5. Membrane Transport and Cell Signaling

Question 1

amphipathic

Answer 1

having both a hydrophilic region and hydrophobic region

Question 2

aquaporin

Answer 2

channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis (the diffusion of free water across a membrane)

Question 3

fluid mosaic model

Answer 3

currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids

Question 4

glycolipid

Answer 4

lipid with one or more covalently attached carbohydrates

Question 5

integral protein

Answer 5

transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane

Question 6

peripheral protein

Answer 6

protein loosely bound to the surface of a membrane or to part of an integral protein and not imbedded in the lipid bilayer

Question 7

selective permeability

Answer 7

property of biological membranes that allows them to regulate the passage of substances across them

Question 8

transport protein

Answer 8

transmembrane protein that helps a certain substance or class of closely related substances to cross the plasma membrane

Question 9

concentration gradient

Answer 9

a region along which the density of a chemical substance increases or decreases

Question 10

diffusion

Answer 10

random thermal motion of particles of liquids, gases, or solids; in the presence of a concentration gradient, it results in the net movement of a substance from a region where it is more concentrated to a region where it is less concentrated

Question 11

isotonic

Answer 11

referring to a solution that when surrounding the cell causes no net movement of water into or out of the cell

Question 12

hypertonic

Answer 12

referring to a solution that, when surrounding a cell, will cause the cell to lose water; “more” nonpenetrating solutes

Question 13

hypotonic

Answer 13

referring to a solution that, when surrounding the cell, will cause the cell to take up water; “fewer” nonpenetrating solutes

Question 14

osmoregulation

Answer 14

regulation of solute concentrations and water balance by a cell or organism

Question 15

osmosis

Answer 15

diffusion of free water molecules across a selectively permeable membrane

Question 16

passive transport

Answer 16

diffusion of a substance across a biological membrane with no expenditure of energy

Question 17

tonicity

Answer 17

ability of a solution surrounding a cell to cause that cell to gain or lose water

Question 18

turgor pressure

Answer 18

the force directed against a plant cell wall after the influx of water and swelling of the cell due to osmosis

Question 19

turgid

Answer 19

swollen or distended, as in plant cells

Question 20

active transport

Answer 20

movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy

Question 21

cotransport

Answer 21

coupling of the “downhill” diffusion of one substance with the “uphill” transport of another against its own concentration gradient

Question 22

electrochemical gradient

Answer 22

diffusion gradient of an ion, affected by both the concentration difference of it across a membrane (chemical force) and the ion’s tendency to move relative to the membrane potential (electrical force)

Question 23

electrogenic pump

Answer 23

an active transport protein that generates voltage across a membrane while pumping ions

Question 24

facilitated diffusion

Answer 24

passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins, requiring no energy expenditure

Question 25

flaccid

Answer 25

limp, lacking turgor

Question 26

ion channel

Answer 26

a transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient

Question 27

gated channel

Answer 27

transmembrane protein channel that opens or closes in response to a particular stimulus

Question 28

membrane potential

Answer 28

the difference in electrical charge (voltage) across a cell’s plasma membrane due to the differential distribution of ions; affects the activity of excitable cells and the transmembrane movement of all charged substances

Question 29

plasmolysis

Answer 29

phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment

Question 30

proton pump

Answer 30

active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process

Question 31

sodium-potassium pump

Answer 31

transport protein in the plasma membrane that actively transports sodium out of the cell and potassium into the cell (3 Na+ OUT for every 2 K+ IN)

Question 32

carrier proteins

Answer 32

transport proteins that hold on to their “passengers” and change shape in a way that shuttles them across the membrane

Question 33

channel protein

Answer 33

transport proteins that have a hydrophilic channel that certain molecules or atomic ions use as a tunnel through the membrane

Question 34

exocytosis

Answer 34

the cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane

Question 35

endocytosis

Answer 35

cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane

Question 36

phagocytosis

Answer 36

type of endocytosis in which large particulate substances or small organisms are taken up by a cell

Question 37

pinocytosis

Answer 37

type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes

Question 38

receptor-mediated endocytosis

Answer 38

movement of specific molecules into a cell by the inward budding of vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances