Aerobic Respiration:
Glucose + Oxygen Carbon Dioxide + Water + Energy
C6H12O6 + 6O2 6CO2 + 6H2O + 35ATP
Anaerobic Respiration:
Glucose Alcohol + CO2
(Source: Work done in class)
To prove that the gas produced by the experiment was indeed carbon dioxide, we bubbled some of the produced gas through some limewater solution. Limewater solution turns cloudy in the presence of carbon dioxide, and when this happened, we could easily say that our experiment was producing carbon dioxide.
The ideal temperature for an enzyme to be in is 36 degrees. (Edexcel Modular book) Therefore we decided to make water baths of the following temperatures (using the beaker and water) for the yeast solution to stand in: 30, 40, 50, 60 and 70 degrees centigrade. We predicted that the yeast would be approximately 10 degrees cooler than the water around it so we would have 2 temperatures above the optimum range and 2 below it. This would hopefully give us a wide spread of results and make our experiment successful. After the preliminary results, we have decided to wrap the beaker containing the water bath in bubble wrap to keep the water the same temperature throughout. As air is a poor conductor, it will insulate the bath and keep the water warm. We did our preliminary experiment using a water bath temperature of 40 degrees. We took a reading of the gas syringe every 30 seconds for 3 minutes. Here are the results that we got:
As you can see, not a lot of gas was produced. This is because the actual yeast temperature was about 30 degrees, which is lower than its optimum range.
We used 20ml of yeast solution in the conical flask and 8g of sugar. This worked very well and so we have decided to keep these quantities constant throughout the main experiment. Our variable will be the temperature of the water bath as this is what we are investigating. As said before, we will keep the water at a constant temperature for the three minutes of each part of the experiment using bubble wrap and we will use a thermometer to gain the correct temperature in the first place. If we didn’t control the temperature for each part, the experiment would be unfair and the results would be inaccurate as a result of this.
Fair Test:
To make sure that we have a fair experiment, we will need to make sure of the following:
- That the same quantities of sugar and yeast solution are used each time.
- That the temperature of the water bath is constant for each part.
- That we take the reading from the gas syringe correctly and at the exact time periods that we have set. (Every 30 seconds for 3 minutes)
- That we keep the yeast solution moving for the whole 3 minutes of each part to ensure that aerobic respiration is occurring.
Method:
Using the measuring cylinder, measure out 20ml of yeast solution and pour it into the conical flask. Make up a water bath to the temperature that you have chosen. Do this by adding hot water from the kettle to cold water from the tap in the beaker. Measure the temperature with a thermometer. Do not fill the beaker too high or when the conical flask is placed inside, it will overflow. When filled, wrap the beaker with bubble wrap to maintain the temperature. You will need the gas syringe and piping set up ready in the clamp stand as in the diagram above. Add your chosen amount of sugar to the yeast, swill around to begin respiration and immediately place the bung with the piping in the top of the flask. After 30 seconds, take the reading on the gas syringe and take note of this. Repeat this every 30 seconds for 3 minutes, taking note of the reading every 30 seconds. After 3 minutes, remove the bung from the flask and get rid of the flask’s contents into the sink. Wash any remaining sugar and solution from the bottom before restarting with another temperature. Also, you must not forget to push the gas syringe plunger back down to the bottom before doing your next part of the experiment.
Safety:
Take care around hot water and clean up any spills to keep from slipping over.
Prediction:
I have predicted that the most gas will be produced when the water bath is at around 50 degrees. This would make the yeast solution about 40 degrees which is the closest chosen temperature of the optimum temperature of 36 degrees. I also predict that the temperatures one above and below 50 degrees (60 and 40) will produce less gas than the 50 degrees part of the experiment, and following, the highest and lowest temperatures (30 and 70) will produce the least gas because the enzymes are too far above or below their optimum range. When the enzymes reach temperature too far above or below their optimum range, they will begin to denature and so respiration will slow and less and less gas will be produced, until respiration stops completely. To understand this, more information on enzymes is needed.
An enzyme is a specific type of protein molecule. Each enzyme has its own individual shape so that it can work with another specific material, called its substrate. Each enzyme molecule has a different shape. It is held in this shape by bonds within the molecule. Temperatures to far above or below the enzymes optimum range cause the bonds to break and the shape will change. This means that the enzyme will not fit with its substrate and so a reaction will not take place. This is known as denaturing. (Source: Work done in class)
Results:
Conclusion:
I have found from my experiment that the most gas was produced when the water bath is at 50 degrees. This would make the yeast solution about 40 degrees which is the closest chosen temperature of the optimum temperature of 36 degrees. I also found that the temperatures one above and below 50 degrees (60 and 40) have produced less gas than the 50 degrees part of the experiment, and following, the highest and lowest temperatures (30 and 70) have produced the least gas because the enzymes are too far above or below their optimum range. When the enzymes reached the temperatures too far above or below their optimum range, they began to denature and so respiration slowed. This is due to the fact that there was less kinetic energy and so less particle collisions were happening, leading to less respiration and less gas being produced until, eventually, if the experiment was continued, respiration would have stopped completely. To understand this, more information on enzymes is needed.
An enzyme is a specific type of protein molecule. Each enzyme has its own individual shape so that it can work with another specific material, called its substrate. Each enzyme molecule has a different shape. It is held in this shape by bonds within the molecule. Temperatures to far above or below the enzymes optimum range cause the bonds to break and the shape will change. This means that the enzyme will not fit with its substrate and so a reaction will not take place. This is known as denaturing. (Source: Work done in class) Here is an example diagram:
Evaluation:
Our experiment was very successful. We didn’t have any problems obtaining our results and our group worked efficiently with the resources and information made available to us. When we were first given our experiment question we thought that the gas syringes would not be available and we would have to find another method for the task. We were very grateful for the syringes as they have made our experiment a lot more accurate than any other method would have made it and have given us the knowledge of how to use them for future experiments.
When performing our experiment, we followed the plan exactly, which is why we got such good results. I had a firm understanding of the way that enzymes behave before the experiment and so I was able to select good ranges and conditions to perform the experiment under.
The hardest part of the experiment was keeping the yeast solution moving. This had to be done to make sure that the solution was always respiring aerobically and producing carbon dioxide gas.
Aerobic Respiration:
Glucose + Oxygen Carbon Dioxide + Water + Energy
C6H12O6 + 6O2 6CO2 + 6H2O + 35ATP
We found it quite easy to take the measuring on the syringe every 30 seconds as there were 3 of us in our group and so we could give one person the job of telling another when to take a reading and the third could then take note of this reading.
With the bubble wrap around the water bath in the beaker, the temperature of the water stayed constant for each part of the experiment. If we were to repeat the experiment, I would like to find a way of taking the temperature of the yeast solution throughout. This wasn’t possible for us as the top of the flask had to remain tightly sealed throughout the experiment to prevent the escape of any gas through the top. If we could have taken the temperature of the yeast, we could have performed the experiment at 36 degrees and used that result as a base to compare everything else to.
