Investigation to find the effect of glucose concentration on fermentation of yeast.
Aim;
The investigation to find the effect of glucose concentration on fermentation of yeast.
In this experiment I am going to investigate the fermentation of different Glucose concentration by yeast. To do this I am going to change the glucose concentration and see how different glucose concentration ferment with yeast. I am going to measure how long it will take the fermentation of yeast to take place, I am going to do this by adding phenolphthalein which is pink when it is alkali to the solution and I am going to measure the time it takes for the phenolphthalein to become colourless which is acidic.
How does it effect the rate and which type of glucose concentration works best?
Glucose -> Ethanol + Carbon Dioxide + Energy (C6H12O6 => 2 C2H5OH +2 CO2 + 2 ATP +heat)
Glucose ethanol + carbon dioxide
C6H12O6 (aq) 2C?H5OH (aq) + 2CO? (g)
The factor I have chosen is to vary is the concentration of glucose. The concentration will be 1.0M 0.8M 0.6M 0.4M 0.2,M 0.0M
Fair test
There are many factors that could effect my investigation such as temperature, the volume of yeast and the volume of glucose. To make a fair test I am going to keep this three factor constant, I will also leave the experiment undisrupted during the course of reprising, this mean I won't stir the substrate.
I also made sure that the thermometers were checked and regularly changed throughout the experiment. As if I had used the same thermometer during the whole experiment the results would be inaccurate, as I would have to wait for the thermometer to reach the certain temperatures again.
I made sure that I used the same amounts of yeast accurately, so that I could get the most accurate results. As if we had more or less water in the boiling tube than we should have, the results would obviously be affected, and the experiment would be very unfair.
Upon looking back at the adjustments made, I believe that I am confident in saying that, I made sure that my experiment was as fair as I could possibly make it.
Prediction.
In my investigation I predict that the fermentation of yeast will increase in speed as I increase the concentration of glucose.
As I increase the concentration of glucose, I am increasing the substrate, which will bind to the active site of the enzyme (zymase), which is in the yeast. The rate of fermentation will increase proportionally as the glucose concentration increase but it will eventually stop.
This is a summary of all evidence so far collected to support a prediction.
. Yeast cell respiration
Yeast cells require glucose for metabolism. They respire it aerobically, then oxidise the ethanol produced. Lack of oxygen causes the build-up of toxic ethanol, which can lead to their death. The larger the population, the greater an effect this will have, leading to the population levelling out as mortality rate increases to mortality rate. This causes the transition from the exponential phase to the stationary phase.
2. The phospholipid bilayer
Yeast cells gain glucose from the medium in which they are suspended, and because glucose is a polar molecule, the rate of its transport across the membrane depends on the availability of hydrophilic protein channels. An increase in glucose concentration has less of an effect at higher glucose concentrations. Therefore, when the rate of reproduction relies on rate of diffusion, it follows the same trend with concentration as facilitated diffusion does.
3. The reproduction of yeast cells
The rate of reproduction can be limited by progress through the cell cycle (in the lag and exponential phases) or, if the level of glucose is low enough, can be limited by the rate at which glucose can be obtained. A higher glucose level could therefore increase the rate of reproduction.
4. Environmental constraints on the population
These, strictly speaking, should include availability of oxygen and glucose and the build up of toxins. Their effect is the same: when the number of yeast cells is sufficient, they have the effect of either putting constraints on the size of the population, or increasing the mortality rate to the natality rate. The effect of either is the levelling-off of the [living population]-[time] graph. A limitation to the experiment arises if one of these other than glucose concentration affects the population growth rate.
5) Stop clock
This is to make sure that all the times are correct therefore no guessing or estimation
Also it can be stopped and the time that the sample is removed from the culture and it can be checked later after one has concentrated on the cell count.
6) Water bath
This is to keep the solution at a constant temperature and to optimise the temperature for of the yeast cells to reproduce so that the limiting factor is the glucose concentration.
