Physiology Sg-4

Front 1

Which of the following statements regarding the structure and function of cell membranes is correct?

Back 1

The phospholipid bilayer is arranged so that the hydrophilic heads of the phospholipid molecule face the extra- and intracellular fluids.

Some proteins integrated into the membrane function as channels associated with transport of ions through the membrane.

Front 2

Diffusion

Back 2

depends upon the random motion of molecules

Front 3

The net flux of a penetrating solute into a cell will increase if the

Back 3

permeability constant for that solute increases.

concentration of that solute in the extracellular fluid increases.

Front 4

In general, polar molecules diffuse more rapidly through the lipid bilayer part of cell membranes than do nonpolar molecules. This statement is:

Back 4

False. Nonpolar molecules diffuse through more rapidly because much of the bilayer is nonpolar.

Front 5

Which of the following statements regarding the movement of molecules across cell membranes is correct?

Back 5

The diffusion of molecules across a cell membrane occurs at a rate that is influenced by the surface area of the membrane and the magnitude of the concentration difference across it.

Front 6

Which of the following statements regarding the diffusion of nonpolar solutes across cell membranes is correct?

Back 6

At equilibrium for solute X, the net flux of X across cell membranes is zero.

At equilibrium for solute X, the concentration of X inside the cell is equal to its concentration outside the cell.

Front 7

The permeability of the plasma membrane to mineral ions

Back 7

is dependent upon channels formed by proteins.

varies from one cell to another.

is affected by differences in electrical charge on the two sides of the membrane.

Front 8

Ion channels in cell membranes

Back 8

may open in response to a change in potential difference across the membrane.

may open in response to binding a ligand.

Front 9

The concentration of

Back 9

sodium and chloride ions in the extracellular fluid is greater than that in the cytosol of cells.

Front 10

Mediated transport across cell membranes

Back 10

is characterized by saturable carriers and a maximum velocity of transport.

Front 11

Carrier-mediated transport

Back 11

involves a specific membrane protein that functions as a carrier molecule.

Front 12

Which of the following is a feature that distinguishes active transport from, facilitated diffusion?

Back 12

Requirement for metabolic energy

Front 13

The mediated transport of a substance across a plasma membrane

Back 13

depends upon the binding of that substance to a specific site on the membrane protein.

Front 14

Which of the following statements regarding the active transport of molecules across cell membranes is correct?

Back 14

Both primary and secondary active transport are dependent upon energy derived from ATP.

Front 15

Glucose

Back 15

enters most cells by diffusion.

enters most cells by active transport.

concentrations inside most cells are generally the same as those in the extra-cellular fluid.

B and C.

None of the above.

Front 16

Which of the following is not a difference between primary active transport and secondary active transport ?

Back 16

Primary active transport uses energy derived from ATP whereas the secondary active transport does not.

Front 17

Which of the following statements regarding the active transport of solutes across cell membranes is correct?

Back 17

Primary active transporters are ATPases, and secondary active transporters are not.
Secondary active transporters require binding of Na ion on the extracellular side of the membrane to transport solute either into or out of the cell.

Front 18

Which of the following statements about the Na, K pump is false?

Back 18

It transports Na+ and K+ in a 1:1 ratio.

Front 19

It transports Na+ and K+ in a 1:1 ratio.

Back 19

diffusion.
primary active transport.
secondary active transport.

Front 20

Curves A, B, C, and D below represent the entry of various molecules into a cell. Therefore,

Back 20

if molecule A crosses the membrane by facilitated diffusion, then curve C may represent the entry of A in the presence of a similar molecule.

Front 21

If the ATP-generating mechanisms in a cell are poisoned and the cell has depleted its ATP reserves,

Back 21

primary active transport of molecules would cease immediately.
eventually there will be no potential difference across the membrane.

Front 22

“Osmosis” refers to the movement of across semi-permeable membranes.

Back 22

water

Front 23

If pure water and a solution containing a nonpenetrating solute are separated by a membrane that is permeable to water,

Back 23

water will diffuse by osmosis until stopped by opposing hydrostatic pressure.

Front 24

If all other conditions remain the same and the concentration of a nonpenetrating solute increases inside a cell,

Back 24

water will tend to enter the cell because the interior has an increased osmolarity.

