A picture showing a de-natured enzyme
The substrate molecule no longer fits in the active site.
Enzymes have many uses, some are in biological washing powders because they help greasy dirt to mix with water and some are used to take away the cloudiness of apple juice and make it clear, enzymes are used through out the food industry.
Enzymes are affected by concentration: only a certain amount of enzymes can work at one specific moment as there is a limited amount of active sites to a substrate so when all the active site are filled the enzyme does not continue to work and this is a limiting factor.
From 1 to 3 the rate of reaction is increasing but from 3 to 4 the rate of reaction will no longer increase as there is no more substrate to act upon and below this explains what is represented on a graph below.
1. This shows in theory what should happen but as 2 shows what actually happens as the rate of reaction is limited by the amount of substrate.
Specific information about my investigation
The purpose of my investigation is to see how the rate of reaction changes when the concentration of potato discs is changed with 20ml of hydrogen peroxide.
The enzyme we are using is Catalase. It is found in the liver and potato cells. Catalase breaks down hydrogen peroxide into water and oxygen, this is important because hydrogen peroxide is produced in many reactions in the cells of the body. Hydrogen peroxide is toxic substance and must be immediately broken down. This also shows that Catalase active site is the perfect shape for the substrate of hydrogen peroxide
Catalase
Hydrogen Peroxide Water and Oxygen
Catalase
2H2O2 2H2O+O2
Catalase is mainly used in the body. I will be able to measure my rate of reaction by the volume of oxygen produced (cm³).
This investigation demonstrates how every living cell breaks down hydrogen peroxide inside our body.
My independent variable is the enzyme concentration (number of potato discs).
My dependent variable is the volume of oxygen given off (cm3).
Other variables include temperature, surface area to volume ratio, pH and time were not changed as the time remained 1 minute per run throughout and they pH was the same. These were all kept the same to help keep the experiment fair and produce good and accurate results. The heating in the room controlled the temperature because this could effect the reaction this was 21ºC, time cannot be controlled but the experiment was completed in the same period of time each time. The surface area to volume ratio is very important because this affects your results greatly and that is why I used the same cork borer and cut the potato slices to the same diameter so it was even every time. If there is more surface area, then more potato is exposed to hydrogen peroxide and this changes the amount of concentration of enzyme available increasing the rate of reaction. Un even sizes of potato discs would have made the results varied and to a poor results investigation.
Preliminary work
In the preliminary investigation we investigated what amount of potato and hydrogen peroxide to use for the main investigation. We used cork borer 5 but the diameter was 1 cm of the potato discs we used 20ml of hydrogen peroxide with 10, 20 and 30 discs.
Method
1. Peel the potato with the knife carefully, then insert the cork borer into the potato and extract the potato cylinder and cut it into discs 10mm diameter on a white tile.
2. Set the apparatus as shown without adding the contents shown in conical flask and without putting the cork.
3. Withdraw 20ml of hydrogen peroxide with a different plastic syringe.
4. Measure 10 discs of potato.
5. Add the 10 discs of potato to conical flask but do not put the cork on yet.
6. When you have the stop clock ready add the 20ml of hydrogen peroxide and quickly cork the conical flask
7.Wash the flask out thoroughly between each run.
8.Then record the result the reading on the glass syringe after 60 seconds.
Results
Number of potato discs oxygen given off (cm3)
- 5
20 11
30 18
We can see that using 1cm diameter potato discs did not produce much oxygen and so I opted to use 0.5cm diameter which produced a lot more oxygen producing improving my final results in the investigation as it produced a larger surface area meaning that more potato was exposed to the hydrogen peroxide increasing the rate of reaction. We felt that the amount of hydrogen peroxide was efficient and did not need to be changed.
We also used in the preliminary work a separating funnel to release the hydrogen peroxide into the conical flask with the potato discs but I found that this was very slow in releasing it and oxygen was probably lost as it was not totally air tight so I chose to use a 20 ml syringe as this would input the hydrogen peroxide a lot faster and use a stopper as no or less oxygen would be lost due to human error.
My Investigation
Apparatus
Hydrogen peroxide
Potatoes
Knife
Cork borer
Glass syringe
Stand with clamp
20ml Plastic syringe
Side-arm Conical flask
Stop clock
Rubber stopper
Weighing scales
White tile
Diagram
Method
1. Peel the potato with the knife carefully, then insert the cork borer into the potato and extract the potato cylinder and cut it into discs of 5mm diameter on a white tile.
2. Set the apparatus as shown without adding the contents shown in conical flask and without putting the cork.
3. Withdraw 20ml of hydrogen peroxide with a different plastic syringe.
4. Measure 10 discs of potato.
5. Add the 10 discs of potato to conical flask but do not put the cork on yet.
6. When you have the stop clock ready add the 20ml of hydrogen peroxide and quickly cork the conical flask
7. Then record the result the reading on the glass syringe after 60 seconds.
8. Wash the conical flask out thoroughly between each run.
You would repeat this method for use with 20, 30, 40, 50 and 60 potato discs. Then repeat it twice for more accurate results.
Safety
- Wear eye goggles just in case your eyes come into contact with hydrogen peroxide, as it is corrosive and could blind you.
