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Testing the biochemicals present in apple and green bean using specific chemical tests.

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Introduction

Biology Experiment Report Aim: To identify the biochemical and compare their contents in apple and green bean using specific chemical tests Principle of method: Carbohydrates, proteins and lipids are the major organic constituents of organisms. Thus they are often called biochemicals. The specific tests for reducing sugar, starch and protein are Benedict Test, Iodine Test and Biuret Test respectively. Before a specific chemical test can be carried out, it is necessary to extract juice from the tissue under investigation. Extraction method is very common in biological investigation. 1. Benedict's test for reducing sugars Benedict's solution contains copper sulphate. Reducing sugars reduces copper(II) ions present in the blue copper sulphate solution into insoluble brick-red copper(I) oxide which is a precipitate. Note. The initial blue colouration of the mixture turns green, then yellow and may finally form a brick-red precipitate. The final colour and amount of precipitate gives a rough indication of the amount of reducing sugar present. 2. Iodine test for starch Iodine solution is a mixture of iodine and potassium iodide solutions. Starch combines with iodine to give the characteristic of blue-black colour. ...read more.

Middle

Apple Brown Remain unchanged Absent Green bean Yellow Remain unchanged Absent The results of the Iodine test of the above two plant materials samples Plant materials Initial colour Final colour Is the protein present of absent? Apple Brown Remain unchanged Absent Green bean Yellow Yellow solution with purple colour precipitate (~1/4) Present The results of the Biuret test of the above two plant materials samples Discussion: From the result of the Benedict's test, the mixture of apple juice and Benedict's solution changed from light blue to brick-red colour. It showed a positive result which means that reducing sugar was present. For the mixture of the green bean extract and Benedict's solution, there was no any change in the solution. Solution remains in blue colour. It showed a negative result which reflected that reducing sugar was absent in green bean. From the result of the Iodine test, the mixture of apple juice and the iodine solution remained brown in colour. It showed a negative result which implied the absence of starch in the apple. While the mixture of the green bean extract and iodine solution had a positive result, which the solution turned from brown to blue-black colour. ...read more.

Conclusion

To improve the test, iodine solution should be added into the bean and a slice apple. The result could be obtained immediately and even a little amount of starch in apple could also be detected by a colour change. Reducing sugar is present in the apple because the sugar can attract insects for the pollination. Starch and protein are stored inside the bean as the nutrients that should be provided for growth of a plant. This experiment also has some problems. First is the incomplete extraction, we need to extract several times by adding water to the residue and filter again. Second is the insufficient grinding, we should grind for a long time, or use a blender instead. For sufficient extraction of starch, we may boil the foodstuff before grinding. Then the result of this experiment can be more accurate. For further investigation, we may investigate the vitamin C content in fruits by using DCPIP solution. During the experiment, we can test how many drops of example is required to decolorize a specific volume of DCPIP solution. The less drops of the juice to turn this solution colourless, the higher the concentration of vitamin C in the solution. Conclusion: Apple contains reducing sugars but there is no starch or protein inside. Green beans contain starch, protein but no reducing sugar. ...read more.

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This account is detailed and shows a clear understanding of the chemical basis for the tests carried out. A few minor details might have been better explained.

Marked by teacher Adam Roberts 26/04/2013

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