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Investigate the effect of enzyme concentration on the activity of catalase in potato tuber cells on hydrogen peroxide measuring the time taken to produce 5 ml of oxygen produced to determine the rate of reaction.

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Introduction

Aim: - To investigate the effect of enzyme concentration on the activity of catalase in potato tuber cells on hydrogen peroxide measuring the time taken to produce 5 ml of oxygen produced to determine the rate of reaction. Method: - 1. Set up apparatus as shown in the diagram below. 2. Using the measuring cylinder add 50 cm3 20vol. hydrogen peroxide solution into the conical flask. 3. Use the cork borer to bore several cylinders from the potato all of equal thickness. Cut the potato cylinders into a length of 4 cm (ensure there is no potato skin present). You will need to cut 45 potato cylinders in total. Make sure you cut all the potato cylinders with the same cork borer and measure the diameter of the potato cylinder to work out the surface area. 4. Ensure your apparatus is set up correctly, that the graduated cylinder is inverted and full of water and placed over the end of the rubber tubing, and your stopwatch and table are ready to record your results. 5. Place one cylinder of potato into the conical flask containing hydrogen peroxide and immediately seal the top tightly with the rubber bung. 6. Holding the graduated cylinder vertically, record the time it takes for 5ml of water to be displaced from the inverted measuring cylinder by the oxygen produced. Only start your stopwatch when the first bubbles appear in the cylinder. 7. Repeat the experiment an additional potato cylinder to the flask each time until 5 cylinders have been used at once. Use fresh hydrogen peroxide each time. 8. Repeat the whole experiment 3 times. Apparatus: - Safety: - When using scalpel and cork borer you need to take care. Hydrogen peroxide is an oxidant, and needs to be kept away from heat. It can be an irritant or corrosive at strong concentrations, so care is needed with the 20vol. ...read more.

Middle

These predictions match my results, which shows the experiment was good. Though our experiment was good there are still some main sources of errors in the experiment, which didn't allow us to get perfect results. I am going to discuss them all and give reasons for how they might affect the results and ways of improving the error. Controlling temperature is a main source of error. As temperature increases, enzyme and substrate molecules gain more kinetic energy and move faster. In an enzyme catalysed reaction, such as the decomposition of hydrogen peroxide, temperature increases the rate at which the enzyme and substrate molecules meet and form enzyme - substrate - complexes and therefore the rate at which the products are formed. As the temperature continues to rise it will eventually reach its optimum temperature, however if it goes above its optimum temperature, the hydrogen and ionic bonds, which hold the enzymes tertiary structure will brake and the enzyme will unfold and the active site will be lost. This means molecular structure is disrupted, the enzyme ceases to function, as the active site no longer is able to accommodate the substrate. The enzyme is said to be denatured but this did not occur in my experiment. The rate and time could have been affected because the room could have heated up as we did our experiment meaning the rate could have increased and the time could have decreased. To control this variable, the temperature should be maintained at a fairly constant level that allowed the enzyme to work effectively (room temperature, approximately 23�C). This can be achieved by using a test tube rack and tongs to handle the apparatus so that the heat from my hands does not affect the Catalase or substrate. This is because my body heat could raise the temperature, increasing the rate of reaction. You can also monitor the temperature by using a thermometer to ensure that it remains constant and does not disrupt the results of the experiment by affecting the activity of catalase. ...read more.

Conclusion

Range for the varying potato pieces: We are working out the range because it is a good measure of the average. It reduces the problem of extreme values and can be used to work out the uncertainty. 1 potato piece - 105, 85, 104 therefore range = 105 - 85 = 20 This number is big but not that big to consider this result to be an anomaly. 2 potato piece - 47, 33, 38 therefore range = 47 - 33 = 14 This number is not that big and shows the result not to be an anomaly. It also shows that the values are quite accurate. 3 potato piece - 28, 28, 25 therefore range = 28 - 25 = 3 This number clearly shows that the results are very accurate. 4 potato piece - 16, 15, 13 therefore range = 16 - 13 = 3 This number clearly shows that the results are very accurate. 5 potato piece - 10, 11, 11 therefore range = 11 - 10 = 1 This number clearly shows that the results are extremely accurate. The range shows that were possible anomalies with 1 and 2 potato pieces but with the results that were calculated this anomaly is not enough to affect pattern or results. Percentage uncertainty: We are working out the percentage uncertainty because it tells us the amount of error in the experiment and to check how valid our results were. A table to show the range, uncertainty and percentage uncertainty of the time taken to collect 5 ml of O2: - Number of potatoes/surface area of potatoes. (cm2) Range (seconds) Uncertainty =range/2 (seconds) Percentage uncertainty % =(uncertainty/median) x 100 1/17.34 20 10 11 2/34.68 14 7 18 3/52.02 3 1.5 6 4/69.36 3 1.5 10 5/86.70 1 0.5 5 Average % uncertainty = 10 At the end of my experiment my % uncertainty was 10. This is low enough to accept my results are valid and to say my conclusion is valid. So the errors discussed above are not significant enough to have affected my results and made my conclusion invalid. ...read more.

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