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The effect of concentration on catalase enzyme

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Prediction ? I predict that there will be a higher concentration of catalase in the animal tissue than in the plant tissue so the discs soaked in animal tissue extract will take less time to rise. This is because the tissue will contain an appropriate amount of enzyme to break down any hydrogen peroxide that it makes. As hydrogen peroxide is a toxic product of aerobic respiration, the concentration will be highest in the most rapidly respiring tissue. Muscle respires rapidly because it needs ATP to contract and liver respires rapidly because it carries out many complex biochemical reactions. The potato and celery do not need much ATP, so respiration rate is slower, catalase present will be less, so discs will take longer to float to the surface. Experimental design The independent variable is the type of tissue source and there will be 5 different ones including both plant and animal material. The dependant variable is the time taken (s) for a disc soaked in catalase to rise up through a solution of hydrogen peroxide. This is a measure of the time taken to produce enough oxygen to make the disc buoyant (less dense than water). ...read more.


Care will be taken when handling it and safety spectacles worn throughout. Any spills will be reported to the teacher and then cleared up promptly under supervision. Results Time taken for disc to rise to surface (s) Catalase source Rep 1 Rep 2 Rep 3 mean Potato 21 23 20 21.3 Celery 22 25 20 22.3 Thigh 20 20 19 19.7 breast 40 36 38 38.0 Liver 5 8 9 7.3 Trends The discs soaked in the liver extract rose to the surface in the shortest time with a mean of 7.3 s. The discs soaked in turkey breast took the longest time to rise to the surface with a mean of 38.0 s. Reliability There was overlap between range bars of results from the potato, celery and thigh tissues, hence the differences in mean are not reliable. Accuracy Some discs took longer to rise because they ?rubbed against? the side. Improvements 1. There is no temperature control, although it was monitored. If the tube of hydrogen peroxide were maintained in a 250C thermostatic water bath until just before the discs were added, it would be constant. ...read more.


Further Work In further work it would be interesting to explore how the time taken for discs to rise (dependent variable) changes with pH. The independent variable would be pH, changed using pH 5, pH 6, pH 7, pH 8, pH 9, pH10 buffers. The controlled variables would be: 1. The concentration of tissue extract (enzyme source) would be 25% 2. Volume and concentration of hydrogen peroxide solution (substrate) will be kept the same for each disc (20cm3 of the 2% solution) 3. The time that the discs were left in tissue extract was kept constant at 30seconds using a stopwatch. 4. Temperature ? the whole experiment will be carried out at 20oC in a thermostatically controlled water bath. 5. 5cm3 of each pH buffer solution will be used. Most body cells work best in a pH close to neutral, hence the time taken for discs to rise will be least at this pH. At a slightly lower or higher pH (6 and 8) the time taken for the disc to rise would be longer as the charges on active site and substrate will repel. At extreme pH the reaction may stop if ionic bonds break and the enzyme denatures. ...read more.

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