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Investigation on a ripening banana to indicate the biochemical changes to make it sweet.

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Introduction

Biology Laboratory Report 3 Date of experiment: 25/11/2010 Title: Investigation on banana to indicate the biochemical changes to make it sweet. Objective: This investigation is to account for the biochemical changes taken place in the banana during the storage period which causes the appearance of sweetness and to test the hypothesis with iodine test and Benedict's test. Biological principle: In iodine test, the I3- ion in the iodine solution would be trapped in the centre of the helical starch molecules to from a blue-black polyiodide complex. Thus we can observe a turn of color from yellow to blue-black if starch is present. Therefore, we can add in iodine solution to the sample solution so that we can account that starch is involved in the biochemical change. In a Benedict's test, the reducing sugar reduce soluble blue copper (II) sulphate in the Benedict's solution to form insoluble red-brown copper (I) oxide, which is a precipitate. Thus, we can add in Benedict's solution to the tested samples to account for any reducing sugar and conclude that reducing sugar is involved in the change. Hypothesis: The biochemical changes is starch was broken down to a certain kind of reducing sugar. Prediction: The banana stored for 1 day should show positive result of iodine test and negative result of Benedict's test, while the banana stored for 3 days should show positive result of iodine test and positive result of Benedict's test. ...read more.

Middle

This is to ensure the variation of the results in different setup in only due to the independent variable, but not other environmental factor. (e) Precaution (I) Benedict's test for reducing sugar -Wear safety spectacles. - Use Water bath for heating process, avoid direct heating. - Before lighting Bunsen burner, check that the gas tubing is properly connected, and ensure that the gas top being turned on is the one connected to the burner to be lightened - During heating, point the mouth of the test-tube away from anyone, including ourselves. (f) Diagram of experimental setup (g) Explanation of the control setup Control setups: Glucose solution, distilled water It can be used to show the negative result and compare with the result in the experimental setup, which help proving the result is due to the chemical but not other factor Results 1 Day 3 Days 5 Days Distilled water Iodine test--- Results Blue-black spots formed Blue-black spots formed Blue-black spots formed Remain yellow Amount of Blue-black spots formed +++++ +++ + -- Conclusion Many starch is presence in the solution Starch is presence in the solution Little starch is presence in the solution Starch is not presence in the solution Benedict's test--- Results Blue-green solution with brick red precipitate Green solution with brick red precipitate Red solution with brick red precipitate Remain blue solution with no precipitate Amount of precipitate formed + +++ +++++ -- Conclusion Little reducing sugar is presence in the solution Reducing sugar is presence in the solution Many ...read more.

Conclusion

This error shows the limitation of this experiment, which is we can not test for extract of raw substances since they will still be cooked in the heating stage of the Benedict's solution and this error can not be avoided. For the case of banana stored for 5 days, this may because the ripening process is still taking place in the banana. The starch stored in the banana has not been completely broken don into sugar, thus starch can still be found in the extract, which causes the formation of the blue-black spot. This error involving the prediction can be avoided if we make a relative prediction in steed. For example, we can make the prediction by comparing the results, like: "The banana stored for 1 day should show a more positive result of iodine test and more negative result of Benedict's test than the banana stored for 3 days." Thus a more objective prediction can be made. Further experiment can be hold to test the exact type of reducing sugar present in the solution. For example, Clinitix paper to test for glucose. Conclusion In conclusion, the biochemical changes involved is starch was broken down to a certain kind of reducing sugar, which is probably glucose. Yet a more accurate result can be carried out with a further experiment. Though the hypothesis can be supported by this experiment, due to the limitation of this experiment, the result on some samples are out of expectation. Therefore, improvements on this experiment are needed. ...read more.

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