In Jones and Jones biology text book it states,
“enzymes work best at a particular pH. Most enzymes work best at a pH of about 7. This is also because they are proteins which are damaged by strong acids or alkalies.”
This helped me with my prediction and I think the enzyme will work best at around a neutral pH like 7 due to the extract. Maybe it will not work as well in acidic solutions because acids break down proteins, and an enzyme is a protein also I think. I also think it will give off less gas at lower pH’s because the enzyme won’t work as efficient at these.
The equipment I will use:
Gas measuring cylinder
Clamp and stand
Water trough
10ml measuring cylinder
mortar and pestle
conical flask with delivery tube
stop clock
Hydrogen peroxide
Weak acid, strong acid, neutral, weak alkali and strong alkali solutions . Celery also.
Diagram of setup
Method
For our method we set everything up like the diagram above.
- We collected all our equipment.
- we filled the water trough half full with water and put the delivery tube into it
- we measured out 5ml of the acid , celery and hydrogen peroxide.
- we put them in the conical flask and immediately placed the bung in ( connected to delivery tube ), placed the gas measuring cylinder over the delivery tube end and began the stop watch,
- we recorded the amount of gas produced every 15 seconds for one minute
- we repeated for strong acid, weak acid , neutral, strong alkali and weak alkali.
We tried to make it as accurate as we could, by using exactly 5ml of each component, not deliberately altering the temperature, only room temperature fluctuations maybe. I was very careful with all of these and I made sure I filled the gas measuring cylinder completely and tried to keep it like that.
Analysis
The following table shows my results for our investigation. We only had time to do 2 sets for all pHs as it was a difficult experiment to do quickly, and we had to wash all equipment after each experiment.
Experiment 1
Experiment 2
The following pages show graphs for averages and lines of best fit.
My results who overall that from acidic to alkali the amount of gas given off increases. This agrees with my prediction. Looking more closely at my results, something I didn’t expect is there. Strong alkali seems to have produced more gas than Weak alkali by 9 cm³. There is many reasons for this which I will refer to in my evaluation. On the acid graphs , near the 60 seconds, they start to level out more. This is probably because there isn’t much of the enzyme left to help he reaction ,so things slow down.
The average amount of gas produced per 60 seconds is shown below.
My results show what I did expect that strong acid doesn’t work as well as weak acid, and neutral works even better , only the alkali results were not in agreement with my expectations.
Evaluation
I have came to the conclusion that my prediction was mostly correct, and that my results did mostly show this; apart from the alkalis. I think maybe my theory was right and maybe my results were wrong. I expected strong alkali to work better than weak alkali, but it didn’t. This could be due to human error. It is possible that I started the stop clock to early for strong alkali or/ and to late for weak alkali. It is possible that a lot of the gas escaped from the weak alkali one when I was putting the bung on the conical flask or putting the gas measuring cylinder over the delivery tube; this would of produced less gas which could account for it having less gas produced than strong alkali.
I also done strong alkali on a different day to weak alkali, this could of affected many things. The room temperature could of varied quite drastically , which would have an affect on my results. And I used different celery on both days. The celery may have contained more peroxidase than another. There are many other things which could have changed, my measurements could have been inaccurate.
If I was to do this experiment again I would collect at least three sets of results before working out an average. This would of helped with them. I would also of tried to keep the temperature constant by doing it all in one day , or maybe even using a water bath. I would of used the same celery for all , and kept my measurements as accurate as I could. I could also do it at more intervals to get a better line of best fit and more accurate graphs in general. Overall I would say my results were quite accurate, but more testing and revising the alkali tests would make this a much more reliable experiment.
By Lawrence Bell
