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Beetroot Experiment. The purpose of this experiment is to determine the effect of temperature on the permeability of cell membranes

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Introduction

2.1 Effect of Temperature on Membrane Permeability Abstract The purpose of this experiment is to determine the effect of temperature on the permeability of cell membranes. As beetroot cell contain a coloured pigment within the cell vacuole called betalain. The leakage of the coloured pigment betalain out of the cell will act as a maker to determine how permeable the cell membrane is at a particular time. To determine the permeability of the membrane uncooked beetroot cylinders will be bathed in water and exposed to different temperatures. The water in which the beetroot has been bathed in will then be measured for is absorbency. Here I demonstrate that there is a positive correlation between temperature and membrane permeability. Introduction Membranes consist of a phospholipid bilayer; this is two layers of phospholipids facing in opposite directions to each other. A phospholipid molecule is made up of a phosphate head connected to a lipid tail3. The phospholipid head orientates itself so that faces the external environment or inwards into the cytoplasm. The non-polar tails are hydrophobic and as a result face inwards to the centre of the plasma membrane4. Figure 1 shows the phospholipid bilayer arranged so that the hydrophobic (water hating) tails are orientated in the middle and the hydrophilic (water loving) heads are facing outwards from the cell1 The Plasma membrane is not rigid and in fact the phospholipid molecules are fluid in that they can move laterally and diffuse, the addition of cholesterol to the cell membrane improves the fluidity if the membrane. In addition to the phospholipids found in the membrane there is a large amount of protein present6. There are two major groups of proteins found associated with the plasma membrane. There are the proteins which are adjacent to the membrane known as peripheral proteins. The second group is the integral proteins which are embedded into the membrane7. Figure 2 shows the complex structure that is the plasma membrane. ...read more.

Middle

(Highest being 10 lowest being 1) Risk Probability Severity Being cut by glass/scalpel 7 6 Being scolded 7 7 Slipping/tripping 4 8 How the probability of these risks can be reduced Being cut by glass/scalpel- be extra aware of these dangerous objects, if glass is smashed get it cleared up safely immediately. Use a suitable cutting surface and cutting mat when using the scalpel and put a protective cover over the blade when walking with it. Being scolded- take care when around hot water baths and know where nearest cold tap is and make it easily accessible. Use tongs when collecting test tubes from the water baths. Slipping/tripping – before I start I will check the room and check there are not any obstructions on the floor (i.e. bags etc). If water is spilt on the floor I will make sure it is cleared up immediately so the floor is not slippery. Results Temperature (°C) Absorbance (from colour Chart) 1st Experiment 2nd Experiment Average 0 0.24 0.24 0.28 15 0.22 0.24 0.25 30 0.30 0.28 0.30 50 0.58 0.55 0.52 70 0.78 0.75 0.78 90 0.80 0.82 0.80 A mathematical calculation can be carried out on this experiment to see if there is a correlation between the temperature and one of the readings in the results; transmission or absorbency. If there is then it is possible to accept or reject our original hypothesis. For this calculation I will be using transmission, as it is an easier figure to use being larger, the average data will be applied to the calculation to get a more accurate result. The hypotheses remain the same from the main experiment found earlier in the report. Data Table: Spearman's Rank Correlation Experiment Temperature Rank temperature Average absorbance Rank Absorbance Difference between ranks (d) d² 1 0 1 0.28 2 -1 1 2 15 2 0.25 1 1 1 3 30 3 0.30 3 0 0 4 50 4 0.52 4 0 0 5 70 5 0.78 5 0 0 6 90 6 0.80 6 0 0 d² = 2 1. ...read more.

Conclusion

This makes any predictions on the results less accurate as you are using quite large temperature ranges. I would have liked to repeat each of the temperature results a third time as I believe that an N=2, is not very significant to base any finding on. I think a third set of results would have been more significantly valid. A major limitation is the actual manner in which the segments are obtained. Although I was careful in trying to obtain segments of the same size and cross sectional area they will never actually be the same. If the surface area of the segments differ only slightly this will have an effect (if only slightly) on the amount of Betalain that can leave the cell through diffusion. It would also have been a good idea to actually check this effect in other cells, from other species and plants and possibly animal cells (although the availability of such may have been limited and the practical methods to identify breakdown of the plasma membrane been difficult). I believe that having results form other species of plants would dramatically improve the accuracy of any conclusions made. Overall I believe that the results of this experiment are valid but there are several practical errors that limit the accuracy of the conclusions based upon it. Cold-induced leakage of amylase from the zymogen granule and sealing of its membrane by specific lipids 1. http://biologyatsmc.wikispaces.com/Cell+Membrane 2. http://www.colorado.edu/intphys/Class/IPHY3730/03plasmamembrane.html 3. Kimball's Biology Pages, Cell Membranes 4. Alberts B, Johnson A, Lewis J, et al. (2002). Molecular Biology of the Cell (4th Ed.). New York: Garland Science. ISBN 0-8153-3218-1. http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.section.1864. 5. Singer SJ, Nicolson GL (Feb 1972). "The fluid mosaic model of the structure of cell membranes". Science 175 (23): 720?31. doi:10.1126/science.175.4023.720. PMID 4333397. http://www.sciencemag.org/cgi/content/abstract/175/4023/720. 6. Lodish H, Berk A, Zipursky LS, et al. (2004). Molecular Cell Biology (4th ed.). New York: Scientific American Books. ISBN 0716731363. 7. Jesse Gray, Shana Groeschler, Tony Le, Zara Gonzalez (2002). "Membrane Structure" (SWF). Davidson College. http://www.bio.davidson.edu/people/macampbell/111/memb-swf/membranes.swf. Retrieved 2007-01-11. ________________ UCI 205340050507X Candidate Number 0507 NEC student number SS121598Page ...read more.

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This is a good account of the investigation. The discussion and evaluation are of a high standard with good use of A level terminology. In other places, however, there could be more attention to detail and more detailed explanations. The author does not seem to be sure how to identify independent and dependent variables.

Marked by teacher Adam Roberts 17/09/2013

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