Chapter 7

For the following questions, match the labeled component of the cell membrane (Figure 7.1) with its description.

5) peripheral protein Answer: D

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly

embedded in a lipid bilayer.

A. H. Davson and J. Danielli B. I. Langmuir C. C. Overton D. S. Singer and G. Nicolson E. E. Gorter and F. Grendel

1) The first to propose that cell membranes are phospholipid bilayers. Answer: E

A. H. Davson and J. Danielli B. I. Langmuir C. C. Overton D. S. Singer and G. Nicolson E. E. Gorter and F. Grendel

2) Membranes are a phospholipid bilayer between two layers of hydrophilic proteins. Answer: A

A. H. Davson and J. Danielli B. I. Langmuir C. C. Overton D. S. Singer and G. Nicolson E. E. Gorter and F. Grendel

3) The membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids. Answer: D

39) At the beginning of the experiment,

39) At the beginning of the experiment, A) side A is hypertonic to side B. B) side A is hypotonic to side B. C) side A is isotonic to side B. D) side A is hypertonic to side B with respect to glucose. E) side A is hypotonic to side B with respect to sodium chloride. Answer: B

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?

A) CO2

The sodium-potassium pump in animal cells requires cytoplasmic ATP to pump ions across the plasma membrane. When the proteins of the pump are first synthesized in the rough ER, what side of the ER membrane will the ATP binding site be on?

A) It will be on the cytoplasmic side of the ER.

Which of the following characterizes the sodium-potassium pump?

A) Sodium ions are pumped out of a cell against their gradient. B) Potassium ions are pumped into a cell against their gradient. C) The pump protein undergoes a conformational change. D) Only A and B are correct. E) A, B, and C are all correct. Answer: E

45) What is (are) the best explanation(s) for the shape of line E after 50 minutes?

A) The bag is isotonic with the solution around it. B) Water is entering and leaving the bag at the same rate. C) Sucrose is entering and leaving the bag at the same rate. D) A and B only E) A, B, and C Answer: D

14) According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?

A) They can move laterally along the plane of the membrane.

What mechanisms do plants use to load sucrose produced by photosynthesis into specialized cells in the veins of leaves?

A) an electrogenic pump B) a proton pump C) a contransport protein D) A and C only E) A, B, and C Answer: E

16) What is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?

A) by increasing the percentage of unsaturated phospholipids in the membrane

In most cells, there are electrochemical gradients of many ions across the plasma membrane even though there are usually only one or two electrogenic pumps present in the membrane. The gradients of the other ions are most likely accounted for by

A) cotransport proteins.

13) The presence of cholesterol in the plasma membranes of some animals

A) enables the membrane to stay fluid more easily when cell temperature drops.

The main difference(s) between facilitated diffusion and active transport is (are)

A) facilitated diffusion moves substances down their concentration gradient and active transport moves them against their gradient. B) facilitated diffusion does not rely on cellular energy and active transport does. C) facilitated diffusion uses channel or carrier proteins and active transport does not. D) A and B only E) A, B, and C Answer: E

34) Initially, in terms of tonicity, the solution in side A with respect to that in side B is

A) hypotonic. B) plasmolyzed. C) isotonic. D) saturated. E) hypertonic. Answer: C

15) The lateral mobility (fluidity) of lipids and proteins in membranes is a consequence of

A) lack of covalent bonds between the lipid and protein components of the membrane. B) weak hydrophobic interactions among the components in the interior of the membrane. C) the presence of liquid water in the interior of the membrane. D) A and B only E) A, B, and C Answer: D

72) In a hypotonic solution an animal cell will

A) lyse.

69) The difference between pinocytosis and receptor-mediated endocytosis is that

A) pinocytosis brings only water into the cell, but receptor-mediated endocytosis brings in other molecules as well.

19) All of the following are functions of integral membrane proteins except

A) protein synthesis.

The selective permeability of biological membranes is dependent on which of the following?

A) the type of transport proteins that are present in the membrane B) the lipid bilayer being permeable to primarily small, nonpolar molecules C) the types of carbohydrates on the surface of the membrane D) A and B only E) A, B, and C Answer: D

Which line represents the bag with the highest initial concentration of sucrose?

Answer: A

Which line represents the bag that contained a solution isotonic to the 0.6 molar solution at the beginning of the experiment?

Answer: C

44) Which line or lines represent(s) bags that contain a solution that is hypertonic at the end of 60 minutes?

B) B

75) In what way do the various membranes of a eukaryotic cell differ?

B) Certain proteins are unique to each membrane.

