Paper 1: Transport across membranes

Question 1

Components of the fluid mosaic model of the cell membrane [6]:

Answer 1

• Phospholipid bilayer
• Glycolipids
• Glycoproteins
• channel protein
• Carrier protein
• Cholesterol

Question 2

Phospholipid bilayer =

Answer 2

Hydrophilic heads face outwards, hydrophobic tails face inwards

Question 3

What makes the fluid mosaic model fluid?

Answer 3

Phospholipids can slide over each other

Question 4

What can easily enter the cell membrane?

Answer 4

Small, non-polar molecules can diffuse thru

e.g co2,o2

Question 5

Why does water struggle to diffuse thru membrane? [2]:

Answer 5

• Water is a polar molecule so doesn’t diffuse thru easily

- It moves into cells thru aquaporins

Question 6

Cholesterol in the fluid mosaic model [3]:

Answer 6

• Binds to hydrophobic tails
• This makes membrane stronger/ more rigid
• Strength n support- especially for cells w/ no cell wall

Question 7

What makes the cell membrane rigid in the fluid mosaic model?

Answer 7

Cholesterol that binds to hydrophobic tails

Question 8

Diffusion [definition]:

Answer 8

The net (passive) movement of molecules from high to low concentration

Question 9

What are the factors that affect the rate of diffusion? [3]:

Answer 9

• Concentration gradient
• Length of diffusion pathway
• Surface area

Question 10

How does concentration gradient affect diffusion?

Answer 10

The steeper the gradient the faster the rate of diffusion

Question 11

How does The length of the diffusion pathway affect diffusion?

Answer 11

shorter distance = faster rate

Question 12

How does surface area affect diffusion?

Answer 12

Bigger surface area = faster rate of diffusion

Question 13

Biological examples of good conc gradient [2]:

Answer 13

• Ventilation of air in lungs

- Fishgills

Question 14

Biological examples of good length of diffusion pathway [2]:

Answer 14

• Capillary walls 1 cell thick

- Alveoli walls 1 cell thick

Question 15

Biological examples of good surface area [4]:

Answer 15

• Villi
• Alveoli
• Christae
• Thylakoids

Question 16

Facilitated diffusion [definition]:

Answer 16

The passive movement of molecules across the cell membrane via a specific transmembrane protein

Question 17

Protein channels [4]:

Answer 17

• Narrow so only small charged/ polar molecules (ions)
• From high to low conc
• Each molecule has its own protein channel (specific)
• Can be used for active transport

Question 18

Carrier proteins [2]:

Answer 18

• Large molecules

- Both active transport & cotransport

Question 19

Active transport [definition]:

Answer 19

The movement of molecules against their concentration gradient using energy from ATP

Question 20

Active transport [3]:

Answer 20

• Against conc gradient
• Uses energy from ATP
• Via carrier protein

Question 21

Cotransport [4]:

Answer 21

• Via carrier protein
• 2 molecules at the same time
• One molecule goes down its conc gradient
• Other molecule goes against its conc gradient

Question 22

The absorption of glucose [3]:

Answer 22

1. sodium-potassium pump
2. Co-transport
3. Facilitated diffusion

Question 23

Sodium potassium pump [3]:

Answer 23

• Na+ ion out
• K+ ion in
• Active transport
• Low conc of Na+ ion in cell

Question 24

Osmosis [definition]:

Answer 24

The passive movement of water from areas of high water potential to areas of low water potential across a partially permeable membrane

Question 25

High water potential [3]:

Answer 25

• High % of water molecules
• Lower % of solute
• Hypotonic

Question 26

Low water potential [3]:

Answer 26

• Low % of water molecules
• Higher solute % (conc)
• Hypertonic

Question 27

Required practical 3- osmosis: procedure [6]:

Answer 27

• Make series of dilutions using sucrose (0.2,0.4,0.6,0.8, 1)
• Put 5 cm3 of each dilution into a test tubes
• Use cork borer to cut 6 identical potato chips
• Dry each chip w/ paper towel then weigh em
• Put each in a test tube for 20 mins
• Dry each potato chip then calculate % change in mass

Question 28

Required practical 3- osmosis: conclusion [2]:

Answer 28

• Potato in low conc of glucose increase in mass & vice versa
• In low conc solutions water potential is higher than potato so water osmosisises into potato lmao

Question 29

Required practical 4- temp on cell surface membrane permeability: procedure [3]:

Answer 29

• Cut beetroot into 6-10 identical cubes then wipe/ clean excess pigment from cutting
• Put each cube in equal vol of distilled water
• Put tube in water bath at range of temps

Question 30

Required practical 4- conc on cell surface membrane permeability: procedure [5]:

Answer 30

• Cut beetroot into 6-10 identical cubes then wipe/ clean excess pigment from cutting
• make dilution series using ethanol + distilled water
• leave sample for 20 mins
• set colorimeter to blue filter and zero it using cuvette
• Filter sample into cuvette and measure absorbance

Question 31

Required practical 4- temp on cell surface membrane permeability: conclusion [3]:

Answer 31

• As temp increases permeability increases
• This cus proteins in membrane denature
• At low temps phospholipids have low energy so packed closely together = more rigid so no entry

Question 32

Required practical 4- conc on cell surface membrane permeability: conclusion [3]:

Answer 32

• Ethanol causes cell membrane to rupture releasing pigment
• Higher conc of ethanol = more membrane disruption so more gaps form
• Thus permeability increases