Science Buddies: "Ask an Expert"

Hi, so I want have to make a hypothetical lab write up and am interested in how temperature affects the anaerobic respiration rate of S. cerevisiae. I will be conducting the experiment with a closed circuit to be able to measure the CO2 released, using the amount of distilled water, starting yeast, and amount of cane sugar used as a control. My science teacher posed questions to me and I have tried to find answers but I can't.

-How long does it take for yeast to reproduce specifically S. cerevisiae?
-How could i measure the reproduction of the yeast?

Hi,

Welcome to Science Buddies! You have a great project idea, and your teacher’s questions are very good ones designed to help you get started on background reading and to decide how to design a quantitative experiment. Here is some information to help you get started:

Here is some general information about the life cycle of Saccharomyes cerevisiae

http://users.rcn.com/jkimball.ma.ultran ... Yeast.html

Here is a review paper that covers the biology of the life cycle of Saccharomyces cereviseae. This is complicated and much of the content is unrelated to your project, but do read and understand as much as you can.

http://www.ncbi.nlm.nih.gov/pmc/article ... 7-0150.pdf

Here is information on yeast metabolism that describes the biochemistry of aerobic and anaerobic metabolism in yeast. Please note that carbon dioxide is produced by Saccharomyces with both aerobic and anaerobic metabolism.

Here is a project idea from the Science Buddies website that describes how to make a homemade device to measure carbon dioxide production from year.

https://www.sciencebuddies.org/science- ... p005.shtml

And here is another project idea that describes an alternative method for measuring yeast metabolism:

https://www.sciencebuddies.org/science- ... p008.shtml

In both of the Science Buddies project ideas, the carbon dioxide measurement is a reflection of the yeast metabolism and reproduction. Actually counting Saccharomyces cereviseae can be done my microscopic observation. Here is a reference that describes counting yeast cells in a hemacytometer.

http://www.ncbi.nlm.nih.gov/pmc/article ... 9-0139.pdf

The Wikipedia article gives the doubling time of Saccharomyces cerevisiae as 1.25 to 2 hours at 30 degrees Centigrade, which is its optimum temperature. Since you are designing a hypothetical experiment, you should know that metabolism doubles with every 10 degree increase in temperature, so the growth rate would be one-half at 20 degrees Centigrade.

http://en.wikipedia.org/wiki/Saccharomyces_cereviseae.



I think this should help you provide answers with a complete explanation for your teacher, but do let me know if you have any questions.


Donna Hardy

Thank you
Instead of temperature, I will most likely do "how does sugar concentrations affect the amount of CO2 produced by yeast?"
I will be keeping the temperature constant so they do not reproduce and the experiment would have to be limited in time in order to avoid reproduction. My only problem would be whether enough CO2 would be released before yeast multiply. Again this is just a hypothetical experiment so I can't really execute the lab to prove anything

Hi,

If you start with actively growing yeast at the beginning of your experiment, the yeast will probably start reproducing right away. Your independent variable is the concentration of the sugar, and the dependent variable is the amount of carbon dioxide produced, so as long as you kept all of the other parameters in the experiment controlled, it would be a good experiment.


Donna Hardy