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Beetroot membrane

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Why does the colour leak out of cooked beetroot? Aim: The aim of the practical was to use beetroot to examine the effect of the temperature on cell membranes and to relate the effects observed to membrane structure. To function correctly, a cell needs to be able to control transport across the partially cell membrane. The betacyanin pigment (red pigment) is located in the cell vacuole of beetroot cells. If the cell membrane is destroyed (phospholipid bilayer + proteins), leakage (diffusion) of betacyanin is induced. Hypothesis: My hypothesis for this experiment is that more betacyanin pigment will leak out as temperature increases. This is because a higher temperature will cause the pigment molecules to vibrate at a higher frequency and move at a quicker speed, causing them to move out of the cell membrane into the water, making the water appear darker, causing a higher mean colour absorbance reading on the colorimeter. Variables: Independent variable - the temperature of the water in the water bath. ...read more.


- 1. Some water may have evaporated in the 60 oC and 70 oC. This would have caused a higher colour absorbance reading due to the fact that pigment was concentrated into less water. 2. All the excess dye will not have been washed away, causing a higher colour absorbance reading. 3. Some of the pigment may have settled out in the cuvette, giving a lower absorbance reading if the light was shining above the precipitate. 4. The beetroot sections may not have been exactly the same length causing variations in the colorimeter reading. If the beetroot was only half an mm longer or shorter that would be thousands of more beetroot cells containing betacyanin. The beetroots may have also had different concentrations of betacyanin pigment. 5. The boiling tubes would not have been in the water bath for the exact amount of time due to the fact that it would be impossible to take out every tube at exactly 30 minutes. ...read more.


Due to spillages, we were unable to obtain results from the 10�C and 20�C water baths. 2. The results have proven my hypothesis correct. The increase of temperature did cause an increase in colour absorbance. Discussion: The increase in colour absorbency can be partially explained using the kinetic theory. When the beetroot molecules are heated in the beetroot, they vibrate and move faster. This then makes the phospholipid bilayer (part of the cell membrane) spread out, exerting a higher pressure on the cell membrane, causing the betacyanin pigments to spill out. The lipid structures in the phospholipid bilayer also become more fluid at higher temperatures, creating a fragile and more porous membrane. The effect of heat on beetroot will also affect the proteins spanning the cell membrane. When heated, the proteins will untangle and break apart because of the vibrations associated with the kinetic theory. This will then form holes in the membrane, damaging the structure of the membrane, leaking the betacyanin pigments out from the cell vacuole. If I had more time, I would have tested the beetroot using different pH solutions and also have taken more readings. ...read more.

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Here's what a teacher thought of this essay

3 star(s)

I have awarded this piece 3 stars because it contains a well written method and some consideration of the key variables. The investigation lacks an in depth introduction which is missing some key facts about the breakdown of membranes with temperature. There are some results missing (due to lab spillages) and the analysis of results is too brief. There is no experimental evaluation of the reliability of the results or the experimental method.
To improve:
A testable hypothesis was formulated but this could be improved by making this quantitative rather than qualitative. The biological knowledge used to explain the prediction was weak. The inclusion of background research would help. The attempts to assess safety are rather superficial.
The data was recorded in a suitably headed table but there was no inclusion of repeats or class data. If all the results were obtained it would have been an acceptable range.
Analysis and Evaluation
The choice and plotting of the graph was good but the graph's points should be joined with straight lines and not a smoothed curve. The explanations were sound and related to fairly basic biological knowledge. The trends could have been described and related to the background theory a little more clearly.
There was no evaluation of the results or method and this would lose marks in an examination piece of coursework. The candidate should discuss suggestions for improving the method and reliability of the results.

Marked by teacher Stevie Fleming 29/05/2013

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