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To investigate the effect of the concentration of starch on an amylase controlled reaction

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Introduction

Aim: To investigate the effect of the concentration of starch on an amylase controlled reaction Introduction (Background Knowledge): I am going to be investigating the effect of the concentration of starch on an amylase controlled reaction. Amylase is a type of digestive enzyme, which is usually found in a human's saliva and small intestine to help digest starch and other long-chained carbohydrates engulfed. An enzyme is a macromolecule (a molecule with a large molecular mass) and a protein that catalyses, or speeds up, a chemical reaction. Enzymes work effectively due to their complex structure and shape. The section of an enzyme where the reaction(s) and combining with reactants (or substrates) take place is called the 'active site'. The enzyme allows the products to form from the substrate by making and breaking chemical bonds easily (and in this case, the starch bonds will be broken). Enzymes are 'recyclable', meaning that they are not used up at the end of reactions and can be used again to combine with other substrate molecules, and thus forming more products. Enzymes are usually specific as to the reactions they catalyze and the substrates that are involved in these reactions. Shape, charge and complementarities of enzymes and substrates are responsible for this specificity. An enzyme is linked to a specific key that fits into a specific substrate - the lock. This is better known as the 'lock and key' model. The picture on the next page explains this in a bit more depth. enzyme + substrate enzyme/substrate complex enzyme + products There are many properties of enzymes including: * Enzymes carry out three main types of chemical reactions - breaking, forming and rearranging bonds. * They are very specific catalysing only one reaction and the same end products are formed every time. * A certain optimum temperature of (usually) 36.7�C is when enzymes act. This is not really the best temperature for the enzyme to work at because denaturation is probably beginning at this temperature. ...read more.

Middle

The concentration of amylase will also be controlled, as it can affect how fast the reaction occurs - the higher the enzyme concentration, the faster the rate of reaction (but to a limit). The volume of starch and amylase will be kept constant, as different volumes take different amounts of time to react with the enzyme. Finally, the pH level will be kept the same, due to the fact that different pH levels affect the work rate of enzymes. However I will also have an independent variable (something I will keep the same) - the concentration of starch - which I will to a different concentration change every time I carry out the experiment. This will allow me to carry out the aim of my investigation. Although, there is a variable that I cannot control - time. This is because, time will be dependant on the reaction rate and I cannot control how long it will take for the reaction to finish. I don't think this will really affect my results, apart from the fact that my graph could be less accurate, as the time scale may be too large. Accuracy: I will try to keep my investigation as accurate as possible so that I can be sure that my final conclusion is one that I can go by and trust. I will do this by carrying out the following checks. To make sure that I am as accurate as possible while measuring how much liquid I have in my measuring cylinder, I will always count the point for the lower meniscus, which will mean that I will be more accurate. I will also be using a digital stopwatch, therefore increasing the accuracy as it will be very reactive and I will also be able to see the split-second times, and allowing me to round up or down to a whole number. One final thing I will do to aid my experiment to be as accurate as possible is use a graduated pipette to transfer liquids from one place to another, making sure that it's accurate to the markings on the pipette. ...read more.

Conclusion

This could be avoided by using a colorimeter, which measures the density of a colour, and therefore would have allowed us to see whether the solution is actually colourless or not. Other miscalculations could include me adding more drops of iodine than needed e.g. adding 4 drops instead of 3 drops each time. The iodine could have then acted as an inhibitor. To deal with this hitch, we could make a fixed mixture of iodine and starch in a beaker, with 1ml iodine to 50ml of starch, and take the volumes from that. The method can also be improved by adding something at the end. Instead of finishing with the colourless liquid, I could also add a step where I measure the product of the reaction with Benedict's solution. This would allow me to see whether maltose is the product of the reaction or not. It would also let me see how much maltose is made. I could also continue experimenting with more concentrations of starch, as in my prediction, I had stated that there will be a point where the rate of reaction will stop increasing and I couldn't find that out with only the 6 different concentrations that I measured. Conclusion: To conclude, I have successfully supported my prediction and found out that as the substrate concentration increases, so does the rate of reaction. I have also found out that the time taken for the enzyme amylase to catalyse starch decreases as the substrate concentration increases. However, I didn't find out whether the rate of reaction stops increasing to a limit even after the substrate concentration continually increases, which is also what I predicted. My results show that there is a trend between the two variables - substrate (starch) concentration and the rate of reaction. I used a graph to represent this trend, as it made it easier to showcase it. The trend appeared because as more and more enzymes are added there will be more successful collisions as there are more active sites free for the substrate molecules to fit into. ?? ?? ?? ?? ...read more.

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