My reason for the above prediction is that yeast is a unicellular fungus, which feeds saprophytically and can respire both aerobically and anaerobically. In the experiment the yeast will be respiring anaerobically and breaking down the glucose stored in it as a waste product of this process it will also form CO2 and alcohol in the form of ethanol. This respiration process is called fermentation. The yeast breaks down the glucose using a series of enzymes.
I deduce from this that the more glucose that is present in the yeast the more will be broken down and therefore more CO2 and ethanol will be produced as waste products at a faster rate.
Preliminary:
I’m going to do a short preliminary experiment to find out which concentration of glucose would be the best to use for the investigation. I shall put 10ml of yeast suspension in each of 6 test tubes, then put one of six different concentrations of glucose solution and put 10ml of each type in each of the test tubes. The glucose concentrations I will be varying are 1g/l, 10g/l, 25g/l, 50g/l, 100g/l and 200g/l. I will then place oil on top of the solutions so that it could respire anaerobically (no air will get to it). Then I will place the six test tubes in one big beaker with water at 30oC, but just below the level of the top of the test tubes so no water will get in. Then put the beaker in a water bath at 30oC then I will time the bubbles. I will time for 5minutes, then observe which test tube had produced the most bubbles.
My results were as follows:
The best concentration is 100g/l. So I shall use this concentration in my main experiment.
Main Experiment method:
I will use a syringe to get 3ml of yeast suspension and 3ml of glucose solution. I will then put the capillary tube on the end of the syringe, then I will get a beaker and fill it almost full of the which ever temperature water I was varying for that particular experiment and then place the syringe into the beaker. Then make sure the capillary tube is horizontal (by resting it on an upside beaker maybe). I will then mark on the capillary tube where the bubble started, start the stopwatch, after 1min I will mark on where the bubble ended up at then work out how far the bubbles had traveled. My range of results will be from 20oC to 60oC and I will repeat each experiment 3 times then find the average.
Equipment:
- 2 Large Beakers
- Syringe
- Capillary Tube
- Yeast suspension
- Glucose solution (100g/l)
- Thermometer
- Stopwatch
- Water Bath
I will set my results out like so;
Results:
We had some problems obtaining the results we required, the yeast suspension and glucose solution weren’t producing the bubble or making it travel very far as expected. Therefore we resorted to doing this experiment on the computer using a program - Science Investigations 1, This was the outcome of my results:
Analysis
From the graph it is obvious that when temperature increases, the distance traveled by the bubbles also increases but up to a certain point (40oC) and then after that the distance travelled by the bubble decreases as the temperature rises, therefore giving a curve on all the graphs.
There were no major anomalies. The line of best fit was a curved line with the major curve in the middle (40oC). The reason for why the results starts off to increase with the temperature but then decreases, because the yeast is an enzymes. Enzymes work better the hotter you get but this is only so up until 37oC then after that cells start to get damaged and denatured until things get so slow the reaction almost stops. This is why our bodies are around 37oC, so that enzymes are in its optimum temperature.
My results definitely match my prediction, The graphs show that my prediction is correct.
Evaluation
My results are as accurate and reliable as possible. No major anomalies were shown. But in the end I did the experiment on the computer so it was always a fair test. I made sure that the temperature was as accurate as it could have been at all times by constantly checking with a thermometer, I kept the capillary tube horizontal throughout so that the bubble wouldn’t be put to neither a advantage nor disadvantage. I also used the same equipment throughout and used the same amount of yeast suspension and glucose solution.
Several things which could have been improved. These are that I could have investigated a broader range or results, instead of 20oC to 60oC, next time I would do from 10oC to 80oC, instead of going up in steps of 10oC I would go up in 5oC which would make much more accurate. To improve accuracy you could use a digital thermometer so you would always have an accurate temperature in contrast to mercury thermometers which can be inaccurate. On the hole I think that this experiment was a success as we did it on the computers in the end and not much can go wrong if we do it on there. But next time maybe a few more pilot test and other small tests, maybe a different method could get better results.
