Chapter 12

Question 1

rates at which various solutes cross the lipid bilayer by simple diffusion

Answer 1

small nonpolar molecules: diffuse rapidly
small uncharged polar molecules: only diffuse if they are small enough
larger uncharged polar molecules: hardly cross
ions: never

Question 2

two main classes of membrane transport proteins

Answer 2

transporters and channels

Question 3

channels

Answer 3

discriminate mainly on the basis of size and electric charge
only ions of an appropriate size and charge can pass through

Question 4

transporter

Answer 4

transfers only those molecules or ions that fit into specific binding sites on the protein

Question 5

is Na2+ most plentiful inside or outside the cell

Answer 5

outside the cell

Question 6

is K+ most plentiful inside or outside the cell

Answer 6

inside the cell

Question 7

membrane potential

Answer 7

voltage difference across a membrane due to a slight excess of positive ions on one side and of negative ions on the other

Question 8

when is the membrane potential expressed as a negative value

Answer 8

interior of the cell is more negatively charged than the exterior

Question 9

passive transport

Answer 9

spontaneous movement of a solute down its concentration gradient across a cell membrane via a membrane transport protein

Question 10

active transport

Answer 10

movement of a solute across a membrane against its electrochemical gradient
requires an input of energy such as ATP hydrolysis

Question 11

membrane potential tends to pull ____ charged ions and molecules into the cell and drive _____ charged solutes out

Answer 11

positively
negatively

Question 12

electrochemical gradient

Answer 12

driving force that determines which way an ion will move across a membrane
combined influence of the ion’s concentration gradient and the membrane potential

Question 13

aquaporin

Answer 13

channel that facilitates the transport of water across membranes

Question 14

osmosis

Answer 14

passive movement of water across a cell membrane from a region where the concentration of water is high to a region where the concentration of water is low

Question 15

turgor pressure

Answer 15

force that builds as water flows into plant and yeast cells by osmosis
drives the expansion of cells that underlies plant growth and maintains the rigidity of plant stems and leaves

Question 16

transporter

Answer 16

membrane transport protein that moves a solute across a cell membrane by undergoing a series of conformational changes

Question 17

pump

Answer 17

transporter that uses a source of energy to actively move a solute across a membrane against its electrochemical gradient

Question 18

three main ways that pumps work

Answer 18

gradient driven pumps
ATP driven pumps
light driven pumps

Question 19

Na+ pump

Answer 19

transporter found in the plasma membrane of most animal cells that actively pumps Na+ out of the cell and K+ in using the energy derived from ATP hydrolysis

Question 20

Ca2+ pump

Answer 20

active transporter that uses energy supplied by ATP hydrolysis to actively expel Ca2+ from the cell cytosol

Question 21

gradient driven pump

Answer 21

protein that uses energy stored in the electrochemical gradient of ions to actively transport a solute across a membrane

Question 22

symport

Answer 22

pump moves a pair of solutes in the same direction across the membrane

Question 23

antiport

Answer 23

pump moves a pair of solutes in the opposite direction across the membrane

Question 24

uniports

Answer 24

gradient-driven transporter that ferries only a single type of solute across the membrane at a time

Question 25

H+ pump

Answer 25

protein or protein complex that uses energy supplied by ATP hydrolysis, an ion gradient, or light to actively move protons across a membrane

Question 26

Channel

Answer 26

protein that forms a hydrophilic pore across a membrane, through which selected small molecules or ions can passively diffuse

Question 27

ion channel

Answer 27

transmembrane protein that forms a pore across the lipid bilayer through which specific inorganic ions can diffuse down their electrochemical gradients

Question 28

selectivity filter

Answer 28

part of an ion channel that determines which ions the channel can transport located in the region where the channel is the narrowest

Question 29

are ion channels continuously open

Answer 29

NO

Question 30

K+ leak channel

Answer 30

ion channel permeable to K+ that randomly flickers between an open and closed state largely responsible for the resting membrane potential in animal cells

Question 31

resting membrane potential

Answer 31

voltage difference across the plasma membrane when a cell is not stimulated

Question 32

patch-clamp recording

Answer 32

technique used to monitor the activity of ion channels in a membrane formation of a tight seal between the tip of a glass electrode and a small region of cell membrane

Question 33

mechanically gated channel

Answer 33

ion channel that allows the passage of select ions across a membrane in response to a physical perturbation

Question 34

ligand-gated channel

Answer 34

ion channel that is stimulated to open by the binding of a small molecule

Question 35

voltage-gated channel

Answer 35

channel protein that permits the passage of selected ions across a membrane in response to changed in the membrane potential