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Biology Coursework: Investigation of How Ph Affects the Rate of Reaction of Catalase

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Introduction

BIOLOGY COURSEWORK: INVESTIGATION OF HOW PH AFFECTS THE RATE OF REACTION OF CATALASE Experiment Methodology These results were obtained using an altered methodology to the original plan. A quantity of sodium hydroxide or hydrochloric acid was added to a 5ml solution of hydrogen peroxide, to form a solution of a certain pH, which was tested by the digital pH meters (and universal indicator paper). The new method was using a test tube to carry out the reaction as usual, but instead using a delivery tube and bung connected to the reaction test tube and the other end that leads to an upturned test tube full of water. The amount of gas is then measured by timing how long it took until 10ml of water in the test tube was displaced by the output of gas from the reaction test tube. The gas produced is oxygen. There were no real safety precautions in this experiment, as it is considered safe using general lab protocol. E.g. the acid should be handled with care and washed off it spilt on hand etc. The accuracy of the results is to be increased by repeating the results at least 2 times. ...read more.

Middle

In acidic solutions of less than 5, the reaction rate appears to decrease very quickly over a short range, quickly tending towards a zero reaction rate. The same applies to pH's over 8, as the graph shows that the reaction rate decreased quickly also. There is one region where the time is relatively quick, between pH's 6 and 7, with the quickest reaction time at approximately pH 6.5-6.6. The causes for these changes will be due to changes in the tertiary structure of the catalase enzyme. Proteins contain amino groups that contain nitrogen and two hydrogen atoms. The nitrogen is electronegative, which means it pulls the electrons of the atoms in its covalent bond forming a -ve charge, and respectively a +ve charge on the hydrogen atoms. An example for a way for the pH to affect the structure of the catalase is with the aqueous hydrogen ions (H+) or the hydroxyl ions (OH-) being attracted to the charges on the atoms in the proteins, such as the amino acid group, or the carboxyl group which is situated after the amino group-carbon bond. When these atoms approach these charges, the charged protein atoms could be attracted to the hydrogen or hydroxyl atoms and break away from the protein. ...read more.

Conclusion

During the experiments there may be changes in the environmental temperature, which affect the temperature slightly. Aside from these two tweaks, the method seems accurate. The limitations of the apparatus used normally would be small. There is not much room for error in the use of the apparatus, except for where the bubbles are collected. The tube needs to be completely sealed so non of the escaping gas can escape and the delivery tube end must be placed directly in the upturned test tube else oxygen may escape. From the collected the results, the shape of the graph will not likely change, except may be shifted to one side as the pH meters may have been reading a lower or higher pH than the real one. Or it may be stretched as the pH meters have an accuracy rating of approximately + 0.01 pH units. This means that the points may be moved to one side or the other. The accuracy of the time is quite accurate, as it was + .1 of a second, which is for example 25 seconds is a very small percentage. The assessment on the conclusions made appears to be accurate given the similarity between the potato pH and the optimum pH. If the accuracy of the pH meters is + 0.1 then the readings can be considered the same given the error range. ...read more.

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Here's what a teacher thought of this essay

3 star(s)

***
Planning- To improve the full method would have to be included as well as more discussion of the key control variables in the experiment. The plan needs to include a justified prediction and a full list of equipment.
Obtaining Evidence A good range of experimental data was obtained in the first experiment. It would have been better to have carried out more replicates rather than carry out a second experiment using different control variables which could therefore not be compared with the first experiment.
Analysing Data The results were described well with a detailed description of the scientific theory behind the experiment.
Evaluation There are some suggestions made to improve the reliability of the method but it would have been helpful to consider other methods of collecting the gas e.g in a burette or using an upturned graduated cylinder which would have allowed the experimenter to record the amount of gas collected in a fixed time rather than wait for 10ml to be collected.

Marked by teacher Stevie Fleming 03/01/2013

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