These three stages will release carbon dioxide, water and ATP.
In anaerobic respiration, as in this case, the Krebs cycle and oxidative phosophorylation are unable to take place and thus only glycolysis can occur. The end products of glycolysis in a yeast cell are carbon dioxide and Pyruvic acid (which is then converted into ethanol).
The activation energy for glycolysis comes in the form of the sugar substrate available; this is the second focus of this investigation. The important factor in the usage of the sugar substrate is it shape, it needs to be suitable for usage by the yeast enzymes.
The sugar substrate I will be using will be either monosaccharides or disaccharides, which is a very important difference; also relevant are the monomers, which make up the disaccharides. These monomers may be easy top break down, but the products of that breakdown may not be able to be used in glycolysis if their shape is drastically different from the most common respiratory substrate glucose.
The sugars that I intend to use are: -
- Sucrose
- Maltose
- Alpha – Glucose
- Lactose
- (possibly fructose)
In order to aid understanding of how the process of glycolysis will occur and to explain the main issues raised in my introduction I shall display the structures of the afore mentioned sugars, and in relevant cases their monomers.
The structures of each of the sugars are as follows: -
From my background information I know that glucose best fits the active sites of the enzymes inherent in the yeast this means it will be easiest for the yeast to use during glycolysis. The higher the difference in the structure of the sugar the less likely it is to match with the active sites in the yeast.
I believe that the most suited from the disaccharide’s will be maltose as it is formed from two molecules of glucose which can be split apart and then used. Fructose will be slower than maltose as it is only formed from one polymer of glucose.
Plan
I will make an active solution of yeast (that is a dry mass of yeast combined with de-ionised water) to eliminate and factors that could produce anomalous data.
This I will then add 25cm3 of this solution to 25cm3 of a sugar solution via a 60cm3 syringe.
The sugar solution of each of the 5 sugars will be 0.25M in strength, this has be shown to be the optimum concentration, for higher than this level can lead to detrimental osmotic problems.
I will then empty the syringe of excess air and attach it to a 300mm capillary tube held within a clamp stand.
Measured (using a china graph pencil) 20cm down the capillary tube will be a mark, I intend to time how long the solution within the syringe takes to travel to this mark using a standard stop watch.
This procedure will be carried about 5 times for each sugar so as to allow averages to be taken and anomalous data to be recognised and discounted.
In this instance the independent variable are the different sugars, the manipulation of these will be in the form of a different sugar being added to the yeast in each individual experiment within my investigation.
Carrying out simple pilot tests has allowed be to finalise my volumes and see which aspects of each experiment need to be kept constant. These will be: -
- The same batch of yeast will need to be used in all the experiments, as a different yeast may respire at a different rate.
- De-ionised water will need to be used when creating an active yeast solution, so as to make sure the respiratory rate of the yeast is not affected too drastically.
- The same distance will need to be marked on the capillary tube, if multiple capillary tubes are used, so as to have a standardised distance used throughout.
- Exact volumes of both sugar and yeast solution shall be used each time, if there were higher volumes of either, the rate of respiration could be affected.
- The same individual will have to do the timing also as there are individual differences in reaction time.
As well as controlling the variables I will need to produce a control experiment allowing me to make reasoned assumptions about my results. The control experiment will consist of using the yeast solution on its own and measuring the respiratory rate, this will show that it is the sugar that has an effect on the respiratory rate of yeast and no other factor.
The dependant variable in this experiment is the amount of CO2 produced. This will be obtained by dividing the time the solution takes to reach the mark on the capillary tube, by the distance it travelled to that mark. This will give the level of Co2 production per second. This measurement will be given in Co2/s in relation to the amount of yeast.
This data , once collected will be logged in a data table and then present in suitable graphs and charts to show trends and identify anomalies.
Apparatus
- 60cm3 syringe.
- Capillary tube.
- Beaker.
- Active yeast solution.
- 5 sugar solutions of 0.25M (glucose, fructose, maltose, sucrose, lactose).
- Stop watch.
- Clamp stand.
- Chinagraph pencil.
Al the apparatus I intend to use is very low risk , and no special precautions will be needed, such as gloves or goggles. The 2 solutions have minimal risk if they came into contact with ones skin there could be possible irritation.
