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Concentration Of Substrate Essay, Research Paper

I have to plan and carry out an experiment to investigate the way in which concentration of a substrate affects the rate of an enzyme-catalysed reaction. I will need to carry out some background information to find out what may affect my experiment.

Background Information:

An enzyme is a biological catalyst. They speed up the rate of a reaction however they are not affected themselves whilst doing this, this is why they are catalysts. Enzymes are made to be specific, this means that they can have only one substrate that they will work on. Each enzyme has an active site that is where their own specific substrate´s molecule will fit into. Enzymes all work best at an optimum temperature that is usually body temperature at 37C. If the temperature that the enzyme has to work at gets too high, normally 40C it will start to become denatured and therefore no longer work on its substrate as the active site has changed shape. Also enzymes usually work best at an optimum pH level, this is normally 7 because enzymes are proteins which are damaged by very acidic or very alkaline conditions. Most reactions work better at higher temperatures, this is because molecules move around much quicker. This makes the molecules have more chance to collide with the substrate. With more collisions there is more chance of a reaction taking place. This makes the rate of reaction faster. At 40C the enzyme starts to be damaged, this slows down the reaction and by around 60C the enzyme will be completely destroyed.

Plan: Safety/Fair:

For this test I will have to make sure everything is done with safety and fairness. Throughout the whole experiment safety glasses must be worn, as Hydrogen Peroxide can be dangerous if it gets into your eyes. All other Lab rules must be followed also. To make sure the experiment is fair I must make sure nothing is changed for different experiments. I will use the same apparatus for each different experiment and I will make sure the same types of celery and Hydrogen Peroxide are used. The equipment should be kept the same to ensure all results are taken without any advantages or disadvantages. Everything in the experiment should be kept the same apart from the concentration of the Hydrogen Peroxide. Each time the celery will be replaced with another 1g of celery, as it will have been used to react with the Hydrogen Peroxide in the experiment before. The celery will be kept covered as much as possible and will only make contact with the Hydrogen Peroxide when the stopwatch is started. When the celery is measured out on the scales some polythene will be placed under it so that none of the celery is absorbed into the scales. All measurements of celery will be made to 2d.p. This will increase accuracy because the minimum and maximum it can weigh will be 0.995g and 1.005g. If it was measured to the nearest gram, the measurements could be from 0.5g to 1.5g which would be totally inaccurate and would make the experiment unfair as amounts could vary hugely.


The first thing I will do will be to put on my safety glasses as this test needs to be made safe before anything can be done. I will then get the equipment I need for the experiment. The equipment I will use is a water basin, a conical flask, a bung, a delivery tube, a measuring cylinder, a syringe, a spatula and a stopwatch. Then I will collect the concentration of Hydrogen Peroxide I will need for the experiment I will be doing; also 1g of celery will be measured out on the electric scales, this will be measured to 2 decimal places as that is what the scales measure in. This is accurate enough for the experiment I will do. I will fill the basin with water next and then fill the measuring cylinder as well. The measuring cylinder will be placed upside down in the basin still full of water, making sure that no water is escapes so that the experiment is fair. I will then stick the liquidated celery to the side of the conical flask; this will be done using a spatula. The next thing that must be done is to put the delivery tube and bung together and place the delivery tube under the measuring cylinder so that any gas pushed through will go into the measuring tube. 5cm of Hydrogen Peroxide will then be measured out using a syringe. This will then be put into the conical flask very carefully; making sure that it doesn´t mix with the celery, then the bung will be put into the conical flask. If the two mix I will have to wash out the flask and start again with new hydrogen peroxide and new celery, as the reactions will have started without the amount of oxygen being recorded. The measuring tube will be kept in place by hand and then simultaneously the flask will be shook, mixing the celery and Hydrogen Peroxide, and the stopwatch will be started. Measurements will be taken from the side of the measuring cylinder every 30 seconds and noted down. All measurements will be made as precise as possible to keep the experiment accurate and fair. Preliminary Work:

I chose to use the different apparatus in my experiment from preliminary work I have done. I could have used liver instead of celery but liver reacts too much too quickly to be able to record the results with any accuracy. This is because it has too many catalaes, so the reactions are made a lot quicker. Once I had chose celery I had the choice of boiled celery or normal celery, this was an easy choice because if I had used boiled celery I would have had no reactions because the enzymes would have denatured due to the high temperatures. Denaturing is when the enzyme loses its shape and cannot work on its substrate. Instead of using a measuring cylinder I could have used a more accurate gas syringe, I couldn´t do this however because they are expensive, therefore not widely available to use. Also the pushing of the oxygen would probably have been too weak to push the syringe enough to record the results. There was a choice between counting the number of bubbles released and the volume of oxygen released. I chose volume because it is more accurate as bubbles can easily vary in size and it is easier to record the volume than counting bubbles.

