First Preliminary experiment
Amylase and Starch
Whilst starting my first preliminary experiment, I decided to investigate whether the concentration of substrate (starch) affects the time taken for color change. I utilized starch and amylase, and constantly kept 5ml of the enzyme (amylase) in a boiling tube (this was our variable), but we changed the amount of the substrate in intervals of 5 (so we used 5ml, 10ml, 15ml) this was our independent variable. After putting 5ml of starch and amylase in a boiling tube, we then added 5 drop of iodine using a buffer. This then indicated if starch was present; it will turn dark blue. Meanwhile we timed how long it took for the color to change completely transparent.
Looking at my results, I noticed that the 10ml concentration of Starch with 5ml of amylase had the fastest reaction time for color change, therefore this was the most suitable and reasonable amount of starch because when we added 15ml of starch it took longer than the 10ml of starch so it slowed down the reaction and indicated to me that 10ml of starch with 5ml of amylase was its optimum. Thus, due to time I could not repeat my tests to check if these results were accurate, and because of this it could have been an outlier.
During the experiment I came across some difficulties. When the solution turned transparent I was not 100% sure of it, so I put a white blank piece of paper with a cross behind the boiling tube to see more accurately if the solution had turned transparent. My results were also affected by human error, as when adding iodine we were only meant to add 5 drops, but we added more. This was because the solution had not turned dark blue.
Second Preliminary
Hydrogen peroxide and Catalase
On my second preliminary experiment, I decided to investigate whether the concentration of hydrogen peroxide changes the volume of gas created. The substrate is hydrogen peroxide and the enzyme is catalase. We first diluted the hydrogen peroxide with water, with concentrations of 25%, 50%, 75%; this gave us a wide range of results. Then we measured 5ml of catalase and 10ml of hydrogen peroxide. During the experiment I added 5ml of catalase and hydrogen peroxide with water consequently. Then I put the bung on and started the timer, and for every 10 seconds I recorded the amount of gas produced; I did this until 50 seconds.
My results show that using a concentration of hydrogen peroxide at 50% made the most gas, but the 75% concentration barley produced any gas and this told me that there barely was a reaction. Whereas using a concentration of 25% made a larger volume of gas quicker than the 50% and 75% concentration.
However, human error played a big role because it would be hard to keep track of the time and stop it at exactly 10 seconds; this would make my results not accurate. Meanwhile we also shook the boiling tube to speed up the reaction and this could have badly affected out results, therefore it would not be a fair test.
Final Method
In this investigation I am going to be conducting the starch and amylase practical. The factor that I am going test is if the concentration of starch affects the time taken for the color to change. I have chosen concentration of starch because I know that with amylase it can form an enzyme substrate complex. This is because I have conducted this method in my first preliminary and is very easy and quick to do, in addition the results I got were quantitative data. In this experiment my control variables are the concentration of amylase, the amount of iodine, and the same equipment used, e.g. boiling tube, however when using my measuring cylinders I am going to using the range of 0-20ml as this will give me more accuracy. I am keeping them the same because I am testing if the concentration of starch with 5mlof amylase affects the time taken for the starch to break down. My independent variable is the concentration of starch. This is my independent variable because we are testing to see if the concentration of starch affects the time taken for the color to change. My dependent variable is the time taken for the starch to break down; wait for color change).
Hypothesis
In my real experiment that I am going to conduct, I predict that a concentration of 10% of starch will be fastest; I believe this because in my first preliminary it was the fastest. This is also supported by the fact that I know 10ml with 5ml of amylase is its optimum as 15ml of starch is too much and 5ml of starch is too little. Moreover there were limitations such as adding too much iodine; this will probably change our result the next time we do it. Looking at the results I have found, I therefore can predict that each time we increase the concentration of starch the time for color change will become slower, for example if 10ml took 2 minutes, then 15ml will take 3 minutes or more. Finally, I will also repeat the experiment at least twice, to make the results more reliable.
Equipment
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Amylase- Used for substrate
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Iodine - To prove whether starch is present (dark blue color).
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Pipette- to make our measurements as accurate as possible.
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Boiling tubes- to hold our solution and allows us to have a more focused concentration of our enzyme.
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Boiling tube rack- to hold our boiling tubes.
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Stopwatch- to measure our measurements.
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Measuring cylinders (10ml) - We chose to use the 10ml measuring cylinders because they have more intervals; allowing us to have more accurate results.
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White paper- From our preliminary experiments we have learnt that if you keep a white paper behind the boiling tube rack then you can see when the solution has turned fully transparent.
Method
- Measure out 5ml of amylase in a boiling tube.
- Using a pipette measure out 5ml of starch and 5ml of water (50%) in a separate boiling tube.
- Add 7 drops of iodine to the starch using a buffer.
- Then add the amylase to the blue starch solution.
- Start timing on the stopwatch until the solution is transparent then stop.
- Record your results of how long it took.
- Carry on doing this with 5ml, 10ml, 15ml and 20ml of starch with 5ml of amylase each. I have worked out these concentrations because it gives me a good range of data.
Risk Assessment
Iodine- Harmful by inhaling and when in contact with skin.
(Avoid contact with eyes, secure the lid firmly on the iodine, clean up ant spillages).
