Factors affecting the rate of respiration in immobilised yeast.
Jaysukh Kerai 10V - SC1 Science Investigation Report - 02/02/03
Title of investigation:
Factors affecting the rate of respiration in immobilised yeast.
Input Variable to be investigated:
The input variable that I will be investigating is the temperature.
Variables to be controlled:
The fixed volume, concentration of the glucose solution will have to be sustained throughout the entire investigation in order to maintain a fair test. The number and the size of the beads will also have to be kept the same, although it (size) may vary slightly, it should not have a major impact on the results.
Prediction:
I predict that the rate of respiration in immobilised yeast will increase with the temperature, until a particular temperature has been reached. I anticipate that as the temperature doubles, the rate of respiration will also double; that is to say that the temperature is precisely proportional to the rate of respiration. The yeast balls will respire and in effect rise, this makes this experiment an anaerobic respiration one.
Scientific reason to explain prediction:
All enzymes have an optimum temperature as to when they actually operate best. Yeast cells are not an exception; they convert glucose into carbon dioxide and alcohol plus energy by the use of the enzyme zymase. Enzymes are actually catalysts, which speed up reactions. These yeast cells undertake the conversion by performing anaerobic respiration. Incidentally, another name for this process is fermentation. This means that the rate at which these enzymes operate is likely to be constant until a certain temperature is reached. Furthermore, most enzymes denature within roughly 45°C, the optimum temperature will probably be around 37°C - 40°C (body temperature). The yeast balls will respire and in effect rise because the glucose solution will diffuse through the thin layer of jelly into the yeast cell, then the yeast balls will release carbon dioxide.
Risk Assessment:
* Wear safety glasses at all times during experiment
* Make sure lab coat is fastened
* Be careful and cautious when handling hot water
* Make sure bags or any other safety hazards are not in the way when carrying something.
* Be careful and cautious when pouring hot water from a kettle
Word and Symbol Equations:
Aerobic respiration:-
Glucose + Oxygen Carbon Dioxide + Water + Energy
C6H12O6 + 6O2 6CO2 + 6H20 + Energy
Anaerobic respiration:-
Glucose Carbon Dioxide + Ethanol + Energy
C6H12O6 2CO2 + 2C2H5OH + Energy
Plan:
Equipment List-
> Boiling Tube - to contain the 30 cm3 of 5% Glucose solution
> Thermometer
> Large Beaker - to act as a water bath
> 30 cm3 of 5% Glucose solution
> Rack - to hold the pre ready glucose solution
> Stopwatch - to record the time taken for each ball to rise
> Kettle - to heat up the water
> 5 immobilised yeast balls
...
This is a preview of the whole essay
Anaerobic respiration:-
Glucose Carbon Dioxide + Ethanol + Energy
C6H12O6 2CO2 + 2C2H5OH + Energy
Plan:
Equipment List-
> Boiling Tube - to contain the 30 cm3 of 5% Glucose solution
> Thermometer
> Large Beaker - to act as a water bath
> 30 cm3 of 5% Glucose solution
> Rack - to hold the pre ready glucose solution
> Stopwatch - to record the time taken for each ball to rise
> Kettle - to heat up the water
> 5 immobilised yeast balls
Stepwise procedure-
. Obtain a water bath, to whatever temperature desired
2. Obtain a boiling tube with 30 cm3 of 5% glucose solution
3. Place 5 immobilised yeast balls in the boiling tube (which is filled with 30 cm3 of 5% glucose solution)
4. Place the boiling tube with the balls in it, in the beaker.
5. Start timer
6. Record the time taken for each ball that rises
The range of temperatures will be from 10°C to 70°C in 10°C intervals. However, these temperatures may not remain constant, so therefore, the results recorded will not be accurate. Once the boiling tube is placed into the water bath (beaker), the stopwatch will be started and the time taken for all the yeast balls to rise will be recorded.
Diagram-
Method:
The input variable that was investigated was the temperature (°C). The output variable that was investigated was the concentration (5%) and the volume (25cm3) of the glucose solution. We did not change our mind in selecting the range of temperatures; incidentally, the range of temperatures was from 10°C to 70°C. The volume and the concentration of the glucose solution was kept constant; however, the volume of water in the beaker was not kept at a constant level. The equipment used in this investigation was a beaker, a boiling tube, a rack, a thermometer, a kettle, five yeast balls, stop watch and 30 cm3 of 5% Glucose solution. The experiment was repeated thee times, this enabled to gain more accurate and reliable results. However, we did not put three boiling tubes in the water bath; we only put one boiling tube in the beaker. The time taken was converted from minutes into seconds. The temperature was measured in degrees centigrade. We did not have five separate stopwatches for a single preliminary experiment, so we had to rush quickly to record our findings.
