Yeast Reproduction In Sugar Substitutes

[parastrehan]

Hi there,

I am doing the experiment 'Yeast Reproduction In Sugar Substitutes' for my science task. Please go have a look at this experiment on the science buddies website. Can anyone please explain how the water is displaced which shows the amount of carbon dioxide produced. How does this process work? I don't understand it. Thanks in advance

[iriss]

Hello,

Thanks for posting in the Ask an Expert forum! It’s great to see that you are thinking about the details of the scientific process as you perform the “Yeast Reproduction in Sugar Substitutes” experiment. This is how the water displacement process works:

1. The yeast in the water bottle breaks down the sugar (or sugar substitute) molecules into carbon dioxide and water.
2. Carbon dioxide is a gas, so it will rise to the top of the bottle and travel through the tube and into the graduated cylinder in your tub or bucket.
3. Because carbon dioxide is so much lighter than water, it will rise (in the form of bubbles) to the top of the graduated cylinder, pushing (aka displacing) some water out of the cylinder and into your bucket.
4. As these bubbles accumulate due to the yeast reproduction process, you should see a noticeable pocket of gas form at the top of your graduated cylinder.
5. You can measure the size of this gas pocket (aka how much water has been displaced) by looking at the measurement markings on the side of your graduated cylinder.

Does this clear things up? Let me know if you have any other questions!

[parastrehan]

Thanks for your reply. I undertsand the concept better now. I have one question just to confirm my experiment design. Do i tape the plastic tube into the graduated cylinder or do i just put it in with no tape?
thanks

[iriss]

Great! I'm glad to hear you understand the concept better now.

As for taping the tube, that's up to you. In order for the experiment to work, the carbon dioxide needs to be able to get from the water bottle through the tube and up to the top of the graduated cylinder. If you can fit the tube into the cylinder easily and you feel confident that it will stay put during your experiment, there is no need to tape it. Otherwise, I would recommend taping it to the inside of the graduated cylinder so you don't have to worry that the tube could fall out and mess up your results.