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Membrane Permeablility Experiment

  • /
  • SL Core /
  • Cells: Activities for Learning /
  • Membrane Permeablility Experiment

What is the effect of temperature of the permeability of beetroot cells?

This experiment is a good first assessment of manipulative skills, data collection and processing. Students measure the diffusion of pigments out of beetroot cells. By increasing the temperature of the heat treatment the leakage through the plasma membrane changes. The intensity of the colour of the leaked betalin pigments can be measured using a colorimeter.

Lesson Description

Guiding Questions

Can we damage the cell membrane with a simple heat treatment?

At what temperature will proteins in the plasma membrane denature?

Activity 1 - Experiment to test membrane permeability of beetroot membranes

Carry out the Experiment using the instructions on the  Students' Worksheet - beetroot experiment

Activity 2 - Writing about the experiment

Complete a written report of your experiment as training for assessment of Analysis & Evaluation.

Analysis

  1. Present the data for the colorimeter readings for each heat treatment in a clear table.
  2. Include a +/- uncertainty for each measurement and check that decimal points correspond.
  3. Include your qualitative observations.
  4. Plot a scatter graph of the data.
  5. Make reference to uncertainties in the graph using error bars or the R2 value of a best fit line.
  6. Use the graph to show the effect of the heat treatment on the diffusion of the purple pigment.
  7. Identify the thermal death point (the point when integral proteins in the membrane denature).
  8. Write a description of what trend the results show.

Evaluation

  1. Write a conclusion which refers to the research question of the experiment and
  2. Conclude whether the conclusion supports your idea about the research question.
  3. include a reference to the structure of membranes, protein structures and the process of diffusion.
  4. Find something in a text book which either supports or disagrees with your conclusion.
  5. Evaluate the limitations of the experiment method, the apparatus and your data
  6. Suggest improvements to the limitations mentioned, giving specific details.

In support of this write-up there is some useful information on this document:

Teachers notes

This is a 'classic' experiment. It can produce a good set of data from ten different heat treatments in one hour, but the experiment is more comfortable with 90 minutes.

Very organised students can give the beetroot cylinders 15 minutes diffusion time, less organised students can get a good set of data using just 10 minutes diffusion time, which makes organisation slightly easier.

If the experiment is unfinished, the beetroot cylinders can be kept in water in the fridge overnight and students can use them in the following lesson. It is prudent to carry out the whole experiment again covering all the temperatures.

It is important that students design their own table of results, and graphs for the IA assessment. It is possible to find secondary sources of data, and text book explanations of the results of this experiment.

If raw beetroot is not available then red cabbage will work. This is best cut into strips and ensuring that all the leaves have a uniform coloration. The strips should also be washed in cold water before the lab.