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Topic 2 – Genes & health
Beetroot practical
Aim: The effect of temperature on cell membranes
How does temperature affect the permeability of beetroot?
Hypothesis & prediction: the higher the temperature the more permeable the beetroot
therefore, the higher the absorption rate.
Beetroots are root vegetables that appear red because the vacuoles in their cells contain a
water-soluble red pigment called betalain. These pigment molecules are too large to pass
through membranes
https://getrevising.co.uk/revision-notes/biology_beetroot_practical_2
https://qualifications.pearson.com/content/dam/pdf/A%20Level/biology-b/2015/teachingand-learning-materials/AS-and-A-level-Biology-B-Core-Practical-5---beetroot-membrane(Student,-Teacher,-Technician-Worksheets).pdf
Variables:
Independent variable:
Dependent variable:
Control variables: size of beetroot cylinders, amount of distilled water in each tube, type of
water bath, type of colorimeter, the volume of coloured liquid in the cuvettes, the
colorimeter filter/wavelength used (blue/green), the part of the beetroot the core was
taken from, use same beetroot to cut out cylinders
Equipment:
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Water baths pre-set at required temperatures
Distilled water
Large beetroot
Cork borer size no. 4 or 5
Ruler
White tile
Knife
10 cm3 syringe
Pipette
Test tubes
Colorimeter
Nine cuvettes
Labels or pens for labelling
Forceps
Method:
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Topic 2 – Genes & health
1) Use a cork borer, knife and ruler to cut 8 x 1cm cylinders of beetroot over a white
tile.
2) Place all the cut pieces in a beaker of distilled water & leave overnight to remove any
dye (betalains) released when the beetroot was cut.
3) Wash and blot dry (with filter paper or a tissue) the 8 pieces of beetroot.
4) Use a syringe to add 10 cm3 of distilled water to eight test tubes. Label each test
tube with a
5) temperature from the pre-set range.
6) Prepare eight water baths pre-set to a range of temperatures between 0 °C and 70 °C
temperatures (e.g. 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C).
7) Check the temperature of each bath is correct using a thermometer. It is unlikely to
be exactly the desired temperature. Record the actual temperature and use this in
your table and graph.
8) Once at the desired temperature, add a piece of beetroot to each boiling tube and
leave for 20 minutes.
9) Remove the beetroot pieces gently with a pair of forceps and then shake the tubes
to disperse the dye.
10) Set a colorimeter to percentage absorbance on the blue/green filter. Calibrate by
filling a cuvette with distilled water first then add 2cm³ of beetroot solution from the
first temperature to a new cuvette.
11) Place this cuvette into the colorimeter to read the percentage absorbance. Repeat
this for all other pieces. Record your results in a suitable table.
12) Plot a graph of absorption against temperature.
Results table & graph:
Absorption (%)
0.66
0.20
0.59
0.83
2.00
2
Absorption (%)
Temperature (°C)
18
31
36
49
53
2,5
1,5
1
0,5
0
0
10
20
30
Temperature (°C)
40
50
60
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Topic 2 – Genes & health
Conclusion:
The higher the temperature, the higher the absorption rate. For example, at 18°C the
absorption rate was 0.66%, whilst at 49°C the absorption rate was 0.83%.
Evaluation:
1) Criticises the method
2) Identifies reliability, accuracy & validity
3) Conclusions & evaluation together are sometimes known as the ‘discussion’
Risk assessment
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Water baths at temperatures above 50 °C may scald. Take care when removing lids to allow
steam to escape away from the face or body.
Take care with sharp items such as the cork borer and knife.