How can the permeability of a cell membrane be investigated in the lab?

A simple test is done by using beetroots and a condition damaging the cell membrane (e.g. alcohol or changing temperature).

When the beetroot membrane is exposed to conditions that damage it, the pigment leaks out. The more pigment that leaks out (indicative of more damage) can be measured by absorbance into a colorimeter. This produces an absorbance value which tells us the amount of light absorbed by each sample.

Higher absorbance values tells us that there has been more damage done to the membrane as reflected by more pigment leaking out.

The permeability of a cell membrane could be investigated using beetroot discs and increasing concentrations of ethanol, or increasing the temperature. As beetroot cells are plant cells, the pigment Betalain is found in the vacuole of the cell surrounded by the tonoplast membrane. Then the intensity of the pigment could be quantified through measurement microscopy and through appropriate equations related to the permeability.

A typical experiment to investigate permeability of cell membranes involves the use of beetroot. A factor affecting the integrity of the cell membrane needs to be changed, such as different temperatures or different alcohol concentrations. When beetroot cells are exposed to conditions damaging the cell membrane, a pigment (betalain) leaks out through the cell membranes. The more damage occurs to the cell membrane, the more pigment leaks out. This can be measured as absorbance using a colorimeter. A colorimeter gives the absorbance value which is the amount of light that is absorbed by each sample. Higher absorbance values indicate more pigment that has leaked out (greater permeability) and therefore more damage to the cell membrane.

Take any plant sample for example onion. Peel the inner layer and place in different solutions of isotonic, hypertonic and hypotonic.

Results will show the permeability of cell membrane.

By doing an experiment using beetroot.

You can carry out something know as the beetroot test. The test consists of using beetroot cells which contain betalain. Higher the permeability the more the betalain pigment is leaked. Therefore, this allows us to test different variables such as temperature, so the more the Betalain pigment leaks the higher the permeablity

The simplest way is to use beetroot cells. Their vacuoles contain betalain which leaks out of the cell with high-permeable membrane. There are some more sophisticated ways to test it: flow cytometry and confocal fluorescence microscopy.

The best way to do this is to use beetroot and a colourimeter. Depending on the independent variable you investigate you can place a known mass of beetroot (cut into pieces of the same size) into 5 different tubes with different values for the independent variable (5 temperatures). You leave the beetroot for a set time (Around 3-5 minutes). Decant the solution only into cuvettes and measure the absorbance using a colourimter. You then plot a graph of your independent variable against absorbance. The more permeable the membrane the greater the loss of pigment will be and therefore more light will be absorbed as it passes through the solution when in the colourimeter.

We used a beetroot in our A Level prac

Viking Tubing experiments can be used with different dilutions of glucose to show the movement of water molecules to investigate osmosis and diffusion rates.

Permeability of Cell membrane can be measured by using beetroot cells that contain betalain which is a purple pigment. If permeability of the cell membrane is higher, more pigment'll leak out of cells. This can therefore be measured by using a colorimeter. 

Hi, quick practical method by OCR

The effect of temperature on membrane permeability                                                                                             STUDENT

Introduction

Beetroot cells contain the purple pigment, betalain, as shown in the diagram below:

This experiment investigates the effect of temperature on membrane structure by considering the leakage of betalain from the beetroot cells over a range of temperatures. The quantitative assessment of this is carried out using a colorimeter.

Aim

·        To investigate the effect of temperature on membrane structure.

·        To understand the use of a colorimeter.

Intended class time

·        1 hour

Chemicals

Not applicable for this activity.

Equipment (per class)

·        Thermostatically controlled water baths at 30°C, 40°C, 50°C, 60°C and 70°C containing test tube racks

Equipment (per 4-6 students/groups)

·        Colorimeter and green filter

Equipment (per student/group)

·        Thermometer

·        1 beetroot cylinders at least 30 mm long

·        Knife / Scalpel

·        Ruler

·        White tile

·        Paper towel

·        6 test tubes

·        6 cuvettes

·        Distilled water

·        10 cm³ syringe

·        Marker pen / Chinagraph pencil / OHP pen / Stickers

·        Forceps

·        Timer

·        Test tube rack

Health and Safety

Take care with the knife when trimming the cylinders of beetroot to the correct length. The water in the water baths over 40°C will be hotter than hand-hot so be aware of this.

Procedure

1.      Take the six test tubes and label each with one of the temperatures from 20°C to 60°C.

2.      Add 10 cm³ distilled water to each tube using the syringe.

3.      Place the correctly labelled test tube in its corresponding water bath for 5 minutes to allow the water to equilibrate to the correct temperature. Record the actual temperature with the thermometer. Leave the tubes in the water baths.

4.      Cut the beetroot cylinder to give six 5 mm cylinders using the knife and ruler on the white tile.

5.      Rinse the cylinders under a running tap and pat dry using paper towel.

6.      Add one 5 mm beetroot cylinder to a tube in each temperature and leave for 15 minutes.

7.      Remove the tubes from the water bath, carefully swirl once and use the forceps to remove the cylinders. Throw the cylinders into a waste receptacle.

8.      One tube at a time, carefully pour the remaining liquid into a cuvette.

9.      Use the colorimeter to measure the absorption for each temperature and record this information in a suitably designed table. The absorption is measured in arbitrary units (AU).

10.  Plot a graph of temperature against absorption and draw an appropriate line.

Extension questions

1.      Describe the relationship between temperature and the rate of leakage of the pigment from the beetroot cells.

2.      Explain your results and the shape of your graph using theory about membrane structure.

3.      What effect might a solvent such as ethanol have on membrane permeability? Explain your answer using ideas about membrane structure.

4.      State four limitations of this procedure.

What to record

As evidence for the Practical Endorsement, you should have your table and graph of the data as described above. All work should be clearly dated.

In addition you should have considered the above questions as the answers to these questions will aid you in preparation for your written examinations.

Kind Regards

Carrie Garbowska

By injecting a coloured dye into the cell of interest and measuring change in colour over time

First! we need to understand, 'What is permeability?'. A substance is permeable if it can allow molecules to pass thorough the membrane. This property is called 'Permeability'. And it mainly depends on the substance's electric charge and to some extent on the molecular mass also. So, Now Lets come to Cell membrane permeability, Cell membrane is selective in nature and only allows some molecules to pass through it. The best way to study the 'Permeability of a cell membrane in the lab is 'Beetroot test'. Keeping in mind, factors like optimum temperature, pressure, light exposure is necessary. "Why only Beetroot?', this question may come to our mind, So the answer to this question is, Beetroot is very rich in pigments which helps to understand the mechanism of cell membrane permeability, and thus Beetroot is used as a specimen for the lab investigation. Increase in temperature during the experiment increases the fluidity of the membrane which increases the mobility of the pigment and at a very high temperature, the pigment oozes out of the cell membrane. The quantity of the pigment can be measured with the help of a colorimeter.

Using a coloured plant tissue, often beetroot, place cut, peeled and washed pieces into water at different temperatures or a range of ethanol concentrations, depending on what you are investigating. Leave for a few minutes and the colour inside the cells will leach out depending on the permeability of the cell membrane. Remove the pieces of tissue and assess the concentration of pigment in the liquid, either by sight, comparison to standards or preferably using a colorimeter. The greater the concentration the more permeable the cell membrane was.