beetroot membrane permeability experiment results

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The Effect of Temperature on Cell Membranes

Published: Jan 29, 2017 Modified: Nov 27, 2019 / By Dr. Isa About 4 minutes to read this article. . [feast_cookies_disclosure] . [feast_privacy_disclosure] . [feast_sponsored_disclosure] . Leave a Comment

Core Practical 3 – From Topic 2 (Genes and Health)

To investigate membrane structure, including the effect of temperature on membrane permeability.

Independent Variable

The temperature of the water in the water bath (Degrees Celcius)

Dependent Variable

The percentage transmission of light through the resulting solution

Control Variables

• Volume of distilled water – 10cm³ of distilled water should be used to fill the boiling tubes each time
• Time left in water – leave each boiling tube containing beetroot for 30 minutes
• Size of beetroot piece – use a ruler and knife to cut cylindrical beetroot pieces of 1cm in length
• Colorimeter used – same colorimeter should be used on the same blue/green setting each time, measuring percentage absorbance. Calibration with distilled water should be carried out each time
• Volume of beetroot solution – 2cm³ of beetroot solution should be added to a cuvette each time

Why Use Beetroot?

Beetroot cells contain pigment called betalains in their vacuoles. We can observe the effect of temperature on cell membranes in beetroot by observing the leakage of this pigment, indicating the weakening of the cell membrane. Betalains display as a dark purple colour in this case.

Diagram of a beetroot cell

• Raw beetroot
• Size 4 cork borer
• Water baths
• Boiling tubes
• Thermometers
• Colorimeter with cuvettes
• Distilled water
• Filter paper/tissue

Keeping a beetroot piece in 10cm³ of distilled water at room temperature can provide control results.

• Use a cork borer and knife to cut 8 x 1cm lengthed cylinders of beetroot over a white tile.
• Place all the cut pieces in a beaker of distilled water and leave overnight to remove any dye (betalains) released when the beetroot was cut.
• Wash and blot dry (with filter paper or a tissue) the 8 pieces of beetroot.
• Fill 8 boiling tubes each with 10cm³ of distilled water and place them into 8 separate water baths of different temperatures (e.g. 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C).
• Once at the desired temperature, add a piece of beetroot to each boiling tube and leave for 30 minutes.
• Remove the beetroot pieces gently with a pair of forceps and then shake the tubes to disperse the dye.
• 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.
• Place this cuvette into the colorimeter to read the percentage absorbance. Repeat this for all other pieces.

Results & Calculations

In order to obtain the percentage transmission for each beetroot solution in the colorimeter, we can use the following equation:

Percentage transmission = 100 – percentage absorbance

Recordings can be noted down in an appropriate table as well as a graph.

As temperature increased, the percentage transmission slightly increased to a point at which it greatly increased.

The betalains pigment was contained in the vacuole of the beetroot cells. The cell membrane contains the contents of the cell like a barrier. The cell membrane is made up of the phospholipid bilayer and protein molecules. These proteins are made up of linked amino acids. The hydrogen bonds within the protein determines its 3D shape. However, as heat increased, the hydrogen bonds got weaker due to the increased kinetic energy of individual atoms. Greater kinetic energy created more gaps in the phospholipid bilayer for the betalains to leak through. At a certain point, broken hydrogen bonds caused proteins to change shape and denature – leaving larger holes in the cell membrane. This is when even greater amounts of betalains leaked through the membrane and so coloured a solution more strongly. In summary, an increase in temperature caused further destruction of the cell membrane, which allowed more pigment to leak out via diffusion.

Evaluation Points 

• Some beetroot may have skin on affecting surface area (random error) – use a bigger beetroot and use cork borer to obtain pieces free from skin
• Difficulty in maintaining temperature (random error) – set water baths for higher temperatures and set refrigerators for lower temperatures
• Accurate reading of the colorimeter (systematic error) – use more precise colorimeter and close cap to ensure outside light does not interfere with reading. Make sure that distilled water is used for calibration
• Accurate size of beetroot (random error) – cut many different pieces from different beetroot and use the most similar sized pieces for the experiment
• From the different parts of the root (random error) – use a large beetroot and take all samples from the round part of the root
• Ensuring same amount of time at the different temperatures (random error) – have 7 other helpers to make sure all 8 boiling tubes are extracted at the same time after 30 minutes

More All 18 Core Practicals

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Practical Biology

A collection of experiments that demonstrate biological concepts and processes.

Observing earthworm locomotion

Practical Work for Learning

Published experiments

Investigating the effect of temperature on plant cell membranes, class practical.

You and your students may be familiar with the observation that colour leaks out of beetroot when it is cooked. Many cookbooks suggest that beetroot should be cooked with their outer skins on, and with a minimum amount trimmed from the top (by the leaves) and tail (by the taproot) to reduce the release of beet colour leaking into the water.

Lesson organisation

This procedure lends itself to detailed evaluation, and provides an opportunity to discuss how you would like students to write up a practical.

