Obtaining Evidence
The factor below were all kept constant
-
The temperature were always kept in 21°C.
- All the chips were from the same potato.
Here are the results that I got
After looking at the results above, I noticed that there had some anomaly in my results by drawing a graph, so I repeated my whole experiment and there are the results I got:
Analysing Evidence
These are the surface area of my and how I cut them:
1st chip which had 1 piece
(5*1*4)+(1*1*2)
=22cm2
2nd chip which had 2 pieces
[(2.5*1*4)+(1*1*2)]*2
=24cm2
3rd chip which had 4 pieces
[(2.5*1*2)+(2.5*0.5*2)+(0.5*1*2)]*4
=34cm2
4th chip which had 8 pieces
[(1.25*1*2)+(1.25*0.5*2)+(0.5*1*2)]*8
=38cm2
5th chip which had 16 pieces
[(1.25*1*2)+(1.25*0.25*2)+(0.25*1*2)]*16
=58cm2
When I have drawn best-fit lines in my graph, I found out that as the surface areas of my chips increase, the volume of oxygen collected in 5 minutes of the potato tissue is placed in the hydrogen peroxide solution is increased. This is because when the chips have more surface areas then there will have more areas for the hydrogen peroxide to diffuse into the potato tissue, so more catalse enzymes are working as the same time, therefore the faster the rate of reaction. The energy needed to start a reaction is called its activation energy and a catalyst lowers the activation energy. This means that comparatively milder collisions will now have enough energy to over come the activation energy barrier.
Enzymes are large molecules and proteins. Each different enzyme has its own special shape. The reactants fit into the enzyme, like a lock and key. The reactant slots into enzymes at its active site
Diagrams to summarize how does enzymes work
Other enzymes can build up big molecules from small ones. Reactions go faster in higher temperature because of the catalase molecules will be moving faster and will therefore collide were often and harder and both of these factors will speed up the reaction. But if the enzyme gets too hot, it changes shape. So the reactants will no longer fit snugly into the enzyme’s active site. It can’t catalyse the reaction because the enzyme is denatured. Enzymes work the best at around 40ºC because they are proteins which are damaged by temperatures above about 40ºC. Also they work best at a pH 7 because they are proteins which are damaged by very acid or very alkaline conditions.
I have seen in my graph as my surface area of my potato chips increase, the volume of the oxygen collected is increased. Therefore the bigger surface area of the potato chips, the faster the rate of reaction of the hydrogen peroxide is being use up and the faster the oxygen is being given off which is I predicted before I did the experiment.
I had worked out the rate of reaction by looking at my repeated graph. I read the volume of oxygen collected after 1 minute for each experiment and found out the rates for each experiment. They are:
After I have drawn best-fit line for my rate of reaction graph, I found out that as the surface areas of my chips increase, the rate of reaction is increased. This shows they are proportional to each other but not directly proportional as I predicted.
Evaluating Evidence
There were some difficulties while I carried out this investigation such as it was very difficult to cut the potatoes into pieces, especially when it reached the 5th chip which need to cut it into 16 pieces, it is because the potatoes were too small to cut and even when I had cut them, maybe they were not in right angle. We need to use the same potato for cutting the potato chips therefore in the beginning I need to have 5 potato chips to be really to cut, but when I left the potato out of the air then the potato chips will dry out. It is easier to cut the potatoes across not lengthwise, but the surface area would then only increase by a small amount. It was very hard to read the readings at exactly every 30 seconds because people have reaction time so this can delay my readings. Also when I was putting the potato chips into the conflict flask, maybe two potato chips were sticking together, this will make less surface areas to let the hydrogen peroxide. In some of the potato chips were floating in the hydrogen peroxide; this makes less surface area of the potato chips. I need to keep the temperature constant throughout the whole experiment but it was different because this is an exothermic reaction, which means when its reacted, it will give out heat, so the temperature may change.
In order to improve my experiment, I can use an implement called thermostatically controlled water—bath. This can keep the hydrogen peroxide in a constant temperature to make the experiment more fair and accurate. I can increase the size of the potato chip in order to help me to cut the chips into pieces more accurate and easier. To stop the potato chips to dry out when I get to the experiment I could use cling film to cover them or not cutting them till the end. This can keep the potato chips wet because if they have dried out, the some of the enzymes will denature. Maybe I could longer the time to let the reaction goes longer to make it more accurate. The same person should read the reading of the burette throughout the experiment in order to make the reaction time the same. I could use a vernier calliper to measure the length of the chips instead of a ruler because this can provide measurements to 2 decimal places, therefore increasing accuracy of the results.
From looking the results and the graph I got of the first experiment, I found out there have lots of anomalous results, so I decided to do a repeat experiment and my results were pretty accurate in my repeat experiment. I could draw the best-fit lines easily and the readings were pretty close to my trends. But there is still one anomalous result which is in my fourth chip at the 3.5 minutes. The point was too low as I was expect, this maybe because the potato chips were stick together or the cell membrane was damaged before I did the experiment or maybe I had miss read the reading on the burette, if I have a chance to do the experiment again I will make sure I read the burette carefully. When I looked at my rate of reaction all the points were very close to the trend.
I think I had sufficient readings to produce a firm conclusion as I have a range of 5 sets of readings already. But in order to make it as accurate as possible I can carry out another experiments by using different kind of cells such as liver and use a different concentration of hydrogen peroxide. To do that I can use the same method to cut the potato chips to cut the liver and put them into 0.8M hydrogen peroxide instead of 1.7M. Also I can take the readings more frequently by taking them every 15 seconds instead of 30 seconds.