Unit 3. Cell Membrane

Question 1

T or F
All cells have a cell
membrane.

Answer 1

T

Question 2

2 functions of cell membrane

Answer 2

a. Controls what enters
and exits the cell to
maintain an internal
balance called
homeostasis.
b. Provides protection and
support for the cell

Question 3

Cell membrane contains almost
proteins called

Answer 3

Membrane proteins

Question 4

It is a double layer of
phospholipids

Answer 4

lipid bilayer

Question 5

T or F
Cell membranes have pores (holes) in it.

Answer 5

T

Question 6

Lipid Bilayer contains: (3)

Answer 6

a. Phosphate head is polar
• (water loving)
b. Fatty acid tails are non-polar
• (water fearing)
c. Proteins embedded in
membrane

Question 7

The property of cell membrane to allow some molecules in
and keeps other molecules out.

Answer 7

Selective permeability

Question 8

In 1972, they proposed that the
membrane is a mosaic of proteins dispersed within the
bilayer, with only the hydrophilic regions exposed to
water. (Who at what model is it?)

Answer 8

Seymour Jonathan Singer and Garth L. Nicolson
Fluid Mosaic Model

Question 9

T or F
A molecule always flip-flop
transversely across the membrane

Answer 9

F
always —> rarely

Question 10

T or F
Variations in lipid composition of cell membranes of many species appear to be adaptations to specific environmental conditions

Answer 10

T

Question 11

• proteins that penetrate the hydrophobic core
• 70% of Cell membrane proteins part
  and parcel of membrane structure

Answer 11

Integral proteins

Question 12

proteins that are bound to the surface of
the membrane

Answer 12

Peripheral proteins

Question 13

They transfer substances against Concentration/Electrical gradients

Answer 13

Pumps

Question 14

Opened and closed by gates

Answer 14

Channel proteins

Question 15

Involved in transport of substances

Answer 15

Carrier Proteins

Question 16

Takes place in membrane reaction

Answer 16

Enzyme proteins

Question 17

They bear appropriate sites for
recognition of Specific Ligands.

Answer 17

Receptor proteins

Question 18

Which statement/s is/are true about the role of membrane carbohydrates
in cell-cell recognition?

A. Cells recognize each other by binding to surface
molecules, often containing carbohydrates, on
the extracellular surface of the plasma
membrane.
B. Membrane carbohydrates may be covalently
bonded to lipids (forming glycolipids) or more
commonly to proteins (forming glycoproteins)
C. Both statements are true.
D. None

Answer 18

C

Question 19

Receptor and co-receptor where HIV binds.

Answer 19

CD4
CCR5

Question 20

T or F
HIV cannot infect a cell lacking CCR5 on its surface

Answer 20

T

Question 21

Which statement/s is/are true?
A. Hydrophobic (nonpolar) molecules, such
as hydrocarbons, cannot be dissolved in the lipid bilayer, thus, cannot pass through the membrane
• Polar molecules, such as sugars, can cross the membrane easily
C. Both statements are true.
D. None

Answer 21

D
- non polar can dissolve and pass through rapidly
- polar molecules cannot cross easily

Question 22

allow passage of hydrophilic substances across the membrane

Answer 22

Transport proteins

Question 23

have a hydrophilic channel that
certain molecules or ions can use as a tunnel

Answer 23

Channel proteins

Question 24

Channel proteins that facilitate
the passage of water

Answer 24

aquaporins

Question 25

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

Answer 25

Carrier proteins

Question 26

T or F A transport protein is specific for the substance it moves.

Answer 26

T

Question 27

Example of Active Transport Mechanism

Answer 27

Primary Transport Secondary Transport

Question 28

Example of Passive Transport Mechanisms

Answer 28

Simple Diffusion Facilitated Diffusion Osmosis Bulk flow filtration

Question 29

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

Answer 29

Diffusion

Question 30

Substances diffuse down their __________, the region along which the density of a chemical substance increases or decreases.

Answer 30

concentration gradient

Question 31

T or F No work must be done to move substances down the concentration gradient.

Answer 31

T

Question 32

T or F The diffusion of a substance across a biological membrane is active transport because energy is expended by the cell to make it happen

Answer 32

F - PASSIVE transport - NO energy is expended

Question 33

Factors that Influence Diffusion Rates (5)

Answer 33

• Distance • Molecular Size • Temperature • Steepness of Concentration Gradient • Membrane of Surface Area

Question 34

Lipophilic substances can enter cells easily because they diffuse through the lipid portion of the membrane

Answer 34

Simple Diffusion

Question 35

■ Membrane channels are transmembrane proteins ■ Used by ions, very small water-soluble compounds ■ Much more complex than simple diffusion.

Answer 35

Channel-Mediated Diffusion

Question 36

is the diffusion of water across a selectively permeable membrane

Answer 36

Osmosis

Question 37

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

Answer 37

Tonicity

Question 38

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

Answer 38

Isotonic

Question 39

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

Answer 39

Hypertonic

Question 40

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

Answer 40

Hypotonic

Question 41

A plant cell in a hypotonic solution swells until the wall opposes uptake; the cell is now _________

Answer 41

turgid (firm)

Question 42

If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; the cell becomes __________, and the plant may wilt

Answer 42

flaccid (limp)

Question 43

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

Answer 43

plasmolysis

Question 44

In _______ diffusion, transport proteins speed the passive movement of molecules across the plasma membrane.

Answer 44

Facilitated

Question 45

moves substances against their concentration gradients and allows cells to maintain concentration gradients that differ from their surroundings

Answer 45

Active transport

Question 46

T or F The sodium-potassium pump is one type of passive transport system.

Answer 46

F passive ----> active

Question 47

is the voltage difference across a membrane

Answer 47

Membrane potential

Question 48

Two combined forces, collectively called the ___________, drive the diffusion of ions across a membrane

Answer 48

electrochemical gradient

Question 49

is a transport protein that generates voltage across a membrane

Answer 49

electrogenic pump

Question 50

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

Answer 50

proton pump

Question 51

occurs when active transport of a solute indirectly drives transport of other solutes.

Answer 51

Cotransport

Question 52

Which statement is INCORRECT about the bulk transport across the plasma membrane that occurs by exocytosis and endocytosis? A. Small molecules and water enter or leave the cell through the lipid bilayer or via transport proteins B. Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles C. Bulk transport requires energy D. None

Answer 52

D

Question 53

transport vesicles migrate to the membrane, fuse with it, and release their contents which many secretory cells used to export their products

Answer 53

Exocytosis

Question 54

the cell takes in macromolecules by forming vesicles from the plasma membrane

Answer 54

Endocytosis

Question 55

Three types of endocytosis

Answer 55

– Phagocytosis (“cellular eating”) – Pinocytosis (“cellular drinking”) – Receptor-mediated endocytosis