Diagram of experiment Set up
Procedures
After setting up my equipment, with 6cm of potato chopped roughly into 40 pieces and with 5cm of water in the bottom of the boiling tube, I will add 1cm of Hydrogen Peroxide using the syringe. Then when the reaction starts I can measure the amount of gas given off. To measure the amount of gas given off I will fill the upturned burette with water and also the beaker (this stops the water escaping from the burette), I can then see how much water has been displaced by the gas going into the burette, when I count this displacement (minus the 5cm for the Hydrogen Peroxide) I can get the amount of gas given off by the reaction.
If there was more time to complete the experiment then I would have repeated the experiment and done it overall two or three times.
Variables
In my investigation there are a number of factors that could potentially affect my results, these can be from misreading results to having an unusual piece of potato.
For my investigation to be fair I must keep the all the variables the same apart from one, which will be the PH buffer. I will vary this to find out the effect that PH has on enzyme activity. What I would not hope to do is to change any variables such as temperature because that would have a great effect on the results.
Risk
With the equipment that I will be using there will be certain risks, these include sharp edges, potential stabbing and poisoning.
There is a lot of glass equipment that can smash or shatter and then have sharp edges, to avoid this I will take care not to drop, give impact or crush (over tightening of the clamps) the glass ware e.g. boiling tube, burette. The needle can also give a high risk of stabbing since it has a very sharp metal point, to avoid this I will take as much care to avoid it when I replace the rubber bung after refilling the boiling tube with potato’s and PH buffer. Water is also used in the experiment so a degree of care will have to be taken to avoid spills onto the floor which could cause slipping, risk of electrocution can also be avoided by keeping the experiment a safe distance from power sources. Another big risk with this experiment is the use of Hydrogen Peroxide; it is extremely harmful to the body because it is toxic. Peroxide can bleach hair or skin and can have irreversible effects to eyesight, so for these reasons goggles must be worn along with rubber gloves and a lab coat.
Results
Analysis
As my graph suggests, PH 5 is incorrect. By using my graph I can estimate and say that PH 5 should have given off about 6.8 cm3 of O2 in 2 minutes. There could have been many reasons why this value is wrong; they could have been things like not having the apparatus airtight so some of the gas could have escaped. The quantities of the solutions may not have been correctly measured, this includes the buffer, the amount of Hydrogen Peroxide or the size or weight of the potato pieces.
Trends
As my graph shows (ii) the reaction is greatest when the reaction takes place with a PH of 7, this agrees with my predictions. Also what I predicted earlier was that the reaction would be worst at a more acid concentration that was also correct because as the graph shows there is less oxygen produced when the PH is 3, apposed to when it is 5. However I cannot comment largely on the alkaline scale because I only went one to a PH of 8, I believe that If a had gone further then the graph would have had a negative gradient from the optimum point, and the alkaline side of graph would have looked like the acidic side.
As the graph does show when there is a low PH of 3 there is little catalytic activity but then as the PH goes up to around 7 the activity increases but then reaches its optimum point and then activity falls again as the enzyme is denatured.
Explanation
From my experiment and my biological knowledge of enzymes I can conclude that.
Temperature affects enzymes in a way that at high temperatures the enzymes and substrate molecules have high kinetic energy. Which basically means is that that the molecules are moving around more in the solution and therefore collide more often and the substrate and enzymes can react quicker. Also with high concentrations of both acids and alkalises the enzymes denature and as the intensity of the PH’s increases it becomes ever more difficult for the substrates to fit into the active site, this slows down or at high extremes stops the reaction. The concentrations of enzymes and substrate molecules also has an effect on the reaction time and amount, a reaction can only go so far if there is not an equal measure of both. If there was 500 enzyme molecules and only 100 substrates then the reaction would only take place up until all the substrates have formed enzyme-substrate molecules, so therefore 400 enzymes will be unused.
