To carry out this experiment I will collect all the equipment that is needed in this experiment the temperature that I will be using are in intervals of 10 as this will help us to see how it increase if it doubled or halved. I was at first going to increase the intervals at 2 but I realised that this will not give us a broad view of a variety temperature. I would also have to take a lot more reading to see if at above 50 the enzymes will denature. The temperature that I will use are 10 , 20 ,30 ,40 ,50 ,60 and 70 . These numbers give me a wide variety and give me more then 5 readings. These reading would also see if my prediction are correct if they denature after 40 .
I will start off this experiment by testing 10 . The way that I will test if the catalase works at this temperature by placing 5ml of hydrogen peroxide (H O ). When doing preliminary work I found that this was a reasonable amount of hydrogen peroxide to be working with. To get the hydrogen peroxide and the liver (I had a choice of either using liver or potato as they both contain catalase but doing the preliminary work I found that liver worked a lot better as more oxygen was given off) to the right temperature, I will place them in a water bath. The water bath will be a beaker, which is filled with water. As the water from the tap is warmer them what I need I will cool the water down by adding ice cubes. I will place a thermometer in the water bath to make sure that the temperature is constant. It is important that the temperature stays constant as it can make the results inaccurate.
When I have the water bath ready I will place the boiling tube that has 5ml of hydrogen peroxide in. I will leave the boiling tube in for a while so that it will have time to change to the temperature 10 . I will leave the boiling tube in for about 2 minutes, I don’t want to leave it in for too long as the hydrogen peroxide will start to break down itself and this will make the results inaccurate. I will time the amount of time it is left in using a top watch the reason for this is so that the boiling tubes have equal amounts of time in the water bath until the liver is added. When I leave the test tube in for 2 minutes I will leave the thermometer in the water bath and I will check the temperature is constant.
While the hydrogen peroxide is in the water bath I will cut the piece of liver that is needed. I will use a sharp knife and a white tile to do this. I did some preliminary work to find out what shape and weight would be needed. Doing the preliminary I found that 0.25 grams of liver would be enough to react with the hydrogen peroxide and give off enough oxygen gas. The shape that I would use would be a long thing rectangular shape. It is important that they are the same shape, as surface area will affect the results so to keep it a fair test I will use the liver with similar weights and sizes.
The reason why I have not placed the liver and the hydrogen peroxide in the same boiling tube straight away is because if I did this the catalase would start to break down the hydrogen peroxide before it reached the temperature that I wanted it to reach, this would them cause inaccurate results.
When I place the liver and the hydrogen peroxide in the same boiling tube I will collect the oxygen gas that is given off. As when catalase reacts with hydrogen peroxide oxygen and water is given off. The reason I am collecting the oxygen gas is because it will show me how well the enzyme is working when the catalyse is put with hydrogen peroxide. There were three was that we could collect the gas and we did preliminary work to find out which method would be the best. One of the methods we tried was to use the gas syringe. We tested this by placing a delivery tube on top of the boiling tube, which had the liver and the hydrogen peroxide in it. The tube was attached to the gas syringe and as the gas was giver off the gas syringe would move to show us the volume given off. The problem with this method was that the gas syringe some times got stuck and didn’t move which made the results inaccurate so we decided not to use this method. The second method we tried was to collect the oxygen in a test tube. Placing a delivery tube on top of the boiling tube that had the liver and the hydrogen peroxide in it did this. The tube led to an inverted test tube under the water. We counted the amount of bubbles that were given off but we realised that not all the bubbles were the same size so it would give an inaccurate result. They way that we will collect the gas is similar to the last method but instead of an inverted test tube under water we will use a 50ml measuring cylinder. This will be done by using a beehive shelf, as it will be easier to direct the deliver tube to the measuring cylinder. As we were using a beehive shelf and a measuring cylinder it did not fit into a beaker so we had to use a bucket. At first we were going to use a 20ml cylinder but doing the preliminary work we found that this was not enough as it I the reaction more oxygen was given off. We will fill half the bucket with water and will put the beehive shelf into the bucket. I will then fill a 50ml measuring cylinder with water and then holding my finger over the top I will turn in around and place it the bucket so that the tube I directly under it. This is so that the gas can be collected. This method will allow us to see the volume of water that was displaced by the oxygen coming from the reaction. To make it a fair test I will time the amount of time for the reaction and doing the preliminary work I found that 1-minute was long enough. W will use a stop watch to time this. I will repeat this experiment with the other temperatures only changing the way the water bath is made as if above 40 is needed I will add hot water instead of ice cubes. Each temperature will be done three times so that any errors that will occur will be taken into account.
In this experiment there are certain variables that I have to keep the same, as they would affect the results, as they affect the way that the enzymes work. The variable that I am changing is temperature. The other variables are pH level (acidity), concentration of hydrogen peroxide and the amount of liver.
The acidity affects the way that the enzymes work. Most enzymes have an optimum pH close to pH7. PH levels can affect enzymes activity in two ways. The first way is where the active center can substrate bind together. The ions that re present here are charged ions and the pH can cause these ions to become uncharged. The uncharged groups formed as a result can no longer connect with substrate an so catalytic activity is lost. The other way that the enzyme molecules can change shape and become denatured. This however is more likely to happen in extreme values of pH. Which tend to weaken the forces holding the enzymes molecules together the pH level that I will use for the enzyme to work is pH7.
The reason why concentration affects the enzymes is because for most enzyme controlled reactions varies with the concentration of the available substrate.
Increasing the concentration of substrate can give an increase reaction rate, but this is only when the concentration of the substrate remains slow. When larger substrate concentration are used, the reaction rate becomes less dependent upon the concentration of substrate can goes towards a fixed maximum determination by the amount of enzymes produced.
At low substrate concentration many of the available enzymes molecule will have active center, which are unoccupied, and the limit the supply substrate molecules. To make it a fair test I will keep the concentration of hydrogen peroxide the same in all experiments. Also as the size of the liver affects the result a as the larger the piece is the more enzymes it has in it so I will weight out all the liver pieces so that they weight 0.25 grams (doing the preliminary work I found that this was enough) with them all having long thing shape.
I will collect all my results I will place them in a table and using this table I will produce a graph.
Diagram
Method
When doing the experiment I found that there were some problems with the plan that had to be changed. There were changes that were made to the equipment used. The equipment that I used to carry out this investigation were:
- Thermometer- this was to measure the temperature of the water bath.
- Ice- to cool the water
- Bunsen burner/Tripod/ gauze- this was used to heat the water. The Bunsen burner was used instead of a kettle as with a Bunsen burner we could monitor the temperature and steadily heat the water to the temperature needed.
- Liver- this contains catalase enzymes
- Hydrogen peroxide- used as the substrate
- Boiling tube/Beakers – hold the hydrogen peroxide and water baths
- Stop watch- Time the reaction
- Knife and white tile- to cut the liver
- Weigh scale- to weigh the liver
In the experiment we used 0.25 grams of the liver and 5 ml of hydrogen peroxide. We left the reaction for 3 minutes. We changed the time instead of 1 minute we did 3 minutes and the reason for this was because we felt that not enough oxygen was given off in this time and the oxygen displaced not a lot of water. We changed the time to 3 minutes as more water was displaced by the oxygen given off, better readings.
Results
1st set of results
2nd set of result
Averages