7) Concentrations using ratios
This enables me to easily gain highly accurate dilutions of my glucose solution because it to eliminates human error due to taking measurements beyond the accuracy of the measuring vessels or the human eye or using several measuring vessels. The percentage concentrations are irrelevant as these can easily be plotted on a graph afterwards and change anyway when the yeast culture is added. This will reduce the percentage error.
Preliminary Work
Respiration in yeast and the effect of temperature
In an experiment, which we looked at how, temperature affects yeast. This was done by looking at how much Carbon Dioxide was produced from identical samples of yeast. We measured the CO? given off in a gas syringe. Then we placed these samples into different water baths, where the water is at different temperature such as 10c, 20c, 30c, 40c, and 50c.
After this we could see from the results that as the temperature increased, the rate at which gas accumulated also increased. However, when it reached around 40c it slowed down and it was even slower at 50c. We can see that the temperature is a variable that we will have to control. By reading (Biology 2) I have found out that the optimal temperature for the yeast to work at is 37c. I am going to do my experiment at 40c.
Conclusions from Trials
Prior to this investigation I carried out a pilot test for the same kind of experiment, but just carrying out one test for each glucose concentrations. But with different amount of glucose, yeast and phenolphthalein.
Although this was a very basic experiment I found that 1.0M of glucose concentration would respire the fastest.
* It became apparent that 1cm3 of yeast was not enough and after several trials I found that 4cm3 of yeast worked well. This meant that more of the substrate was needed.
* The temperature was important in deciding how quickly the yeast would respire and at 40oC a better yield. At higher temperatures the yeast started to stop respiring.
* Instead of collecting the gas via a measuring cylinder and collecting the CO? produced I used phenolphthalein to see the color change as an alternative. This was found to be more accurate as I could see the colour change-taking place, and practically it was easier to set up.
* It was found that the predictions on the rate at which the substrates were respired were correct. The highest Glucose concentration was the quickest.
Apparatus, equipment
What I will be using for my investigation
Why I will be using them.
4-cm3 1.0M glucose solution
To see how this different glucose concentrations effects the fermentation of yeast.
4 cm? 0.8M glucose solution
4 cm3 0.6M glucose solution
4 cm3 0.4M glucose solution
4 cm3 0.2M glucose solution
4cm3 0.0M distilled water
2cm3 of phenolphthalein
...
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* It was found that the predictions on the rate at which the substrates were respired were correct. The highest Glucose concentration was the quickest.
Apparatus, equipment
What I will be using for my investigation
Why I will be using them.
4-cm3 1.0M glucose solution
To see how this different glucose concentrations effects the fermentation of yeast.
4 cm? 0.8M glucose solution
4 cm3 0.6M glucose solution
4 cm3 0.4M glucose solution
4 cm3 0.2M glucose solution
4cm3 0.0M distilled water
2cm3 of phenolphthalein
To see how long it will take for the phenolphthalein to become colour less, from purple alkali colour to colour less acidic solution.
4cm3 of yeast
To see how this amount of yeast would respire with the amount of glucose that I would be using on this experiment.
Glass Marking Pen
To mark my test tubes, so I know which test tube contains which substrate.
Stopwatch
To time how long it will take for the reaction to take place. And a colour change to take place.
Water bath
To heat my substrate (different glucose concentrations, yeast, phenolphthalein) up to 40c.
3 Thermometer
To control the temperature of the water bath, and the experiment.
8 Syringes
To measure the amount of substrate that I will use.
Clam and Stand
The test tubes can stand in the water bath.
Variables
In this experiment I will need to monitor these variables,
* Temperature
* Volume of glucose concentration
* Volume of yeast
* Volume of phenolphthalein.
In order to make sure that the variable being manipulated is the one making the difference, other possible variables need to be controlled.
Temperature affects both the times required to attain maximum activity and the maximum rate of gas production and the time taken for the color change to take place.
Generally, the gas production rate doubles over a range of 0-40°C. this is the Q10 rule.
Using a thermostatically controlled water bath I can control the temperature and part of the trial experiments I will find a suitable temperature for the yeast to respire at.
