phospholipids and water, what would you expect to see when you observe the solution using an electron microscope? A) The lipids and water will have separated into two distinct layers because the lipids are partially nonpolar. B) Some lipids will have formed tiny vesicles filled with water. C) All the lipids will have formed planar bilayer membranes. D) Most lipids will have completely dissolved in solution because they are partially polar.

B

In what way do the membranes of a eukaryotic cell vary? A) Phospholipids are found only in certain membranes. B) Certain proteins are unique to each membrane. C) Only certain membranes of the cell are selectively permeable. D) Only certain membranes are constructed from amphipathic molecules. E) Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm.

B

Steroid hormones are large communication molecules that are modified cholesterol molecules. How do you think they enter a cell? A) Their size probably allows them to diffuse through the plasma membrane. B) Their lipid nature probably allows them to diffuse through the plasma membrane. C) Their protein structure probably allows them to diffuse through the plasma membrane. D) They must require a protein transporter, because the plasma membrane is completely impermeable to molecules.

B

Steroids are considered to be lipids because they ________. A) are essential components of cell membranes B) are not soluble in water C) are made of fatty acids D) are hydrophilic compounds E) contribute to atherosclerosis

B

Under what circumstances does membrane transport require energy? A) wherever large molecules are moved within a cell B) whenever a solute is moved against its electrochemical gradient C) whenever an ion moves through a phospholipid bilayer membrane D) whenever oxygen moves through a phospholipid bilayer membrane

B

Which of the following is a characteristic feature of a carrier protein in a plasma membrane? A) It is a peripheral membrane protein. B) It exhibits a specificity for a particular type of molecule. C) It requires the expenditure of cellular energy to function. D) It works against diffusion. E) It has no hydrophobic regions.

B

A patient was involved in a serious accident and lost a large quantity of blood. In an attempt to replenish body fluids, distilled water—equal to the volume of blood lost—is added to the blood directly via one of his veins. What will be the most probable result of this transfusion? A) It will have no unfavorable effect as long as the water is free of viruses and bacteria. B) The patient's red blood cells will shrivel up because the blood has become hypotonic compared to the cells. C) The patient's red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells. D) The patient's red blood cells will shrivel up because the blood has become hypertonic compared to the cells. E) The patient's red blood cells will burst because the blood has become hypertonic compared to the cells.

C

Celery stalks that are immersed in freshwater for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the freshwater ________. A) and the salt solution are both hypertonic to the cells of the celery stalks B) and the salt solution are both hypotonic to the cells of the celery stalks C) is hypotonic and the salt solution is hypertonic to the cells of the celery stalks D) is hypertonic and the salt solution is hypotonic to the cells of the celery stalks E) is isotonic and the salt solution is hypertonic to the cells of the celery stalks

C

For a protein to be an integral membrane protein, it would have to be ________. A) hydrophilic B) hydrophobic C) amphipathic, with at least one hydrophobic region D) completely covered with phospholipids E) exposed on only one surface of the membrane

C

Gramicidin is an antibiotic that increases the permeability of bacterial cell walls to inorganic ions. What is the most likely mode of action of gramicidin? A) It acts by active transport. B) It causes membranes to fuse with one another. C) It forms a channel in the membrane. D) It removes electrical charges from solutes.

C

Which of the following affects the osmolarity of a solution? I) concentration of cations II) concentration of anions III) concentration of water A) only I B) only III C) only I and II D) only II and III E) I, II, and III

C

Which of the following is TRUE of osmosis? A) Osmosis only takes place in red blood cells. B) Osmosis is an energy-demanding or "active" process. C) In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration. D) In osmosis, solutes move across a membrane from areas of lower water concentration to areas of higher water concentration.

C

Which of the following is the best explanation for why cholesterol decreases the permeability of biological membranes? A) Cholesterol binds to the outside surface of a membrane, thus blocking the movement of solutes. B) Because cholesterol is amphipathic, it forms tiny vesicles that trap solutes. C) Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane. D) Cholesterol has four rings in its structure that can sequester ("trap") solutes.

