Here are the results for the pre-test:
As you can see both experiments gave me reasonable results because in pH 4.4 and 8.4 the least pressure is produced but pH’s 6.5 & 7.5produce the most pressure which is correct according to my research. I decided to choose 5KPa because it will take less time to do the actual experiment, hence saving time. The other conditions such as the amount of potato and the volumes of H2O2 and pH solution also worked well so I have decided to keep these as they are.
Range:
I am using 5 different pH. pH 4.4, 5.2, 6.5, 7.5 and 8.4 for accurate results leading to an accurate analysis.
Fair Test:
- When measuring the volume in a measuring cylinder make sure you take the reading from the lower meniscus
- Always make sure the digital balance is on 0.00g before you start to weigh the potato
- Put the Petri dish on the balance and then set it to 0.00g
-
Use the same volume of H2O2 each time the experiment is repeated
- Use the same volume of pH solution each time the experiment is repeated
- Use the same amount of potato each time the experiment is repeated
- Make sure the stop-watch is on 0.00 secs before you start timing
- Make sure the experiment is carried out in the same way each time it is repeated
- Make sure the measuring cylinders and the conical flask is washed, each time the experiment is repeated, with distilled water
Safety:
- Follow these instructions when dealing with Hydrogen peroxide
- If swallowed: wash out mouth and give a glass or two of water. Seek medical attention as soon as possible
- If liquid gets in eyes: flood the eyes with gently running tap water for 10 mins. Seek medical attention
- If spilt on skin or clothes: flood area with large quantities of water. Remove contaminated clothing and soak. If large area is affected or blistering occurs, seek medical attention
- Wear goggles when dealing with hydrogen peroxide and pH solution
- Do not spill any of the two liquids
- Avoid contact with any of the two liquids
Method:
Apparatus: Diagram:
- Bung
- Conical Flask
- Delivery tube
- Pressure Sensor
- Stop-watch
- Petri dish
- Digital balance
- 2 Measuring cylinders
- pH solution 4.4, 5.2, 6.5, 7.5 and 8.5
-
Hydrogen peroxide (H2O2)
- Grated Potato
- Syringe
- Paper
- Pen
- Spoon
- Grater
- Distilled water
Method:
-
Gather the apparatus e.g. H2O2, pH solution 4.4, and potato etc
- Grate the potato
- Measure 3g of potato by putting the Petri dish on to the digital balance and setting it on 0g and then put the potato on the Petri dish until the scale reads 3g
-
Measure 20cm³ of H2O2 with the other measuring cylinder making sure you read from the lower meniscus
- Measure 10cm³ of pH 4.4 solution in a measuring cylinder making sure you read it from the lower meniscus
-
Put the pH 4.4 solution and H2O2 in the conical flask
- Attach the syringe to one of the outlets of the bung
- Attach the delivery tube in the other outlet
- Set the stop-watch on count-up
- Put the grated potatoes into the conical flask with a spoon and immediately close the flask with the bung and while doing this attach the other end of the delivery tube to the pressure sensor
- As soon as you’ve put the tube in the pressure sensor start the clock
- Hold the syringe while doing the experiment
- Measure the time it takes for the pressure to reach 5KPa and record the time on a table
- Repeat the experiment for pH solutions 5.2, 6.5, 7.5, 8.5.
- Before repeating experiment each time, wash the conical flask and the measuring cylinders with distilled water
Prediction:
I predict that the enzyme Catalase will work the fastest in neutral pH 7.5. This is because if the pH is too acidic or too alkaline, Catalase will denature in other words change its structure, so that it no longer has sufficient effect on Hydrogen peroxide.
Every enzyme has its optimum conditions in which it works best in. Catalase works best in neutral pH and because pH 7.5 is neutral it will give the fastest reaction between Hydrogen peroxide and Catalase. As the pH increases or decreases the enzyme will become less and less effective. This is because slowly and gradually the enzyme will start to denature, which means it will change shape; it also means that the active site of the enzyme where the substrate fits into and breaks down will change its structure, disallowing the substrate to break down. This is because each enzyme is especially designed to break down one particular substrate; this can be explained by a theory called the lock and key theory. The enzyme is designed in such a way that the one particular substrate fits perfectly into the active site of the enzyme just like a lock is designed. Only the especially designed key can fit into that one particular lock. If the structure of the active site is even slightly altered it can affect in the substrate not fitting into it, disallowing it to be broken down. ()
I predict that the graph will look something like this:
The predicted graph shows that as the pH increases the time taken decreases until it reaches pH 7, after pH 7.5 it starts to gradually increase as the pH increases. At the beginning the graph shows negative correlation until it reaches pH 7. It then shows positive correlation as the pH increases further. This is because at the beginning of the graph, the pH is acidic and so as we can see shows that it takes longer for H2O2 to break down but as the pH comes closer to neutral the time taken gets less and less until it reaches neutral pH 7. After that, the pH starts becoming alkaline and so the time taken starts increasing again. This is what I predict will happen.
