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Investigating the breakdown of hydrogen peroxide using celery tissue to supply the enzyme catalyst

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Introduction

Investigating the breakdown of hydrogen peroxide using celery tissue to supply the enzyme catalyst Variables * Amount of celery * Concentration of celery, more or less watered down. * Concentration of Hydrogen Peroxide (H202) * The amount of H202 * The temperature of H202 I am going to vary the concentration of the hydrogen peroxide. I think that varying the concentration of the liquid will be the best experiment to do and will hopefully give a strong set of results, which will enable me to obtain clear conclusions. Prediction The rate of an enzyme- controlled reaction depends on the temperature, pH, and concentrations of the enzyme and its substrate. The more enzyme molecules produced by a cell, the faster the reaction will proceed. Similarly, an increase in the substrate concentration will speed up the reaction if there are enough enzymes molecules to cope with the additional substrate. Therefore by diluting the hydrogen peroxide with water, this will decrease the rate of decomposition of the H202, and the less gas will be given off. The enzyme in the experiment is catalase. Hydrogen peroxide is poisonous and the catalase works to render the hydrogen peroxide harmless by breaking it down to water and oxygen. If the concentration of H202 is less, then there is more water present, and there are less hydrogen peroxide molecules, so there is less for the catalase to render harmless, so less H2O and O2 is produced. ...read more.

Middle

To make this easier the gas burette will be clamped in place, so it doesn't have to be held. Safety * Eye protection must be worn as H202 is being used, and can cause serious damage to the eye. * Care must be taken when using knives to cut up the celery. * Bags must be tucked under the benches as they may cause an accident. Method * The apparatus was set up as shown in the diagram * 35grams of celery was cut up and mixed with 20cm3 of water, which was blended for 1 minute. * 10cm3 of the celery mush was then placed in a conical flask * The gas burette was filled with water and clamped in place over a bath of water * 10cm3 of the hydrogen peroxide (in whatever concentration) was added to the celery * The stop clock was started * As quickly as possible, the bung was placed in the top of the conical flask and the delivery tube angled so that the gas would be directed up the burette. * After 30 seconds the stop clock was stopped * The amount of gas collected was noted, by reading the scale on the gas burette. * Each concentration was repeated three times to confirm the validity of the data and so an average can be made. Results Ratio of hydrogen peroxide to water (cm3) ...read more.

Conclusion

If I were to carry out the experiment with the hydrogen peroxide at different temperatures, my prediction would be that the higher the temperature, the more gas would be given off. This is because, to make reactions work between the enzyme and H202 there must be a certain amount of force to combine them together, they have to collide to set the reaction off. The total kinetic energy of the reactant molecules must be at least as big as the activation energy. So if the H202 was heated up, the kinetic energy would be larger, so there will be more chance of collisions, so the overall reaction would occur faster. This is true up until a certain point. As enzymes are specific, they work best between a small range of temperatures. If the temperature is too high, then the enzymes are denatured, they change shape and they can no longer combine with the substances. I could also extend the concentration experiment further by looking at the quote " an increase in the substrate concentration will speed up the reaction if there are enough enzyme molecules to cope with the additional substrate." As I put in my analysis, in my experiment there were enough enzyme molecules, but I could do an experiment to find out the specific concentration where the concentration is too high for the enzyme molecules to cope with. Jo Waddell 11M Page 1 5/2/2007 ...read more.

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Here's what a teacher thought of this essay

4 star(s)

This is a good essay that discusses the break down of hydrogen peroxide. The method is clearly laid out and there is a good analysis of the results.

There are areas of discussion about enzymes that are valid and correct but it is lacking in the finer detail. At A level, I would expect more scientific discussion regarding tertiary structure but the writer may not have covered that area. If you were looking for reference to discuss enzymes and rate of reaction - this would seem a good practical to use and build up the explanation.

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Marked by teacher Sam Morran 08/01/2013

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