Module 2: Biological membranes

Question 1

What is a membrane?

Answer 1

a structure that separates the contents of the cell from their environment and also separates the organelles within cells

Question 2

What is the name given to the formation of separate membrane bound areas in a cell

Answer 2

compartmentalisation

Question 3

What is the name of the membrane that surrounds cells and organelles and how permeable is it?
What is its width?

Answer 3

the plasma membrane
its partially permeable
7nm

Question 4

What are the components of the plasma membrane?

Answer 4

the phospholipid bilayer
intrinsic proteins
extrinsic proteins
glycoproteins and glycolipids
cholesterol molecules

Question 5

Describe the structure of the phospholipid bilayer

Answer 5

is made up of phospholipids that have polar hydrophilic phosphate heads and non polar hydrophobic fatty acid tails

Question 6

Describe the structure of an intrinsic protein and give the names of an intrinsic protein

Answer 6

they have an amino acid containing a hydrophobic R group on their surface which interact with the hydrophobic core keeping the proteins in place

-channel protein

Question 7

What does a channel protein do

What does a carrier protein do

Answer 7

it provides a hydrophilic pathway that allows polar molecules to cross the membrane

plays an important role in passive and active transport by changing its shape

Question 8

What does the bilayer do

Answer 8

it allows the membrane to be selectively permeable by preventing large/charged molecules from directly diffusing across

Question 9

What is the role of glycoproteins

What is an antigen?

Answer 9

they play a role in cell adhesion and cell signalling by acting as receptors/antigens

a molecule on the cell surface that triggers an immune response

Question 10

What is the role of glycolipids

3 points

Answer 10

they can be used as antigens and they also help maintain stability and facilitate cell recognition

Question 11

Describe the structure and function of an extrinsic protein and name one

Answer 11

they contain amino acids that have hydrophilic R groups on their outer surface that interact with polar heads
-they are involved in molecule transport
-carrier protein

Question 12

What are the main functions of the plasma membrane?
7

Answer 12

-keeps cell components inside the cell
-controls movement of substances in/out of the cell
-isolates organelles from the rest of the cytoplasm which allows cellular processes to occur separately
-acts as a site for biochemical reactions
-allows a cell to change shape
-contains receptors for other molecules (hormones)
-enables adjacent molecules to stick together

Question 13

What is the name given to the plasma membrane model and why?

Answer 13

the fluid mosaic model
because the membrane is fluid and the arrangement of phospholipids and proteins creates a mosaic pattern

Question 14

What is the role of cholesterol

Answer 14

it regulates membrane fluidity and adds stability

Question 15

What are the different transport systems that happen across membranes

Answer 15

simple diffusion an facilitated diffusion
osmosis
active transport
endo and exocytosis

Question 16

What is diffusion

Answer 16

the passive net movement of small , non polar , lipid soluble molecules from an area of high to low concentration (down their concentration gradient)

Question 17

How is facilitated diffusion different to simple diffusion

Answer 17

it requires a transport molecule and a membrane

Question 18

What is osmosis

Answer 18

the passive diffusion of water molecules from an area of low solute concentration to an area of high solute concentration across a partially permeable membrane

Question 19

What is active transport

Answer 19

the net movement of molecules across a partially permeable membrane from an area of low to higher concentration against its concentration gradient

Question 20

What does active transport require

Answer 20

ATP

Question 21

What does exo/endocytosis do and how do they differ

Answer 21

they transport large particles by enclosing them in vesicles made from the plasma membrane
exo-out of the cell
endo-into the cell

Question 22

What is a solvent and what is the main solvent used by biological organisms

Answer 22

its a liquid that dissolves other substances
water

Question 23

What is meant by water potential
What units is it measured in

Answer 23

the tendency of water molecules to move
kiloPascals (kPa)

Question 24

What is the water potential of pure water and if solute is added to a solution does this make the water potential less or more negative?

Answer 24

0kPa
more negative , water potential cant be greater than 0

Question 25

Do water molecules move from less negative to more negative or vice versa?

Answer 25

they always move from a less negative solution to a more negative solution

Question 26

What is meant by osmotic concentration and is it affected by insoluble molecules

Answer 26

the volume of dissolved solutes in a solution
no

Question 27

Is solute potential always negative or always positive?
Is pressure potential always negative or always positive?

Answer 27

s-always neg
p-always pos

Question 28

What does it mean if a solution is isotonic to the cell

Answer 28

the solution has the same osmotic conc./water potential as the cell so there is no net movement

Question 29

What does it mean if a solution is hypertonic to the cell

Answer 29

the solution has a higher osmotic concentration than the cell so there is net movement out of the cell

Question 30

What does it mean if a solution is hypotonic to the cell

Answer 30

the solution has a lower osmotic concentration than the cell so there is net movement into the cell

Question 31

In animal cells , what is the effect of net movement in and out of the cell?

What effect do they have on plant cells?

What does plasmolysis and turgid mean?

Answer 31

in- causes the cell to lyse (burst)
out-causes it to shrink

in-makes the cell turgid and the vacuole becomes too full
out-causes plasmolysis and vacuole shrinks

plasmolysis-cell membrane pulled away from the cell wall
turgid-membrane pushed right up against cell wall

Question 32

What factors affect the rate of diffusion? 3

Answer 32

concentration gradient
membrane thickness
surface area of membrane

Question 33

When does active transport need to be used? 2

When does bulk transport have to be used?

Answer 33

when cells need to move substances quickly

when they need to move substances against their concentration gradient

when extremely large/large quantities of substances need to be transported across the membrane

Question 34

What 2 factors affect membrane permeability and structure?

Answer 34

temperature and solvents

Question 35

What happens to the plasma membrane when the temperature is increased?

Answer 35

the phospholipids have more kinetic energy so move more which makes the membrane more fluid
HOWEVER if temperature continues to increase the membrane loses its structure and becomes more permeable
carrier and channel proteins also denature at high temperatures

Question 36

Why does a high temperature cause the membrane to lose its structure?

Answer 36

because the phospholipids gain more and more kinetic energy meaning they collide with each other with great force , causing gaps to emerge in the bilayer and eventually breaking down the molecules due to the collisions

Question 37

What effect does a solvent have on membrane structure and permeability

Answer 37

they dissolve the membranes

non polar molecules such as alcohol molecules can enter the cell membrane and stay between the phospholipids disrupting the membrane which makes it more permeable