Izzi
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Joined: Tue Oct 09, 2007 9:48 am

Yeast repiration

Postby Izzi » Sat Oct 13, 2007 9:05 am

I am conducting the aerobic and anaerobic yeast respiration experiment. I have run the experiment 10 times for each respiration type and I have the results. I hypothesized that because yeast metabolism of sugar in the presence of oxygen is more efficient and more energy is derived that it would produce more CO2. However my data shows the opposite to be true. The anerobic respiration produced 100ml of CO2 in less time than the aerobic respiration. I want to know if these results are correct. Please help. Thank you

MelissaB
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Postby MelissaB » Sat Oct 13, 2007 9:27 am

Izzi,

In science, there are not 'correct' answers--there's only what you observe. You did the experiment and obtained your results, and they are perfectly valid results. Some of the most important discoveries in science--including antibiotics!--came from results other people would consider 'incorrect' or that the scientists did not anticipate.

What you need to think about now are the potential explanations for your results. Some of them have to do with the organisms themselves, and others with the experimental setup. For example, the experiment instructions do not tell you how much air to leave in your -air bottle; if you left a lot your anerobic conditions might not have been as anerobic as you thought they were! On the other hand, it may be that yeast do produce more CO2 under anerobic conditions...but is that what your experiment really measures? I would argue that it tells you something about the rapidity of the CO2 production but not necessarily the amount (if I'm reading your post correctly). Could it be that under anerobic conditions the yeast metabolize faster, but in the end metabolize less?

Izzi
Posts: 3
Joined: Tue Oct 09, 2007 9:48 am

Yest respiration

Postby Izzi » Sat Oct 13, 2007 9:46 am

Of course the experiment does not indicate the size of graduated cylinder to use. I used a 100ml graduated cyliner and in each run of the experiment the CO2 output for either experiment reached 100 ml in less than 20 minutes. The time difference for each version of the experiment was negligible but a slim margin in favor of anaerobic respiration. The experiment explains that I am to use a 1 liter bottle and place the 2 cup yeast solution in the bottle. As a result there is significant space between the level of the yeast solution and the bottle cap. Perhaps this is a flaw in the experiment. But there is no way to extract the air from the bottle without distorting the bottle and bringing the yeast solution too close to the cap. In general my conclusion based upon these results is that the CO2 output is about the same under each type of respiration. I am unable to determine if the results would be different over greater time periods because of the limitations of the graduated cylinder. Also this seems beyond the scope of the explanation of the experiment in science buddies.

MelissaB
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Postby MelissaB » Sat Oct 13, 2007 11:41 am

But you didn't actually measure total output--you stopped when the yeast had produced 100 mL of CO2. How do you know that eventually the aerobic solution would not have produced much more CO2 than the anerobic solution? I'm not trying to criticize you, just get you thinking about some of the things the judges are likely to ask about.

Izzi
Posts: 3
Joined: Tue Oct 09, 2007 9:48 am

Yeast Respiration

Postby Izzi » Sat Oct 13, 2007 12:59 pm

You are quite right. But the experiment is limited by the equipment. Even if I were to use a 250 ml graduated cylinder, which by the way, is well beyond that which is contemplated by the rather criptic instructions for this experiment reflected on science buddies, you will likely reach the limit of this equipment before exhausting the CO2 output of either version of the experiment. There must be a reasonable limit and who is to say what that limit should be. Certainly the science buddies project does not adequately deal with this issue. I can, of course, start over again with the larger graduated cylinder, yet I can not help feeling that I was misled by the vague nature of the science buddies project explanation rendering my previous work a complete waste of time and effort. Ultimately it is my responsibility to test my hypothesis and provide scientifically viable results. You intimate that I must push further, so I will scrap what I have done so far and start anew. Perhaps science buddies should amend this project on the website so that students can avoid my predicament in the future and utilize their time and effort not only efficiently but effectively.

MelissaB
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Postby MelissaB » Sat Oct 13, 2007 2:05 pm

Izzi,

There is no reason to scrap what you have done so far--you have collected data on the rate at which a reaction takes place, which is a very important variable and allows you to draw some conclusions about the reaction.

I did mean to imply that you 'must' go further--I just meant to get you thinking about some potential explanations for your results and what steps you might take next if you were interested. In the real world, scientists rarely stop after one experiment, and knowing what experiments you might want to do next given the results of your previous experiment is an extremely important skill.

If you do choose to take this further, I suggest putting a smaller amount of yeast and/or sugar in each of the containers so the amount of CO2 produced won't overfill your container.

