Deck 3: The Plasma Membrane and Membrane Potential

Question 1

Which of the following statements concerning the plasma membrane is correct?

A) the plasma membrane appears as a trilaminar structure under a light microscope.
B) the carbohydrates on the outer surface of the membrane serve as receptor sites for binding chemical messengers in the environment of the cell.
C) the lipid bilayer serves as a barrier to passage of H2O-soluble substances through the membrane.
D) carrier proteins shuttle back and forth across the membrane as they carry passenger molecules from one side to the other.
E) the plasma membrane is impermeable to any substance that is not lipid soluble or is greater than 0.8 nm in diameter.

Answer 1

the lipid bilayer serves as a barrier to passage of H2O-soluble substances through the membrane.

Question 2

In the cyclic AMP second messenger system, binding of the first messenger to a surface receptor leads to activation of ____, which induces the conversion of intracellular ____ to cyclic AMP.

A) adenylate cyclase, ATP.
B) adenylate cyclase, ADP.
C) phospholipase C, ATP.
D) phospholipase C, ADP.
E) protein kinase, ATP.

Answer 2

adenylate cyclase, ATP.

Question 3

Select the structure that promotes cell adhesion.

A) calmodulin.
B) collagen.
C) elastin.
D) CAMs
E) TSH.

Answer 3

CAMs

Question 4

Which statement regarding membrane proteins is incorrect?

A) channels are water-filled pathways.
B) channels maybe highly selective.
C) membrane proteins may catalyze specific reactions.
D) CAMs serve as binding sites for specific ligands.
E) proteins may work in conjunction with carbohydrates to provide recognition of "self."

Question 5

Receptor sites on the outer surface of the plasma membrane are

A) ATP.
B) carbohydrates.
C) cyclic AMP.
D) DNA.
E) proteins.

Question 6

Which of the following is not part of the extracellular matrix?

A) collagen
B) elastin
C) fibronectin
D) complex carbohydrates
E) all of the above are part of the extracellular matrix

Question 7

Which of the following allows intercellular movement of ions?

A) watery, gel-like ground substance.
B) connexons.
C) collagen.
D) elastin.
E) fibronectin.

Question 8

The cellular component that, once activated by the binding of an extracellular messenger to a surface receptor, in turn activates cyclic AMP is

A) phospholipase C.
B) adenylate cyclase.
C) calmodulin.
D) calcium.
E) cyclic guanosine monophosphate.

Question 9

The plasma membrane

A) appears under an electron microscope as a double dark line with a light space between.
B) is composed primarily of a double layer of phospholipid molecules with proteins interspersed throughout the phospholipids in a mosaic pattern.
C) separates the intracellular and extracellular fluid.
D) two of these answers.
E) all of these answers.

Question 10

Select the incorrect statement about the plasma membrane.

A) cholesterol contributes to its stability.
B) membrane proteins are inserted in a lipid bilayer.
C) it consists mostly of proteins.
D) its lipid bilayer is not a rigid structure.
E) membrane carbohydrates are only on its outer surface.

Question 11

The phospholipids within the plasma membrane

A) form a bilayer with the nonpolar tails buried in the center and the hydrophilic heads lined up on the outer and inner surfaces.
B) serve as a barrier to passage of water-soluble substances between the ICF and ECF.
C) are constantly moving
D) both (a) and (b) only
E) all of these answers.

Question 12

Which of the following are common means by which binding of an extracellular chemical messenger with a cell's receptor brings about a desired intracellular response?

A) opening or closing of specific channels to regulate ionic movement across the plasma membrane.
B) activation of an intracellular second messenger system.
C) alteration of protein shape and function as a result of phosphorylation.
D) only (a) and (b) above.
E) all of these answers.

