5.2 The Plasma Membrane And Cell Wall

Question 1

plasma membrane

Answer 1

phospholipids with embedded proteins make up the membrane surrounding all cells

Question 2

what is the defining feature of all cells? why?

Answer 2

the plasma membrane because it actively maintains intracellular conditions compatible with life.

Question 3

cell wall

Answer 3

a defining boundary in many organism, external to the cell membrane, that helps maintain the shape and internal composition of the cell

Question 4

homeostasis

Answer 4

the active regulation and maintenance, in animals, organs, or cells, of a stable internal physiological state in the face of a changing external environment

Question 5

how does the plasma membrane maintain homeostasis?

Answer 5

it is selectively permeable

Question 6

selectively permeable

Answer 6

lets some molecules in and out freely, lets other in and out under certain conditions, prevents other molecules from passing through at all

Question 7

the plasma membrane’s ability to act as a selective barrier is the result of:

Answer 7

the combination of lipids and embedded proteins of which it is composed

Question 8

the hydrophobic interior of the lipid bilayer prevents:

Answer 8

ions and charged/polar molecules from diffusing freely across the plasma membrane

Question 9

many macromolecules (proteins/polysaccharides) can’t cross the plasma membrane because:

Answer 9

they’re too large

Question 10

gases, lipids, and small polar molecules can move across the lipid bilayer because:

Answer 10

they are small

Question 11

what allows the export and import of certain molecules that can’t cross the cell membrane on their own?

Answer 11

protein transporters

Question 12

diffusion

Answer 12

the random motion of individual molecules, with net movement occurring where there are areas of higher and lower concentration of the molecules

Question 13

the simplest form of movement into and out of cells is:

Answer 13

passive transport which works by diffusion

Question 14

the frequency with which molecules collide have important consequences for:

Answer 14

chemical reactions which depend on the interaction of molecules

Question 15

diffusion leads to a net movement of:

Answer 15

the substance from one region to another when there is a concentration gradient (areas of higher concentration to lower)

Question 16

some molecules diffuse freely across the plasma membrane as a result of:

Answer 16

difference in concentrations between the inside and outside of a cell

Question 17

some molecules that cannot move across the lipid bilayer directly can move passively toward:

Answer 17

a region of lower concentration through protein transporters

Question 18

facilitated diffusion

Answer 18

diffusion through a membrane protein, bypassing the lipid bilayer

Question 19

diffusion and facilitated diffusion both result from:

Answer 19

the random motion of molecules

Question 20

net movement of the substance occurs when:

Answer 20

there are concentration differences

Question 21

in facilitated diffusion, the molecules moves through a ______. in simple diffusion, the molecules moves directly though the _____.

Answer 21

membrane transporter; lipid bilayer

Question 22

what are the two types of membrane transporters?

Answer 22

channel and carrier

Question 23

channel

Answer 23

a transporter with a passage that allows the movement of molecules through it (depends on their shape and charge)

Question 24

some membrane channels are gated which means:

Answer 24

they open in response to some sort of signal (ex. chemical or electrical)

Question 25

carrier

Answer 25

a transporter that facilitates movement of specific molecules

Question 26

membrane carriers exist in two conformations:

Answer 26

one that is open to one side of the cell, and another that is open to the other side of the cell

Question 27

binding of the transported molecule induces a conformation change in the membrane protein, allowing:

Answer 27

the molecule to be transported across the lipid bilayer

Question 28

even though the plasma membrane is hydrophobic:

Answer 28

water molecules are small enough to move passively through to a limited extent by simple diffusion

Question 29

aquaporin

Answer 29

a protein channel that allows water to flow through the plasma membrane more readily by facilitated diffusion

Question 30

osmosis

Answer 30

the net movement of a solvent, such as water, across a selectively permeable membrane toward the side of higher solute concentration

Question 31

high solute concentration equals:

Answer 31

low water concentration

Question 32

low solute concentration equals:

Answer 32

high water concentration

Question 33

during osmosis, the net movement of water is:

Answer 33

toward the side of the membrane with higher solute concentration until it is opposed by another force

Question 34

passive transport works to the cell's advantage only if:

Answer 34

the concentration gradient is in the right direction

Question 35

active transport

Answer 35

the "uphill" movement of substances against a concentration gradient requiring an input of energy

Question 36

during active transport, cells move substances through:

Answer 36

transport proteins embedded in the cell membrane

Question 37

most of the energy used by a cell goes towards:

Answer 37

keeping the inside of the cell different from the outside, a function carried out by proteins in the plasma membrane

Question 38

protein pumps

Answer 38

use energy directly to move a substance into or out of a cell (ex. sodium-potassium pump)

Question 39

primary active transport

Answer 39

active transport that uses the energy of ATP directly

Question 40

antiporters

Answer 40

transporters that move molecules/ions in opposite directions (ex. sodium-potassium pump)

Question 41

symporters/cotransporters

Answer 41

transporters that move two molecules in the same direction

Question 42

a concentration gradient stores:

Answer 42

potential energy that can be harnessed to drive the movement of other substances across the membrane against their concentration gradient

Question 43

protons (and other ions) move from areas of:

Answer 43

like charge to areas of unlike charge, driven by an electrical gradient

Question 44

electrochemical gradient

Answer 44

a gradient that combines the charge gradient and the chemical gradient of protons and other ions

Question 45

secondary active transport

Answer 45

active transport that uses the energy of an electrochemical gradient to drive the movement of molecules

Question 46

what do many cells use to maintain their size?

Answer 46

active transport

Question 47

hypertonic solution

Answer 47

one with a higher solute concentration that that inside the cell: water leaves cell and cell shrinks

Question 48

hypotonic solution

Answer 48

one with a lower solute concentration that that inside the cell, water moves into the cell and cell lyses or bursts

Question 49

isotonic

Answer 49

at the same solute concentration

Question 50

animals solve the problems of osmosis by keeping the intracellular fluid:

Answer 50

isotonic with extracellular fluid

Question 51

cells use active transport of ions to maintain:

Answer 51

equal concentrations inside and out; sodium-potassium pump plays an important role in keeping the inside of the cell isotonic with the extracellular fluid

Question 52

contractile vacuole

Answer 52

a type of cellular compartment that takes up excess water and waste products from inside the cell and expels them into the external environment

Question 53

how do organisms such as plants, fungi, and bacteria maintain cell size and shape?

Answer 53

cell wall surrounding the plasma membrane (provides structural support and protection to the cell)

Question 54

the cell wall resists expansion and allows pressure to:

Answer 54

build up in a cell when it absorbs water; this pressure resists further expansion and opposes the driving force for the water to enter

Question 55

turgor pressure/hydrostatic pressure

Answer 55

pressure within a cell resulting from the movement of water into the cell by osmosis and the tendency of the cell wall to resist deformation

Question 56

vacuole

Answer 56

a cell structure that absorbs water and contributes to turgor pressure (different from contractile vacuole)

Question 57

why do plants wilt when dehydrated?

Answer 57

loss of water from the vacuoles reduces turgor pressure and the cells can no longer maintain their shape within the cell wall

Question 58

plant cell wall is composed of:

Answer 58

polysaccharides (cellulose)

Question 59

the cell wall is composed of different components including:

Answer 59

carbohydrates and proteins