What affect does the concentration of sugar have on the rate of respiration of yeast? Apparatus:
1. Stopwatch with a resolution of 0.001 seconds
2. 4 test tubes
3. 200 ml of yeast in a beaker
4. 200 ml of glucose solution
5. 500 ml of limewater
6. 2 delivery tubes
7. 1 test tube rack
8. 1 water bath set to 37°C
9. 2 pipettes
10. 3 measuring cylinders with a resolution of 1ml, ranging from 0-30ml. 11. 200 ml of water
Hypothesis:
The higher the concentration of sugar: the faster the rate of respiration. I predict this outcome as the rate of respiration depends upon three main factors: glucose, temperature and oxygen…as the oxygen concentration and temperature remain the same; the increase in the concentration of glucose (sugar) should lead to an increase in the rate of respiration. Variables:
The independent variable for this experiment is the concentration of sugar. The range of the concentration of sugar is 0-100% (inclusive), in intervals of 25%. The chosen range is suitable as it is easy to dilute water with the glucose solutions with the given concentrations and the range is wide enough to see a change in the dependant variable, yet the intervals are equally spaced to allow us to record patterns. The dependant variable is the time taken (in seconds) for the limewater to begin to turn cloudy. In order to make it a fair test, the same person will use the stopwatch to account for reaction times and debates between when the water has begun to turn cloudy. This means that the results will be consistent for each group, and there is less room for human error.
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Apart from substrate concentration, which I will be changing in this experiment, it is important to keep the other variables the same to ensure the results are reliable and to get a fair test – results must change because of a difference in the input variable, not because of a different variable. I can monitor the temperature and check it stays the same by using a thermometer. I can keep the pH ...
We will use a stopwatch with a resolution of up to 0.001 seconds to ensure that the results are as precise as possible. We will also repeat our investigation three times using the same method and equipment to ensure that it is repeatable and we will compare our results with another group’s who have used the same method to see if our results are reproducible. In order to get data that is as accurate as possible, we will repeat our measurements three times and use the mean to draw conclusions from. We will also operate extremely carefully while using instruments that are of the highest available quality to gain accurate results.
The control variables in this investigation are as follows:
* Volume of limewater
* Volume of yeast
* Temperature
* Type of test tube and beaker
* Person using the stopwatch and determining the cloudiness of the limewater. Method:
1. Measure 20 ml of yeast using a pipette and a measuring cylinder. 2. Pour the yeast into a test tube.
3. Measure 30ml of limewater using another pipette and measuring cylinder. 4. Pour the limewater into a test tube.
5. Measure 20 ml of glucose solution using a pipette and a measuring cylinder. 6. Pour the glucose solution into the test tube containing yeast. 7. Quickly connect the delivery tube between the test tube containing the yeast and sugar solution and the test tube containing the limewater, taking care that the stopper end is in the yeast and sugar test tube and the longer end is partially immersed into the limewater. 8. Carefully place the two interconnected test tubes into a test tube rack. 9. Place the test tube rack into the water bath.
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Water can move through the different cells due to the difference of water potentials in the cells. If there is a higher solute concentration in the cell than outside the cell, the water will move into the cell. However, if the concentration of inside the cell is lower than the outside, water will not move into the cell. This process is called osmosis. Research question; This investigation will ...
10. Start the stopwatch and record the time taken for the limewater to start to turn cloudy. 11. Repeat each reading three times.
12. Repeat steps 1-11, except using 75%, 50%, 25% and 0% concentration of sugar. The sugar solution should be diluted with water to form the specific concentrations (i.e. using 22.5 ml of glucose solution with 7.5 ml of water to form 75% concentration.) Risk Assessment:
It is important to wear safety goggles as the limewater is corrosive and will damage the eyes if it comes into contact with them. Hair should be tied back and ties should be tucked into shirts as the substances involved in the experiment can become entangled with loose objects, posing a safety risk. Bags should be tucked under tables to avoid people colliding with bags and dropping test tubes or the limewater. Test tubes should always be placed in a test tube rack to avoid damage to test tubes. Table of Results:
Concentration of sugar (% )| Time taken for limewater to begin to turn cloudy (seconds)| Mean| 0| 1605| 1680| 1625| 1637|
25| 1205| 1180*| 1225| 1215|
50| 860| 900| 790*| 880|
75| 450*| 425| 430| 428|
100| 300| 360| 420| 360|
*all values in a red cell with white font are anomalous and have not been included in the calculation of the mean. We encountered 3 anomalies in our results, which have been highlighted in the above table. There are various reasons for the occurrence of these anomalies: human error (person timing didn’t start/stop stopwatch at the correct time), random error (the concentration of the sugar was incorrectly measured) or a systematic error such as the stopwatch was incorrectly calibrated or the battery was running low. Conclusion:
My results illustrate that the higher the concentration of sugar, the faster the rate of respiration of yeast as the limewater turns cloudy faster. This is shown by the dramatic decrease in the time taken for the limewater to turn cloudy from 0% sugar (1637 seconds) to 100% sugar (360 seconds), thus proving that there is a direct correlation between the concentration of sugar and the rate of respiration. Evaluation:
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An investigation into the effects of sugar concentration on yeast activity Introduction: Yeasts are eukaryotic micro organisms belonging to the kingdom fungi. Yeasts live on sugars and produce ethanol and carbon dioxide as by-products. [James Mallory, 1984]When Yeasts are given water and sucrose they convert the sucrose into glucose then convert the glucose into carbon dioxide and ethanol ...
I think that I should have re-tested my anomalies to get more accurate results, which would have made my experiment more repeatable. Furthermore, there could have been discrepancies in determining when exactly the limewater started to turn cloudy, which could potentially lead to results that are not accurate as the degree to which the limewater has begun to turn cloudy could differ. To correct this error, we could place an ‘x’ in faint marker pen on the bottom of the test tube, and we could stop the stopwatch when the ‘x’ is no longer visible due to the cloudiness of the limewater. There was also a difficulty with the water bath as it took a number of seconds to transfer the equipment to the water bath while the stopwatch had already started, although I do not think that this had a significant effect on our results as the respiration would only optimally occur at the temperature of the water bath.