Question 13

Leak channel:

A) are made from lipids
B) are always open
C) are specialized glucose channels
D) allow sodium to leak out of the cell
E) allow potassium to leak into the cell

Question 14

Integrins

A) create a filamentous meshwork in the inner surface of the membrane.
B) act as membrane-bounded enzymes.
C) are used for cell recognition purposes.
D) span the membrane, providing a mechanical link between the outer membrane and the cell's surrounding.
E) none of these answers.

Question 15

The plasma membrane

A) is composed primarily of phospholipids and proteins arranged in a fluid mosaic structure.
B) has a trilaminar appearance under an electron microscope.
C) acts as a mechanical barrier.
D) all of these answers.
E) none of these answers.

Question 16

Which of the following is not a function of membrane proteins?

A) they serve as channels.
B) they serve as a barrier for water soluble substances
C) they serve as carriers.
D) they serve as receptor sites
E) they serve as membrane-bound enzymes.

Question 17

Collagen

A) provides tensile strength.
B) is most abundant in tissues that must be capable of easily stretching and then recoiling.
C) promotes cell adhesion.
D) is a rubber-like protein fiber.
E) forms the intercellular filaments of a desmosome.

Question 18

Which of the following is the most common second messengers?

A) cyclic AMP.
B) calcium.
C) ATP.
D) both cyclic AMP and calcium.
E) all of these answers.

Question 19

Which of the following statements concerning gap junctions is incorrect?

A) gap junctions are communicating junctions.
B) at a gap junction, filaments of unknown composition extend between the plasma membranes of two closely adjacent but not touching cells, acting as "spot rivets" to anchor the cells together.
C) gap junctions are formed by small connecting tunnels that link two adjacent cells and permit exchange of small water-soluble particles between the cells.
D) gap junctions play an important role in transmission of electrical activity throughout an entire muscle mass.
E) connexons are an important structural component of gap junctions.

Question 20

Phospholipids

A) consist of a polar, hydrophilic, phosphate-bearing, head and two nonpolar hydrophobic, fatty-acid tails.
B) are aligned in a lipid bilayer in membranes.
C) serve as carrier molecules.
D) only (a) and (b) above.
E) all of these answers.

Question 21

Facilitated diffusion

A) involves a carrier molecule.
B) requires energy expenditure.
C) is how water enters the cells.
D) both (a) and (c) above.
E) all of these answers.

Question 22

Which of the following descriptions of movement of molecules across the plasma membrane is correct?

A) if two similar molecules can both combine with the same carrier, the presence of one of these molecules decreases the rate of entry of the other.
B) in simple diffusion, the rate of transport of a molecule is directly proportional to the molecule's extracellular concentration.
C) when a carrier becomes saturated, the maximum rate of transport is reached.
D) two of these answers.
E) all of these answers.

Question 23

Assuming a membrane is only water soluble and there is no significant hydrostatic pressure, water will osmose from

A) an isotonic solution to a hypotonic solution.
B) a hypotonic solution to a hypertonic solution.
C) a hypertonic solution to a hypotonic solution.
D) a hypertonic solution to an isotonic solution.
E) a hypotonic solution to an isotonic solution.

Question 24

Which decreases the rate of diffusion for a substance through a membrane?

A) increasing the concentration gradient.
B) increasing the molecular weight of the substance.
C) increasing the permeability of the membrane.
D) increasing the surface area of the membrane.
E) opening the channels in the membrane.

Question 25

____ are adhering junctions, ____ are impermeable junctions, and ____ are communicating junctions.

A) tight junctions, gap junctions, desmosomes
B) desmosomes, gap junctions, tight junctions
C) desmosomes, tight junctions, gap junctions
D) gap junctions, tight junctions, desmosomes
E) none of these answers.

Question 26

The concentration gradient for Na⁺

A) favors its movement into the cell at resting potential.
B) favors its movement out of the cell at resting potential.
C) is maintained by the Na⁺-K⁺ pump.
D) both (a) and (c) above.
E) both (b) and (c) above.

Question 27

What aspect of the membrane prevents water soluble substances from crossing the membrane?

