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Nanye Osae-Asare BEETROOT REPORT PLAN The aim of the following experiment is to use beetroot to examine the effect of temperature on cell membranes and relate the effects observed membrane structure. Hypothesis I predict that upon heating beetroot to a certain temperature colour will leak out and give out a reading on a colorimeter. Scientific Background Beetroot is a vegetable which is used greatly in food making and an important ingredient in recipe books. It is usually recommended that you don't remove the outer skin of the beetroot and don't cut off all the stalk and root if you want to avoid getting lots of red dye in the cooking water. Beetroot contains red pigments called betalains, located within the cell vacuole. Normally the pigments cannot pass through membranes but they leak out when the beetroot is cooked or put in alcohol. The beetroot is protected by a cell membrane. The cell membrane functions as a semi-permeable barrier, allowing a very few molecules across it while fencing the majority of organically produced chemicals inside the cell. Electron microscopic examinations of cell membranes have led to the development of the lipid bilayer model (also referred to as the fluid-mosaic model). The most common molecule in the model is the phospholipids, which has a polar (hydrophilic)
2 boiling tube racks 9. Crushed ice 10. 8 Boiling tubes 11. Thermometer(one per water bath) 12. Colorimeter to measure amount of colouration produced. 13. Cuvettes 14. Stop clock 15. Distilled water 16. Pipettes for measuring 2cm3 and 5cm3 17. Small measuring cylinders. Procedure 1. Cut sections from a single beetroot using a size 4 cork borer. Cut eight, 1cm length slices from these sections. Be careful not to spill beetroot juice on skin or clothing since it stains very badly. 2. Place the slices in a beaker of distilled water. Leave overnight to wash away excess dye. 3. Next day, place eight labelled boiling tubes each containing 5cm3 distilled water into water baths at 0oC, 10oC, 20oC, 30oC, 40oC, 50oC, 60oC and 70oC. Leave for 5 minutes until the water reaches the required temperature. Place one of the beetroot sections into each of the boiling tubes. Leave for 30minutes in the water baths. 4. Decant the liquid into a second boiling tube and remove beetroot sections using a technique that does not squeeze the slice e.g. spear with a pointed seeker. Shake the water/solution to disperse the dye. 5. Switch on the colorimeter and set it to read % absorbance. 6. Set the filter dial to the blue/green filter.
Colorimeter reading was lowest at 0oC 4. There was a significant rise in colorimeter reading from that at 50oC and 60oC. Explanation for results 1. Colorimeter reading stood for the amounts of betalain solution that passed through the cell membrane of the beetroot. As temperature increased, so did the size of pores in the membrane which allowed more and more betalain to escape from the cell. This supports the fact that temperature and colorimeter reading was directly proportional. 2. At 70oC the pores in the beetroot's were open the widest allowing the most betalian solution to leave the vacuole through the cell membrane. This explained why the colorimeter reading was highest for the beetroot tat was heated in the 70oC water bath. 3. At 0oC, the low temperature causes the pores to constrict and less amount of betalian solution is allowed to pass through the cell membrane. Since less amount of betalain is allowed to pass through, this means that colorimeter reading will be low. The results show that this was indeed the case. 4. From 0oC to 40oC, the molecules of the betalin solution possess relatively the same amount of energy. From 50oC betalin molecules have acquired a greater amount of energy and are free to move. This combines with the effect of temperature on the cell membrane pores to allow a greater than usual amount of betalin solution to leave to cell via the cell membrane. Evaluation 1.
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Here's what a teacher thought of this essay
Overall, this report of an investigation into the effect of temperature on the permeability of biological membranes is well-structured with a fair degree of supporting theory. Most of the key areas are covered in a logical order allowing the reader to follow the scientific process. There are, however, a number of weaknesses that would need to be addressed before submitting this as A'Level coursework.  The hypothesis needs to refer to the relationship between IV and DV;  The introduction needs to be wholly focused on the area of biology under investigation - membrane structure and effect of heat on permeability;  Control variables need to be discussed in full with the aim of increasing the validity of the results;  The results themselves need to be discussed in the light of sound biological facts with references to previous work by other biologists on the same hypothesis.
Marked by teacher Ross Robertson 15/04/2013
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