Based on the model of sucrose uptake in Figure 7.19 (in the text), which of the following experimental treatments would increase the rate of sucrose transport into the cell?

B) decreasing extracellular pH

70) The interior of the phospholipid bilayer is

B) hydrophobic.

73) Endocytosis moves materials ________ a cell via ________.

B) into; membranous vesicles

11) All of the following molecules are part of the cell membrane except

B) nucleic acids.

What kinds of molecules pass through a cell membrane most easily?

B) small and hydrophobic

Which of the following statements is correct about diffusion?

C) It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.

Carrier molecules in the membrane and metabolic energy are required for

C) active transport.

17) The surface of an integral membrane protein would be best described as

C) amphipathic.

What is the voltage across a membrane called?

C) membrane potential

4) Which of the following types of molecules are the major structural components of the cell membrane?

C) phospholipids and proteins

74) Cholesterol enters cells via

C) receptor-mediated endocytosis.

41) Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?

D) The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.

40) If you examine side A after 3 days, you should find

D) a decrease in the concentration of NaCl and a decrease in the water level.

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

D) integral proteins.

Which of the following processes includes all others?

D) passive transport

12) The original model for the bilayer structure of cell membranes, which was prepared in the 1920s, was based on which of the following?

D) the understanding that phospholipids are amphipathic molecules

What are the membrane structures that function in active transport?

E) integral proteins

33) Water passes quickly through cell membranes because

E) it moves through aquaporins in the membrane.

71) Oxygen crosses a plasma membrane by

E) passive transport.

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

It exhibits a specificity for a particular type of molecule.

If a membrane protein in an animal cell is involved in the cotransport of glucose and sodium ions into the cell, which of the following is most likely not true?

Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell.

20) Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

The double bonds form a kink in the fatty acid tail, forcing adjacent lipids to be further apart.

36) A patient has had a serious accident and lost a lot of blood. In an attempt to replenish body fluids, distilled water, equal to the volume of blood lost, is transferred directly into one of his veins. What will be the most probable result of this transfusion?

The patient's red blood cells will swell because the blood fluid is hypotonic compared to the cells.

Which of the following statements about membrane structure and function is false?

The types of proteins that are exposed on one side of a membrane are nearly identical to those exposed on the other side of the membrane.

35) After the system reaches equilibrium, what changes are observed?

The water level is higher in side A than in side B.

Which of the following is correct about integral membrane proteins?

They are usually transmembrane proteins.

Which of the following factors would tend to increase membrane fluidity?

a greater proportion of unsaturated phospholipids

The movement of a substance across a biological membrane against its concentration gradient with the help of energy input

active transport.

The movement of potassium into an animal cell requires

an energy source such as ATP or a proton gradient.

Of the following functions, which is most important for the glycoproteins and glycolipids of animal cell membranes?

cell's ability to distinguish one type of neighboring cell from another

An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?

cell-cell recognition

The sodium-potassium pump is called an electrogenic pump because it

contributes to the membrane potential.

What is the cause of familial hypercholesterolemia?

defective LDL receptors on the cell membranes

Ions diffuse across membranes down their

electrochemical gradients.

All of the following processes take material into cells except

exocytosis.

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?

facilitated diffusion

All of the following membrane activities require energy from ATP hydrolysis except

facilitated diffusion.

Which of the following adheres to the extracellular surface of animal cell plasma membranes?

fibers of the extracellular matrix

What membrane-surface molecules are thought to be most important as cells recognize each other?

glycoproteins

37) Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are

hypertonic to fresh water but hypotonic to the salt solution.

A cell whose cytoplasm has a concentration of 0.02 molar glucose is placed in a test tube of water containing 0.02 molar glucose. Assuming that glucose is not actively transported into the cell, which of the following terms describes the tonicity of the external solution relative to the cytoplasm of the cell?

isotonic

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 not be a factor that determines whether the molecule enters the cell?

lipid composition of the target cells' plasma membrane

What is one of the functions of cholesterol in animal cell membranes?

maintains membrane fluidity

An organism with a cell wall would have the most difficulty doing which process?

phagocytosis

White blood cells engulf bacteria through what process?

phagocytosis

The membrane activity most nearly opposite to exocytosis is

phagocytosis.

10) 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

the hydrophobic interactions that hold the membrane together are weakest at this point.

After a membrane freezes and then thaws, it often becomes leaky to solutes. The most reasonable explanation for this is that

the integrity of the lipid bilayer is broken when the membrane freezes.

In addition to exporting materials from the cytoplasm of the cell, the process of exocytosis is also important in

the production of cell walls by plant cells.