Results:
Results table-
Rate of Respiration Table A
Temperature
Average
(°C)
Rate = 1/time (seconds)
0
N/A
20
0.00059
30
0.00147
40
0.00243
50
0.00285
60
0.00438
70
N/A
Analysis and Conclusion:
In 'Table B', all the results for the time taken for each ball to rise at different temperatures have been recorded. As the investigation was repeated three times for each temperature, there are four results columns: 1st Experiment, 2nd Experiment, 3rd Experiment and Average. From my results, I was able to plot a graph to show temperature against time using the averages I worked out in 'Table B'. Error bars were also included, to show the accuracy of my times recorded. The idea of the error bars is that the longer the bar, the less reliable or accurate the results are. As you can see from my graph, at 20°C the size of the bar is very long. This evidently, means that my result at that particular point is not very accurate. However my other error bars are quite short in length, this means that my results in that particular area are more accurate. It is therefore evident from the graph that, as the temperature is increased, the time taken for the balls to raise decreases; however, this does not show the rate of respiration. Therefore, another graph was drawn to show the temperature against the rate of respiration. To calculate this (rate of respiration) the final averages were taken and was divided by one. Table A for these calculations are shown. From the graph, a best fit curve was drawn and it is clear that this particular enzyme in yeast cells is most active between 50°C and 60°C, which is obviously the optimum temperature. This result does not match up to my prediction; maybe because the atmospheric conditions in which we did the experiment was cold, (it was snowing at the time). Therefore, the enzymes probably needed extra heat to get them operating. I believe if we had done this investigation in warmer atmospheric conditions the optimum temperature would be around 40°C (body temperature). According to the best fit curve, this temperature is at 59°C. It is apparent from the graph that as the temperature increases then, so does the rate of respiration. This trend supports the prediction made earlier and the prediction that the temperature is directly proportional to the rate of respiration appears to be somewhat true for the temperature is approximately double to that of the rate of respiration. The increase in temperature with the rate of respiration is only true up to the optimum temperature, which is at 59°C after which the rate begins to decrease. The reason why the rate of respiration increases with the temperature until its optimum temperature is because as the temperature increases, the molecules are moving faster; therefore the anaerobic respiration occurs quicker because the substances from the glucose solution enters the active site of the enzyme quicker. The reason why the rate of respiration declines after its optimum temperature has been reached is because the enzymes becomes denatured and the active site is lost, as it has changed; and as a result, the substrate no longer enters the site because it does not 'fit'. The reason why enzymes denature is because all enzymes are proteins and at high temperatures, protein breaks down. This is what has occurred in this investigation at around 62°C. As mentioned above, the temperature would rise until a certain temperature has been reached and that this temperature (the optimum temperature) would be 59°C. This temperature has clearly been achieved, which confirms the prediction and that this enzyme, zymase, is no different to other enzymes that all have an optimum temperature.
Evaluation:
By looking at the graph comparing temperature against time, the error bars show how similar the results recorded were. Most of the repeated temperatures were quite similar and by referring to the graph, the most accurate results obtained, in accordance to how much the error bars were off the average result, was when the temperature was at 30°C. The other results were not very accurate or reliable as the length of these bars confirm by beliefs. However, most of the results gathered were close to the best fit curve. There was one anomalous data: when the temperature was at 60°C. A possible reason why those results may be anomalous is that the temperature may not have been kept constant for the whole time so therefore it may have changed slightly. As mentioned before, the temperatures may not remain constant or exact, although they would be assumed that they remained, constant. Once the temperature had been reached, the balls were placed in 30cm3 of 5% glucose solution and then into the water bath. This method was used because other methods may have affected the results even greater. For example, if a water bath was not used, the temperature of the glucose solution may have deceased quicker than if it was in a water bath because if the solution were only in a boiling tube, the surrounding room temperature would cause that of the temperature in the boiling tube to decrease faster. By using a water bath, the temperature of the boiling tube would remain constant for a greater length of time because it would take longer for the water bath of larger volume to decrease in temperature, thus affecting the temperature of the boiling tube and consequently the results. Another reason why there was an anomalous result could have been the size of the immobilised yeast balls. A further reason could be that there are a different number of yeast cells in each ball; however, this would affect the result minimally. Although it is more likely to have been the temperature that caused the anomalous data. The volume of the water in the water bath was not kept constant, if we had done so, it may have strengthened our dependability and reliability of our results. The hardest thing to control was indeed the temperature, we were unable to keep it constant, because the temperatures kept on declining dramatically (sometimes by 7 °C). In order to keep the temperature as accurate as possible we had to add some more hot water, this what made the volume of the water inconstant. During each preliminary experiment, we were very busy doing something or another, one time we missed the balls rising to the surface of the glucose solution, so we had to estimate roughly what time each ball rose. This caused that particular result to be very unreliable. We estimated on the counts of our previous repeats and the time that was running. Apart from that, the other preliminary experiments went accordingly. As a whole, I would say our results were relatively reliable enough to say that the conclusion is correct. Furthermore, other groups obtained the same pattern of results in reference to the graphs. If we had, another chance to repeat the experiment the yeast balls should be recently made so that they would work properly, instead of being stored and possibly becoming defective. Further work could be carried out to ensue that the results sustained are accurate and reliable and if given more time, more results could have been acquired, therefore giving a more accurate average.