The graph, which shows the amount of pressure produced per second, will look something like this.
This shows that pH 7-7.5 produces the most amount of pressure in a second. The two extremes produce the least amount of pressure. I predict that if my previous prediction is correct then the most amount of product will be produced in pH 7-7.5.
Analysis:
The results show that the enzyme Catalase works best in the neutral pH 7.5. When the pH was too high (alkaline) or too low (acidic) Catalase was not as fast as it was in the neutral pH. When the pH was 4.4, the average time taken to reach the pressure of 5KPa was 17.76s, which is in an acidic pH. As the pH increased to 5.2 the average time taken was 6.89s, which was still in the acidic pH but less acidic than pH 4.4. The next pH was 6.5 with an average time of 5.78s, which although still in the acidic zone is only mildly acidic. The next pH was neutral pH 7.5 which gave the average time of 3.32s. The last pH used was 8.4 which is in the alkaline zone and gave average time of 7.30s. By looking at these results you can see that if the pH is acidic or alkaline Catalase doesn’t work as well as it does in neutral pH. This proves my prediction very closely and suggests that the optimum pH for Catalase is the neutral pH 7.5.
The table below shows how much pressure is produced per second in the different pHs.
The table shows the reaction between Hydrogen peroxide and Catalase produces most pressure per second in pH 7.5. We can see that the pH affects the activity of Catalase quite a lot. If the pH is acidic it results in Catalase not working as fast. If the pH is too alkaline then again it results in Catalase not working as fast. When the pH is neutral that is when Catalse works at its best and produces the best results.
Let’s look at the graphs and what they show us. The graph that shows the affect of pH on Catalase starts off showing a negative correlation showing that as the pH increased the time taken decreased up until it reached 7, when it starts increasing and showing a positive correlation. The graph matches my predicted graph. It shows that when the pH was low (acidic) it took longer for Catalase to produce pressure of 5KPa but as the pH gradually increased and came closer to neutral the time taken became less. In fact when it reached pH neutral it took the least amount of time. As the pH started increasing further and beyond neutral pH 7.5, the time taken started increasing as well, because now the pH was alkaline.
The graph showing the rate of reaction (pressure/time) proves the same thing but shows the rule from a different aspect. We can see that as the pH increased the amount of product produced increased too until it reached pH 7.5. This shows that as the pH got closer to neutral it produced more product. When the pH increased further and away from the neutral pH the amount of product produced decreases. This means that the best pH was the neutral pH 7.5 because it produced the most product.
Looking at the graph’s I can say that my results are very accurate in illustrating the following conclusion.
The reason for Catalase working slow in acidic and alkaline conditions is that its optimum pH is 7. This is the pH, which is best for Catalase. This means that when the pH is acidic the enzyme starts denaturing, changing its structure. When the structure changes the enzyme cannot react with the substrate. Every enzyme has its own characteristic shape. It is especially designed to breakdown one particular substrate. The enzyme has an active site where the substrate goes and fits in. To explain why only one particular substrate can fit into the active site, we have to look at the lock and key theory. A key is especially designed to fit into one particular lock and only that key is able to fit in to the lock successfully to open it. It is the same with an enzyme and its substrate. ()
The same case is with Catalase and Hydrogen peroxide. Catalase is especially structured for Hydrogen peroxide to fit in.
