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Identifying Variables.

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Introduction

Identifying Variables Independent Dependent Control Enzyme concentration - in my experiment, I used different concentration of enzymes (1%, 0.75% 0.5% 0.25%) to see how the rate of reaction affects by the concentration of enzymes Rate of reaction - time taken milk to be cleared - temperature ( room temperature) PH - I didn't control it and it might have changed Volume of enzyme - 5cm3 Volume of substrate which is marvel casein - 5cm3 Start timing as soon as enzyme's added Shake the concentration of marvel and enzyme gently and occasionally which is not very controlled What are the reasons for controls? * We did the experiment at the same temperature of room temperature the reason that temperature affects the rate of reaction. In fact over a range or 0 - 40 degree the rate of an enzyme controlled reaction doubles for every rise of 10 degree. Because according to Collision theory, heat increases molecular motion, thus the reactants move more quickly and chances of their bumping into each other are increased. As a result there is a greater probability of a reaction being caused. But after 40 degree (optimum point) enzyme denatures and is no more proportional to the rate of reaction because the structures of the enzyme and its active sites have been disrupted. Therefore we tried to do the experiment at the same time for accuracy of result. * Also under conditions of constant temperature every enzyme functions most efficiently over a narrow pH range. When the pH is altered above or below the optimum point, the rate of enzyme activity slows down. ...read more.

Middle

If activity is measured over a period of time, I predict that my graph at a point the rate of reaction will level off as numbers of enzyme molecules will outnumber substrate molecules. Therefore, I can say that it has reached ' the limiting factor' where the rate will not increase and there aren't enough substrates to pair off with the enzymes to produce increasing product. This is the graph of what I predict for the experiment Analysis The graph shows that the rate of reaction increases as the enzyme concentration increases as long as the substrate concentration is maintained at a high level, pH is kept constant and temperature is kept constant as I predicted in my prediction. It is because as enzyme concentration increases more active sites will become available so the rate of the enzymatic reaction will increase. The substrate concentration has to be maintained at a high level, because there should be enough substrate to fit with enzymes otherwise enzymes are useless. Also we have to keep temperature constant since as heat increase molecular motion, thus the reactants move more quickly and chances of their bumping into each other are increased until it reaches to its optimum point where the enzyme starts to denature. And pH has to be kept constant because enzyme is very sensitive to pH so changes of pH cause the enzyme shape to alter so the enzyme would no longer fit into substrates. I predicted a proportional line. I predicted a linearly proportional line in which if you double the enzyme concentration than you will also double the rate of reaction, due to double the amount of collisions by molecules however, my graph didn't fallow my prediction. ...read more.

Conclusion

Therefore I didn't include the third experiment when I calculated the rate of the reaction. As a matter of fact, the graph trend was very similar to what I predicted and gave me a good enough to conclude that as the concentration of enzymes increases then the rate of reaction increases. Further works I wanted to see my graph meeting a plateau<leveling off> which I predicted in my prediction. However I could not observe it from my graph since the range of the concentration of enzymes was too narrow. Therefore for my further works I would just repeat the experiment with increased range of the concentration of enzymes which will be 0 ~ 5 percent so that I can hopefully see my graph leveling off and can conclude that I observed my graph levels off at a certain point as numbers of enzyme molecules will outnumber substrate molecules. Therefore, I can say that it has reached ' the limiting factor' where the rate will not increase and there aren't enough substrates to pair off with the enzymes to produce increasing product. I would also want to do another experiment to give evidence that enzymes are sensitive to the temperature because I think that my third experiment went wrong mainly because of different temperature. Method I would get samples of starch solution and the enzyme amylase (which breaks starch down into simple sugars) are misted together and kept at different temperatures. Samples from each experiment are tested with iodine at regular intervals. The result and conclusion In the presence of starch iodine turns blue-black, but when there is no starch present the iodine stays yellowy brown. It is evidence such as this which demonstrates the effect of temperature on the rate of enzyme-controlled reaction. ...read more.

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