Chapter 7: Plasma membrane function

Question 1

Plasma Membrane (PM)

Answer 1

is the boundary that separates living cell from its surroundings.

Question 2

PM exhibits selective permeability,

Answer 2

allowing some substances to cross it more easily than others.

Question 3

Variations in LIPID composition of PM of many species…

Answer 3

are adaptations to specific environmental conditions.

Question 4

Ability to change the lipid compositions in response to temperature changes has evolved in organisms that live where temperatures vary.

Answer 4

Lipids are hydrophobic because they consist mostly of hydrocarbons, which form nonpolar covalent bond

Question 5

Phospholipids are the most

Answer 5

abundant lipid in the PM

Question 6

Phospholipids are

Answer 6

amphipathic molecules, containing hydrophobic and hydrophilic regions

Question 7

Fluid mosaic model

Answer 7

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

Question 8

Phospholipids in the PM can move within the bilayer

Answer 8

– Most of the lipids, and some proteins, drift laterally

– Unlikely for a molecule to flip-flop transversely across PM

Question 9

As temperatures cool, membranes switch from a fluid state to a solid state

Answer 9

– Temperature at which a membrane solidifies depends on the types of lipids & steroid cholesterol the PM contains
– At moderate temperatures, cholesterol reduces membrane fluidity; at low temperatures, it hinders solidification

Question 10

Membranes rich in unsaturated fatty acids are more fluid than

Answer 10

those rich in saturated fatty acids

Question 11

Membranes must be fluid to work properly; they are usually about

Answer 11

as fluid as salad oil

Question 12

A membrane is a collage of different proteins,

Answer 12

embedded in fluid matrix of lipid bilayer

Question 13

There are different types of

Answer 13

– Integral membrane proteins

– Peripheral proteins

Question 14

Proteins determine most of the

Answer 14

membrane’s specific functions

Question 15

Major functions of membrane proteins

Answer 15

– Transport; Enzymatic activity
– Signal transduction
– Cell-cell recognition
– Intercellular joining
– Attachment to the cytoskeleton and extracellular matrix (ECM)

Question 16

Membranes have

Answer 16

distinct inside and outside faces

Question 17

The asymmetrical distribution of proteins, lipids, and associated carbohydrates in the PM is determined

Answer 17

when membrane is built by products made in the ER and Golgi apparatus

Question 18

A process PM controls

Answer 18

A cell must exchange materials with its surroundings

Question 19

As PM are selectively permeable, they regulate cell’s molecular traffic

Answer 19

• Hydrophobic (nonpolar) molecules, and gases can dissolve in the lipid bilayer and pass through the membrane rapidly
• Polar molecules (such as sugars) do not cross membrane easily
• Hence, small/uncharged/nonpolar/lipid-soluble molecules pass most easily thru the lipid core of a PM

Question 20

Passive Transport

Answer 20

is diffusion of a substance across a membrane with no energy investment

Question 21

DIFFUSION

Answer 21

is the tendency for molecules to spread out evenly into the available space

Question 22

Although each molecule moves randomly,

Answer 22

diffusion of a population of molecules may be directional

Question 23

At dynamic equilibrium,

Answer 23

molecules cross the membrane at the same time.

Question 24

Substances diffuse down their concentration gradient

Answer 24

(the region along which the density of a chemical substance increases or decreases)
– No work must be done to move substances down the concentration gradient

Question 25

– Diffusion of a substance across PM is passive transport because

Answer 25

no energy is expended by cell to make it happen

Question 26

OSMOSIS

Answer 26

is the diffusion of water across a selectively permeable membrane

Question 27

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

Answer 27

higher solute concentration until the solute concentration is equal on both sides

Question 28

Tonicity

Answer 28

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

Question 29

Isotonic solution:

Answer 29

Solute concentration is same as that inside cell; no net water movement across PM

Question 30

Hypertonic solution

Answer 30

Solute concentration is greater than that inside cell; cell loses water

Question 31

Hypotonic solution

Answer 31

Solute concentration is less than that inside cell; cell gains water

Question 32

Hypertonic or hypotonic environments

Answer 32

create osmotic problems for organisms

Question 33

Osmoregulation

Answer 33

ontrol of solute concentrations and water balance, is a necessary adaptation

Question 34

Protist Paramecium

Answer 34

is hypertonic to the pond water it lives in (a hypotonic environment) has a contractile vacuole that acts as a pump to actively transport water out

Question 35

Plant cell walls help maintain water balance

Answer 35

– A plant cell in a hypotonic solution swells until the wall opposes uptake; the cell is now turgid (firm) – If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may plasmolyze (wilt)

Question 36

Transport Proteins

Answer 36

allow passage of hydrophilic substances across the membrane

Question 37

A transport protein is specific for the substance it moves across the membrane

Answer 37

channel proteins, and carrier proteins are transport proteins.

Question 38

channel proteins

Answer 38

They have a hydrophilic channel that certain molecules or ions can use as a tunnel -provide corridors that allow a specific molecule or ion to cross PM -Aquaporins -Ion channels

Question 39

carrier proteins

Answer 39

They bind to molecules and change shape to shuttle the molecules across the membrane

Question 40

facilitated diffusion

Answer 40

transport proteins speed passive movement of molecules across PM

Question 41

Facilitated diffusion is passive because

Answer 41

solute moves down its concentration gradient & the transport requires no energy

Question 42

Aquaporins

Answer 42

for facilitated diffusion of water

Question 43

Ion channels

Answer 43

that open or close in response to a stimulus (gated channels)