Chapter 7

Question 1

amphipathic

Answer 1

has both a hydrophilic (water loving) region and a hydrophobic (water fearing) region

Question 2

fluid mosaic model

Answer 2

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

Question 3

cholesterol within the cell membrane

Answer 3

reduces membrane fluidity at moderate temperatures by reducing phospholipid movement, but at low temperatures it hinders solidification by disrupting the regular packing of phospholipids

Question 4

unsaturated hydrocarbon tails

Answer 4

kinked, prevent packing, enhancing membrane fluidity

Question 5

saturated hydrocarbon tails

Answer 5

pack together, increasing membrane viscosity

Question 6

integral proteins

Answer 6

penetrate the hydrophobic interior of the liquid bilayer

Question 7

transmembrane proteins

Answer 7

span the membrane

Question 8

peripheral proteins

Answer 8

are not embedded in the lipid bilayer at all, loosely bound to the surface of the membrane

Question 9

functions of membrane proteins

Answer 9

transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to the cytoskeleton and extracellular matrix

Question 10

glycolipid

Answer 10

a lipid with one or more covalently attached carbohydrates

Question 11

glycoproteins

Answer 11

a protein with one or more covalently attached carbohydrates

Question 12

selective permeability

Answer 12

the membrane allows some substances to cross more easily than others; non polar, hydrophobic molecules (like hydrocarbons, CO2, O2) can cross the lipid bilayer easily; polar, hydrophilic molecules (like sugars water, charged molecules) cross the lipid bilayer slowly

Question 13

transport proteins

Answer 13

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

Question 14

aquaporins

Answer 14

channel proteins that allow water to cross a lipid bilayer

Question 15

diffusion

Answer 15

movement of particles of any substance so that they spread out into available space

Question 16

concentration gradient

Answer 16

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

Question 17

passive transport

Answer 17

diffusion of a substance across a biological membrane without requiring energy

Question 18

osmosis

Answer 18

the diffusion of water across a selectively permeable membrane

Question 19

tonicity

Answer 19

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

Question 20

isotonic

Answer 20

no net movement of water across the plasma membrane; makes animal cells normal and plant cells flaccid

Question 21

hypertonic

Answer 21

referring to a solution that when surrounding a cell will cause the cell to lose water; makes animal cells shriveled and plant cells plasmolyzed

Question 22

hypotonic

Answer 22

referring to a solution that when surrounding a cell will cause the cell to take up water; makes animal cells lysed and plant cells turgid (normal)

Question 23

osmoregulation

Answer 23

the control of solute concentrations and water balance

Question 24

facilitated diffusion

Answer 24

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

Question 25

ion channels

Answer 25

channel proteins that transport ions

Question 26

gated channels

Answer 26

open or close in response to a stimulus

Question 27

active transport

Answer 27

pumps a solute across a membrane against its concentration gradient, requiring energy

Question 28

sodium-potassium pump

Answer 28

a transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell

Question 29

membrane potential

Answer 29

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 30

electrochemical gradient

Answer 30

the diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (chem force) and the ion’s tendency to move relative to the membrane potential (elec force)

Question 31

electrogenic pump

Answer 31

a transport protein that generates voltage across a membrane; main one of plants, fungi, and bacteria is the proton pump

Question 32

cotransport

Answer 32

the coupling of the downhill diffusion of one substance to the uphill transport of another against its own concentration gradient

Question 33

exocytosis

Answer 33

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

Question 34

endocytosis

Answer 34

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