The amount of yeast will have an effect on the rate of reaction, as the yeast contains the enzyme (zymase), so if I increased the amount of yeast the rate of reaction will take place in a different way it could be both slower and faster. The yeast contains enzymes which could change the rate of reaction depend on the amount of substrate.
The amount of glucose will also change the rate of reaction depending on the other substrate that I will be using.
The amount of phenolphthalein will also change the rate of reaction.
The more phenolphthalein I use the longer it will take the color change to take place.
Phenolphthalein
Phenolphthalein is an organic compound (C20H14O4) used as an acid-base indicator. The compound is colorless in acidic solution and pinkish in basic solution (with the transition occurring around pH 9).
Phenolphthalein does not dissolve very well in water, so for titration's it is usually prepared in alcohol solution. When adding a drop of indicator to an acid you will sometimes detect a slight cloudy white colour. This is actually a precipitate of solid phenolphthalein, as the high local concentration exceeds the solubility product. It will usually disappear if you shake the solution, since enough solvent becomes available to dissolve the solute.
Method, suitable number
. I set up the equipment as shown in the diagram
2. I am going to transfer 4cm3 of the 1.0M glucose concentration culture into each test tube.
3. Then I will add 2cm3 of phenolphthalein in to the glucose in the same test tube.
4. Then I will fill up 4cm3 of yeast in syringe, and put it in to separate test tube from the glucose.
5. I will then heat the two test tubes in a hot water bath at 40C.
6. To keep record the temperature of the solutions, I am going to but a thermometer in to each test tube that I will be using.
7. When they both get to 40c, I will take them out of the water bath and add them together.
8. When I have added them together I will gently rotate the test tube so that the solution is mixed properly
9. I will start the stopwatch.
0. When a total color change has taken place I will stop the stopwatch and record the time taken for the reaction to take place.
1. I will repeat this procedure three times for each glucose concentration.
2. Now I will repeat the whole experiment three times for each glucose concentration, so that the results are reliable
13. I am going to repeat steps one to ten three times for each glucose concentration, which are 1.0M 0.8M 0.6M 0.4M 0.2M 0.0M.
Each experiment of different concentration will repeated three times and finds the average results.
4. When I have gathered the results I am going to analyse them with a statistical test, and drawing graphs.
5. I am going to use six different type of glucose concentrations.
What is fermentation?
Fermentation is the process by which the living cell is able to obtain energy through the breakdown of glucose and other simple sugar molecules without requiring oxygen.
In alcoholic fermentation, such as occurs in brewer's yeast and some bacteria, the production of lactic acid is bypassed, and the glucose molecule is degraded to two molecules of the two-carbon alcohol, ethanol, and to two molecules of carbon dioxide.
Glucose -> Ethanol + Carbon Dioxide + Energy
(C6H12O6 => 2 C2H5OH +2 CO2 + 2 ATP +heat)
Conclusion:
Yeasts and enzymes cause fermentation. Alcohol fermentation is the formation of alcohol from sugar. Yeast; when under aerobic conditions, convert glucose to pyruvic acid via the glycolysis pathways, then go one-step farther, converting pyruvic acid into ethanol, a C-2 compound. Yeast cells will use oxygen if it is present, and break down sugars all the way to CO2 and H2O. In the absence of oxygen, yeast will switch to an alternative pathway that does not require oxygen. The end products of this pathway are CO2 and ethanol. The first pathway yields a lot more energy per sugar molecule consumed, and so it is the "preferred" pathway if oxygen is present.
? Glucose + Oxygen = Carbon Dioxide + Water + Energy
? Glucose => Ethanol + Carbon Dioxide + Energy
? (C6H12O6 => 2 C2H5OH +2 CO2 + 2 ATP +heat)
In this experiment, I can see that the lower concentration the higher rate of CO? given off from the results, the water level drops the most in the 0.5 Mole cylinders.
