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AS biology coursework on enzymes

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Introduction

BIOLOGY COURSEWORK ON ENZYMES AIM: To investigate the effect of substrate concentration on the rate of an enzyme catalysed reaction. INDEPENDENT VARIABLE: My independent variable will be the substrate concentration used in my experiment. It is the factor that I will change throughout my experiment. I have decided to use five different ranges of starch so I can see how substrate concentration affects the rate of reaction. In theory as substrate concentration increases, the rate of reaction will increase up to a point. This is because there are many more substrate molecules available to lock onto the enzymes active sites. Once the enzymes active sites have all been filled up, adding more substrate concentration will not have an affect on the rate of reaction anymore which means slows down the rate of enzyme/substrate complexes being formed. Below is a table showing how I will gather my five different ranges of substrate concentration that I will use in my experiment. Substrate Concentration / % Substrate Volume / cm3 Distilled Water Volume / cm3 Enzyme Volume / cm3 0.2 2.0 8.0 10.0 0.4 4.0 6.0 10.0 0.6 6.0 4.0 10.0 0.8 8.0 2.0 10.0 1.0 10.0 0.0 10.0 As seen from the table my total volume for each range will add up to 20cm3. I am using five different ranges of substrate concentration and some of them will be less than 10cm3 (1%). This will mean that in order for me to reach a total volume of 10cm3 substrate, I will have to add different amounts of distilled water to keep the volume the same for each experiment. For my first experiment I will add 2cm3 of starch into a test tube followed by 8cm3 of distilled water. I will then add 10cm3 of amylase to get a total volume of 20cm3. I will carry out my other 4 experiments in this order but the amount of starch, distilled water and amylase will wary of course (this is explained more in my method). ...read more.

Middle

Test tube 1 will have 8cm3 of distilled water Test tube 2 will have 6cm3 of distilled water Test tube 3 will have 4cm3 of distilled water Test tube 4 will have 2cm3 of distilled water Test tube 5 will have 0cm3 of distilled water 6] Add two drops of iodine to each test tube using a dropping pipette. A blue/black colour should appear once added. 7] Draw a black cross on a white tile and hold it up against the test tube that you will be testing first. You should not be able to see the cross anymore. 8] Add 10cm3 of amylase into the test tube. As soon as the amylase concentration is in contact with the starch and distilled water concentration, start the stopwatch. A reaction should now start to take place. 9] When the reaction is over, you should see a colorless solution and the black cross should be visible. Compare your result to the control and if both solutions look the same or similar than stop the watch and record your results in table. 10] Do the same for all the other labeled test tubes. (10cm3 of amylase added to 0.4%, 0.6%, 0.8% and 1.0% of substrate concentration) 11] Now repeat each chosen range another 2 more times to get reliable results using the exact same method. ANALYSIS I drew my rate of reaction graph by putting substrate concentration/% along the x axis and rate of reaction x10-3/s-1 along the y axis. I got my x axis values by taking the substrate concentrations from my table and y axis values by using a formula (1/t), where t equals average time taken for the blue/black colour solution to go clear. Looking at my table I can see that as substrate concentration increases, the average time taken decreases. This means that the rate of reaction will increase as more substrate concentration is added to the solution because a colourless solution starts to appear more quickly. ...read more.

Conclusion

This meant that the time taken for the solution to clear had decreased and the rate of reaction had increased due to less molecules being present for collision. I can control this by using a micropipette instead of a dropping pipette to keep the number of iodine drops same in size. As I poured my amylase, substrate and distilled water concentrations into my test tubes, some of the amounts may have stayed inside the graduating pipette where it could not be seen. Small amounts remaining will cause there to be less substrate molecules or less enzyme molecules. This could have affected my results in terms of rate of reaction. If there was slightly more amylase molecules compared to the starch molecules in the solution due to some starch remaining in the pipette, than the time taken for the solution to clear would be longer and the rate of reaction would have decreased. This is because there will be less substrate molecules to collide with the enzyme molecules forming fewer enzyme/substrate complexes. However, if there was slightly more starch molecules compared to the enzyme molecules in the solution due to some amylase remaining in the pipette, than the time taken for the solution to clear would be quicker and the rate of reaction would have increased. This is because there will be more substrate molecules to collide with the enzyme molecules forming more enzyme/substrate complexes. I could improve this course of action by taking more time on transferring chemicals with the graduating pipette to make sure all the liquid has been removed and the right measurements have been taken in. In overall there were no major errors made which affected my conclusions but the results I got from my table didn't really follow a fine pattern due to errors mentioned above. Trends and patterns I got totally backed up my biological knowledge stating that the rate of reaction will increase and substrate concentration increases. If I had to carry out this investigation again in the future I will use a higher range in order to get more accurate reliable results. ?? ?? ?? ?? ...read more.

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