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The main task of this experiment is to find out the concentration/volume of glucose present in samples of three different fruits. The fruits are fresh grapefruit, lemon and orange.

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Introduction

Biology Practical Assessment Skill Planning The main task of this experiment is to find out the concentration/volume of glucose present in samples of three different fruits. The fruits are fresh grapefruit, lemon and orange. Here is a table showing the different items that are to be used in the experiment. It also states the quantity and concentration and volume of each apparatus if appropriate. Item Quantity Concentration and volume Colorimeter 1 N.A. Cuvettes 2 Hold up to 10mls Distilled water 1 bottle 16ml Graduated pipette 1 Holds up to 10ml Test tubes 8 Hold up to 27ml each Test tube rack 1 N.A. Hot water bath 1 N.A. Chinagraph pencil 1 N.A. Coloured pencils (A range of different colours) N.A. Benedicts Solution 1 bottle 320ml Glass rod 1 N.A. 4% Glucose solution 1 bottle Here is a table showing reasons for why the items listed were chosen and their application. Item Application Reason for choice Colorimeter To give absorbance readings for samples Most Suitable method of getting accurate, absorbance readings Cuvettes Used to put substances into, to put into colorimeter Standard apparatus used with the colorimeter Distilled water To dilute solutions Needed in the process of serial dilution to change concentrations of glucose 10ml graduated pipette To measure solutions accurately Most accurate and most suitable choice of measuring the solutions 8 x Test tubes To place solutions into Transparent, so it is easy to analyse the colour of the solutions for results, and has a suitable volume area to hold solutions Test tube rack To hold test tubes Sole purpose of test tube racks are to hold test tubes Hot water bath Maintain a chosen temperature This heats up the test tubes containing the solutions for reactions to occur Chinagraph pencil To label the ...read more.

Middle

This is resolved by using the pipette correctly. The glass rod will have to be cleaned after every time it has been used to stir solutions. This is as some solution could stay on the rod and when it is used to stir the next test tube, it could affect the solutions. Whenever I put a number of test tubes in to a water bath, I will place them in a rack, then place the whole rack in the water bath and on removing, remove the whole rack. This will ensure that all the test tubes have had the same amount of time in the water bath. To make an experiment valid, there should be a range of about 5-10 tests. Altogether in the whole experiment, there shall be eight tests conducted. These are made up of five tests of the serial dilution and the three fruit acting as unknowns. If care is not taken into when doing the experiment, the results obtained shall not be legitimate as they may be wrong. When actually reading the results, care will have to be taken of how they are read e.g. the highest reading on the colorimeter because the reading may not stay still. Measuring the solutions will have to be done properly with care. If the solution volumes tend to change and not be accurate of one test tube, the rest of the test tubes will be affected too. The water bath will have to set to exactly 100�C. the tubes should only be placed in the water bath when the water has reached 100�C and it should remain that temperature throughout. The graduated pipette is accurate as it is suitable for measuring small quantities. ...read more.

Conclusion

Using the same cuvette decreases chances of incorrect results as other cuvettes may absorb more light or may be thicker/thinner. 6. After each sample, rinse out the cuvette as this prevents the next sample being diluted more. Make sure the outside of the tube is dry before it is placed into the colorimeter. The following table shows all the quantities of the different solutions used in the experiment Test tube % Of Glucose Amount Of Distilled Water / ml Volume Of Glucose / ml Benedict's Solution / ml 1 4 0 4 40 2 2 4 4 40 3 1 4 4 40 4 0.5 4 4 40 5 0.25 4 4 40 6 Lemon 0 0 40 7 Grapefruit 0 0 40 8 Orange 0 0 40 The following shows the table that would be used when taking down the results of the three repeats (#1 being the first experiment and so forth). Concentration Of Glucose / % Absorbance Reading #1 Absorbance Reading #2 Absorbance Reading #3 4 2 1 0.5 0.25 Lemon Grapefruit Orange The following shows the table that would be used to show the average results of each glucose concentration. Concentration Of Glucose /% Average Of Absorbance Readings Notes 4 2 1 0.5 0.25 Lemon Grapefruit Orange When the average results have been calculated and been tabulated, a graph can be drawn. From the graph, conclusions can be made if there are any trends or patterns. From the graph, anomalous results can be pointed out and can be discussed to why these occurred. The dependent variable goes along the y-axis, which are the absorbance readings and the independent variable shall be along the x -axis, which is the glucose concentration measured in mg cm-3. This is the structure of the graph on which the results will be recorded. y-axis Absorbance x-axis Concentration of glucose mg cm-3 ...read more.

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