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Beetroot pigments

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Assessed Practical Plan I plan to investigate the effects of varying temperature on the movement of pigment molecules across a membrane, travelling out of beetroot cells. Aim: The aim of this investigation is to determine the effect that temperature has on the rate of diffusion of beetroot pigments when slices of beetroot are placed in various temperatures of water. Background Knowledge: The pigments found in beetroot are known as betalain pigments. Some areas of a beetroot may contain more pigment molecules than others. These molecules appear to be polar molecules as they are soluble in water. Molecules which have groups with dipoles are said to be polar. They are usually attached to water molecules. They also have dipoles, and these molecules are hydrophilic, and tend to be soluble in water. The process by which the betalain molecules leave the cell, can be explored by considering the following: * Simple Diffusion * Facilitated Diffusion * Osmosis * Bulk Transport * Active Uptake We can eliminate the possibility that betalain pigments travel by osmosis, since osmosis only involves the movement of water molecules, whereas in this experiment we are researching the movement of beetroot pigment molecules. Also, the possibility of the betalain pigments travelling through the membrane by active uptake or bulk transport can be discarded, as both of these processes require energy and ATP in moving molecules against their concentration gradient. Furthermore, simple diffusion is the movement of molecules through phospholipids. Therefore, this means the molecules must be lipid soluble and non-polar, and the beetroot molecules are not. ...read more.


After trying an experiment with 3 pieces of beetroot in each test tube, I decided to carry out one with only one piece in each tube and found out that the trend in results was easier to see and the colorimeter did not flash as the absorbance did not exceed 2 arbitrary units. I decided to time the experiment for 3 minutes and shook the test tube every 30 seconds. This increased the rate of diffusion enabling me to deduce a trend from the results. The test tube and its contents did not cool down, as I only took them out of the water bath every 30 seconds to shake them, and I replaced them promptly. As soon as the experiment was finished, and the 3 minutes had expired, I poured the solution into a curvette straight away, to eliminate the chance of further diffusion from the beetroot piece. This would decrease the accuracy of my results. Here is a table of my results collected during my preliminary investigation: Temperature (oC) Absorbance (Arbitrary Units) 20 0.31 30 0.45 40 0.69 50 0.91 60 1.31 Apparatus: Apparatus Number Size Justification Colorimeter 1 Measures the absorbance of particular wavelengths of light by a specific solution. Curvette 15 To pour the solution in and place in the colorimeter to analysis its absorbance. Test tube 15 To add the beetroot slices and the distilled water together. Test tube rack 3 To hold the test tubes securely while measuring out the distilled water. ...read more.


6. Rinse the beetroot discs by placing them in a beaker and adding tap water. This eliminates any pigment which has spilled out of the cut cells. Place the beetroot discs on the tile so that they are ready to use. 7. Select a test tube containing distilled water, of a chosen temperature, and using forceps, place one piece of beetroot inside. Start the stop watch immediately and shake the test tube once every 30 seconds. Ensure that any test tube in a water bath is put back while the experiment is taking place, this prevents the test tube or its contents decreasing in temperature and affecting the accuracy of the results. 8. After 3 minutes has passed, immediately pour the solution into a cuvette, to eliminate the chance of further diffusion. 9. In order to produce a control colorimeter reading, draw some water from the control test tube using a pipette, and transfer to a cuvette. Insert the cuvette into the colorimeter and obtain a reading, taking care to avoid touching the glass as much as possible, to reduce grease deposits on the glass as this may affect the colorimeter reading. The reading should be 0.00 arbitrary units. 10. Pour the solution from the experiment into another cuvette and measure the absorbance. 11. Repeat steps 7-10 until each of the temperature have been repeated at least three times. 12. Record your results in a table similar to the one below. Temperature (oC) Absorbance (Arbitrary Units) Mean absorbance (Arbitrary units) Repeat 1 Repeat 2 Repeat 3 60 50 40 30 20 Analysis of Results: 1. Find the mean absorbance at each temperature 2. Plot a graph, showing mean absorbance against temperature. ...read more.

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Here's what a teacher thought of this essay

3 star(s)

A good description of the experimental plan including results from a preliminary experiment. However, the author does not appear to have a clear grasp of variables and the background information about phospholipid membrane structure could be more detailed.

Marked by teacher Adam Roberts 05/09/2013

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