There is more fermentation take place while the enzyme in the yeast is in a lower concentration of glucose solution. This is because; there are less glucose molecules in the less concentrated glucose solution, so the surface area for yeast to react with is much bigger than in concentrated glucose solution. The yeast changes the glucose into ethanol, carbon dioxide and energy, the fermentation took place. There will be more yeast work on one glucose molecule in the less concentrated glucose solution, because there are less glucose molecules in the solution, so the rate of fermentation will be much faster than that in the concentrated glucose solution. (OCR Biology 2, chapter one A2)
Phenolphthalein colour less (acidic)
Pink (alkaline)
CO2+ H?O H?CO3
Overproduction by yeast.
Overproduction of yeast takes place by time, the organisms have the reproductive potential to increase their population, this population increase of the yeast can be effected by the environmental factors come to play to keep their numbers down these factors maybe abiotic, that is caused by non living components of the environment such as water supply or the temperature of the room and the nutrient levels in the yeast.
(OCR Biology 2 chapter 5 A2)
Enzymes
Enzymes are catalysts. Most are proteins. (A few rib nucleoprotein enzymes have been discovered and, for some of these, the catalytic activity is in the RNA part rather than the protein part.
(OCR Biology 1 chapter 5 AS)
Enzymes bind temporarily to one or more of the reactants of the reaction they catalyse. In doing so, they lower the amount of activation energy needed and thus speed up the reaction.
* They have an optimum pH and temperature under which they can work most effectively. Most enzymes have an optimum pH of around 7 and an optimum temperature of around 30 C to 40C (e.g. the optimum temperature of human enzymes is about 37C). They are very sensitive to pH and temperature changes. Temperature change can break the hydrogen bonds and pH change can alter the ionic bonds in enzymes, both of which can denature the enzyme
* Respiration involves a number of enzymes, which, work with a number of substances in order to make ATP. In order for ATP to be successfully made there are a number of chemical reactions that occur. These include Glycolysis, the link reaction, the Krebs cycle and oxidative phosphorylation and the electron transport chain.
* (OCR Biology 1 respiration AS)
Glycolysis is the splitting of glucose. Glucose is eventually split in 2 molecules of pyruvate. ATP is needed for this, however ATP is released in later stager. There is a net gain of two ATP molecules per glucose molecule.
(OCR Biology 2 chapter 1 A2)
Enzymes: Organic Catalysts
Enzymes allow many chemical reactions to occur within the homeostasis constraints of a living system. Enzymes function as organic catalysts. A catalyst is a chemical involved in, but not changed by, a chemical reaction. Many enzymes function by lowering the activation energy of reactions. By bringing the reactants closer together, chemical bonds may be weakened and reactions will proceed faster than without the catalyst.
(OCR Biology 1 chapter three AS)
Space filling model of an enzyme working on glucose. Note the shape change in the enzyme (indicated by the red arrows) after glucose has fit into the binding or active site.
Factors Affecting Enzyme Action
The activity of enzymes is strongly affected by changes in pH and temperature. Each enzyme works best at a certain pH (left graph) and temperature (right graph), its activity decreasing at values above and below that point. This is not surprising considering the importance of.
As I have stated in my definition, enzymes are highly specific. This is because the active site of an enzyme is an inverse copy of the shape of the substrate molecules it is designed for. This means no other substrate molecules are able to join with the enzyme molecule. This idea of enzyme - substrate rigidity is known as the lock and key hypothesis, meaning only the correct 'key' (substrate) will work the 'lock' (enzyme.) The diagram below shows how the enzyme will only accept certain substrate molecules. Only molecule E is the correct shape.
The enzyme does not however, stay in one shape. It is flexible, allowing the substrate to maneuver into place before taking its shape for catalysing the substrate. This movement is caused by chemical reactions and ionic repulsion and attraction between the two / three molecules.
Factors affecting enzyme activity
There are many factors that affect the catalysing action of enzymes.