Front 25

If a cell is placed in a hypotonic solution, it

Back 25

will swell.

Front 26

If a cell is placed in a hyperosmotic solution, it

Back 26

may swell, shrink, or stay the same size, depending upon the concentration of penetrating and nonpenetrating solutes in the solution.

Front 27

The reason solutions for injection or infusion into people normally contain either 150 mM NaCl or 300 mM glucose is that

Back 27

these solutions are isotonic to the blood and cells.

Front 28

An example of a hypertonic solution is:

Back 28

400 mM urea.

Front 29

Which of the following solutions is not isotonic to human cells?

Back 29

300 mM urea.

Front 30

Regarding the tonicity and osmolarity of solutions, which of the following statements is not true?

Back 30

Isotonic solutions are always isoosmotic.

Front 31

Which of the following statements regarding endocytosis and exocytosis is correct?

Back 31

Endocytosis is a method by which large molecules may be brought into a cell.

Exocytosis is a method by which large molecules may be secreted from a cell.

Front 32

Endocytosis is a method by which large molecules may be brought into a cell.
Exocytosis is a method by which large molecules may be secreted from a cell.

Back 32

Epithelial cells are polarized.

Epithelial cells lining the small intestine have Na, K -ATPase pumps only in their basolateral membranes.

Front 33

Which of the following are possible combinations of mechanisms for transport of a particle against a concentration gradient across an epithelial cell?

Back 33

Passive diffusion on the apical side into the cell followed by primary active transport on the basolateral side.

Secondary active transport on the mucosal side followed by facilitated diffusion on the serosal side.

Front 34

During the active transport of glucose across an epithelium, energy is used to

Back 34

power the Na -glucose cotransporter.

Front 35

Exocrine glands differ from endocrine glands in that the former

Back 35

are formed from infoldings of embryonic epithelium whereas the latter are not.

Front 36

Entry of glucose from the blood into tissue cells occurs by

Back 36

osmosis

Front 37

A ligand is a molecule that binds to

Back 37

a protein by noncovalent bonds.

Front 38

A binding site on a protein is

Back 38

an area of the protein with a shape complementary to that of a ligand.

determined by the amino acid sequence of the protein.

Front 39

The affinity of a ligand for its binding site is determined by

Back 39

the number and position of mutually attracting electrical charges.

the number and position of mutually attracting hydrophobic surfaces.

the presence or absence of interfering or hindrance determinants.

Front 40

The affinity a binding site has for a ligand

Back 40

can be influenced by the shape of the binding site.

can be influenced by the presence of charged groups on the ligand and the binding site.

is a measure of how readily a bound ligand can be released from the protein.

Front 41

Binding site A requires twice the concentration of ligand to achieve saturation as does binding site B. From this one can conclude that

Back 41

binding site B has a higher affinity for the ligand than does binding site A.

Front 42

Which of the following does not describe the 50%-saturation point of a solution of ligands and proteins?

Back 42

It refers to the amount of protein required to bind 50% of the ligand.

Front 43

A competitive antagonist for a ligand

Back 43

blocks the binding of the ligand to its binding site and prevents activation of the protein.

Front 44

Two ligands, A and B, bind to a site on protein X. Their binding curves are shown below. When ligand A binds, it produces a biological effect. Ligand B produces no effect when it binds. Therefore:

Back 44

The binding site on X has a higher affinity for A than for B.

Increasing the concentration of B in the presence of A will decrease the biological effect.

Front 45

Allosteric proteins

Back 45

contain more than one kind of binding site.

undergo a change of shape when a ligand binds to the regulatory binding site.

Front 46

The term “allosteric modulation” refers to

Back 46

the change in the shape and functional state of a protein that occurs when a ligand binds to a receptor site.

Front 47

When a chemical binds noncovalently to a protein at a distance from its functional site and causes a conformational change in the site that prevents the natural ligand from binding, this is an example of

Back 47

allosteric modulation

noncompetitive antagonism.

Front 48

Phosphorylation or dephosphorylation of proteins is a common means of

Back 48

covalent modulation of the proteins.

the activation or inactivation of kinases.

Front 49

Modulator molecules

Back 49

bind to proteins and cause a conformational change that facilitates or inhibits the binding of the functional ligand to its binding site.

Front 50

Protein kinases

Back 50

are enzymes.

are allosteric.