*(Averages have been rounded to nearest whole number.)
My preliminary results showed what I expected them to; I expected the number of bubbles to increase with the number of potato cubes added. So more gas was produced when more enzymes where added. I repeated my experiment 3 times for a more accurate, reliable result. There was only had one outlier in my experiment (highlighted in red above.)
For my real experiment in order to get more reliable results I will:
- Weigh the potato cubes accurately as if they are a different mass the reactions between the enzymes and substrate will be affected and this will have a direct impact on my results. I will weigh my potato cubes using a balance.
- Instead of counting the bubbles I am going to measure to volume of gas using a measuring cylinder. In doing this my results will be more reliable as bubbles can vary in size and volume.
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Measure the amount of hydrogen peroxide I use using a burette. (A burette has an error of give or take 0.01 mL in comparison to a measuring cylinder which has the accuracy give or take 0.1mL).
Method:
Equipment I will use:
- Measuring cylinder
- Delivery tube
- Test tube
- Clamp stand
- Beaker
- Cutting tile
- Knife
- ‘Chipper’
- Hydrogen peroxide
- Bowl
- burette
- Water
- Balance
Firstly I start off by cutting the potato up using the ‘chipper’ when they are cut up into chips I cut my strip up into five cubes; I decided to cut them into cubes so it would be easier to control the surface area. I weigh all of my cubes on a balance and they all weigh 1.50g precisely. Before I start for health and safety reasons I put my safety goggles on. I set up my clamp stand and burette then I poured my hydrogen peroxide in to the burette, measuring out 20mL. I then prepare my equipment by filling my bowl up with water; I then place my measuring cylinder vertically in the bowl full of water ensuring it is full. I then stick the end of the delivery tube into my measuring cylinder, this way I can see clearly how much gas is produced and I face the measurements along the side of the measuring cylinder facing me. I will make my experiment accurate by instead of counting the bubbles I will time how long it takes to collect 20cm3 of oxygen. I am measuring the volume of gas produced this time instead of counting the bubbles because in my previous experiment I counted the amount of bubbles produced in the time space of three minuets, this did not prove accurate or very reliable as the size of the bubbles are variable. I then decided measuring the volume of gas produced would prove a fairer, more accurate test with much more reliable results. I pour my 20mL of hydrogen peroxide into the boiling tube and then I put my first cube into the boiling tube and immediately after I put the bung of the delivery tube into the top of the boiling tube and I start my timer. When 20cm3 of oxygen is collected I stop my timer and record my results. I then repeat this process, adding an extra potato cube each time. Though I change the 20mL of hydrogen peroxide for each individual experiment, by doing this each time will ensure my experiment is fair and there should be a similar amount of collisions between the ‘active site’ and ‘substrate’. If I didn’t change the hydrogen peroxide each time there would be fewer collisions.
Variables:
Independent variables- I changed the amount of potato cubes I added to the hydrogen peroxide, I did this to see how much the reaction would speed up if I were to add more enzymes to the reaction because as the amount of potatoes in the reaction increases, so does the amount of enzymes because the enzymes are in the potatoes. This will have had an effect because there will be more enzymes resulting in more collisions.
Dependent variable- I will measure the time taken to produce 20cm3 of oxygen when potato cubes are added to hydrogen peroxide. I will control this by using a timer.
Controlled variables- the variables I kept the same were the amount of Hydrogen peroxide I used, I controlled this by measuring the amount I used using a burette, the size of each individual potato cube, I controlled the weight of each potato cube by weighing them accurately on the balance, I had to keep these the same weight because I wanted to keep adding the same amount of enzymes each time to get a good set of results. The strength of the hydrogen peroxide (20 vol) this is important as the strength of the hydrogen peroxide will affect the amount of enzymes, I kept the temperature of the hydrogen peroxide the same as if the temperature was too hot it would break down and denature the enzymes.
I will repeat my experiment a few times for reliability.
Results:
(*Outliers are highlighted above)
Analysis/conclusion:
From the information recorded on my graph, my graph shows a very steep drop from one cube to two cubes, when I added just one cube of potato to the solution the reaction was very slow in contrast to when I added to cubes to the hydrogen peroxide. Looking at my results it is apparent to me that the higher the concentration of enzymes the faster the rate of reaction resulting in more oxygen being produced. The more enzymes there are the more reactions there will be between the ‘active site’ and the ‘substrate’ causing oxygen to be produced.
Evaluation:
All of my error bars are very small, suggesting my results are reliable and accurate, all aside from my recording with one potato cube; the error bar is slightly bigger than the others. Obviously in my experiment there will be things that went wrong that couldn’t be helped such as it can be difficult to read the measuring cylinder precisely. The results I got matched my prediction which was that the reaction will produce 20ml of gas quicker when the concentration of enzymes in higher. I did my experiment four times for reliability purposes and so I could see the consistency in my results. I am confident in saying my data is reliable, I believe this because I have very few outliers, my error bars are very small and I know my data is reliable because the pattern shown in my graph is consistent. The equipment I used was all fairly precise and I was careful in my measurements. I had one outlier in my results this may again be put down to reasons that can’t be helped or may be a mistake on my part in measuring the amount of hydrogen peroxide inaccurately.
