The Plasma Membrane

Question 1

The ______ membrane is the boundary that separates the living cell from its surroundings

Answer 1

plasma

Question 2

The plasma membrane exhibits ______ ________ allowing some substances to cross it more easily than others

Answer 2

selective permeability

Question 3

_______ are the most abundant lipid in the plasma membrane

Answer 3

phospholipids

Question 4

Phospholipids are _______ molecules, containing hydrophobic and hydrophilic regions

Answer 4

amphipathic

Question 5

The ____ ______ model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it

Answer 5

fluid mosaic

Question 6

In 1935, Hugh Davson and James Danielli proposed a _______ model in which the phospholipid bilayer lies between two layers of globular proteins

Answer 6

sandwich

Question 7

___________ studies of the plasma membrane supported the fluid mosaic model

Answer 7

freeze-fracture

Question 8

Freeze-fracture is a specialized preparation technique that _____ a membrane along the middle of the phospholipid bilayer

Answer 8

splits

Question 9

Phospholipids in the plasma membrane can move within the ____

Answer 9

bilayer

Question 10

Most of the lipids, and some proteins, drift ______

Answer 10

laterally

Question 11

As temperatures cool, membranes switch from a _____ state to a ____ state

Answer 11

fluid to solid

Question 12

Membranes rich in unsaturated fatty acids are more _____ that those rich in saturated fatty acids

Answer 12

fluid

Question 13

Membranes must be fluid to ____ properly; they are usually about as fluid as salad oil

Answer 13

work

Question 14

At warm temperatures (such as 37°C), cholesterol ______ movement of phospholipids

Answer 14

restrains

Question 15

At cool temperatures, cholesterol ______ fluidity by preventing tight packing

Answer 15

maintains

Question 16

A _______ is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

Answer 16

membrane

Question 17

_______ determine most of the membrane’s specific functions

Answer 17

proteins

Question 18

______ proteins are bound to the surface of the membrane

Answer 18

Peripheral

Question 19

_____ proteins penetrate the hydrophobic core (they are ingrained in the membrane)

Answer 19

Integral

Question 20

Integral proteins that span the membrane are called ______ proteins

Answer 20

transmembrane

Question 21

The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, often coiled into _____ _____

Answer 21

alpha helices

Question 22

Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix

Answer 22

the 6 major functions of membrane proteins

Question 23

Cells _______ each other by binding to surface molecules, often carbohydrates, on the plasma membrane

Answer 23

recognize

Question 24

Membrane carbohydrates may be ________ bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)

Answer 24

covalently

Question 25

Carbohydrates on the ______ side of the plasma membrane vary among species, individuals, and even cell types in an individual

Answer 25

external

Question 26

The ___________ distribution of proteins, lipids, and associated carbohydrates in the plasma membrane is determined when the membrane is built by the ER and Golgi apparatus

Answer 26

asymmetrical

Question 27

_________ (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly

Answer 27

Hydrophobic

Question 28

_____ molecules, such as sugars, do not cross the membrane easily

Answer 28

polar

Question 29

______ proteins allow passage of hydrophilic substances across the membrane

Answer 29

transport

Question 30

Some transport proteins, called _____ proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel

Answer 30

channel

Question 31

Channel proteins called _________ facilitate the passage of water

Answer 31

aquaporins

Question 32

Other transport proteins, called ____ proteins, bind to molecules and change shape to shuttle them across the membrane

Answer 32

carrier

Question 33

A transport protein is specific for the...

Answer 33

substance that it moves

Question 34

Although each molecule moves _______, diffusion of a population of molecules may exhibit a net movement in one direction

Answer 34

randomly

Question 35

At ______ _______, as many molecules cross one way as cross in the other direction

Answer 35

dynamic equilibrium

Question 36

Substances diffuse _____ their concentration gradient, the difference in concentration of a substance from one area to another

Answer 36

down

Question 37

No work must be done to move substances down the _______ _____

Answer 37

concentration gradient

Question 38

The diffusion of a substance across a biological membrane is ______ transport because it requires no energy from the cell to make it happen

Answer 38

passive

Question 39

______ is the diffusion of water across a selectively permeable membrane

Answer 39

Osmosis

Question 40

Water diffuses across a membrane from the region of _____ solute concentration to the region of _____ solute concentration