Because of this, all other factors will be kept the same throughout the experiment to avoid introducing other variables. Factors that affect the rate of an enzyme-controlled reaction are:
- Temperature
- PH of Solution
- Substrate concentration
- Enzyme concentration
- Presence of an inhibitor
To maximize the rate of reaction, I will keep my yeast (and therefore the enzymes) at 40 degrees centigrade by means of a water bath. This temperature has been chosen, as it is the optimum temperature for the enzymes to operate at. Beyond this point, although the number of collisions with the active site is increased (the kinetic theory,) The temperature causes the enzyme to denature (change shape) and therefore become ineffective
(WWW.GOOGLE.CO.UK)
The effect of substrate concentration on the rate of enzyme activity.
As substrate concentration increases the initial rate of reaction also increases. The more substrate molecules there are around, the more often an enzyme's active site can bind with substrate. However if we keep increasing the substrate concentration keeping the enzyme concentration constant, there comes a point where every enzymes active site is working constantly, if more substrate is added the enzyme simply cannot work faster substrate molecule are effectively 'queuing up' for an active site to became vacant the enzyme is working at its maximum possible rate known as Vmax. (OCR Biology 1 chapter 3 AS)
The enzymes used in this experiment
In this investigation, the respiration of yeast was seen as a good solution. Yeast respires, producing CO2 gas. And on this experiment I will look at the colour change of the phenolphthalein, as respiration is an enzyme controlled series of reactions, introducing an inhibitor will affect the rate of respiration, and thus the volume of gas collected. Yeast Initially mitochondria were to be used, but the process of extraction was deemed too complicated for the limited time available.
Also respire both aerobically and anaerobically. This is useful, as the reaction will not stop if there is no air in the dough.
Safe working
My investigations I will be safely conducted by wearing a laboratory coat and goggle, when I am handling chemicals such as yeast.
Hot water bath is dangerous so I will take care when handling the ware bath.
Any equipment that is broken is dangerous, such as broken glass, so I will take extra care when handling glass, and equipment that will break when they are dropped.
I will also tuck stoles under the tables so no one trembles over them. . I also made sure that I had a set of Safety goggles on at all times, to avoid any situations, with flames. I also made sure that I was wearing my laboratory coat at all times, for some sort of protection, to any spilt water or other hazards.
Reliability of Method
To make sure that our experiment would be reliable we took a number of precautions. First of all I decided that I would repeat the experiment for all of the different glucose concentration three times for each concentration. Also I decided to take a large number of recordings at short intervals, 1 minute. The measurements of the glucose, yeast and phenolphthalein should be accurate due to the fact that I will look at the meniscus at eye level of the test tube. Stirring the yeast will also increase the reliability.
Precautions
I must take the following precautions during the execution of this experiment:
. Watches out for parallax error- always take measurements at eye level.
2. Wipe up any spillage immediately after they occur.
3. Check the temperature of the water baths every time I take a sample out and adjust it if it is too high/low.
5. Shake the test tubes before extracting a sample to ensure even distribution as the cells may settle out.
Why did we put all the boiling into the water bath?
The temperature of the glucose solution is one of the factors that can affect the rate of reaction, if the temperature is too high, the yeast will denature, if the temperature is too low, the yeast will be inactive. Yeast will not work very efficiently at the room temperature, so if we do this experiment at the room temperature, that might took very long time, so we put the boiling tubes into warm water (40?), too let the yeast work more efficiently. And we put all of the tubes into the same water bath, to ensure that all the boiling tubes are keeping in the same environment.
The experiments I have done are based on fermentation. Fermentation is the process of making alcohol. In fermentation the two important substances are the yeast and sugar in the form of glucose. The process turns glucose in to ethanol, alcohol, and carbon dioxide. It can be written as:
Glucose ethanol + carbon dioxide
C6H12O? [RM1](aq) 2C?H5OH (aq) + 2CO? (g)
The whole takes about 8 or 10 steps long for it to complete. In each of the steps there is a need of ENZYMES. Enzymes have a 3D structure of, (Helix). In every layer, pitches, they are joined by hydrogen bonds, which can be easily broken down. These enzymes are used for breaking down the glucose molecules. This will release energy, which is necessary for the yeast cells to use for multiplying. The reaction could be written as:
Substrate + enzyme product + enzyme
The substrate stand for glucose solution and the products are ethanol, carbon dioxide and energy. All of the enzymes are form of protein and protein molecules are amino acids. Therefore as the temperature increases the rate of reaction also increase. The rate of reaction could be calculated by timing the time taken for a color change to take place.
