The predicted outcome (graph)
Factors that can affect the outcome:
Temperature: (a factor I am going to keep constant)
The temperature will have a great affect on the results because according to the kinetic theory, the higher the temperature the reaction takes place in, the higher the rate of reaction is. However, in this experiment the process of fermentation depends on enzymes. All enzymes have a certain temperature they work fastest at (also known as optimum temperature). If the temperature exceeds the optimum temperature, enzymes starts to denature and the shape of their active site (unique to only fit its substrate) will change shape, therefore will not be able to function anymore.
I will put the yeast and glucose (when mixed) into a 40oC water bath. I will do my best to keep it constant. To do this, I used insulation (cotton wool surrounding the beaker which contains hot water). I will place a thermometer in the beaker and keep a close eye on the temperature. If it falls, I will add more hot water to the water bath until it reaches 40oC, I will add cold water if it exceeds.
pH: (a factor I am going to keep constant)
Certain enzymes work best at certain pH. Therefore, I will keep the pH to be neutral (using distilled water to make my solutions).
Amount of yeast: (a factor I am going to keep constant)
The amount of yeast is crucial, more yeast means more enzymes to breakdown the glucose, as a result, the rate of fermentation will increase.
I will keep on using 10% yeast solution, 10ml.
Amount of glucose: (a factor I am going to change)
As explained in my prediction, the more glucose present, the chances of the glucose molecule contacting the active site of the enzyme unique to breaking the glucose down will increase, so the rate of respiration of yeast will increase.
Safety:
Whilst this experiment is relatively safe, there are still safety considerations that must be adhered to:
- Due to the dangerous nature of many of the compounds involved in this experiment, it is important that safety goggles or safety glasses are worn during all tests.
- It is equally important to avoid skin contact with the compounds, as some are irritants. This can be done by ensuring that a suitable method is followed precisely so that there are no unexpected events that would lead to skin contact.
Range:
I will take 5 readings (total of 15 because I take 3 measurements of each reading).
Initial glucose solution concentration will be 2% and with increments of 2% concentration, the final glucose solution concentration I will test is 10%. This will provide me with a wide range of results for analyzing and see whether it conflicts or matches with my prediction.
Accuracy and Reliability:
I will take 3 measurements of gas produced at each reading I will take. I will then use the arithmetic mean of these measurements in my analysis to calculate average rate of reaction. This should help to minimize unreliable results. Whilst I am doing my experiment, I will note the results down on a table, in order to spot any obvious anomalies.
The measurements themselves will be taken as carefully as possible. Time will be measured using the stop-watch (precise to ±0.1 second), volume of gas produced with the gas syringe (precise to ±1 cm³), the mass of the yeast with measuring balance (precise to ±0.01g) and the amount of glucose with a measuring cylinder (precise to ±0.5ml)
Apparatus:
Yeast, glucose solution (with different concentrations), boiling tube, 250ml beaker, gas syringe, boss, clamp, stand, boiling tube rack, electrical balance, 2x measuring cylinder, spatula, delivery tube with rubber bung, cotton wool
Diagram:
Method:
- Firstly collect all apparatus and set up like the diagram on the previous page.
- Pour the 10% yeast solution and measure 10ml using measuring cylinder.
- Measure 10ml of glucose solution (2% - initial) using measuring cylinder.
- Pour the 10ml of 10% yeast solution into a boiling tube.
- Reset the gas syringe if needed (moving it back to 0 ml).
- Pour some hot water (amount doesn’t matter) into a beaker.
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Use a thermometer and check the temperature. If it is less than 40oC, add more hot water, if it is more than 40oC, pour out some hot water or add more tap water.
- Put the 10ml of glucose solution and mix well using glass rod for 10 seconds
- Immediately connect it to the gas syringe.
- Start the stop watch and wait for 2 minutes.
- When 2 minutes is reached, stop the stopwatch and record results (the volume of gas produced) in a table.
- Repeat step 2-8 but with different concentrations of glucose (2%, 4%, 6% and 8, 10% concentration).
Pretest:
I started off using 10% yeast solution and 10% glucose solution (10ml). I followed my method. When the time to stop the stop watch was reached, I looked at the volume of gas produced by it was 0. I decided to extend the time to 5 minutes, but very little volume of gas was produced.
I decided to use 10 minutes. 25cm³ of gas were produced. Then I tried using 2% glucose solution (10ml), it produced 20cm³. Although the two results are really close, I have decided that I will use the planned range (2%, 4%, 6%, 8%, and 10%), which I assume will give me sufficient evidence to support my prediction.
