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An Investigation into how the varying concentration of a substrate affects the rate of reaction of Catalase.

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Introduction

An Investigation into how the varying concentration of a substrate affects the rate of reaction of Catalase In this investigation, I am going to explore how varying the concentration of Hydrogen Peroxide (H2O2) affects the rate of reaction of the enzyme, catalase. Background Knowledge Enzymes are organic catalysts. Catalysts are chemical substances that speed up a reaction but remain unaltered throughout the reaction. They are made in all living cells and control the chemical reactions that keep the cell alive as well as speeding up the metabolic processes. Enzymes are proteins and their molecules are made up of long chains of amino acids. Enzymes can be divided into two groups. Intracellular enzymes occur inside cells and control metabolism. Extra cellular enzymes are produced by the cells and achieve effects outside the cell. E.g. digestive enzymes. o Enzymes are specific which means that an enzyme that acts on one substance won't act on another. The substance an enzyme reacts with is its substrate. They fit together like a lock and key. The place where the molecule fits into is called the active site. When the substrate is inside the enzyme it's called an enzyme substrate complex. The enzyme breaks the substance into smaller molecules called products. These are produced when the reaction has finished. The enzyme remains the same and so can be used again. o Enzymes work very rapidly and the speed of action of an enzyme is called its turnover number. By this I mean, the number of substrate molecules which one molecule of the enzyme turns into products per minute. o They can work in either direction. o Enzymes are inactivated by excessive heat. They work best at an optimum temperature (40�C) and if this temperature is exceeded the enzymes become denatured. Denatured means that the chains of amino acids holding the enzyme together break and so it loses its shape irreversibly. ...read more.

Middle

I will measure the length of the potato to the nearest 0.1cm and I will measure the time at exactly 3 minutes to keep the time constant and so the test is fair. Prediction Using my background knowledge, I predict that as the concentration of the hydrogen peroxide increases the rate of reaction will also increase. I think this will happen because if you increase the concentration of the substrate there are more molecules per cm� and they are more densely packed. Therefore there is a much higher chance of the molecules colliding and reacting. I predict that the rate of reaction will reach a plateau because the higher the concentration the more saturated the active sites of the enzymes are and so the enzymes are working as hard and as fast as they can to break the substrate molecules into products. Therefore the enzymes can't work any harder and so the rate of reaction won't increase any more and will reach a plateau. I will display my results on a graph: Rate of reaction cm�/ min Concentration of hydrogen peroxide/ vol I expect the graph to look like this because it shows the rate of reaction increasing as the concentration of hydrogen peroxide increases, as predicted. The graph levels off because the enzymes are overworked in higher concentrations, which is what I'm predicting. I also expect the line of best fit on the graph to go through the origin because when there's no hydrogen peroxide; there will be no rate of reaction. To help plan my method, I carried out some preliminary experiments to see if the experiment worked best with a whole tuber or one, which was cut up into pieces. To do this I: 1. Cut 2 pieces of potato using the cork borer. 2. Used the scalpel to make them 3cm and cut one tuber into 3 1cm pieces. 3. ...read more.

Conclusion

By doing this it made the experiment much more efficient and I achieved good results. The equipment I used was suitable and I would not change it. If I did the experiment again I would cut all my potatoes before starting the experiment - for the original readings and the repeats-so that the surface area of the potatoes were the same. I would try and stop collecting gas at the exact time for each experiment to prevent inaccuracies. I would also do more repeats if I had more time to make my results really reliable. Because my results didn't fully match my prediction I would have to get additional and sufficient evidence for the conclusion. To do this I could use higher hydrogen peroxide concentrations to see if the active sites of the enzymes became saturated and so see if the line of best fit reached a plateau on my graph and therefore try and prove my prediction. Because higher concentrations are not available to me, I could instead try the same concentrations as I have done for this experiment but use smaller bits of potato so there would be fewer enzymes to decompose the hydrogen peroxide. The line of best fit would then level off because there will be a point when the substrates are queuing up to get into the active sites, and so the reaction will be taking place as quickly as possible, and so the rate of reaction will remain constant I could also try using concentrations of hydrogen peroxide with smaller intervals (10, 10.2vol, 10.4vol) so I had more points to plot on the graph and so the line of best fit would be more definite. I could use a larger potato, like 6cm, to see if more enzymes mean a quicker rate of reaction. The rate of reaction would be quicker because there is more enzyme and so more molecules per cm�, which means there's a higher chance of he molecules colliding with the substrate molecules. ...read more.

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