Answer 40

lower;higher

Question 41

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

Answer 41

tonicity

Question 42

________ solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane

Answer 42

isotonic

Question 43

________ solution: Solute concentration is greater than that inside the cell; cell loses water

Answer 43

Hypertonic

Question 44

________ solution: Solute concentration is less than that inside the cell; cell gains water

Answer 44

hypotonic

Question 45

___________, the control of water balance, is a necessary adaptation for life in such environments

Answer 45

Osmoregulation

Question 46

Cell walls help maintain _____ balance

Answer 46

water

Question 47

A plant cell in a ______ solution swells until the wall opposes uptake; the cell is now turgid (firm)

Answer 47

hypotonic

Question 48

If a plant cell and its surroundings are _______, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt

Answer 48

isotonic

Question 49

In a hypertonic environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called ________

Answer 49

plasmolysis

Question 50

Passive Transport Aided by Proteins

Answer 50

Facilitated Diffusion

Question 51

In facilitated diffusion, _______ ________ speed the passive movement of molecules across the plasma membrane

Answer 51

transport proteins

Question 52

_______ proteins provide corridors that allow a specific molecule or ion to cross the membrane

Answer 52

channel

Question 53

channel proteins for facilitated diffusion of water

Answer 53

aquaporins

Question 54

channel proteins like Ion channels that open or close in response to a stimulus are called _____ _______

Answer 54

gated channels

Question 55

Carrier proteins undergo a subtle change in shape that translocates the _____-______ _____ across the membrane

Answer 55

solute-binding site

Question 56

Some diseases are caused by _________ in specific transport systems, for example the kidney disease cystinuria

Answer 56

malfunctions

Question 57

Active Transport - uses energy to move solutes _____ their gradients

Answer 57

against

Question 58

Facilitated diffusion is still ______ because the solute moves down its concentration gradient

Answer 58

passive

Question 59

Some _______ proteins, however, can move solutes against their concentration gradients

Answer 59

transport

Question 60

_____ transport moves substances against their concentration gradient

Answer 60

active

Question 61

Active transport requires ______, usually in the form of ATP

Answer 61

energy

Question 62

_____ transport is performed by specific proteins embedded in the membranes

Answer 62

active

Question 63

Active transport allows cells to __________ concentration gradients that differ from their surroundings

Answer 63

maintain

Question 64

Membrane ________ is the voltage difference across a membrane

Answer 64

potential

Question 65

The sodium-potassium pump is one type of active ______ system

Answer 65

transport

Question 66

______ is created by differences in the distribution of positive and negative ions

Answer 66

voltage

Question 67

An _________ pump is a transport protein that generates voltage across a membrane

Answer 67

electrogenic

Question 68

The sodium-potassium pump is the major electrogenic pump of _____ cells

Answer 68

animal

Question 69

The main electrogenic pump of plants, fungi, and bacteria is a _____ pump

Answer 69

proton

Question 70

_________ occurs when active transport of a solute indirectly drives transport of another solute

Answer 70

Cotransport

Question 71

______ commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell

Answer 71

Plants

Question 72

_____ transport across the plasma membrane occurs by exocytosis and endocytosis

Answer 72

Bulk

Question 73

Small molecules and water enter or leave the cell through the _____ _____ or by transport proteins

Answer 73

lipid bilayer

Question 74

______ molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles

Answer 74

Large

Question 75

Bulk transport requires ______

Answer 75

energy

Question 76

In _________, transport vesicles migrate to the membrane, fuse with it, and release their contents

Answer 76

exocytosis

Question 77

Many _______ cells use exocytosis to export their products

Answer 77

secretory

Question 78

In __________, the cell takes in macromolecules by forming vesicles from the plasma membrane

Answer 78

endocytosis

Question 79

________ is a reversal of exocytosis, involving different proteins

Answer 79

Endocytosis

Question 80

In ________ a cell engulfs a particle in a vacuole | The vacuole fuses with a lysosome to digest the particle

Answer 80

phagocytosis

Question 81

In _________, molecules are taken up when extracellular fluid is “gulped” into tiny vesicles

Answer 81

pinocytosis

Question 82

In __________________, binding of ligands to receptors triggers vesicle formation

Answer 82

receptor-mediated endocytosis