METHOD
- First I put 100mm of hydrogen peroxide each in five test tubes.
- Put a thermometer in the test tube.
- Heat or cool the hydrogen peroxide until it is at 10ºC.
- Take the thermometer out.
- Take a stopwatch to one hand and start it when you put the yeast ball in the hydrogen peroxide.
- Put the yeast ball in the hydrogen peroxide, stop the stopwatch once the yeast ball has risen to the top.
- Record the results.
- Repeat the experiment for temperatures, 20ºC, 30ºC, 40ºC, and 50ºC.
PREDICTION
I think that the yeast balls will rise to the top the quickest at about 37ºC. When the hydrogen peroxide is at a great temperature than this the yeast will take the longest time to rise. At a temperature lower than this then the yeast balls will take longer to rise, but not as long as when the hydrogen peroxide is at a greater temperature than 37ºC. I think this because enzymes work best at 37ºC, and the yeast needs oxygen to make it rise to the surface, and the enzymes here produce oxygen. The enzymes will produce the most oxygen in the quickest time at 37ºC, therefore the yeast will rise quickest at this temperature because it will have the most oxygen in the quickest time. The enzymes turn the hydrogen peroxide into oxygen by the following equation:
Hydrogen Peroxide Water + Oxygen
H2O2 H2O + O
SCIENTIFIC RESEARCH AND EXPLANATIONS
YEAST
Yeast is one of various single-celled fungi, (especially the genus Saccharomyces) that form masses of minute circular or oval cells by budding. When placed in a sugar solution the cells multiply and convert the sugar into alcohol and carbon dioxide. Yeasts are used as fermenting agents in baking, brewing, and the making of wine and spirits. Brewer's yeast S. cerevisiae is a rich source of vitamin B.
Yeast artificial chromosome (YAC) fragment of DNA from the human genome inserted into a yeast cell. The yeast replicates the fragment along with its own DNA. In this way the fragments are copied to be preserved in a gene library. YACs are characteristically between 250,000 and 1 million base pairs in length. A cosmid (a fragment of DNA from the human genome inserted into a bacteria cell) works in the same way.
I know that the more common enzymes work best at around 40ºC. Their optimum temperature is actually 37ºC. If this temperature begins to rise or drop the reactions slow down, this will continue to happen until the enzyme is denatured. It becomes denatured at around 60ºC. This happens because the enzyme becomes misshapen. This means that the enzyme will no longer work because it will no longer fit, the active site will be ruined. The enzymes react like a lock and key, only one lock fits the key. When the two join then you get the chemical reaction. When too much heat gets applied then the lock gets changed and so the key doesn’t fit the lock so there is no reaction.
EXPERIMENT RESULTS
ANALYSIS
WHAT I HAVE FOUND OUT
From my results I can see that when the temperature is somewhere between 30ºC to 50ºC, the yeast cells rise the quickest, and therefore are producing the most amount of oxygen in the shortest space of time.
GRAPH OF RESULTS
TRENDS AND PATTERNS IN MY RESULTS
In my results I can see that the line on my graph goes up and then comes back down though steeper, in an also most 'U' shape.
WHAT THE GRAPH SHOWS
On the line graph of my results the line goes in a kind of 'U' shape which the right side of the line is steeper than the left. Where the line is at it's lowest point is where the enzymes are in the optimum temperature to work and so, therefore, are producing the most oxygen in the shortest amount of time. When the temperature of the hydrogen peroxide is above it's optimum we can see that the performance of the enzymes rapidly decreases. When the temperature of the hydrogen peroxide is lower than its optimum for the enzymes, their performance rate decreases, though less rapidly than if the temperature was above the optimum.
From my results I can see that the enzymes rise quicker as the temperature of the hydrogen peroxide gets hotter until the temperature reaches 40ºC. At around this temperature the enzymes performance suddenly drops, and therefore don't make that much oxygen very quickly, and so the yeast balls take longer to rise as they don't have as much oxygen helping them to rise. Because the graph line goes in a 'U' shape, this shows that there is an optimum temperature, when the enzymes make the most oxygen in the shortest space of time.
OTHER GRAPHS TO SHOW MY RESULTS
MY PREDICTION
From my results I can see that my prediction was correct. The yeast balls rise to the top the quickest at about 37ºC. When the hydrogen peroxide is at a greater temperature than this the yeast take the longest time to rise. At a temperature lower than this then the yeast takes longer to rise, though not as long as when the hydrogen peroxide is at a greater temperature than 37ºC.
This is because enzymes work best at 37ºC, and the yeast needs oxygen to make it rise to the surface, the enzymes here produce this oxygen. The enzymes will produce the most oxygen in the quickest time at 37ºC, therefore the yeast will rise quickest at this temperature because it will have the most oxygen in the quickest time. The enzymes turn the hydrogen peroxide into oxygen by the following equation:
Hydrogen Peroxide Water + Oxygen
H2O2 H2O + O
I know this because, as we can see on the graph, the yeast balls produce the most oxygen around 40ºC because this is where the line on the graph peeks. Before this peek the line rises slowly showing that the performance of the yeast improves slowly as the temperature rises. After the line has peeked the line on the graph turns steeply downward, showing that the yeast performance drops considerable as the temperature rises above 40ºC.
EVALUATION
ACCURACY OF MY RESULTS
I think that my results were fairly accurate and precise though there was obviously a little variation in my results for each temperature as in each test there are sometimes different results eg;
In this case for the 40ºC, the results vary from 16 to 17 seconds. These results must be still fairly accurate though, as there is only one-second difference here.
ANOMALOUS RESULTS
The only anomalous result as the one for the 50ºC as it was completely out of sequence of the other results. This isn't really wrong though for two reasons. The first is that I did the test for this temperature three times, like the others, and the result was still near enough the same. Secondly I had expected this result in my prediction, that the performance of the yeast enzymes would drop dramatically when the temperature of the hydrogen peroxide rose above 37ºC. If this result is truly wrong or anomalous then the problem could be that the hydrogen peroxide wasn't properly heated, or another variable (see page 2) had been change at the same time, making the test unfair and invalid.
THE METHOD
I think that my method was fairly good, of course there are ways to make it better. Firstly you could get a very sensitive set of scales and make sure that all the yeast balls used in the experiment are the same size and weight. Secondly you could do the same thing to the yeast balls but to the hydrogen peroxide, making sure the hydrogen peroxide is always the same amount. Thirdly you could rather than timing the yeast balls, put the yeast balls in different test tubes that are still the same size but contain different temperatures of hydrogen peroxide. You put the yeast balls in at the same time and just record which yeast balls of which temperature reaches the surface first. Also, rather than using temperatures 10ºC apart, I'd use ones a lot closer, and I'd also get a lot more results, so rather then doing temperatures from 10ºC to 50ºC I'd use temperatures from -10ºC to 70ºC. The other thing that would need improving in the experiment is the fact that heating the hydrogen peroxide and measuring it will just a bunsen burner and a thermometer is very inaccurate. You'd have to use another method of heating the hydrogen peroxide, and keeping it at a constant temperature, otherwise the hydrogen peroxide will cool down during the experiment.
MORE EVIDENCE
To really support my theory, I would definitely need more evidence, but the only evidence, which would be worth anything to prove my theory, would have to be in more tests.
EXTENDING THE EXPERIMENT
If I extended the enquiry further I believe I would probably find that enzymes are very particular about the temperature they work in. I also believe that if the temperature went low are high enough the enzymes would stop working altogether and possible even die.