Variables:
- Dependent = time that water needs to pass 5 cm in manometer tube, time
- Independent= pH of the buffers
- Controlled= size and number of potato discs, volume of buffers, distance of 5 cm, pressure, temperature, level of buffer in manometer tube
Method:
- Prepare Create buffers (Table 1)
- Cut cylinders of potato tuber.
- Cut 60 discs 1 mm thick and put them under water
- Construct the apparatus shown on the Drawing 1.
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Place 5 cm3 of buffer solution at pH 3.0
- Dry the potato discs
- Place 10 discs in the solution
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Add 5 cm3 H2O2
- As reaction starts, time how long does it take for the fluid to rise through the distance
- Open the clip at the top of boiling tube
- Repeat the test at same pH
- Do the same test at pH 4,5,6,7,8.
Observations:
It is important to shake the tube before repeating the test, so that enzymes will be equally distributed.
Drawing 1: The experiment
Uncertainties:
- Length of potato- 1 cm (each disc 0.1 cm times 10)
- Distance of tube- 0.1 cm
-
Volume of buffer- 0.1 cm3
-
Volume of H2O2- 0.1 cm3
Rounded to 2 decimal place
Rounded to 1 decimal place
Rounded to 1 decimal place
Using the formula
S – standard deviation
Σx – sum of value x
Σx2 - sum of value x2
n – number of readings
I calculated Standard Deviation of time for each pH.
Rounded to 1 decimal place
None of the data fits in 68% of the results, so I decided to exclude 2 of 6 trials to get a more reliable results.
Rounded to 1 decimal place
Rounded to 1 decimal place
Rounded to 1 decimal place
Using the formula , the standard error was calculated:
Rounded to 1 decimal place
Rounded to 1 decimal place
Next, I calculated the rate of reaction- I divided 100 by the average time taken for the water to travel distance of 5 cm.
Rounded to 2 decimal place
Graph 1: Average time taken for the hydrogen peroxide to be broken downand its dependence on pH.
Graph 2: Rate of hydrogen peroxide breakdown under the influence of catalase in different pH. Catalase its dependence on pH.
CONCLUSION:
The experiment prove the hypothesis correct. The optimum pH in which the catalase works the most efficient is pH of 7. This means that the closer the pH is to 7, the faster oxygen will be produced. The rate of reaction increases with pH up to 7 pH, when the activity is the highest, above this pH the rate of reaction decreases-the denaturation occurs (Graph 2). What is more, the higher pH, the less time is needed to produce oxygen. It also show how big influence on the activity of enzyme has pH. Still, the optimum is close to 7 pH, so the this enzyme can be efficient in living organisms.
The errors and inaccurate results may be caused by:
- Inaccuracy of equipment (ruler, manometer tube, clip)
- Potatoes of different kind
- Difference In thickness and size of potato
- Not exact amounts of substance
- Not mixed solution
- Not exact pH
- Different amount of enzymes in potato
- Not exactly dried potato discs
- Not exactly cleaned boiling tubes
- Lopsided apparatus
- Uneven apparatus
- Unclean syringe
- Leaky spring clip
- Imprecise clock
- Human reaction in measuring time
- Lack of organisation
To improve the result, I could:
- Follow the plan step-by-step
- Make more measurements to reduce the uncertainty
- Pick a potato of the same kind so the amount of enzyme is the same in each potato disc
- Be more precise when cutting a potato to have the same size of discs
- Check and use the equipment which isn't faulty
- Use the clock with measures time with more decimal places to decrease the uncertainty
- Make sure I do the experiment correctly by consulting the teacher or biochemical books
If the improvements I recommended were made, the results of the experiment would be more precise and accurate. Some of the errors were unavoidable, but some of them like human reaction or lack of organisation could be handled better and therefore avoided.
