How enzymes work
An enzyme is a biological catalyst, which is used to speed up the rate of a reaction so less energy is needed, and it is not used up in the reaction. Some enzymes facts:
- Enzymes are large molecules
- Each enzyme has its own special shape
- The reactants fit into the enzyme like a lock and key
- Enzymes work best at their optimum temperature (40°C)
- Enzymes work best at their individual optimum pH
- They are found in our parts of our body, and are used in chemical reactions, which occur inside of us. Our body temperature is 37°C, which is very near the optimum temperature, making our bodies perfect for enzymes to work.
- The reactant slots into the enzyme at its active site. The diagram below shows how this happens:
So when the reactant (hydrogen peroxide) slots into the catalase molecules, the catalase breaks it down to from water and oxygen particles.
Prediction:
I predict that as the concentration increases, so will the amount of oxygen formed and the height of foam within my chosen time. The reason I think this is because as the concentration increases, so do the number of hydrogen peroxide particles in the same volume. For a reaction to occur, particles must collide together, so if there are more hydrogen peroxide particles, it means there are more successful collisions with the catalase molecules. Therefore making the reaction happen faster and produce more oxygen and foam in the same amount of time. If the concentration decreases, then the amount particles do too, so it would take longer for them to collide with the same number of catalase molecules and they would therefore produce less oxygen and foam.
I predict the end result will look like this:
In my trial experiment I decided to use 10 cm³ overall because any more than that would not allow much space for foam to be formed. I decided on four different concentrations: 100% = 10 cm³ of hydrogen peroxide
75% = 7.5 cm³ of hydrogen peroxide
50% = 5 cm³ of hydrogen peroxide
25% = 2.5 cm³ of hydrogen peroxide
I will dilute the hydrogen peroxide with water.
I tested the highest and lowest concentrations to see how long it would take to produce foam and oxygen, so I could set the time I would stop at and take the measurements. From the results of my trial experiment, I decided that an appropriate time to leave the reaction going for is 5 minutes. Within this time, the one with the 25% hydrogen peroxide can produce a readable volume of oxygen and foam, and the one with 100% hydrogen peroxide can produce enough without the foam overflowing. I also decided to use 3 cm cylinders of potato and only one piece in each test. To make my test fair I will repeat it THREE times so I have more raw data to compare.
Method:
Equipment –
- 16 test tubes
- Test tube rack
- Stickers (to mark the test tubes so you don’t get them confused)
- 2 measuring cylinders (one to measure the hydrogen peroxide and water, and one to measure the amount of oxygen collected)
- Potato (keep the same one throughout the whole experiment)
- Cylinder shaped potato cutter (to make sure the cross section of the potato is the same each time – this along with keeping the same length will ensure the surface area of the potato is constant throughout the experiment. The same cutter should also be used)
- 2 beakers (one to keep the hydrogen peroxide in and one to keep the water in which should be a room temperature)
- Knife (to cut the potato with)
- Ruler(to measure the potato and foam with)
- Stopper with delivery tube (to stop any oxygen from escaping and directing it to the right place)
- Washing bowl
- Clamp stand (to hold up the cylinder
- Stop watch (to time the experiment)
- Thermometer (to measure the temperature of the room and the hydrogen peroxide with water)
Safety –
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Goggles and gloves must be worn when working with hydrogen peroxide – it has too many oxygens, which it tries to get rid of, which will burn your skin and eyes.
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Mark the beaker with hydrogen peroxide in it (with a sticker) – incase you touch it without knowing.
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If hydrogen peroxide spills onto your hand, you must wash it under water quickly
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Arrange apparatus as shown above
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Measure out the hydrogen peroxide and water into correct parts using a measuring cylinder then pour into test tube and measure the temperature (the temperature of the water should be room temperature)
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Using the cylinder shaped potato cutter, get some potato and using the knife cut it to 3 cm
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Now add the potato piece in the hydrogen peroxide (and water) and put the stopper in place. Remember to start the stopwatch at this point
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After 5 minutes, measure the height of foam and take note of the volume of oxygen collected. Write the results in your table.
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Repeat with the other concentrations, then repeat all four concentrations 3 times to ensure it is a fair test.