Cutting the cores to size and placing in water baths takes only a few minutes. During the thirty minutes heating (or chilling) time, you can discuss writing up or evaluating the procedure.

If you have access to only one colorimeter, one group could gather quantitative results while the others gather subjective, qualitative information. The number of beetroot cores used will depend on the number of water baths available.

Students can work individually or in pairs. To save time, reduce the number of temperatures used and collate results to provide repeats at each temperature.

Apparatus and Chemicals

For each group of students:.

Beetroot cores, cut with a size 4 cork borer and soaked in distilled water overnight ( Note 1 )

Thermometers, 1 for each water bath

Kettle, to provide boiling water for the water baths

Ice bath (a beaker of water surrounded by ice)

Scalpel, 1, or sharp vegetable knife

Forceps or mounted needles to ‘handle’ beetroot cores

Ruler, up to 15 cm, 1

Distilled water, in wash bottle

Measuring cylinder, 10 cm 3 , 1

Test tubes, 1 for each temperature of water bath

Paper towels

For the class – set up by technician/ teacher:

Access to several water baths set at a range of temperatures, or beakers containing water at different temperatures ( Note 3 )

Health & Safety and Technical notes

Always carry cutting tools in a small tray. Cut away from you. Replace the cutting tool in the tray when not in use.

Read our standard health & safety guidance

1 Beetroot must be raw, not cooked. Use a size 4 cork borer and cut with care using a cutting board. Cut enough cores to make eight 2 cm lengths per working group. Leave the cores overnight in a beaker of distilled water. The pigment from any cells that have been cut by the cork borer will leak into the water. Rinse away any pigmented water in the morning and replace with fresh water.

If you do not have a cork borer, cut the beetroot with a bread slicer (or onion slicer) to make even-sized slices, then cut the slices into even-sized chips. If beetroot is not available, use discs of red cabbage. You will need ten or more discs for each tube. If it is not possible to prepare beetroot in advance, students could cut the cores/ chips at the start of the lesson, wash in distilled water and blot dry.

2 Note: Beetroot juice will stain clothing (and, temporarily, skin) but is not hazardous. Students may wish to wear labcoats to protect their clothing from stains.

3 Check the temperature of the water baths regularly and top up with boiling water or add extra ice if the temperature has changed.

SAFETY: Take care carrying scalpels or knives around the laboratory. Always carry in a tray.

Preparation

a Cut bores of beetroot with a size 4 cork borer and soak overnight in a beaker of distilled water ( Note 1 ).

b Set up a series of water baths at different temperatures.

Investigation

Procedure c Collect 3 or 4 beetroot cores from the beaker provided. Cut each core into 2 cm sections until you have enough for one core for each temperature of water bath that you will be using. Put your 2 cm sections into a test tube with plenty of distilled water.

d Label a set of test tubes (one for each temperature of water bath) with the temperature and your initials. Add exactly 5 cm 3 of distilled water to each test tube and place the tubes, one in each water bath, for 5 minutes to equilibrate to the water bath temperature.

e Remove the beetroot cores from the distilled water and blot gently on a paper towel. Decide whether forceps or mounted needles are best for handling the tissue and what damage this might cause to the cores.

f Place one 2 cm beetroot core into each test tube and leave in the water bath for 30 minutes.

g After 30 minutes, shake the test tubes gently to make sure any pigment is well-mixed into the water, then remove the beetroot cores.

h Describe the depth of colour in each test tube. A piece of white card behind the tubes will make this easier to see. Arrange the tubes in order of temperature of the water bath. Describe any relationship between the amount of pigment released from the beetroot and the temperature.

i If you have access to a colorimeter, set it to respond to a blue/ green filter (or wavelength of 530 nm) and to measure absorbance. Check the colorimeter reading for distilled water.

j Measure the absorbance of each tube and plot a graph of absorbance against temperature. Describe any trends or patterns in your results.

Teaching notes

The dark red and purple pigments in beetroot are located in the cell vacuole and are chemical compounds called betalains . The pigments cannot pass through membranes, but can pass through the cellulose cell walls if the membranes are disrupted – by heat (for example cooking), by surfactants, or after a long period pickled in vinegar.

Questions 1 and 2 on the student sheet ask the students to produce a hypothesis about the beetroot cells and make a prediction. Then they have to evaluate the procedure and see if they think it is a valid test of the hypothesis and will produce reliable results. They may wish to alter the procedure in the light of their thoughts.

The procedure allows for students to identify systematic and random variables. It is a good opportunity to practice graphical treatment of results, including standard deviation error bars to assess the variation in repeats.

Students can work individually or in pairs. To save time, it might be a good idea to suggest that the number of temperatures used is reduced and students combine results to provide repeats at each temperature.

Here is a sample of results obtained with a colorimeter – measuring transmission of light at 530 nm (rather than absorbance).

Health & Safety checked, May 2009