1g of the celery and 5cm of the Hydrogen Peroxide should be enough for this experiment to produce easily read results, which will also be accurate enough for me to see clearly which is best for reactions.


I would expect from this reaction that the quickest and most reacted concentration would be the 100%. I would then expect 75%, 50%, 25% and then the slowest to react would be the 10% concentration.

I would expect 100% to react quickest because it has the most Hydrogen Peroxide molecules in it. With more of these molecules inside the solution, it is more likely that a collision will take place, molecules must collide in order to react. This means that a reaction is more likely to take place, in a shorter time, making the rate of reaction quicker. More collisions are needed because only one in every 10 to the 14 collisions lead to a successful reaction taking place. The more reactions that take place increases the amount of oxygen produced in the shortest time. The orders of reaction starting with the fastest are as follows: 100%




10% Results:

The results I gained from the experiment are shown in the tables below, the first show all the results for each experiment. The last shows the average figures from all 3 experiments.


My results show me that the higher the concentration of a substrate, the quicker the reaction rates of that substrate and the enzyme working on it. The 100% concentration produced the most 02 in the shortest time, which gives it a higher reaction rate than the others. This shows that my prediction was correct, the highest concentration would produce the most 02 in the shortest time. Also the anticipated results I produced in my plan were correct, as the lines are almost identical to the lines produced in my results. The next highest reaction rate is the 75% concentration, this is because it had the second highest concentration therefore there would have been the second most amount of collisions. As my prediction and background information show, more collisions produces more reactions. The results then show that in order the reaction rate gets lower as each concentration gets lower. My graphs also show that the reaction rate for !00% concentration is quickest because it´s line is steepest therefore it shows once again that more O2 was produced in a shorter time.

My results support my prediction, because as I said, the higher concentration the quicker more of the O2 is produced. Therefore my prediction was correct, from what my results show.


From my results I have found that the higher the concentration of Hydrogen Peroxide, the quicker the reaction rates, producing oxygen.

I have succeeded in what I planned to do, which was to find out how the concentration of H3O2 affects the amount of oxygen produced in an enzyme catalysed reaction. The results I got were what I had expected and predicted and I did not get any anomalous results. The results I got were what I wanted so I was fairly happy with them.

The experiment could have been made more accurate by using other ways of doing things that were important to the experiment. More accurate measurements could have been used as the measuring cylinders used were only to either every 0.5cm2 or 1cm2. This is not really very accurate. Using a gas syringe, which measures much more accurately, could have solved this. Another inaccuracy is when the experiment was started, the measuring cylinder may have still had some air bubbles inside it, this is not fair as air is not pure oxygen, it also has CO2 and Nitrogen in it. This makes the results slightly less accurate. Another thing is that when the celery and the Hydrogen Peroxide were put into the flask, they may have mixed slightly causing some oxygen to be lost.

I feel my experiment was a good procedure to use because it gave good results that were similar to what I had expected. Other ways to make it more accurate would be to only use the juices formed when the celery was mashed up, this is the area which contains the enzymes, not the cell wall which was also present in the celery we used. Sometimes we could have had totally juice for the experiment but other times it could have been mostly cell wall, this would have affected the results. The results may be inaccurate because the experiments were done on two different days, which means two different celery plants were used. Therefore one could have contained more catalase than the other, making results inaccurate. I also know that the temperature can effect the rate of a reaction. The temperature was not the same on both days so this may have changed the results slightly. The enzymes may have denatured in some experiments because of the celery being exposed to the air, some people may not have sealed the container properly. This experiment could be furthered by using more accurate data-loggers that would provide more accurate results, taken at every exact 30 seconds. Also a different machine could have been used to measure the exact amount of enzymes in each experiment. Also more substrate concentrations could have been used to prove the whole experiment was correct. Another thing to be done would be to do more repeats for each concentration, this would make results more accurate when finding averages. This experiment could also be done the same except changing something else each time, like the amount of celery, keeping the same concentration of the substrate.

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