On each enzyme there are active sites, which can accommodate certain substrate. Active sites break down substrate into small pieces. When energy is produced it breaks down the structure of enzymes thus making them unable to break down the substrate. This is called DENATURATION. (OCR Biology 1 Chapter 3 AS)
Evaluation:
From the experiment I have done I did the best I could to produce the out come of the results to be perfect enough of the conclusion. Though out the experiment the out come of the results showed the expected pattern. And I think that the way I did the experiment is the best possible way that the experiment could have been done.
The results that I collected have come out to be well more than I expected, this is because the experimental procedure was appropriate and the range of readings that I took gave me good sets of results that followed a particular trend on the graph.
Also the method I have carried out for the experiments I think it is the best way that I could come out with. This is because I use the method of repeating the experiments three time to get as accurate results as possible by taking the average result form the repeated ones.
My experiment in my opinion was performed at the best possible way it could be performed, but there were a few changes, which could have been made.
The accuracy of the results was quite sufficient; however one of my results does seem anomalous.
The reliability of my experiment was quite fair and supportive
Of my results. The results were as near enough as expected but there was anomalous which to alter the curve of the graph. To ensure this I could have possibly performed the experiment more times, for more tests.
The methods that concocted to investigate the fermentation of yeast
was appropriate the aim, because it enabled me to make relevant conduction and to find the time taken for the phenolphthalein to become colourless.
Anomalous result.
There is one anomalous result in my experiment and I am going it mark it on the graph.
The concentration of 0.6M is bit high, and this could that the enzyme in the yeast started to denature, as the temperature of the water bath was one degree too high. This could also be that It took me bit longer to start the stopwatch.
Limitation results in source of error.
These are the factors that I expect to be the greatest limitations on my experiment:
. Yeast cells reproduce asexually when they have been lying around for a long time, which means that the first sample of the yeast that I used would be much slower then the later sample of the yeast that I used. As the yeast would reproduce and produce more enzymes at a longer time, which meant that there, were more enzymes for the substrate present making the reaction faster.
2.Denaturation of the enzymes at high temperatures. This makes it impossible to have a higher temperature than around 40 degrees Celsius. This means that when the other conditions are favourable, temperature could become the limiting factor. So if the water bath gets bit over 40 degrees Celsius the enzymes in the yeast could start denaturing.
This would effect my results by experiment not even reacting, as the enzyme active site would be denatured. And the time taken for the reaction to take place would be longer. And the bigger the temperature the faster the enzymes would denature.
Accuracy of the results
My results were mostly accurate due to that I did my experiment to minimal mistakes and error.
In this section I will consider the values from the spearman's test and the number of anomalies, and decide how confident I can be that the results were not purely by chance. As the spearman's test show 99. % Of accuracy.
Reason anomalous result.
There is one anomalous result in the results that I plotted on the graph, which is different from the results that I have obtained in my results. And the possible causes for these anomalous results are.
* The yeast that I used was prepared exactly before the experiment was carried; if the yeast were left too long it would asexually reproduce. And the yeast would contain more enzymes, which would make the experiment much faster, which would produce an anomalous result.
* The fact that the water bath was electronically controlled meant that the error in maintaining the water temperature was theoretically insignificant. If the test tubes were not filled with water of the same temperature, then the substrate could not have been the right temperature.
The values obtained from my statistical test shows 99. % Accuracy, which shows that the anomalous results are very low if they are any.
This however takes the results that I called anomalous into account- hence the high value. This is not very high considering that this is the spearmans rank of the raw data. There were few results that seemed to vary significantly to be recognised as anomalies.
