Required Practical 4- Permeability Of Cell Membranes Flashcards
Control variables? Why?
-same beetroot used- different beetroots have different numbers proteins in phospholipid bilayer
-surface area of cylinder - different sized cylinders diff number proteins in membrane (cut using cork borer)
-time left in water bath- temp could cause damage to proteins
-volume of distilled water- dilute/concentrate solution
Why place beetroot discs in beaker of water after cutting?
Wash away excess pigment which has leaked out due to cell surface membrane damaged/ruptured
What happens to permeability as temperature increases?
-permeability of cell surface membrane also increases
-phospholipids gain more kinetic energy- membrane become more fluid
-as proteins in membrane denature as heat damages bonds in tertiary structure
-creates gaps in membrane- easier for molecules to pass through it
-low temps- phospholipids have little energy, closely peaked together-membrane more rigid = decrease in permeability as molecules restricted from crossing membrane
How does concentration of ethanol affect permeability
-Ethanol causes cell surface membrane to rupture (phospholipids dissolve in alcohol)
-releases betalain pigment from cell
-higher concentration= more disruption to membrane, more gaps form
=increase permeability
Why are tubes of water placed in water bath?
Equilibrate to constant temperature
Why handle cylinders carefully?
To prevent damaging cell membrane- which would allow pigment to leak out
How measure?
-Use colorimeter to measure absorption
-calibrate with distilled water
-use blue filter- as it is opposite to red on colour wheel
Limitations?
-Cuvettes may differ slightly in thickness/scratched- slightly thicker cuvette will absorb more light, scratches will disperse light
-> overcome by using the same cuvette for every reading or repeating several times and finding mean
-Beetroots cylinders may be slightly different sizes so some cylinders may contain more/less pigment
—> overcome with a lot of repeats
-Pigment distribution within the beetroot maybe uneven
—> overcome by a lot of repeats using say beetroot
-Temperature of water bath may fluctuate
—>overcome by monitoring
Suggest how the increase in temperature of water cause the release of red pigment
-damage to cell surface membrane
-Membrane proteins denature
-Increases fluidity
Investigate effect temp on permeability membrane
1.Cut beetroot into 6 identical cubes with a scalpel.
2.Place each cube in a different test tube with equal volumes of distilled water.
3. Place each test tube into water baths ranging from 30-80° C. Leave for 20 minutes.
4. Filter each solution out into a cuvette and measure the
absorbance using a colorimeter.
