Paper 1: Transport across membranes Flashcards
Components of the fluid mosaic model of the cell membrane [6]:
- Phospholipid bilayer
- Glycolipids
- Glycoproteins
- channel protein
- Carrier protein
- Cholesterol
Phospholipid bilayer =
Hydrophilic heads face outwards, hydrophobic tails face inwards
What makes the fluid mosaic model fluid?
Phospholipids can slide over each other
What can easily enter the cell membrane?
Small, non-polar molecules can diffuse thru
e.g co2,o2
Why does water struggle to diffuse thru membrane? [2]:
- Water is a polar molecule so doesn’t diffuse thru easily
- It moves into cells thru aquaporins
Cholesterol in the fluid mosaic model [3]:
- Binds to hydrophobic tails
- This makes membrane stronger/ more rigid
- Strength n support- especially for cells w/ no cell wall
What makes the cell membrane rigid in the fluid mosaic model?
Cholesterol that binds to hydrophobic tails
Diffusion [definition]:
The net (passive) movement of molecules from high to low concentration
What are the factors that affect the rate of diffusion? [3]:
- Concentration gradient
- Length of diffusion pathway
- Surface area
How does concentration gradient affect diffusion?
The steeper the gradient the faster the rate of diffusion
How does The length of the diffusion pathway affect diffusion?
shorter distance = faster rate
How does surface area affect diffusion?
Bigger surface area = faster rate of diffusion
Biological examples of good conc gradient [2]:
- Ventilation of air in lungs
- Fishgills
Biological examples of good length of diffusion pathway [2]:
- Capillary walls 1 cell thick
- Alveoli walls 1 cell thick
Biological examples of good surface area [4]:
- Villi
- Alveoli
- Christae
- Thylakoids
Facilitated diffusion [definition]:
The passive movement of molecules across the cell membrane via a specific transmembrane protein
Protein channels [4]:
- 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
Carrier proteins [2]:
- Large molecules
- Both active transport & cotransport
Active transport [definition]:
The movement of molecules against their concentration gradient using energy from ATP
Active transport [3]:
- Against conc gradient
- Uses energy from ATP
- Via carrier protein
Cotransport [4]:
- Via carrier protein
- 2 molecules at the same time
- One molecule goes down its conc gradient
- Other molecule goes against its conc gradient
The absorption of glucose [3]:
- sodium-potassium pump
- Co-transport
- Facilitated diffusion
Sodium potassium pump [3]:
- Na+ ion out
- K+ ion in
- Active transport
- Low conc of Na+ ion in cell
Osmosis [definition]:
The passive movement of water from areas of high water potential to areas of low water potential across a partially permeable membrane
High water potential [3]:
- High % of water molecules
- Lower % of solute
- Hypotonic
Low water potential [3]:
- Low % of water molecules
- Higher solute % (conc)
- Hypertonic
Required practical 3- osmosis: procedure [6]:
- 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
Required practical 3- osmosis: conclusion [2]:
- 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
Required practical 4- temp on cell surface membrane permeability: procedure [3]:
- 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
Required practical 4- conc on cell surface membrane permeability: procedure [5]:
- 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
Required practical 4- temp on cell surface membrane permeability: conclusion [3]:
- 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
Required practical 4- conc on cell surface membrane permeability: conclusion [3]:
- Ethanol causes cell membrane to rupture releasing pigment
- Higher conc of ethanol = more membrane disruption so more gaps form
- Thus permeability increases