More generally, my results are fairly consistent, as well as being consistent with the prediction, which is an indication that they are reliable. Some of the finer points of the progress of the population with time remain to be conclusively proven, but the primary quantitative prediction as to the effect of glucose concentration on the rate of reaction, and the time taken for the phenolphthalein to change colour. Appears to be conclusively and reliably proven this was proven by the spearman rank coefficient test, which showed that my results were 99% accurate.
* This could also be that It took me bit longer to start the stopwatch.
Significant limitation and source of error.
There will have been a margin of error in each piece of equipment that I used for my experiment.
Syringe. The syringe was gradually to the nearest tenth of millimetre but there was a likely to be a possible error when trying to measure 5ml exactly.
Water bath. This made it very difficult for a set temperature to be kept constant, as the temperature on the water bath was most of the time one degree less or degree more than 40 degree Celsius.
Stopwatch. There could have been problem with the timing, as there are some human errors involved when starting the reaction, and when the end points has been reached, there is possibility that I stopped the stopwatch bit too early or too late, this would produce an anomalous result if the margin where too big.
Improvements to the experiment.
The temperature of the surrounding water was thematically controlled water bath. Once the experiment has started the water bath was not kept at constant temperature, this meant that the temperature could get up a bit after 30minutes and after I had to cooled it down with cold water, this meant that the water bath lost a great deal of heat energy to the atmosphere and the cold water added.
Yeast that I used in my experiment was a yeast that was prepared just before I started to carry out the experiment, by the time I was on the middle of the experiment the yeast has reproduced sexually, and extra enzymes were present in the yeast which meant that the experiment were much faster then some of the first test that I took.
Making a newly made yeast every 30 minutes meant that the experiment were kept to minimal anomalous results, and the results were mostly at the same rate.
Stopwatch. I started the stopwatch for my self for the pilot test that I did at the beginning of the experiment, this was not so accurate as I always started bit too late, I improved this for the real experiment that I recorded on my table and graphs, by letting one my friend to start for me, this showed more accurate results, as they started exactly when the reaction started to take place.
The equipment that I used to conduct my experiment was not as accurate as it could have been. Obviously it is not possible to make perfect accurate equipment, and eliminate error. However more accurate equipment is available. The following improvements should be made for further work.
* I would be using a more accurate water bath.
* I would be using a pipette rather than a syringe to measure the 5ml of distilled water, different glucose concentration, yeast and the phenolphthalein, more accurately.
Reliability of the evidence.
Looking back upon my results and experiment on the whole, I think it is fair to say that my investigation was performed with a great standard. And it is also extremely reliable; the values obtained from my statistical test shows 99. % Confident, this shows that the anomalous results are very low.
I also found that the rate of respiration gradually increased, before it reached its greatest point (peak), and that the yeast has respired. The color change slowly continues to be put out, and a total color change has taken place. My results seem to back up this proposal.
Main source of error.
* The yeast that I used was prepared exactly before the experiment was carried; if the yeast were left too long it would asexually reproduce. And the yeast would contain more enzymes, which would make the experiment much faster, which would produce an anomalous result.
* Yeast that I used in my experiment was a yeast that was prepared just before I started to carry out the experiment, by the time I was on the middle of the experiment the yeast has reproduced sexually, and extra enzymes were present in the yeast which meant that the experiment were much faster then some of the first test that I took.
Making a newly made yeast every 30 minutes meant that the experiment were kept to minimal anomalous results, and the results were mostly at the same rate.
The yeast culture was not shaken at the beginning therefore the yeast might not be spread out through out the culture.
Validity of conclusion.
The results that obtained were reliable enough for me to give a 40C, within which the true value of the temperature at which the yeast respires best at, despite the very large source of error in this experiment, I am confident that the specific temperature for the yeast to respire at lies within this range. This is because I plotted the mean value of a class of twelve students, and then I plotted I mean value of a class of my experiment. The spearman's test that calculated for my figures was not too large it showed 99. % Accurate.
[RM1]