Prior to this investigation I carried out a shorter experiment of the same kind but just using percentage of glucose concentrations of three and five- percent. Although this was a very basic experiment I found that the five- percent concentration was quicker at producing 2ml of CO2 than the three- percent concentration. In this experiment I used 5 grams of yeast in both concentrations.
The basic method for my experiment is as follows:
1 I will change the percentage of glucose concentration in the yeast.
2 I will measure the rate of reaction (time taken) for the yeast to produce 2ml of CO2 as a waste product.
3 I will keep the temperature the same and ensure to use all the same apparatus in each experiment.
4 I will keep the mass of yeast used in each experiment the same.
The apparatus I will use is shown in the diagram below:
1 Test tubes of all percentages of glucose concentrations in yeast.
2 Delivery tubes.
3 Beaker of water.
4 Syringe with a block in the end so as no gas can escape.
The full method I will be using is as follows:
The apparatus will be set up as shown above. The syringe will be filled with water and carefully placed in the beaker over the end of the delivery tube, ensuring that no water escapes when doing so, this is done so as when the Co2 produced by the yeast it will come out the end of the delivery tube and displace the water in the syringe. As soon as this is done the timer will be started and stopped when exactly 2ml of CO2 has been formed and caught.
This process will be used on six test tubes each containing five grams of yeast and each with differing percentages of glucose concentrations. The percentages of glucose concentrations will be one- percent, three percent, five percent, seven percent, nine percent and I will also use a test tube containing water to use as a control.
Each experiment will be repeated a second time so as to find any anomalous results and if any are found that experiment will be repeated once more to verify the correct result.
When dealing with yeast and alcohol I must make sure not to inhale or consume in any way anything during the experiment as a lot of it may be harmful in someway. Also if any glass is broken for any reason it must be cleared up properly and safely.
I found some secondary information on the Internet and put it together with some of my background knowledge to form the following information.
FERMENTATION is the breakdown of sugars by bacteria and yeast using a method of respiration without oxygen (anaerobic respiration). It involves a culture of yeast and a solution of sugar, producing ethanol and carbon dioxide with the aid of the enzymes. This is an 8-10 step process requiring different enzymes each time, but it can be simplified like this.
All the ENZYMES are protein chains of amino acids. They exist in the form of helix structure with hydrogen bonds holding the pitches together. On the amino acid molecules, there is R a group. They react with each other to form peptide bonds, transforming the chain into a 3-dimensional structure. Along the chain there are active sites where interaction between the enzyme and the substrate happens. These sites are sensitive to heat, like the hydrogen bonds that hold the 3D molecule together. When heat is applied to the enzyme, energy is given into the molecule. The active sites deform and the hydrogen bonds break, denaturing this enzyme. It would not be able to function as usual, and this is not reversible. This is called DENATURATION. The 3D helix structure would breakdown and the active sites would change in shape; they would not be able to accommodate the substrate any more. The analogy of this is to compare a key to a keyhole. If the keyhole has changed, the same key would not fit in any more, and the lock would not be unlocked. The same thing happens here, and fermentation could not continue after this has occurred. Also when the temperature is too low, the enzymes would not work because there is not enough energy for activities to happen.
Concentration of the solutions should make the yield of fermentation higher as they become more concentrated. This would be because the sugar molecules are more abundant as the concentration increases, so the probability that the enzymes come into contact with the molecules is higher. However, more concentrated solutions mean less osmotic pressure.
Analysis
Form the graphs what I have found out was that on the comparison of volume of CO2 produced of different concentration of sugar solution the concentration that has the most CO2 produced is 100% and the least is 200%. This is because that supposing the more concentrated the solution is the more ethanol and CO2 will be produced because more can be react with the enzymes. But in fact it is not because the osmotic pressure which is that the water will flow from less concentrated solution into more concentrated solution. This result for the yeast cells to loose water to the solution, which makes the yeast less efficient.
For the rate of fermentation the one that has the fastest rate is 100% and the least is 200%. What I could also noticed from this graph is that the rate increases proportionally as concentration increase. The rate of reaction, in this case, is the movement of the meniscus per minute. The rate of reaction depended on the surrounding temperature and the concentration of the solution therefore the more concentrated the solution is the faster the rate. For this graph though it is not so accurate because that the rate in the beginning of the experiment is ever so fast that it changes the look of the graph so much. Therefore I ignore the first volume of the result because if I have included it into the line the gradient of the graph will not be accurate enough and this will result in the change of the rate of reaction. The rate of reaction table could be seen in the obtaining evidence along with the other results. The formula for calculating the rate of the reaction is:
The change in volume of carbon dioxide (y)
The change in time per minute (x)
It is a shame that I did not have enough time to do the rest of the experiment such as the sugar concentration of 50% because I do not have enough time to complete it. Though I have not done the other experiments I still have enough of the results to conclude the experiment.
Although I did not do 50% sugar concentration I could still say that the best sugar concentration will still be 100% because it has the nearest osmotic pressure on both the solution and the yeast cells. The main conclusion here is that the most important factor is the osmotic pressure that effects the whole experiment.
Due to my prediction what I have predicted was nearly all right except on which was that the amount of carbon dioxide given off will increase as the concentration of sugar increase was wrong because that it is exactly the opposite. Except that the other prediction is the same as the result.