Same potato; in the practical we tried to use the same potato, because each potato has a different amount of catalase inside it. This depends on the age of the potato for example: a two-week-old potato could have less than half the amount of catalase than a new potato.
Same people; we used the same people to read results, meniscuses, to syringe the hydrogen peroxide, too cut the potato, and to time. We did this because then each time the margin of human error would be the same each time, therefore making the results more accurate.
Same equipment; for the practical we used the same equipment every time we read results. We did this so we knew that the equipment was air tight and assembled correctly, giving us accurate results.
Same volume and concentration of hydrogen peroxide; because we carried out the experiment over one day, we knew that the concentration was the same each time we measured more. Each time after the results had been read when we went to collect the substrate, we collected the same amount (10ml3) of hydrogen peroxide.
Same pH; enzymes are very pH sensitive and can only work in a pH suitable for themselves.
Safety: to make the practical safe we wore goggles because we were working with chemicals (bleach).
Method: Here is the diagram that I worked from when setting up the practical
In addition to this here is an equipment list:
Measuring cylinder
Water bath
Potato
Cork borer
Scalpel
Bung
Delivery tubes
Syringe
Hydrogen Peroxide
Conical flask
Stop watch
Scalpel
Ruler
Tile
Safety goggles
- I set up the equipment list as in the diagram.
- Using the cork borer I cut three cylinders of potato at 4cm long each (using ruler).
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I filled up the syringe to the 10ml3 with hydrogen peroxide.
- I placed one of the three potato cylinders into the conical flask and replaced the bung securely, so allowing no air to enter into the flask.
- I then pushed the hydrogen peroxide into the conical flask and didn’t take the syringe out (so I didn’t let any air in),I timed a minute (to see how much oxygen was produced) and recorded the results the table.
- I repeated this two more times and took an average (see table).
- I then took three results each for when there was two pieces, four pieces, eight pieces and sixteen pieces and took there averages
Results:
To make these results more accurate we have measured the radius of the cork borer (5mm) and the height (40mm) of the cylinder. We have done this to work out the surface area. The equation for surface area of a cylinder is 2πrh + 2πr2.
Here is a graph to show these results:
The graph shows a pattern in the results that as we increase the surface area, we in turn are increasing the production of oxygen.
The graph shows that the rate of oxygen production is in direct proportion to the surface area (e.g. if we double the surface area we double the volume of oxygen produced).
From this experiment I have learnt that we are in control of how much enzyme attacks a cell, we can change this by cutting through cells which increases the surface area decreasing the rate of reaction. This diagram shows how enzymes are believed to work.
Enzymes are constantly moving around and often collide with one another. When a substrate collides with the correct molecule of an enzyme it fits into a depression on the surface. The depression is commonly known as the active sight. After the enzyme has reacted with the substrate it deposits it leaving the enzyme free to be used again. Each enzyme can only be used for one type of substrate (and is rather like a key that fits into a lock- one key fits one lock)
I think that this practical was a success because my results matched what I predicted. The practical was also a success because the results were accurate.
During the practical I detected an odd result (highlighted in pink)
This increased the average volume of gas produced by a large amount. If I was able to redo this practical again I would take that chance because I now know how quickly you have to work and how well organised you need to be too complete the practical on time and successfully. I would also take this chance too see what went wrong in the first line of results and too do my best to prevent this from happening again, when redoing this practical.
The factors which effected the results are accuracy and reliability. The points of the fair test effected reliability (temperature, same potato, same people –to read results-, same equipment, same volume and concentration of hydrogen peroxide, same pH). This affected the range of results (24.3- 9.0 =15.3), this is making the range larger (it should be roughly 6.0) therefore decreasing the accuracy of the results. The equipment used effected the accuracy, we used a ruler and scalpel to measure the potato to one decimal place (of length), and used the same pieces of equipment each time we read results. Every time we used the same person to read results so that the margin of human error was the same each time. Each time we syringed hydrogen peroxide into the conical flask we displaced an air bubble, which was at the top of the syringe.
I believe that over a longer course of time I could improve the method by making it more detailed, which would therefore increase the accuracy of the results.