A) membrane phospholipids.
B) how much cholesterol is present.
C) the number and types of membrane proteins.
D) the charge of the membrane.
E) none of these answers.

Question 28

During osmosis,

A) water moves down its own concentration gradient.
B) water moves to an area of higher solute concentration.
C) the solute moves against its concentration gradient.
D) only (a) and (b) above.
E) all of these answers.

Question 29

If a typical body cell is placed in a 0.25% saline solution, the cell

A) will gain water
B) will crenate (shrink)
C) will lose water.
D) will remain unchanged.
E) none of these answers.

Question 30

The electrical gradient for K⁺

A) favors its movement out of the cell at resting potential.
B) favors its movement into the cell at resting potential.
C) opposes the concentration gradient for K⁺ at the equilibrium potential for K⁺.
D) both (a) and (c) above.
E) both (b) and (c) above.

Question 31

Which of the following is incorrect about water movement across the membrane?

A) water can only move across the membrane through water channels
B) the movement of water is referred to as osmosis
C) water can slip between and pass through phospholipid molecules
D) water channels are known as aquaporins
E) water tends to be attracted to an area with a higher solute concentration

Question 32

The sodium-potassium pump moves ____ sodium ions out of the cell for every 2 potassium ions it moves into the cell.

A) 3
B) 5
C) 7
D) 11
E) 13

Question 33

Carrier-mediated transport

A) involves a specific membrane protein that serves as a carrier molecule.
B) always moves substances against a concentration gradient.
C) always requires energy expenditure.
D) two of these answers.
E) all of these answers.

Question 34

Select the correct statement about diffusion.

A) it depends on the random motion
B) it involves active forces.
C) its rate increases as the temperature decreases.
D) molecules move from a lower concentration to a higher concentration.
E) the chemical gradient of a substance does not affect it.

Question 35

A cell is placed in a hypotonic solution. The cell will

A) lose water by diffusion
B) gain water by osmosis
C) lose water by exocytosis
D) gain water by pinocytosis
E) remain unchanged

Question 36

Diffusion results from

A) ATP-driven processes.
B) use of ion gradients.
C) inherent kinetic energy of matter.
D) selective permeability.
E) loss of positive charge.

Question 37

Which of the following substances is most likely to passively diffuse across the plasma membrane by dissolving in the membrane?

A) a cation
B) an anion
C) a nonpolar or nonionized molecule
D) a polar molecule
E) a molecule less than 0.8 nm in diameter

Question 38

Tight junctions

A) prevent passage of materials between epithelial cells.
B) force materials to pass through cells.
C) are commonly found in digestive tract linings.
D) all of these answers.
E) none of these answers.

Question 39

In a water solution containing dissolved salt:

A) salt is the solute
B) water is the solute
C) salt is the solvent
D) the solute is stationary
E) the solution is heterogeneous

Question 40

By osmosis, water always moves to an area of higher

A) electrical intensity.
B) fluid pressure.
C) mitochondrial activity.
D) solute concentration.
E) water concentration.

Question 41

The rate of carrier-mediated transport is limited by

A) protein location in the membrane.
B) osmolarity.
C) tonicity.
D) competition with other molecules.
E) none of these answers.

Question 42

With secondary active transport, the movement of

A) Na⁺ into the cell by the cotransport carrier is downhill.
B) Na⁺ into the cell by the cotransport carrier is uphill.
C) glucose by the cotransport carrier is uphill.
D) two of these answers.
E) none of these answers.

Question 43

The resting membrane potential is

A) much closer to the equilibrium potential for Na⁺ than to the equilibrium potential for K⁺.
B) much closer to the equilibrium potential for K⁺ than to the equilibrium potential for Na⁺.
C) is always -90mV
D) both (a) and (c) above.
E) both (b) and (c) above.

Question 44

Glucose is usually reabsorbed from the filtrate in the kidney back into the blood through carrier proteins, hence, glucose in the urine is considered abnormal. What condition below might result in glucose in the urine?