- When using the hydrogen peroxide always be careful as it is corrosive and burns the skin and mush be washed with water immediately if the come into contact.
- You must be careful when using the knife to cut the potato and also when using the cork borer as the edges are sharp.
- You must be careful not to damage any apparatus as the glass syringe may slip out if too much oxygen is produced and smash.
- All obstructions like bags must be cleared away as they can cause accidents too.
- Make sure white tile is used so u do not damage the work surfaces when cutting the potato discs.
Fair Testing
To keep this investigation fair I will keep the following the same:
- Use the same volume of hydrogen peroxide.
- Use the same cork borer so the discs of potato have the same surface area and volume as if they do not the result of the investigation will be incorrect and invaluable.
- Use the same batch of potato, hydrogen peroxide.
- Measure the temperature of the room with thermometer so the investigation is done at room temperature.
- Make sure the side-arm conical flask is washed out thoroughly between each experiment.
- Use the same equipment and method so there are not changes in results.
Results
Analysis
The graph is labelled average amount of oxygen given off when hydrogen peroxide reacts with enzyme Catalase found in the cells of potato discs.
The graph shows how the average amount of oxygen given off when hydrogen reacts with the enzyme Catalase found in the cells of potato discs.
The graph contains a good positive correlation which looks like it is going to curve off but the is one result at the concentration being 30 discs of potato is lower than expected but still not anomalous as it is still continued in the trend of increasing like the other results, this displays that more and more oxygen is being given off when the concentration of enzyme is increased. This could have happened using inaccurate measurements of hydrogen peroxide or inaccurate cutting of potato discs. It shows that the concentration of enzyme was not as high as the others
By the graph beginning to curve off this proves that the rate of reaction was limited by the amount of hydrogen peroxide used in the investigation, this shows that just like in my scientific background as soon as all the substrate is broken down then there is nothing more for the enzymes to do, the reaction is a limited by the amount substrate to work on so when all of the hydrogen peroxide has be broken down into water and oxygen the reaction stops and this is represented by the curve on the graph. The amount of substrate is the limiting factor in this investigation. What you really needed to do is increase the amount of hydrogen peroxide as well as increasing the amount of potato discs and this would give a straight line along the graph.
The gaps between the results were pretty even showing that there was no rapid increase between any point but that is a rapid decrease between the points of 50 potato slices and 60 potato slices as there was only a gap of 2cm3. This is also displaying that less and less oxygen is being given off as the concentration of enzyme is increased not the amount of substrate. This is another one of the reasons why the graph is beginning to level off.
My scientific background supports my hypothesis and graph that the rate of reaction is limited by the amount of substrate and this is shown as the graph numbers begin to decrease by less oxygen being produced. The graph and results support my hypothesis and scientific background as the rate of reaction seemed to be limited by the amount of substrate.
I conclude then, that my investigation displays that the rate of reaction is limited my the amount of substrate that is hydrogen peroxide and this also supports my hypothesis as I have declared this in that section using valuable information from my scientific background which clearly displays this fact in the section the effect of concentration on an enzyme when the enzyme concentration is changed and the amount of substrate stays the same.
Evaluation
I feel that my method could have been improved by carrying out the experiment on a larger scale using more concentrations of enzymes and being repeated a lot more for higher accuracy.
I feel using new equipment everyone would have effected the results highly as none of the experiments equipment would have been contaminated by the previous experiment, but still if there was more time we could have washed the conical flasks out more thoroughly.
I feel that a better gas syringe would have also improved results as the syringe did not really slide properly and this may be due to friction between the two pieces of glass.
I feel that if we had more time to cut the potatoes then our results would have improved because some of the potato discs may have not be cut accurately enough and this would have affected the surface area volume ratio, affecting the final results.
I feel computer data logging would have been useful as this could have took accurate readings of how much was given off simultaneously with the time and this would have made the results more accurate.
Obviously repeating the experiment many more time would have improved our results but once again there was not enough time to do this.
Further investigation
I feel that for my further investigation I would carry on the same investigation but continue increasing the concentration using the same equipment, same size cork borer and same amount of hydrogen peroxide. I will do this to see if the graph continues to level off to prove that the rate of reaction is limited by the amount of substrate. So do this for 70, 80, 90, 100, 110, 120 potato discs. I feel the results this further investigation will produce justify my hypothesis.
- Peel the potato with the knife carefully, then insert the cork borer into the potato and extract the potato cylinder and cut it into discs of 5mm diameter on a white tile. Do 70 discs.
- Set the apparatus as shown in the diagram of the previous experiment without adding the contents shown in conical flask and without putting the cork.
- Withdraw 20ml of hydrogen peroxide with a different plastic syringe.
- Measure the required amount of potato discs.
- Add the discs of potato to conical flask but do not put the cork on yet.
- When you have the stop clock ready add the 20ml of hydrogen peroxide and quickly cork the conical flask
Then record the result the reading on the glass syringe after 60 seconds.
Wash the conical flask thoroughly.
- Repeat this method for 80, 90, 100, 110, 120 potato discs.
Bibliography
“Biology for you” by Gareth Williams
“Biology” by Mary and Geoff Jones
www.bbc.co.uk/gcsebitesize
Letts – Revise AS biology
‘Key science new edition’ by David Applin
