The Effect of Glucose Concentration on Anaerobic Respiration in Yeast

Dependant: Number of Bubbles produced after the reaction

Apparatus:

• 2* conical flasks
• Delivery tube with bung
• Dropper
• Yeast
• Glucose of different concentrations (10%, 15%, 20%, 25%, 30%)
• Water bath
• Stopwatch
• Measuring Cylinder

Method:

1. I am going to do 5 tests & each test will be performed 3 times to get an average result.
2. In one conical flask, I will mix together 25ml of yeast & 25ml of a glucose solution
3. With a delivery tube with a bung in the top of it and leave it for 5 min so it gets acclimatized
4. In the other conical flask I will put enough water to cover the end of the delivery tube.
5. On the first test I will use a 10% concentration of glucose.
6. On the second test I will use a 15% concentration of glucose.
7. On the third test I will use a 20% concentration of glucose.
8. On the fourth test I will use a 25% concentration of glucose.
9. On the fifth test I will use a 30% concentration of glucose.
10. I will then put the yeast & glucose mixture in a warm water bath and count how many bubbles of CO2 are produced within 5 min.

Results:

Graph:

Conclusion: 

From my graph, we can see that as the concentration of glucose solution increases, the amount of CO2 produced also increases. If the CO2 is produced, that means that respiration is occurring. The continual increase of carbon dioxide means that the rate of respiration increases as the concentration becomes less dilute and stronger. From the experiment, I’ve seen that rate of respiration is at its slowest when there was a little glucose solution present. When the concentration of glucose was 10%, the amount of bubbles produced is relatively low, only 26 in 5 minutes. The difference between the amount of bubbles produced at 10% sugar concentration and 30% sugar concentration is visible. (103 bubbles in 5 minutes at 10% concentration). This suggests that concentration has a large impact on the rate of respiration. The concentration of a solution can speed up or slow down the rate of respiration depending on how concentrated the solution is. In this experiment the strongest concentration speeded up the rate of respiration, while the weakest concentration slowed up the production of CO2.

Evaluation:

In my opinion, the experiment was quite successful. Although there were some things that might be measured differently. Number of bubbles may not be the best way to measure the rate of respiration in yeast, since human eye can make mistakes. Also it was very hard to keep the water bath’s temperature constant at a room temperature (25° C), so I had to pour hot water from time to time in order to prevent decrease in temperature. Next time it would be very interesting to investigate higher concentration of Glucose, in order to see after what level of concentration, rate of respiration falls. I suppose the results that I obtained during this experiment were reliable enough to support my hypothesis.  

Reference: