Bio quiz #2 Plasma Membrane

Which component in the accompanying figure plays a critical role in cell-cell recognition?

B

According to the fluid mosaic model of cell membranes, phospholipids ______.

can move laterally along the plane of the membrane

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

A salmon moving from a river into an ocean.

Which component in the accompanying figure is hydrophilic?

B

Familial hypercholesterolemia is characterized by ________.

defective LDL receptors on the cell membranes.

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

isotonic solution, and the plant cell is in a hypotonic solution.

When a plant cell, such as one from a tulip leaf, is submerged in a hypertonic solution, what is likely to occur?

Plasmolysis will shrink the interior of the cell.

Which of the following types of molecules lack hydrophilic domains?

Cholesterol

Which of the following membrane activities requires energy from ATP hydrolysis?

Na+ ions moving out of the cell

Which of the following statements about diffusion is true?

It's a passive process

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

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

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_____.

The fresh water is hypotonic & the salt solution is hypertonic to the cells of the celery sticks.

The solutions in the two arms of this U-tube are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose. Side B is half- filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels on both sides are equal. In the U-tube illustrated above, ________. (Answers were in reference to isotonic, hypertonic or hypotonic)

Isotonic

Which of the following processes includes all others? (the answers referred to transport of molecule methods)

Passive transport - transport of an ion down its electrochemical gradient, osmosis, facilitated diffusion, diffusion of a solute across a membrane.

Which of the following types of molecules are hydrophilic and therefore excluded from the hydrophobic portion of the phospholipid bilayer?

Peripheral membran proteins

A white blood cell engulfing a bacterium is an example of _____.

Phagocytosis

Which of the following will be true when the system illustrated above reaches equilibrium? (Answers were in reference to the direction of water movement)

The water level will be higher in side A than in side B

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

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

Endocytosis moves materials _____ a cell via _____.

into; membranous vesicles

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

lysosomes

If the concentration of phosphate in the cytosol is 2.0 mM and the concentration of phosphate in the surrounding fluid is 0.1 mM, how could the cell increase the concentration of phosphate in the cytosol?

Active transport

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

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

Which of the following statements about osmosis is correct?

The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis. (Aquaporins facilitate water movement across membranes and thus speed up the process of osmosis).

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 ________.

cotransport proteins.

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

embedded in a lipid bilayer

Based on the data provided, the intracellular molarity of dissolved solutes in sweet potato cells is approximately ________.

0.4 M

Which component in the accompanying figure is a protein fiber of the extracellular matrix?

A

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

It exhibits a specificity for a particular type of molecule.

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?

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

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

contributes to the membrane potential

A sodium-potassium pump ________.

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

The force driving simple diffusion is _______, while the energy source for active transport is ____.

the concentration gradient and ATP

Diffusion of ions across membranes through specific ion channels is driven by ________.

their electrochemical gradients

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

CO2

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

Certain proteins are unique to each other.

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 their veins. What will be the most probable result of this transfusion?

The patient's red blood cells will swell & possibly burst because the blood has become hypotonic compared to the cells.

Which component in the accompanying figure is cholesterol?

E

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

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

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

A

In this diagram of the plasma membrane of two adjoining cells, identify the protein indicated by the white arrow, including its function.

A receptor protein that binds with a signaling molecule and relays the message into the cell by activating other molecules inside the cell. Signaling proteins are part of signal transduction pathways that transmit external chemical signals into the cell.

Active and passive transport of solutes across a membrane typically differ in which of the following ways?

Active transport always involves the utilization of cellular energy, where's passive transport does not require cellular energy. (Active and passive transport can be distinguished by whether or not they use cellular energy).

For a protein to be an integral membrane protein, it would have to be ____.

Amphipathic, with at least one hydrophobic region.

Which line or lines in the graph represent(s) bags that contain a solution that is hypertonic at 50 minutes?

B

Five dialysis bags, constructed of a type of membrane that is permeable to water and impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed), and the percent change in mass of each bag was graphed. Which line in the graph represents the bag that contained a solution isotonic to the 0.6 M solution at the beginning of the experiment?

C

Which component in the accompanying figure is a microfilament (actin filament) of the cytoskeleton?

C

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?

Hydrating drinks with high concentration of salts and glucose.

Which of these CANNOT rapidly pass directly through the phospholipids of the plasma membrane?

Ions, such as hydrogen ions, and hydrophilic molecules, such as water and glucose, cannot rapidly pass directly through the phospholipids of a plasma membrane. To move rapidly through the membrane, they must pass through membrane transport proteins.

Which of the following are least likely to diffuse through the phospholipid bilayer of a cell membrane?

Small ions

Cell membranes are asymmetrical (have a sidedness). Which of the following statements if the most likely explanation for the membrane's asymmetrical nature?

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

Which of the following statements about a typical plasma membrane is accurate?

The two sides of the plasma membrane have different lipid & protein composition.

The solutions in the arms of a U‐tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. If you examine side A after three days, you should find _____.

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

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

cell-cell recognition

The difference between pinocytosis and receptor-mediated endocytosis is that ________.

