Temperature
-As temperature increases, molecules move faster. In an enzyme catalysed reaction, such as the decomposition of hydrogen peroxide, this increases the rate at which the enzyme and substrate molecules meet and therefore the rate at which the products are formed. As the temperature continues to rise, however, the hydrogen and ionic bonds, which hold the enzyme molecules in shape, are broken. If the molecular structure is disrupted, the enzyme ceases to function as the active site no longer accommodates the substrate. The enzyme is denatured.
-We can just use the room temperature (20-23ºC) in this experiment.
Substrate Concentration
-When there is an excess of enzyme molecules, an increase in the substrate concentration, produces a corresponding increase in the rate of reaction. If there are sufficient substrate molecules to occupy all of the enzymes´ active sites, the rate of reaction is unaffected by further increases in substrate concentration as the enzymes are unable to break down the greater quantity of substrate.
-To control the substrate concentration, identical quantities of the substrate were used for each reading. To ensure that this was measured precisely, 20ml-measuring cylinder were used to accurately gauge to exact quantities.
Inhibition
-Inhibitors compete with the substrate for the active sites of the enzyme (competitive inhibitors) or attach them to the enzyme, altering the shape of the active site so that the substrate is unable to occupy it and the enzyme cannot function (non-competitive inhibitors). Inhibitors therefore slow the rate of reaction. They should not have affected this investigation, however, as none were added.
The volume of catalase solution will not be changed as well. So the temperature, inhibition, substrate concentration, and volumes of enzyme are kept constant So that it is a fair test.
Method
1. Make the concentration of 20%, 40%, 60%, 80% and 100% of celery extract solution. I want use 4ml of celery extract and 16ml of water as 20% of celery extract solution, 8ml of celery extract and 12ml of water as 40% of celery extract solution, 12ml of celery extract and 8ml of water as 60% of celery extract solution, 16ml of celery extract and 4ml of water as 80% of celery extract solution, and 20ml of celery extract as 100% celery extract solution. Pour each one of the solutions in a test tube, and place them on the test tube rack. To make sure that the concentrations are accurate, a syringe or a measuring cylinder will be used to measure the volume. (E.g. Measure 16ml of water in a measuring cylinder (or a syringe) and use a syringe (or a measuring cylinder) to measure 16ml of Celery extract solution, pour both of the water and Celery extract in a beaker to make the concentration of 20% of enzyme solution.)
2.The equipments are assembled as shown in figure 1.
Clamp & Boss
100ml Gas syringe (collect O2)
3-way tap 2 of 10ml syringes for add catalase
Boss & Clamp A rubber bung with 2 holes
Conical flask (contain 20ml of hydrogen peroxide)
Stand
Figure 1.The apparatus for this experiment
3.The conical flask will contain 20ml of hydrogen peroxide solution. I will use a gas syringe to add enzyme solution into the conical flask. The gas syringe on the top of the apparatus will collect the oxygen gas Produced by the reaction.
4.I will begin to record the time when the enzyme solution comes into the flask. Try each concentration of the solution once, and write down the time used for collect 30ml of oxygen gas.
5. Repeat the experiment 3 times if it is possible; to calculate the average, make the results more accurally.
Risk assignment
1.Hydrogen peroxide is a dangerous substance. It can cause serious injury to the eyes and skin. It is therefore necessary that goggles be used for eye protection. In addition, eye irrigation equipment should be readily available in case of an emergency.
2. Hair should be tied back, ties must be tucked into the shirt and the working area must be clean, tidy and dry. Make sure there is no obstacle in the working area so that you can easily move around as. This allows you to perform the experiment safely and unimpeded care should be taken to ensure that liquid is not spilled onto the floor to cause slippage.
Prediction
The enzyme molecules have active sites that help them to recognize their substrates in a very specific way. Just like a key only fits into a specific lock, each enzyme has its own specific lock, each enzyme has its own specific substrate. This is called the lock and key theory. The enzymes never actually get consumed in the process; they just increase the rate of reactions.
I think the concentration of 100% of enzyme solution will produce 30ml of oxygen gas by the shortest time, because it has more enzyme molecules than other solutions, in the plant the enzyme is undiluted, and therefore the most efficient solution is likely to be 100%.
Conclusion
A preliminary test was carried out to practice the techniques of measuring small volumes with the syringe and making accurate concentration of enzyme. It was also beneficial, because some problems were encountered with the assembly of the equipments, which would have had a negative effect on the experiment if they had not been detected beforehand.