bio 111 exam 2

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1) For a protein to be an integral membrane protein, it would have to be _____.

amphipathic, with at least one hydrophobic region

2) 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?

Permeability to glucose will increase.

3) According to the fluid mosaic model of cell membranes, phospholipids _____.

A) can move laterally along the plane of the membrane

4) 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

5) Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. At higher temperatures, these regions _____.

B) are less fluid than the surrounding membrane

6) Singer and Nicolson’s fluid mosaic model of the membrane proposed that membranes_____.

C) consist of protein molecules embedded in a fluid bilayer of phospholipids

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

B) cell-cell recognition

8) Which of these are NOT embedded in the hydrophobic portion of the lipid bilayer at all?

C) peripheral proteins

9) Why are lipids and proteins free to move laterally in membranes?

D) There are only weak hydrophobic interactions in the interior of the membrane.

15) Cell membranes are asymmetrical. Which of the following statements is the most likely explanation for the membrane’s asymmetrical nature?

C) The two sides of a cell membrane face different environments and carry out different functions.

16) In what way do the membranes of a eukaryotic cell vary?

B) Certain proteins are unique to each membrane.

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

A) The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.

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

B) small and hydrophobic

19) Which of the following most accurately describes selective permeability?

D) Only certain molecules can cross a cell membrane.

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

A) It exhibits a specificity for a particular type of molecule.

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

A) CO2

22) Which of the following allows water to move much faster across cell membranes?

D) aquaporins

23) You are working on a team that is designing a new drug. For this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells?

C) similarity of the drug molecule to other molecules transported by the target cells

24) Diffusion _____.

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

25) Which of the following processes includes all others?

C) passive transport

26) When a cell is in equilibrium with its environment, which of the following occurs for substances that can diffuse through the cell?

A) There is random movement of substances into and out of the cell.

27) Which of the following is true of osmosis?

C) In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.

30) A patient was involved 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?

B) The patient’s red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells.

36) Celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the fresh water_____.

B) is hypotonic and the salt solution is hypertonic to the cells of the celery stalks

37) What will happen to a red blood cell (RBC), which has an internal ion concentration of about 0.9 percent, if it is placed into a beaker of pure water?

C) The cell would swell because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.

38) Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells? The animal cell is in _____.

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

39) In which of the following would there be the greatest need for osmoregulation?

B) a salmon moving from a river into an ocean

40) When a plant cell, such as one from a rose stem, is submerged in a very hypotonic solution, what is likely to occur?

D) The cell will become turgid.

41) A sodium-potassium pump _____.

B) move three sodium ions out of a cell and two potassium ions into a cell while consuming an ATP for each cycle

42) The sodium-potassium pump is called an electrogenic pump because it _____.

B) contributes to the membrane potential

43) Which of the following membrane activities requires energy from ATP?

B) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid

44) The voltage across a membrane is called the _____.

B) membrane potential

45) Ions diffuse across membranes through specific ion channels down _____.

D) their electrochemical gradients

46) Which of the following would increase the electrochemical gradient across a membrane?

B) a proton pump

47) 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 _____.

cotransport

48) 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

49) Which of the following is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal?

D) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.

50) Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean?

A) Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.

51) Several epidemic microbial diseases of earlier centuries incurred high death rates because they resulted in severe dehydration due to vomiting and diarrhea. Today they are usually not fatal because we have developed which of the following?

D) hydrating drinks with high concentrations of salts and glucose

52) The force driving simple diffusion is _____, while the energy source for active transport is _____.

B) the concentration gradient; ATP

53) An organism with a cell wall would most likely be unable to take in materials through _____.

C) phagocytosis

54) White blood cells engulf bacteria using _____.

phagocytosis

55) Familial hypercholesterolemia is characterized by _____.

A) defective LDL receptors on the cell membranes

56) The difference between pinocytosis and receptor-mediated endocytosis is that _____.

C) pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.

57) In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis?

C) on the inside surface of the vesicle

58) A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in _____.

A) lysosomes

60) What would be observed by live-cell fluorescence microscopy immediately after HIV entry if HIV is endocytosed first, and then later fuses with the endocytotic vesicle membrane?

B) The red fluorescent dye-labeled lipids will appear in the infected cell’s interior.

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