Louise
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Re: Yeast Respiration

Postby Louise » Sun Oct 14, 2007 9:16 am

Izzi wrote:You are quite right. But the experiment is limited by the equipment. Even if I were to use a 250 ml graduated cylinder, which by the way, is well beyond that which is contemplated by the rather criptic instructions for this experiment reflected on science buddies, you will likely reach the limit of this equipment before exhausting the CO2 output of either version of the experiment. There must be a reasonable limit and who is to say what that limit should be. Certainly the science buddies project does not adequately deal with this issue. I can, of course, start over again with the larger graduated cylinder, yet I can not help feeling that I was misled by the vague nature of the science buddies project explanation rendering my previous work a complete waste of time and effort. Ultimately it is my responsibility to test my hypothesis and provide scientifically viable results. You intimate that I must push further, so I will scrap what I have done so far and start anew. Perhaps science buddies should amend this project on the website so that students can avoid my predicament in the future and utilize their time and effort not only efficiently but effectively.


Hi Izzi,
I'm sorry your experiment did not work the way you expected. I agree with everything Melissa says, but I wanted to address a few points you raise about the procedure. In general, a procedure is intended as a starting point. You say the instructions are cryptic; I would not say that, but I would agree that they are not specific. Generally the more advanced the project, the more the details are left to the student to optimize. The size of the graduated cyclinder isn't specified, nor is the temp of the water or the collection time. These are parameters _the researcher_ is supposed to optimize. A few places the instructions say something like this (use the temp your yeast package recommends, modify the collection time, etc.) You, me, and Melissa could each go buy yeast at the store, do this experiment, and get completely different volumes of gas produced. A big part of this is that yeast quality varies a lot from brand to brand (how it is formulated- regular, rapid rise, for bread machine, etc.) and from store to store (how it is stored). Water quality also enters in to this, though unless your water was really terrible, this should be more minor effect. I hope this makes sense to you. The projects are designed to help, but we do expect that some exeperimental ddesign and modification be done by the researcher. So, if after reading this post, and checking the project again, you believe that this project is truly flawed, I hope you will write the sciencebuddies admin and let them know. (the email is scibuddy AT sciencebuddies.org) We here in the forums don't design the projects, and don't have the power to modify them.

Anyway, your experiment measured something, and it appeared that it was reproducible over 10 trials. You, as the researcher, need to decide what this data is telling you. Does it test your hypothesis or is it testing something else? If you didn't test your hypothesis, is the 'something else' that you tested interesting? Or do you want to start over and redesign to test the original hypothesis?

One last point... after reading the project guide and your posts, it seems like ran a slightly different experiment than what was proposed in the science buddies page. You measured the time to fill 100 mL cylinder with gas, the sciencebuddies project is to run all trials at the same time and measure the total volume. (With the time to be determined by "your particular conditions"- that is, you should run until the reaction is complete. The best way to do this is with a test reaction- see when the volume stops changing, and then add a little extra time to make sure you account for experimental variability). Also, at one point you say anaerobic takes less time- is this really true within your experimental error? If so, this is an interesting fact, as Melissa mentions, especially when coupled to an experiment that measures the total output. So, if you do decide to start over and measure total gas production, I still think these results are interesting, and should be included in your report.

Good luck with your project. If you do decide to start over, ChrisG has been talking to a student about this project as well and has some advice about how to make the system as anaerobic as possible. He said:

Another issue to consider is that the online procedure instructs you to leave a small amount of air above the water in the bottle with the yeast, but the procedure is not specific about how much air to leave in the bottle. Some of the oxygen from this air will diffuse back into the water during the experiment. Suppose you have 0.9 L of water and 0.1 liter of air. Air contains about 21% oxygen, so 0.1 liter of air contains 0.021 liters of oxygen, or 21 cubic centimeters (cc) of oxygen. Aerobic water contains about 6 cc of oxygen per liter, so 0.9 liters contains only about 5-6 cc of oxygen. This 5-6 cc is the amount of oxygen that you can control by boiling and re-aerating the water, and it is much less than the amount of oxygen in 0.1 L of air. So, be careful! If you leave some air in the bottle and are not very careful about how much air is in each bottle, it is possible that your "aerobic" bottle might actually have less oxygen than an "anaerobic" bottle. I recommend filling the bottles with as much water as possible (leaving as little air in the bottle as possible ) and also being very careful to leave the same amount of air in each bottle so that it won't complicate your results.


This is one case where I think the instructions could be more clear.


Louise


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