Enzymes work on a lock and key mechanism
The molecules are thought to have holes of a certain shape depending on the enzyme, this means that only substrates with a similar structural shape to the hole will react. There could be many substrates that can fit in that hole or only one substrate depending on the complexity of the hole.
The enzyme I am dealing with is catalase it speeds up the breakdown of hydrogen peroxide into water and oxygen
Hydrogen peroxide water + oxygen
2H2O2 catalase 2H2O + O2
Catalase is found in potato cells, when added to hydrogen peroxide the reaction is immediate and because oxygen is given off you can measure the rate of reaction by measuring the rate that oxygen is given off.
Linking background with theory.
The rate of reaction will increase if you increase the concentration of hydrogen peroxide, this is because the higher the concentration the more chance of enzymes and substrate molecules colliding, if the temperature an other vital condition mentioned in the background are kept stable.
As the reaction is taking place and hydrogen peroxide is broken down into water and oxygen the concentration of hydrogen peroxide will also be decreasing, there will now be less hydrogen peroxide molecules to collide with the enzyme so the longer the reaction takes place the slower the rate of reaction will be.
Preliminary results
Apparatus
- Bung
- Conical flask
- Hydrogen peroxide
-
Knife (for accurate potato size)
- Margarine tub
- Measuring cylinder
- Potato
-
Scales (for accurate potato size)
- Stop clock
- Water
-
Cork borer (for accurate potato size)
Method
- Set up apparatus as shown above.
- Fill 6 test tubes with 20cm3 hydrogen peroxide each one containing a different concentration, below in actual experiment method are the concentrations.
- Put the chosen size of potato into the conical flask.
- As soon as you add one of the test tubes of acid place the bung on.
- Start the clock.
- When you have collected When you have collected 5cm3 of gas, stop the clock
- Record the time
- Wash the equipment and repeat the experiment with a different strength acid.
- When you have done all 6 acids, repeat the above but this time collect 10cm3 of gas.
Results
Preliminary conclusion
I have decided to collect 5cm3 of gas because with the limited time I have to do the experiment the 10cm3 of gas would take a lot longer to do then the 5cm3 and I might run out of time or have to rush, which could result in mistakes being made. So in away collecting 5cm3 could make my results more reliable.
Method
- Set up the apparatus as shown above, without the potato and hydrogen peroxide
- Fill 6 boiling tubes with 20cm3 hydrogen peroxide each one containing a different concentration, below are the different concentrations
- Put the chosen the 5 cm pieces of potato into the conical flask (spud cylinder 3)
- Get the bung ready to quickly put it on the conical flask as soon as you add the acid so to prevent gas escaping
- Add the acid and start the stop clock
- Stop the stop clock when you have collected 5cm3 of gas
- Record the time, wash equipment and start experiment again with a different strengths of hydrogen peroxide.
Results
Conclusion
My evidence shows me that the higher the concentration the faster the rate of reaction and lower the concentration the lower the rate of reaction. The results also show me that water does not react with the potato.
Their were no major anomalies apart from the one highlighted above and so I would retake the measurements making sure that the apparatus is set up correctly, I would also make sure that the pieces of potatoes were fresh in case the ones previously used had reacted with the air and gone brown before I did the experiment as this would effect the rate of reaction giving a false result. I would make sure the pieces of potato were the correct size as stated in the method as different sizes would affect the results. I would make sure that the water used to wash the equipment used in the experiment did not dilute the hydrogen peroxide as this could affect the rate of reaction. If I did not have time to redo the anomalies I would take the average of the two other measurements leaving out the anomalies,
The results fully support my prediction that the higher the concentration of H2O2 the faster the rate of reaction will be. The graph drawn up from my results shows a negative gradient, showing that the lower the concentration the lower the rate of reaction. The line of best fit on my graph is a straight line which would normally tell me that the concentration of hydrogen peroxide and the rate of reaction are directly proportional but actually I would expect that if I carried the experiment on for a longer period of time the graph would start to tail off showing the concentration and rate of reaction are not directly proportional I would expect the graph to tail off because the longer the experiment took place the fewer H2O2 molecules their would be to collide (the concentration has lowered due to the reaction) and so the rate of reaction would lower, to prove this I would have to repeat the experiment leaving the H2O2 and potato to react for a longer period of time.
The reliability of my experiment is good but not perfect and the major source of error, is most likely to come from human error. I also feel that errors could come from the potatoes as different potatoes have different amounts of water in them, their could be a gas bubble in the measuring cylinder which would throw out the results and so have a different mass. I could improve my experiment by removing the bung an replace it with a self sealing bung this would lower the chances of gas escaping, I could also replace the measuring cylinder with a gas syringe which would improve the accuracy of the results and therefore not allowing gas bubbles to be present which could affect the results, I don’t know what to do about the different concentration of water present in the potato as drying or cutting could affect the amount of surface area which would affect the results. To improve the experiment further I could go up in 10% concentrations of hydrogen peroxide to add more results and so increase reliability of the experiment.