Practical 5 - Investigation into the permeability of cell membranes using beetroot Flashcards
Permeability
How much substance can crops a membrane in a particular amount of time
Method for this practical
1-Cut 5 pieces of beetroot, 1cm long, from the cylinders provided
2- Wash under running water to remove the pigment released from cells during cutting
3- test tube with 5cm3 distilled water into a water bath to equilibrium for 5 minutes
4- 1 piece of beetroot into each test tube for 30 minutes
5- After 30 minutes, shake the test tubes gently to ensure pigment is well mixed and remove beetroot cones
6- Describe the depth of colour (white card behind can help)
7- Use a colorimeter to respond to a blue/green filter (wavelength 530nm) and measure absorbance/percentage transmission of each tube
How long do we cut all of the beetroot slices and why is it important that they’re all cut the same?
1cm, to have no affect on the amount of betalain passing through the membrane
How is the water bath controlled?
Thermostatically
How much water do we place into each test tube and what type of water is this?
5cm3 distilled water
Why do we wash running water over the beetroot before starting the real testing?
To remove the pigment released from cells during cutting
What type of data does a colorimeter give and why is this useful?
Quantitate - more accurate
Which filter do we set the colorimeter to?
The blue/green filter (520nm wavelength)
What does the colorimeter measure?
Absorbance/percentage transmission
Draw and label a beetroot cell
(Check notes)
What’s the name of the bright coloured pigment found in the vacuole of the beetroot cell?
Betalain
Where is betalain found in the beetroot cell?
In the vacuole
Describe betalain
-bright coloured purple pigment
-water soluble
How does betalain exit the cell?
Has to diffuse down a concentration gradient
Independent variable - definition and what was it in this practical?
The variable that WE change
Temperature of the water bath
Dependant variable - definition and what was it in this practical?
The variable that we measure
Light absorbance (a.u.)
Unit of light absorbance
A.u
Control variables - definition and what were they in this practical?
Things to remain constant
Surface area of the beetroot and temperature of the water bath
2 hazards involved in this practical
Sharp scalpel
Water bath is over 60 degrees
Risk involved with a sharp scalpel
Cutting or piercing the skin
Risk involved with water baths being over 60 degrees
Scalding
Over which temperatures does the water impose a risk of scalding?
60 degrees
Control measure of a sharp scalpel
Cut downwards onto a white tile
Control measure of the water baths being over 60 degrees
Ensure that beaker water baths are set up so they’re stable
Use test tube holders to move the test tubes
How many times should we repeat this practical and why?
3 times
Improves reliability
Identify anomalies
Calculate a mean
Why is it important to calculate a mean?
Reduces the affects of anomalous data
What is the conclusion from this practical?
The higher the temperature, the higher the permeability (higher light absorbance)
How come the light absorbance is higher in the samples in higher temperatures which have higher permeability?
They’re darker, and dark colours absorb more light
What’s the reason for higher temperatures giving higher permeability (up to 40 degrees Celsius)?
Higher temperatures = increase in kinetic energy = phospholipids, proteins and pigment in the molecule move more
This creates gaps that the pigment can diffuse out of the cell through
What’s the reason for higher temperatures giving higher permeability (above 40 degrees Celsius)?
Protein components of the membrane begin to denature + the cell membrane becomes fully permeable to the pigment if all of the proteins denature
This forms large pores that the betalain pigment can diffuse through easily
At what point would the cell membrane become fully permeable?
If all of the proteins denature due to the very high temperatures (above 40 degrees Celsius)
What’s the only part of the cell that denatures to allow betalain to diffuse through the membrane?
Proteins
What do proteins do at higher temperatures?
Denature, so that the cell membrane become fully permeable to the betalain
Which two factors can cause pigment to diffuse out of a cell’s membrane?
Acid (denatures proteins)
Ethanol (dissolves phospholipids and fatty acids)
What does acid do to proteins?
Denatures them
What can denature proteins?
Acid
What does ethanol do to phospholipids/fatty acids?
Dissolves them
What can ethanol dissolve?
Phospholipids/fatty acids
What can dissolve phospholipids/fatty acids?
Ethanol
What does acid denature?
Proteins
