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CORE PRACTICAL 4
Purpose: To investigate the effect of alcohol concentration on membrane permeability.
1. Use a size 4 cork borer to cut cylinders of fresh beetroot tissue. Place on a tile and
cut into 1cm wide discs.
2. Place the slices in a beaker of distilled water. Leave overnight to wash away excess
3. Next day, place one of the beetroot sections into a boiling tube containing 5cm3
distilled water. This is 0% alcohol concentration. Repeat with seven test tubes
containing, 10%. 20%, 30%, 40%, 50%, 60% and 70% alcohol. Leave boiling tubes for
4. Switch on the colorimeter and set it to read % absorbance.
5. Using a pipette accurately, measure 2 cm3 distilled water into a cuvette. Place the
cuvette into the colorimeter, making sure that the light is shining through the
smooth sides. Adjust the colorimeter to read 0 absorbance.
6. Place 2cm3 of the dye solution into a colorimeter cuvette and take a reading for
absorbency. Repeat the readings for all the alcohol concentrations.
SAFETY: Take care using cork borer and knife.
Factors to be controlled
- The storage conditions and age of beetroot must be taken into account
- The diameter and thickness of the discs must be standardised
- The volume of ethanol in the test tube must be controlled
- The number of discs in the test tube must be the same for all trials
- The duration of ethanol treatment must also be standardised
- The volume of red pigment in the cuvette must be standardised
Independent variable: Percentage of alcohol
Dependent variable: Size of beetroot
Ethanol% 0 10 20 30 40 50 60 70
Absorbanc 0 0.08 0.09 0.02 0.48 0.79 0.84 0.83
As the ethanol % so does the absorbance, therefore more of the red liquid has diffuse out
when there has been a higher % of ethanol. This is because alcohol dissolves the lipids in the
cell membrane, therefore the membrane loses its structure and the red liquid can diffuse
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