We make use of yeast in three main ways. Making alcoholic drinks in the process of brewing. Making bread, this ferments the sugar releasing C02, which make the dough expand. Producing fuel, alcohol is used in cars, either on its own or mixed with petrol as gasohol.
We did some prior work to find out which carbohydrate respires the most. Over a period of 6 days we tested, fructose, glucose, maltose, sucrose and starch. We recorded the weight of each and then found out the over all weight loss. We found this to be sucrose.
Total weight loss
From this I have found the sucrose has the greatest weight loss and so next I shall use this and change the concentration. From that I could see if there are any patterns.
The loss on mass shows that it respires at a higher level and so gives of carbon dioxide, water and energy.
Do different carbohydrates work better at different conditions? To find this I could change the pH.
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.
Apparatus:
During this experiment I used
- Beakers
- Water traps
- 5 carbohydrates, which were fructose, glucose, maltose, sucrose and starch.
- The concentration of our selected carbohydrate in this case sucrose.
1%, 5%, 10%, 15% and 20% concentration.
- Mass weighing scales.
- Bung
- One-way gas filter.
Method:
Once the best carbohydrate was found, it being sucrose. We then changed the concentration of the sucrose, form 1% to 20% each time increasing by 5%.
We kept the same mass of yeast the same volume of water. All of the conditions were kept the same all that was changed was the concentration.
Over a period of a week we took the readings of the sucrose to see what the mass was of the different concentrations. Although there was a period of two days where we didn’t take the readings this was because it was the weekend. These days were then made up.
This experiment was performed fairly the only factor that may have been unfair was the fact we missed two days readings, although when we made them up the results seem to be fair. This experiment was very safe as well nothing was out of
place and everybody work sensibly. There isn’t any reason why it shouldn’t be safe for people watching.
Once the sucrose solution has been added to the beakers the yeast will be added into the beakers. Once that has been completed and everything has been added you mass each beaker and record the results. It would be better to take the readings three times each so that you can average them out and so fairer results can be taken.
Water should be added to the u-bend of the tube to stop other gasses getting into it. If this did happen then it would affect the mass.
The conditions that will be kept the same are the temperature of the surroundings, and the amount of yeast that would be added. Also making sure that the yeast came from the same cause. If the temperature was higher this would mean that the particles would have more kinetic energy and so would mover much more faster speeding up the reaction. The water within the u-bend must be kept the same if it was higher in one and not in another the carbon dioxide wouldn’t be able to diffuse into the surroundings because of the barrier.
Diagram:
OBSERVATION:
Total mass loss (g)
ANALYSIS:
It is clear to see that the graph shows the lines go down indicating mass loss. This shows us that carbon dioxide has been released and the mass lost is taken to be this amount.
These results show how when the concentration has been increased the total mass loss increases. Although up to 20% concentration it seems to fall. So from this it is clear that 15% is its optimum%.
The lower the percentage of sucrose the lower the amount of sugar molecules there are in the same volume and there for the chance that a sugar molecule will bump into a yeast cell and then pass through the membrane is decreased.
The steepness of the lines show how quick the reaction has taken place. If the lines gentle then it would show how the reaction would have been slow. The lines from 15% concentration show the steepest line; therefore indicating it reacted faster and so respired much quicker.
The reason for the 20% solution overall mass loss being less maybe because the rate of reaction in the 15% solution was increased due to the increased movement to this experiment giving the sugar molecules more kinetic energy or the 15% solution gaining more sunlight and hence heated more which would also have given the sugar molecules more kinetic energy.
As I did predict, as the concentration increases the more energy will be produced, although once again 20% is the exception.
EVALUATION:
I think that my plan did work quite well. There weren’t any mistakes that can be noted and my predictions were backed up quite well with some knowledge.
I was able to show that 15% concentration of sucrose reprised much better than any other. Although this doesn’t show that just because 20% lost less mass doesn’t mean that if 25% or 30% would have been less as well. For this to be identified I would have to extend this investigation further testing different concentrations.
The measurements I took were accurate. We took the average mass loss, which made this even more accurate. The fact of using electronic scales made our readings precise.
The results were really quite good although there were some anomalous results but nothing noticeable at first. Well the mass loss of the 20% concentration was less then the 1% concentration on the first and second day. This does seem strange because the 20% would have respired quicker than the 1%. This might have happened because of a few things. One may have been subject to more light or have been shaken more than another. This does increase the kinetic energy and so the molecules would be bumping into one another increasing the chance of entering the yeast cell.
This experiment I feel has been carried out very well and so is very reliable. Maybe to have made sure we could have put the beakers into a heating bath to make sure the temperatures were the same. Although this might not have made any difference the results might have still shown the same outcome.
To extend this further I could use different types of yeast, maybe the next better carbohydrate at respiration, this being maltose. As I said before using other concentration possibly going higher to find trends, 25% or 30% concentration.
Different pH’s could be tried out because different carbohydrates work at different optimums.
To find out how much has been produced we can use a gas syringe, which would hopefully make it more reliable.