I will record my results in a table:
Diameter of cylinder cross section = 5 mm
Radius (r) = 2.5 mm
Height of cylinder (h) = 3 cm = 30 mm
Surface area of a cylinder = 2лrh+2лr² = [2 x л x 2.5 x 30] + [2 x л x 2.5²]
= 471.2 + 39.3
= 510.5 mm²
= 51.05 cm²
Obtaining Evidence
I have also decided to include a rate of reaction table and graph:
Analysis
My graphs show me that my prediction was right, that as the concentration of hydrogen peroxide increases so does the volume of oxygen collected and height of foam in the same amount of time (5 minutes). I completed the experiment 3 times all in the same conditions and using the same potato to ensure it was a fair test, and also give me a range of results to work from. My first three graphs show the results for the volume of oxygen collected and the height of foam made against the concentration for EACH experiment. Each graph shows a positive correlation, which proves my prediction. By looking at my raw data and my graphs, I can see that my results were very similar and sometimes the same in two or more experiments. In all the results, there is a pattern of approximately 0.5 cm³ between each concentration reading for both the volume of gas collected and the height of foam. There were however some results which do not fall into this pattern, but they are not far out. For example,
This shows that as the concentration increases by 25% the difference between each reading is approximately 0.5 cm³. There is one factor that all of them have in common, which is that the volume of oxygen is always more than the height of foam produced. The differences range from 0.4 cm³ and 0.9 cm³. For example,
This shows that as the concentration increases by 25% the difference between the volume of oxygen and the height of foam is also approximately 0.5 cm³. By looking at the first three graphs, I can tell that experiment 1 gave the results with the most definite pattern, as the lines of best fit for both the volume of gas and height of foam are almost parallel, whereas in the other two, there are a few (more) obvious anomalous results which do not fit into the line of best fit. Most of these anomalous results were in the 75% concentration, which was 7.5 cm³ hydrogen peroxide, and 2.5 cm³ water.
When I predicted what my graph would look like, I thought the curved line of best fit would show a positive correlation and I was right, but it is not straight from 0. At 0% concentration, nothing happens because there is no hydrogen peroxide for the catalase to react with, so whatever results I obtained for 25% concentration, the line of best fit jumped directly to that result, then curved to the angle of the next point (50%).
My fourth graph is my ‘averages’ graph, for all three sets of results. This also has a positive correlation, and is very much like the other three because the results were all very similar. Both lines again run almost parallel to each other, and just like the previous graphs, the difference between the readings is approximately 0.5 cm³. For example,
And,
My last graph shows the rate of reaction. I decided to include this, as it will help me explaining the science behind it all. I only used the average results for the volume of oxygen collected to get the readings for this graph. The graph shows that as the concentration increases, so does the rate of reaction. This is because there are more hydrogen peroxide particles in the same volume, which means there is more chance for successful collisions to occur with the catalase molecules. This makes the reaction faster and means that more oxygen and foam is produced in the same time (5 minutes) than there would be if there was a low concentration. When the hydrogen peroxide particles collide with the catalase molecules, the hydrogen peroxide particle slots into the catalase molecule’s ‘active site’, where the enzyme (catalase) breaks the reactant (hydrogen peroxide) into water and oxygen. The more particles there are, the more it can occur meaning more product is formed quicker. My ‘rate of reaction’ graph shows that as the concentration increases by 25%, the rate of reaction increases by approximately 0.001 cm³/second.
Evaluation
The procedure I used to carry out this experiment was fairly accurate. I kept the ‘constants’ (as shown in my plan) constant and each experiment was left untouched so that all the results were valid. However, I feel I still could have improved on my method. I could have weighed the potatoes to make certain they were the same weight, which they should be because I used the same size for each one and the same potato throughout my whole experiment. If I were to do the experiment again, I would make sure I do this, and also to make my results even more accurate, I could have taken note of the volume of oxygen and height of foam at more regular intervals such as every 30 seconds. This would help me get a more precise set of results and graph and I would be able to see each stage of the reaction more clearly, which would have helped my analysis a bit more. This is not a major drawback though, and the results I did get a good and what I expected.
The results I got fit the pattern I predicted well even though there are a few anomalies. The main anomalies are in the 75% concentration but they are not too far out of the line of best fit. For example, in the ‘averages’ graph, the volume of gas collected at the 75% concentration is only 0.2 cm³ more than the 50% concentration, but has a bigger difference of 0.46 cm³ with the 100% concentration. The biggest difference in volume of gas in the ‘averages’ graph however, was a difference of 0.6 cm³ between the 25% and the 50% concentrations.
In the first three graphs, the differences are only ‘approximately’ 0.5 cm³, because the results aren’t all the same, but they are not far out. The lowest difference is 0.2 cm³ in the 2nd experiment in the ‘volume of oxygen produced’ column between the 50% and 75% concentrations, and the highest difference is 0.8 cm³ in the 3rd experiment in the ‘volume of oxygen produced’ column between the 25% and 50% concentrations. These differences are only 0.3 cm³ more or less than 0.5 cm³, so they are still viable.
There was only one anomaly in my ‘rate of reaction’ graph, which was the reading for the 25% concentration of hydrogen peroxide. Between the rests of the readings, there was a difference of 0.001 cm³/second, but between the 25% and the 50% concentration reading, there was a difference of 0.002 cm³/second.
The reason for all these anomalies is that maybe my method slipt up a bit somewhere which meant some results were very close together and some were very far apart. The only difficulty I encountered when doing my experiments, was starting the stop watch, because I needed to put the stopper into the test tube at the same time, but I got over this problem by asking someone close by me to start it for me.
I could have taken my investigation further, by heating the hydrogen peroxide to 40°C, which is the optimum temperature for enzymes. This would have meant that the enzyme would be at its peak activity rate, so more oxygen and foam would have been formed in the same time 5 minutes), because there would have been more successful collisions.