A) high levels of glucose in the blood.
B) transport maximum for renal glucose reached.
C) excess consumption of glucose.
D) competitors for glucose carriers.
E) all of these answers.

Question 45

Pinocytosis is a form of

A) active transport.
B) cytokinesis.
C) endocytosis.
D) exocytosis.
E) hemolysis.

Question 46

Which of the following statements concerning the Na⁺-K⁺ pump is incorrect?

A) the phosphorylated conformation of the Na⁺-K⁺ pump has high affinity for K⁺ when exposed to the ICF.
B) the Na⁺-K⁺ pump has ATPase activity.
C) the Na⁺-K⁺ pump establishes Na⁺ and K⁺ concentration gradients across the plasma membrane; these gradients are critically important in the ability of nerve and muscle cells to generate electrical impulses essential to their functioning.
D) the Na⁺-K⁺ pump helps regulate cell volume by controlling the concentration of solutes inside the cell to minimize osmotic effects that would induce swelling or shrinking of the cell.
E) the ion concentration gradient established by the Na⁺-K⁺ pump drives cotransport carriers to move glucose against its concentration gradient across intestinal and kidney cells.

Question 47

Exocytosis of secretory products is triggered by the entry of ____ into the cell in response to a specific neural or hormonal stimulus.

A) K⁺
B) Na⁺
C) Ca²⁺
D) ATP
E) A^-

Question 48

According to Fick's law of diffusion, which of the following changes would decrease the rate of net diffusion of a substance across a membrane?

A) an increase in the substance's concentration gradient
B) an increase in the permeability of the membrane to the substance
C) an increase in the surface area of the membrane
D) an increase in the thickness of the membrane
E) none of these answers.

Question 49

Assume that a membrane that is permeable to Na⁺ but not to Cl^- separates two solutions. The concentration of sodium chloride on side 1 is much higher than on side 2. Which of the following ionic movements will take place?

A) Na⁺ will move until its concentration gradient is dissipated (i.e., until the concentration of Na⁺ on side 2 is the same as the concentration of Na⁺ on side 1).
B) Cl^- will move down its concentration gradient from side 1 to side 2.
C) a membrane potential, negative on side 1, will develop.
D) a membrane potential, positive on side 1, will develop.
E) more than one of these answers.

Question 50

Which of the following does not require energy expenditure?

A) net movement of potassium into the cell.
B) net movement of sodium into the cell.
C) iodine uptake by thyroid gland cells.
D) transport of hydrogen ion into the stomach lumen in association with hydrochloric acid secretion during digestion of a meal
E) both (b) and (d) above.

Question 51

In which process is energy required but not directly used to produce movements against concentration gradients?

A) osmosis
B) primary active transport
C) secondary active transport
D) simple diffusion
E) facilitated diffusion

Question 52

What term refers to the effect a non-penetrating solute in a solution has on cell volume?

A) osmolarity
B) osmotic pressure
C) tonicity
D) osmosis
E) solubility

Question 53

The large, negatively charged intracellular proteins (A^-) cannot permeate the cell membrane because

A) they are greater than 0.8 nm in diameter and are not lipid soluble.
B) there are no carriers for them.
C) no concentration or electrical gradient exists for them.
D) two of these answers.
E) all of these answers.

Question 54

Function of the Na⁺-K⁺ pump is an example of:

A) carrier-mediated transport.
B) diffusion.
C) exocytosis.
D) pinocytosis.
E) active transport.

Question 55

Membrane potential

A) refers to a separation of charges across the membrane or to a difference in the relative number of + and - charges in the ECF and ICF.
B) is measured in units of millivolts with the sign always designating the charge on the outside.
C) is less at the equilibrium potential for K⁺ than at resting membrane potential.
D) cannot be measured easily.
E) all of these answers.

Question 56

Primary active transport moves which of the following ions across the membrane?

A) sodium
B) potassium
C) hydrogen
D) calcium
E) all of these answers.

Question 57

Which of the following moves across the membrane by facilitated diffusion?

