Movements of Solutes and Water Across Cell Membranes (Ch.4)

Question 1

simple diffusion

Answer 1

the movement of molecules from one location to another solely as a result of their random thermal motion

Question 2

flux

Answer 2

the amount of material crossing a surface in a unit of time

Question 3

diffusion equilibrium

Answer 3

no further change in the glucose concentrations of the two compartments will occur because of the equal rate of diffusion in both directions between the compartments

Question 4

polar vs. nonpolar cell diffusion across membrane

Answer 4

polar molecules diffuse into cells very slowly or not at all
nonpolar molecules diffuse rapidly across the membrane; dissolve in lipid bilayer

Question 5

ion channels

Answer 5

allow ions to diffuse across the membrane
transmembrane proteins

Question 6

net flux

Answer 6

the difference between two one-way fluxes of a solute

Question 7

channel gating

Answer 7

opening or closing ion channels (altering diffusion)
includes ligand gated, voltage gated, and mechanically gated channels

Question 8

membrane potential

Answer 8

separation of electrical charge across a plasma membrane
imbalance of ions across the membrane

Question 9

electrochemical gradient

Answer 9

combination of a membrane potential and a difference in ion concentrations across a membrane

Question 10

mediated transport

Answer 10

the movement of molecules or ions across a membrane by binding the transported solute to a transporter protein in the membrane

Question 11

transporters

Answer 11

proteins that move a substance across a membrane; have binding sites with chemical specificity, affinity, and saturation

Question 12

facilitated diffusion

Answer 12

mediated transport process that moves molecules from higher concentration to lower concentration across a membrane; continues until the two concentrations become equal
- passive

Question 13

passive transport

Answer 13

does not require metabolic energy

Question 14

active transport

Answer 14

mediated transport process that moves molecules against an electrochemical gradient (low to high) across a membrane by means of a transporter and ATP

Question 15

primary active transport

Answer 15

phosphorylation of the transporter by ATP drives the transport process
ex: Na+/K+ ATPase pump

Question 16

secondary active transport

Answer 16

binding of an ion (often Na+) to the transporter
cotransport or countertransport

Question 17

cotransport

Answer 17

same direction, such as into a cell

Question 18

countertransport

Answer 18

opposite directions

Question 19

osmolarity

Answer 19

total solute concentration in a solution
1 osmol = 1 mol of solute particles
- the higher the osmolarity of a solution, the lower the water concentration

Question 20

osmosis

Answer 20

diffusion of water across a membrane through aquaporins from a region of higher water concentration to a region of lower water concentration

Question 21

aquaporins

Answer 21

water channels

Question 22

semipermeable membrane

Answer 22

a membrane permeable to water but not to solutes

Question 23

nonpenetrating solutes

Answer 23

cannot freely diffuse through the lipid bilayer Na+ and Cl- are the major ones in the extracellular fluid (300 mOsm/L)
K+ and various organic solutes are the major ones in the intracellular fluid (300 mOsm/L)

Question 24

tonicity

Answer 24

a measure of the ability of a solution to add or remove water from cells due to osmosis

Question 25

isotonic solution

Answer 25

does not cause a change in cell volume

Question 26

hypotonic solution

Answer 26

causes cells to swell in volume due to having a lower concentration of nonpenetrating solutes outside than the cell interior

Question 27

hypertonic solution

Answer 27

causes cells to shrink in volume due to having a higher concentration of nonpenetrating solutes outside than the cell interior

Question 28

endocytosis

Answer 28

process in which regions of the plasma membrane invaginate and pinch off to form vesicles that enclose a small volume of extracellular material

Question 29

pinocytosis

Answer 29

fluid endocytosis cells engulf extracellular fluid and its solutes

Question 30

phagocytosis

Answer 30

cells engulf bacteria or other large particles

Question 31

receptor mediated endocytosis

Answer 31

clatherin-coated pits are formed by pinching off regions of membrane that contain receptor-ligand complexes

Question 32

endosome

Answer 32

transfer the vesicle contents to lysosomes

Question 33

lysosome

Answer 33

digests the vesicle contents by lysosomal enzymes

Question 34

exocytosis

Answer 34

process where intracellular vesicles fuse with the plasma membrane - adds components to the plasma membrane - releases cellular products into the extracellular fluid

Question 35

paracellular pathway

Answer 35

movement of molecules across an epithelium through the spaces and tight junctions between epithelial cells

Question 36

transcellular pathway

Answer 36

movement of molecules across an epithelium through the cell - moves first into the cell across the apical membrane, then through the cytoplasm, and then out across the basolateral membrane, or the reverse

Question 37

apical membrane

Answer 37

lumen facing side

Question 38

basolateral membrane

Answer 38

basement membrane; blood side

Question 39

isoosmotic solution

Answer 39

a solution containing 300 mOsm/L of solute regardless of its composition of membrane penetrating and nonpenetrating solutes

Question 40

hyperosmotic solution

Answer 40

a solution containing greater than 300 mOsm/L of solutes regardless of its composition of membrane penetrating and nonpenetrating solutes

Question 41

hypoosmotic solution

Answer 41

a solution containing less than 300 mOsm/L of solutes regardless of its composition of membrane penetrating and nonpenetrating solutes