C

Which of the following membrane activities requires energy from ATP? A) facilitated diffusion of chloride ions across the membrane through a chloride channel B) movement of water into a cell C) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid D) movement of glucose molecules into a bacterial cell from a medium containing a higher concentration of glucose than that inside the cell E) movement of carbon dioxide out of a paramecium

C

Which of the following types of molecules are the major structural components of the cell membrane? A) phospholipids and cellulose B) nucleic acids and proteins C) phospholipids and proteins D) proteins and cellulose E) glycoproteins and cholesterol

C

You have just discovered an organism that lives in extremely cold environments. Which of the following would you predict to be TRUE about the phospholipids in its membranes, compared to phospholipids in the membranes of organisms that live in warmer environments? A) The membrane phospholipids of cold-adapted organisms will have longer hydrocarbon tails B) The membrane phospholipids of cold-adapted organisms will have more saturated hydrocarbon tails. C) The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.

C

In an experiment involving planar bilayers, a solution of table salt (sodium and chloride ions in water) is added on the left side of the membrane while pure water is added on the right side. After 30 minutes, the researchers test for the presence of ions on each side of the membrane. The right side tests negative for ions. What can you conclude? A) The experiment failed. B) The water somehow blocked the movement of ions across the membrane. C) The left side would probably also test negative for ions. D) Ions cannot cross planar bilayers.

D

Ions diffuse across membranes through specific ion channels down ________. A) their chemical gradients B) their concentration gradients C) their electrical gradients D) their electrochemical gradients E) the osmotic potential gradients

D

Lipids that form membranes have what kind of structure? A) polar heads and polar tails, which allows them to interact with water on both sides of the membrane B) completely polar, which allows them to dissolve in water C) polar heads and nonpolar tails; the nonpolar tails interact with water D) polar heads and nonpolar tails; the polar heads interact with water

D

Refer to the figure. If you examine side A after three days, you should find ________. A) a decrease in the concentration of NaCl and glucose and an increase in the water level B) a decrease in the concentration of NaCl, an increase in the water level, and no change in the concentration of glucose C) no net change in the system D) a decrease in the concentration of NaCl and a decrease in the water level E) no change in the concentration of NaCl and glucose and an increase in the water level

D

When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are ________. A) peripheral proteins B) phospholipids C) carbohydrates D) integral proteins E) cholesterol molecules

D

Where would you most likely find an integral membrane protein? A) on the inside surface of the cell membrane B) on the outside surface of the cell membrane C) floating freely in the cytoplasm D) spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell

D

Which of the following crosses lipid bilayers the fastest? A) a sodium ion B) a small, polar molecule like water C) a large, polar molecule like glucose D) a small, nonpolar molecule like oxygen (O2)

D

Which of the following increases the strength of the hydrophobic interactions in lipid bilayers and thus makes them less permeable to polar molecules? A) the presence of double bonds B) increasing temperature C) removing cholesterol D) increasing length of the hydrocarbon chains

D

Why are lipids and proteins free to move laterally in membranes? A) The interior of the membrane is filled with liquid water. B) Lipids and proteins repulse each other in the membrane. C) Hydrophilic portions of the lipids are in the interior of the membrane. D) There are only weak hydrophobic interactions in the interior of the membrane. E) Molecules such as cellulose can pull them in various directions.

D

Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells? A) simple diffusion B) phagocytosis C) active transport pumps D) exocytosis E) facilitated diffusion

E

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 ________. A) passive diffusion B) facilitated diffusion C) active transport D) osmosis E) cotransport

E

When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that ________. A) the integral membrane proteins are not strong enough to hold the bilayer together B) water that is present in the middle of the bilayer freezes and is easily fractured C) hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing D) the carbon—carbon bonds of the phospholipid tails are easily broken E) the hydrophobic interactions that hold the membrane together are weakest at this point

E

Which of the following allows water to move much faster across cell membranes? A) the hydrophobic interior of a cell membrane B) the sodium—potassium pump C) ATP D) peripheral proteins E) aquaporins

E

Which of the following is most likely TRUE of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal? A) Sodium and glucose compete for the same binding site in the cotransporter. B) Glucose entering the cell down its concentration gradient provides energy for uptake of sodium ions against the electrochemical gradient. C) Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell. D) The cotransporter can also transport potassium ions. E) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.

E

Lipids ________. A) are insoluble in water B) are made from glycerol, fatty acids, and nitrogen C) contain less energy than proteins and carbohydrates D) are made by dehydration reactions E) contain sulfur polymers

a

Phospholipids and triglycerides both ________. A) contain serine or some other organic compound B) have three fatty acids C) have a glycerol backbone D) have a phosphate

c