IntroductionA Catalase is an enzyme, which is a protein, which acts as a catalyst in reaction. Hydrogen peroxide is built up naturally in the organisms, but is harmful for them. Catalase have a specific structure that allows them to bind with the substrate and complete the reaction. Changes in environment e.g. temperature, etc. can alter the structure of the catalase and it may no longer react with the substrate. The substrate concentration gives us an understanding of what is the proportion of dissolved substance (in my case hydrogen peroxide) within a unit of volume. The reaction of the enzyme with a substrate can be outlined : “enzyme and substrate(s) bind temporarily to form an enzyme–substrate complex. The binding site on the enzyme is known as the ‘active site’ and is structurally complementary to the substrate(s).”(http://www.oxfordreference.com/view/10.1093/oi/authority.20110803100111657) Catalase speeds up the reduction of hydrogen peroxide. Another example of an enzyme would be the enzyme found in saliva that helps digest the food. I am going to test how the concentration of the substrate, hydrogen peroxide, will affect the rate of catalase activity in potato. Potatoes have enzyme to remove extra hydrogen peroxide from their tissues. Enzymes that are found in a potato can turn hydrogen peroxide into oxygen and water. It is engaging to explore the enzyme activity, because human body involves processes with enzymes. The study of rate of enzyme activity can give a better understanding of the enzymes and what they do and allow me to approach the problem analytically. Also, in future, the study of enzyme activity can lead on to discoveries of new methods of curing diseases in living organisms, which is a major step forward in medicine for humanity. VariablesIndependent variable: Concentration of the substrate (hydrogen peroxide)Dependent variable: amount of oxygen producedControl variables: Temperature of the substrate.The increasing temperature will give more energy to the reaction and the results can be affected, because the excessive energy will make the particle move faster and thus more collision will occur between the proteins and the substrate. It is important to control because the temperature can affect the rate of reaction. To control this variable measure the temperature with a thermometer before each trial and make sure it is 24*C.Volume of the substrate. The volume may have an effect on the results because larger volume of substrate will have more hydrogen peroxide molecules in it, so the activity of catalase may be higher. To control this variable use a graduated syringe to ensure a 10 ml constant volume is used during experiment.surface area of potato. The surface area of the potato is important to control because the larger surface area will have more catalase molecules , hence the results may be affected. It is important to control because the surface of the potato sample can affect the rate of reaction. To control this variable cut the potato with a cutter with the same diameter and crop the pieces with a scalpel if necessary. The cutter is shown below. https://www.google.com.ua/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjNspqqstrYAhUMKlAKHUbmBeYQjB0IBg&url=http%3A%2F%2Fbrilliantbiologystudent.weebly.com%2Fosmosis.html&psig=AOvVaw1s38SsbWIoMKPrgIRx7V8i&ust=1516120282289660Same equipment for all samples. Use the same set of equipment for all the trials (after washing between each trial)HypothesisThe increase in concentration of the substrate will increase the activity of catalase, because larger concentration means there is more molecules that can react with the enzymes, hence more oxygen will be reduced from the hydrogen peroxide.MethodTo make different concentration of hydrogen peroxide, add the required proportion of water in the 3% solution. To create a 2.5% concentration you would need to add 8.3 ml of hydrogen peroxide for every 1.7 ml of water. Concentration of mixtureHydrogen Peroxide (3%) mixture amount (ml)Water Amount (ml)3.0%1002.5%184.108.40.206%220.127.116.11%551.0%3.36.7Cut 5 identical pieces of potato. To ensure the samples are the same size and shape use a cylindrical cutter, which cuts the potato the same volume and shape and measure their length using a ruler. Place the potato into the test-tube. Attach a rubber tube to the whole in the test-tube.Place the the end of the rubber tube into a beaker containing water, so that it is fully under water.Before pouring the substrate into the test tube, use a thermometer to measure the temperature and measure the volume (10 ml) using a graduated cylinder so that these variables are same for all trials, and then pour it into the test tube and seal the top.To ensure the rate of bubbles is the same for all trials use the same rubber tube for all trials (with the same volume).Start the timer when you see a first bubble appear in the water with the end of the rubber tube.Count the amount of bubbles produced for 2 minutes.Repeat the same process 5 times for each time you change the concentration of the substrate. The apparatus should look like this. science.taskermilward.org.ukResults AnalysisFigure 1 Amount of bubbles produced in 2 minutesConcentration of substrateTrial 1Trial 2Trial 3Trial 4Trial 5AverageStandard of deviation3.0%505266686059.28.12.5%454848464918.104.22.168%40333437322.214.171.124%2927292825126.96.36.199%2627262323251.9Figure 2Figure 2 shows a graph which represents the rate of change of the amount of bubbles produced by the potate placed into different concentration solutions. The graph shows a strong positive correlation, which means that as the concentration of the substrate that the potato is placed into, increases the amount of bubbles produced, hence the rate of the catalase activity increased. The change of the average between 1% and 1.5% was 2.6 bubbles per 2 minutes, between 1.5% and 2% was 7.6 bubbles per 2 minutes, and the difference between 2% and 2.5% and the difference between 2.5% and 3% was 12 bubbles per two minutes. On the other hand, high r2 value 0.95 suggests that all the mean values are extremely close to the trendline, which suggests more sufficient evidence for the pattern. Moreover, the absence of abnormal values suggests that the experiment was carried properly and the control variables were controlled. ConclusionIn conclusion, after analysing the data the hypothesis can be supported by the results. The increase in the concentration of the substrate will increase the rate of activity of the catalase. When the concentration of the substrate was 1.5% the average amount of bubbles produced for five trials was 25, whereas when the concentration of the substrate was 3% the average number of bubbles produced for five trials was 59.2. Hence there is a strongly positive correlation between the catalase activity and the concentration of the substrate. This is because the greater concentration of Hydrogen peroxide means a greater number of its molecules in the substrate, hence more active sites will be involved in the reaction.EvaluationEvaluation of control variablesTemperature of substrateThe temperature was around the room temperature for all the trials. To ensure that this variable is controlled more precise, the temperature of the substrate could have been measured with a more precise thermometer, to ensure more reliability.Volume of substrateThe volume of substrate was controlled using a graduated syringe. To ensure more reliability, a more precise measuring tool could have been used.Surface area of potatoTo ensure the surface area was the same, I used the same volume of a cutter and measured the length of the potato samples. However, the end samples might have been not accurate enough and vary in surface area. This could have contributed towards less reliable results, as surface area is a key feature for the reaction time.EquipmentI used the same equipment for all the trials and washed it between each other. The washing might have been not enough to clear the materials from the previous trials and this could’ve affect the results. For more accurate result, a fresh set of equipment can be used for each trial.Concentration of substrateI started with a 3% hydrogen peroxide substrate to create mixtures with lower concentrations. I ensured the ratio is correct by calculating the proportions. Number of trialsAlthough the number of trials was kept equal, I could have carried out more trials to increase the reliability of the experiment.