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

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

small and hyrophobic

When the system illustrated above reaches equilibrium, the sugar concentrations on both sides of the U-tube will be ________.

1.5 M sucrose, 1.5 M glucose

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

A greater proportion of unsaturated phospholipids.

Which of the following molecules dramatically increases the rate of diffusion of water across cell membranes?

aquaporins

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. In this bacterial cell, phosphate transport is an example of ________.

Cotransport

Cell membranes have distinct inside and outside faces. Which of the following statements is the most likely explanation for the membrane's asymmetrical nature?

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

Which of the following structures would decrease the electrochemical gradient across a membrane?

A potassium channel

Diffusion _____.

Movement of molecules from an area of higher concentration to an area of lower concentration.

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

On the inside surface of the vesicle.

The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. At the beginning of the U-tube experiment illustrated above, which of the following statements is true? (Answers were in reference to isotonic, hypertonic or hypotonic)

Side A is hypotonic to side B.

A research team is working on the design of a new drug for the treatment of lung cancer. To be most effective, this drug must specifically enter the cytoplasm of lung cells while not entering the cells of other tissues. Which of the following characteristics would likely enhance the specificity of this drug?

Similarity of the drug molecule to other molecules normally transported lung cells.

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

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

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 substance that blocks sodium ions from binding to the co-transport protein will also block the transport of glucose.

A type of agricultural crop, winter wheat, is able to have its cell membrane remain fluid even in extremely cold temperatures. What property of its cell membrane may account for this?

Cholesterol

Based on Figure 7.18 (below), which of these experimental treatments would increase the rate of sucrose transport into a plant cell?

Decreasing extracellular pH

Which of the following most accurately describes selective permeability?

Only certain molecules can cross a cell membrane.

In the U-tube experiment illustrated above, which of the following statements correctly describes side B at equilibrium? (Answers were in reference how NaCl and glucose concentrations would change)

The concentration of NaCl will increase, the concentration of glucose will decrease, and the water level will increase.

The permeability of a biological membrane to a specific polar solute may depend on which of the following?

The types of transport proteins in the membrane.

Which of the following statements correctly describes osmosis?

The water moves across a membrane from an area of lower solute to areas of higher solute concentration.

Which of the following correctly describes some aspect of exocytosis or endocytosis?

These two changes the surface area of the plasma membrane. (The fusion or budding of transport vesicles at the plasma membrane either adds or removes proteins and phospholipids, thus changing the surface area).

Which of the following best describes the structure of a biological membrane?

Two layers of phospholipids with proteins either crossing the layers or on the surface of the layers.

According to the fluid mosaic model, a membrane ________.

is composed of a fluid bilayer of phospholipids with embedded amphipathic proteins.

A voltage across a membrane is called the _____.

membrane potential

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?

Hypotonic; the salt concentration in the solution is lower than it is in the cell, so water enters the cell, causing it to burst.

What specific name is given to the process by which water crosses a selectively permeable membrane?

Osmosis

Three lab groups carried out an experiment to identify the concentration of sucrose in six solutions. Each unknown contained one of the following sucrose concentrations: 0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and -1.0 M. Cubes of sweet potato (1 cm3) were soaked for 24 hours in each solution and weighed to determine the change in mass. Each data entry represents the average of three sample replicates expressed as percent change in mass following a 24-hour soak in the unknown solutions. From the data given, which statement most accurately describes what is occurring in response to a particular unknown solution?

Osmosis of water molecules from unknown solution A likely caused the increase in mass observed.

Which of the following processes includes all the others?

Passive transport

Which of these are NOT embedded in the hydrophobic portion of the phospholipid bilayer?

Peripheral proteins

A phospholipid bilayer with equal amounts of saturated and unsaturated fatty acids displays a specific permeability to glucose. What effect will increasing the proportion of unsaturated fatty acids in the bilayer have on the membrane's permeability to glucose?

Permeability to glucose will increase

Which component is a peripheral protein?

D) D

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

Phagocytosis

Human immunodeficiency virus (HIV) infects cells that have both CD4 and CCR5 cell surface molecules. The viral nucleic acid molecules are enclosed in a protein capsid, and the protein capsid is itself contained inside an envelope consisting of a lipid bilayer membrane and viral glycoproteins. One hypothesis for viral entry into cells is that binding of HIV membrane glycoproteins to CD4 and CCR5 initiates fusion of the HIV membrane with the plasma membrane, releasing the viral capsid into the cytoplasm. An alternative hypothesis is that HIV gains entry into the cell via receptor-mediated endocytosis, and membrane fusion occurs in the endocytotic vesicle. To test these alternative hypotheses for HIV entry, researchers labeled the lipids on the HIV membrane with a red fluorescent dye. In an HIV-infected cell producing HIV virus particles, the viral glycoprotein is expressed on the plasma membrane. How do the viral glycoproteins get to the plasma membrane? They are synthesized ________.

by ribosomes in the rough ER and arrive at the plasma membrane in the membrane of secretory vesicles.