The effect of temperature on the permeability of beetroot membrane

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The effect of temperature on the permeability of beetroot membrane

A1: Develop a hypothesis

  • What do you understand to be the nature of the problem?

Beetroot contains pigments called betalain pigments which give them their distinctive red colour. This pigment is found in the vacuole of the beetroot and in order to release it the vacuole must be broken down. In order to break the vacuole down I am going to use heat shock. When treated with heat the phospholipid bilayer becomes damaged and turns into fluid. When treated with heat the beetroot membrane will break down releasing the red betalain pigments.

As I use different levels of heat shock the amount of betalain released should be relative to the increase in temperature. Therefore in theory the higher the temperature the more betalain pigment released so the redder the sample.  

  • Outline the biological basis of the problem

As I am using heat shock the cell membrane will become damaged. When cell membranes become damaged they release the contents of the cell in this case betalain. The cell membrane of beetroot is composed of a phospholipid bilayer. This bilayer is made up of hydrophyllic heads and hydrophobic tails, so when these become damaged by heat they can no longer restrict what enters and leaves the cell. Within the beetroot there are a number or vacuoles containing the red pigment betalain, so when the phospholipid bilayer is broken down the betalain will be released. I will be able to record the extent to which the membrane has been broken down by measuring the absorption of light in the sample.  The water in the cell membrane also expands due to the higher temperatures and this helps to break down the membrane. The cell membrane is also composed of proteins which uncoil at higher temperatures and become denatured.

  • Link your ideas together to suggest an explanation

The betalain pigment is found within the vacuole in the beetroot and when the cell membrane is broken down by heat the contents are released. Therefore as the cell membrane becomes broken down by heat the contents of the vacuole will be released. As a result the red betalain pigments will be released and their distinctive red colouring will be visible.

As I am going to be using different levels of heat shock treatment the amount of betalain released should be relative. Therefore the greater the heat the more betalain released so the redder the sample will be. This is because at greater heat intensities there will be more kinetic energy so the breakdown of the membrane will be faster and much greater. At higher temperatures the lipids contained in the phospholipid bilayer become fluid so the membrane becomes more fragile, not being able to perform its job. The proteins which also make up the cell membrane start to untangle and break apart as a result of heat. So holes begin to appear in the cell membrane allowing the cell contents to escape.

As the beetroot pigment betalain moves into the water it will absorb more of the light so the percentage absorption will increase depending on the amount of betalain released.

  • State precisely in a hypothesis, the most appropriate explanation

At lower temperatures the cell membrane will be able to function and prevent what is entering and leaving the cell. However as the temperature increase the cell membrane loses this ability and the betalain pigments will start to seep though. At higher temperatures the cell membrane will be broken down more so there will be a greater release of the betalain pigment.

  • Predict the result of a test of the hypothesis to indicate the direction of the link

As the temperature increases the phospholipid bilayer and the proteins which make up the cell membrane become damaged. Therefore the cell membrane loses its ability to keep the contents of the cell inside. As a result the betalain pigment found in the vacuoles seeps through and causes red pigmentation. So therefore as the temperature increases the cell membrane itself becomes more permeable. So more pigment will be released, as a result as the temperature increase the percentage absorbance will also increase.

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A2: Plan a procedure

  • Using suitable equipment and apparatus, list the steps to be followed (there is no need to list apparatus unless unusable items are suggested)
  • Using a 5mm corer, core enough beetroot to make 45 specimens all 5mm in length.
  • Rinse all of the beetroot to remove any excess betalain.
  • Place 5ml of water into 3 test tubes measuring the water using a pipette.
  • Prepare the waterbath.
  • Place all three of the test tubes into the waterbath and regulate the temperature using a thermometer.
  • Place the beetroot discs into the test tubes.
  • Leave for 15 ...

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A very lengthy report dictated by a very rigid framework of imposed headings that were unquestionably very unhelpful. They interrupted the normal flow of information and led to considerable repetition. The writer has not always grasped the meaning of key words - reliability, accuracy and validity. A risk assessment was not carried out and control variables were given rather short shrift. In view of the absence of individual and class data, it is difficult to assess the validity of the overall investigation. Nonetheless, within the constraints placed upon the writer, this report reflects a very significant effort.