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Biology AS Planning Exercise Jan 08.

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Introduction

AS Planning Exercise. The ripening of a banana produces reducing sugars. Initially, in an unripe banana there are a lot of starch grains present. However, as the banana ripens the starch will be converted into sugar. As this is an enzyme controlled process, temperature will be a significant factor and therefore I will be investigating the effect of temperature on the ripening of a banana. I will do this by measuring the amount of reducing sugars in excess Benedict's solution that has been reacted with banana filtrate. Prediction As the temperature increases up to 45oC the rate of ripening will increase. When it exceeds 45 oC the rate of ripening will decline. Explanation The ripening of a banana is enzyme controlled. The enzymes involved are amylases and maltases. Enzymes are globular proteins which have a tertiary structure. The active site is by far the most important part of the enzyme because it comes into contact with the substrate. The shape of the active site is specific to the substrate molecule. ...read more.

Middle

Smear slice of ripe banana onto a slide 3. Place a drop of iodine solution on the slide 4. Cover the slide with a cover slip 5. Place the slide under a microscope at low power. Adjust by increasing the power and focusing until banana cells are visible 6. Count the number of starch grains in 20 cells 7. Repeat this procedure using an unripe banana slice This method (counting starch grains) proved to be very unreliable. It is extremely easy to lose count of the number of starch grains as they are all lying on top of each other which may mean that the some of the starch grains may be counted more than once or missed. Therefore I will be reacting banana filtrate with excess Benedict's. Apparatus Banana Scalpel Balance Thermostatically controlled water bath Blender Filter paper Filter funnel 10cm3 Excess Benedict's solution Beaker Foil Cover Sticky labels Colorimeter Measuring Cylinder Method 1. Using a scalpel cut a banana into 9 50g slices. Weigh to ensure that they are the correct mass. ...read more.

Conclusion

A colorimeter works by measuring the amount of light absorbed by the solution. This is a superior method as opposed to using judgement because there may be individual differences in judgement of colour, particularly if the individual is colour blind. After the initial set of experiments have been conducted, a further series of experiments will be carried out. These will be using intermediate temperatures around the result obtained in the initial set of experiments. This will enable me to determine the exact temperature at which the rate of ripening is at its peak. Reliability of Results Each individual experiment will be carried out 4 times. This will increase reliability as any anomalies will be apparent and so can be disregarded. Table of Results Temperature (�C) Transmission of Benedict's Filtrate (%) Expt 1 Expt 2 Expt 3 Expt 4 Mean 25 30 35 40 45 50 55 60 65 Graph To Show the Effect of Temperature on The Ripening of A Banana. Validity of Results A problem with this method is that the Benedict's measures other reducing sugars such as fructose and galactose which are not involved in the ripening of a banana. ...read more.

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