A) oxygen
B) sodium
C) glucose
D) potassium
E) water

Question 58

The Na⁺-K⁺ pump

A) pumps Na⁺ into the cell.
B) pumps K⁺ into the cell.
C) pumps K⁺ out of the cell.
D) has a higher affinity for K⁺ when the carrier is phosphorylated.
E) more than one of these answers.

Question 59

If pure water and a solution containing a nonpenetrating solute are separated by a membrane,

A) water will diffuse by osmosis until the concentrations between the two compartments become equal.
B) both water and the solute will diffuse across the membrane down their concentration gradients until a state of equilibrium is established.
C) water will diffuse by osmosis until stopped by an opposing hydrostatic pressure.
D) no movement will take place across the membrane.
E) it is impossible to predict what will happen.

Question 60

Which term is associated with transport maximum (Tm) of a carrier?

A) specificity
B) saturation
C) competition
D) passive diffusion
E) leak channels

Question 61

According to the fluid mosaic model of membrane structure, the plasma membrane consists primarily of a bilayer of mobile phospholipid molecules studded with an ever-changing mosaic pattern of proteins.

Question 62

The surface carbohydrates within the plasma membrane serve as cell adhesion molecules (CAMs) that cells use to grip a hold of one another and to surrounding connective-tissue fibers.

Question 63

A first messenger is an intracellular chemical messenger that triggers a preprogrammed series of biochemical events within a cell to bring about a desired response.

Question 64

Gap junctions are composed of CAMs and keratin.

Question 65

The two dark lines in the trilaminar appearance of the plasma membrane are believed to be caused by the preferential staining of the hydrophilic polar regions of the membrane constituents.

Question 66

Gap junctions play an important role in transmission of impulses for heart contraction.

Question 67

Sheets of epithelial cells are joined by gap junctions.

Question 68

The resting membrane potential of a typical nerve cell is

A) +50 mV.
B) +70 mV.
C) 0 mV.
D) -50 mV.
E) -70 mV.

Question 69

Select the correct statement about membrane permeability and ion potential.

A) the concentration of potassium ions is the same extracellularly and intracellularly.
B) the concentration of potassium is higher extracellularly than intracellularly.
C) the concentration of sodium is higher extracellularly than intracellularly.
D) the membrane is more permeable to anions than to potassium.
E) the membrane is more permeable to sodium than to potassium.

Question 70

The primary barrier to passage of water-soluble substances across the plasma membrane is the outer layer of carbohydrates.

Question 71

The carbohydrate found in plasma membranes is functions as channels and pumps.

Question 72

Extracellular messengers binding on surface receptors may exert effects on cells via all the following means, except:

A) opening gated channels.
B) opening a gated channel through activation of a G protein.
C) activation of the adenylyl cyclase system.
D) binding to sites and then being endocytized.
E) ultimately activating protein kinases.

Question 73

Under an electron microscope, the plasma membrane appears as a trilaminar structure consisting of two dark layers separated by a light middle layer.

Question 74

The only means by which an extracellular chemical messenger can bring about a desired intracellular response is to activate a second messenger system.

Question 75

One extracellular messenger molecule can ultimately influence the activity of only one protein molecule within the cell.

Question 76

In the plasma membrane the polar ends of the phospholipid molecules are hydrophobic.

Question 77

At resting membrane potential

A) the membrane is more permeable to K⁺ than to Na⁺.
B) the membrane is more permeable to Na⁺ than to K⁺.
C) Cl^- is at its equilibrium potential.
D) both (a) and (c) above.
E) both (b) and (c) above.

Question 78

The hydrophobic interior of the lipid bilayer of the plasma membrane blocks the passage of water-soluble substances.

Question 79

The binding of a hormone to a receptor stimulates the cell to produce a single second messenger molecule.

Question 80

In the lipid bilayer of the plasma membrane, the hydrophobic tails of the phospholipids orient toward the center of the membrane, away from water.