So changes made:
Step 10) Start the stop watch and wait for 10 minutes.
Step 11) When 10 minutes is reached, stop the stopwatch and record results (the volume of gas produced) in a table.
Obtaining:
The boxes that are coloured yellow indicate that they are anomalies and I didn’t use them to calculate the rate of respiration.
Analysis:
My graph clearly shows that as I increase the amount of manganese oxide, I will increase the rate of reaction of yeast reacting with glucose and creating ethanol and carbon dioxide. This supports my prediction fully (prediction: the greater the concentration of glucose solution, the greater the rate of respiration :
C6H12O6 (aq) 2C2H5OH (l) + 2CO2 (g)
Glucose ethanol + carbon dioxide
Yeast enzyme
[Note: energy is produced also at the end]
We can clearly see that with the line of best fit drawn the points are not that far away from this line, showing a quite strong relationship
The rate of the respiration (when the reaction is at it’s 600th second) for 2% concentration of glucose solution used is 0.033cm³/sec, for 4% it is 0.033cm³/sec, for 6% it is 0.036cm³/sec, for 8% it is 0.037cm³/sec and for 10% it is 0.42cm³/sec. This also supports my prediction because the rate of decomposition is increasing when the concentration of glucose solution.
In theory, the graph should show a steep gradient at the beginning of the decomposition and begins to steep at the end because of the faster rate in respiration, as a result reacting with glucose faster so less glucose molecules will be left for reacting. By looking at the graph, it does show a steeper gradient at the beginning but the gradient didn’t change much, and maintaining the steepness. This might be because the breaking down process is too slow to see any real effect. The rate of respiration of the 10% glucose concentration has the fastest rate compared to the others because there are highest concentration of glucose compared to the others, therefore increases the rate of respiration the fastest. The increase in concentration of glucose has therefore contributed to increase in rate of respiration.
More concentrated solutions contain more particles in the same place, making them more likely to collide (in this case collide and fit in the active site of the enzymes). The increase in the number of collisions increases the rate of respiration (the breakdown of glucose into ethanol and carbon dioxide).
The anomalies in my obtaining might be because of small inaccuracies in measuring and/or slight temperature inaccuracy.
Some of the results could be wrong, however I can still pull some conclusions from this, which is that we can definitely see that as the concentration of glucose increases, the faster ethanol and carbon dioxide are produced as a byproduct of the reaction.
Evaluation:
Overall I think this investigation went pretty well. The method I used was quite easy to do and didn’t give many anomalies. I used gas syringe to collect my results because gas syringe is the easiest to set up and the easiest to use, providing me with more time to obtain results and to make sure I am doing everything correctly.
The measurements I did were quite accurate because I used very precise measurements. Most of the results were reliable as well because of my repeats (which I also did for concentrations that had an anomaly. Though there had to be some errors. Human errors such as reaction time might have a slight effect on the results. The temperature of the water bath might be exactly 40oC but might be ±1 degree because the gap of 39 and 40, 40 and 41 is so small it is hard to see with the naked eye. Also, 1 degree change has a major impact on the results, since enzymes are really sensitive to temperature change. Improvements can be done to counter this problem, I could use electronic temperature readers to detect the temperature of the water bath. This should be able to counter the temperature problem. There might be small inaccuracies in the measuring of volume of glucose solution, volume of yeast solution and the result recording of the gas made. Although the inaccuracies are very small, it can still affect a little to the ending result. I could use the measuring cylinders with 0.1ml markings to measure the volumes so it is more precise.
However, I would like to obtain more results, using higher concentrations of glucose. This is because I did only up to 10% concentration of glucose solution, which is very low. Therefore, the graph drawn didn’t represent a full picture of the experiment, which if did, might conflict with my prediction. Although all results up to 10% concentration of glucose did agree with my prediction, but that doesn’t mean if the glucose concentration is 70% it will still agree with my prediction, which is what I want to understand fully and investigate about. On the other hand I didn’t have enough time to do so many readings. So if there was an extension in time for me to obtain more results, I could most probably give a stronger evidence for my prediction or prove it wrong.
Possible Extensions:
- Investigate the best pH for the yeast enzymes to work the fastest rate in.
- Investigate the best temperature the yeast enzymes work at the fastest rate in.
- Investigate the rate of respiration of yeast when the variable is the concentration of yeast.
- Investigate whether a change in concentration of glucose or a change in concentration of yeast will affect the respiration of yeast the most.