Following on from the effect of pH on structure, we can now understand that when the pH changes the enzymes structure, the enzyme cannot react with the substrate. But let’s look at why the pH changes the structure of the enzyme. The reason is to do with ionic concentrations. Enzymes are very complex macromolecular entities and so can only function within very specific pH range. pH of the media is responsible for the charged state of the charge-bearing amino acids in the polypeptide chain, which can be directly or indirectly linked to specific activity. At extreme pH’s enzyme can lose activity irreversibly due to denaturing as well. There is also the possibility of the substrate of the enzymatic reactions being reversibly or irreversibly affected by pH of the medium. Enzymes are made of protein and protein molecules bend, coil, and fold in different axes to make definite 3-dimensional shapes and they are held in these shapes by hydrogen bonds. The specific 3D shape of a protein molecule is necessary for its proper functioning and as I mentioned earlier the Hydrogen bonds help maintain this 3D structure. ()
Since enzymes are also protein, they also have the 3D structure, which is necessary for their proper activity, as I have already explained earlier. Increasing or decreasing the pH beyond the optimal range alters the hydrogen bonds, thus disturbing the 3D shape of the enzyme and making it inactive. Thus, every enzyme has an optimal range of pH that is necessary to keep its Hydrogen bonds appropriate for maintaining the particular 3D structure of the enzyme. () This explains to us why most product was produced in pH 7-7.5 and why less product was produced as the pH increased or decreased beyond 7-7.5.
My prediction states that most product will be produced in pH 7-7.5 range and after looking at the results and the evidence I know that my prediction was correct.
Evaluation:
In my investigation, the method I used involved the pressure sensor in gaining the results. Using this method allowed me to get the accurate results that I got, which helped me reach the an appropriate conclusion.
Looking at the graphs that I produced I can see all results are close to the line of best fit. I found no anomalous results in my experiment.
The method that I used was quite accurate and there are no major changes, which I would like to make to it. The results that I gained were fairly accurate in me reaching an appropriate conclusion, as they were lying reasonably close to the line of best fit and were following the correlation of the line. This was because the method was well thought out on my part and I had made sure to recheck my method repeatedly so that it made sense and allowed me to get accurate results. Some examples of this were reading from the lower meniscus when measuring liquids in a measuring cylinder.
Having said that, I feel that my results can be made more reliable to support an accurate conclusion if certain things are considered. In order for the results be more reliable, I can use a wider range of pH solutions, maybe 10 or 11 instead of just 5. I can also make these pHs closer together, which will help me to get a more precise graph as more points will be put on the graph which are closer together and so will give a line of best fit which will illustrate the results a lot more precisely. There are things that can be one more accurately by taking greater care, so that the results obtained would be relatively accurate. There are things like measuring the correct volume of the pH solution and H2O2. Not measuring the exact volume each time can lead to minor differences in the results and so the experiment isn’t as fair as possible to give us very reliable results. Same thing is with measuring the potato incorrectly. Other things that can lead to anomalous results are the contamination of either solution with other substances. Things like mixing up the pH solution can also lead to anomalous results.
Below is the experiment again, but with the changes I suggested to make the results more reliable and accurate.
Apparatus:
- Bung
- Conical Flask
- Delivery tube
- Pressure Sensor
- Stop-watch
- Petri dish
- Digital balance
- 2 Measuring cylinders
- pH solution 4, 4.5, 5, 5.5, 6, 6.5,7, 7.5, 8, 8.5, 9
-
Hydrogen peroxide (H2O2)
- Grated Potato
- Syringe
- Paper
- Pen
- Spoon
- Grater
- Distilled water
-
Gather the apparatus e.g. H2O2, pH solution 4, and potato etc
- Grate the potato
- Measure 3g of potato by putting the Petri dish on to the digital balance and setting it on 0g and then put the potato on the Petri dish until the scale reads 3g
-
Measure 20cm³ of H2O2 with the other measuring cylinder making sure you read from the lower meniscus
- Measure 10cm³ of pH 4 solution in a measuring cylinder making sure you read it from the lower meniscus
-
Put the pH 4 solution and H2O2 in the conical flask
- Attach the syringe to one of the outlets of the bung
- Attach the delivery tube in the other outlet
- Set the stop-watch on count-up
- Put the grated potatoes into the conical flask with a spoon and immediately close the flask with the bung and while doing this attach the other end of the delivery tube to the pressure sensor
- As soon as you’ve put the tube in the pressure sensor start the clock
- Hold the syringe while doing the experiment
- Measure the time it takes for the pressure to reach 5KPa and record the time on a table
- Repeat the experiment for pH solutions 4.5, 5, 5.5, 6, 6.5,7, 7.5, 8, 8.5, 9.
- Before repeating experiment each time, wash the conical flask and the measuring cylinders with distilled water
By Kausar Hussain 10S Candidate no. 8410