Beetroot Membrane Permeability Practical – Temperature and Ethanol
BiologyCell BiologyAges 15–16Virtual lab
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Next in Cell Biology
Cut beetroot discs, rinse them, soak them in water from 0 to 70 °C or in ethanol from 0 to 100 %, then read the leaked betalain in a colorimeter. Plot absorbance and explain the damage to the membrane.
Lesson: Membrane structure and permeability: effect of temperature and ethanol on beetroot cells, colorimetry
What it shows
Beetroot cells keep a red pigment, betalain, in their vacuoles. The molecules are too large to cross a healthy membrane, so colour in the water around a disc shows that the membranes have been damaged. In this lab you cut discs, rinse them, soak each one at a chosen temperature or in a chosen ethanol solution, and read the liquid in a colorimeter. You plot absorbance, find where it rises fastest and connect it to protein denaturation and disrupted phospholipids. The method is the school practical; the rates are estimates that give the usual result.
How to use
Set the Temperature or Ethanol, Soak time, Filter and Rinse discs. Press Next step to work through the method, or Run all steps for one tube. Whole series takes one disc for each condition. Readings go into the table and the graph. Use Inside the membrane to move the sliders and see the cause, then press Record observation.
Parameters you can change
- Experiment Temperature, Ethanol, Inside the membrane
- Temperature 0–70 °C
- Ethanol 0–100 %
- Soak time 5–30 min
- Colorimeter filter Blue-green, Blue, Red
- Rinse discs
Questions to explore
- Between which temperatures does absorbance rise most steeply, and what is happening to the membrane there?
- How does skipping the rinse change the reading at 20 °C, and why does it matter most at low temperatures?
- Why does the blue-green filter give a much larger reading than the red filter for the same liquid?
