Science Buddies: "Ask an Expert"

Hello, my name is Jane. This year we are required to do a science fair project that is mandatory for those students taking the Earth Science high school course in 8th grade while the regular science classes do it next year in high school. For this science fair project we were allowed to choose any subject that would interest us. My teacher recommended this site to us and I am wondering if someone can help me out with this project. My science partner and I are working on a project about the effect ultraviolet light has on bacteria mortality. Since we had recently discovered that we could not obtain the bacteria unless we got our teacher or someone else in the school to help us with it and that we had to do it in a lab with supervision, we decided to use a safer form of bacteria that is used in everyday life: baker's yeast which, I don't think, we don't need supervision and help for that much. Since we do not think that we can get to a laboratory from where we live often, we decided to do this project at home. I have already purchased and received the UV light from Ebay. My science partner has the baker's yeast at her house and if we do not have enough, we can get it at a supermarket nearby. I have a few questions about this project and I hope someone is willing to help me out.

The first two questions are: What agar would the yeast grow best on and can it be put onto petri dishes? If so, how do we go about putting the yeast onto the petri dishes?

The third and fourth questions are: Do you have any suggestions on how to conduct the experiment? For example, two questions we have is how far should the UV light be from the petri dishes and where should we conduct this experiment?

The fifth question is: We are going to have to conduct this lab for a few days, a week at the most. During the time we are not conducting the experiment, where and how should we store the petri dishes?

Also, our earth science teacher has kindly gave our class more time to do the projects. He extended the due date to February 6, 2006 or somewhere around that time. While we are trying to figure out how to do this experiment, we are researching for information on ultraviolet light and bacteria mortality. I think that it will be easier to find information about ultraviolet light and its effects, but I'm not sure how to find information about bacteria mortality. If there are any good sites for obtaining information about anything that will help our research, kindly tell us! Any links to places where we can purchase supplies needed for this project and/or getting information will be greatly appreciated!

Thank you for taking out time to read this post. Thank you in advance for the help. My science partner and I greatly appreciate your help.


Sincerely,
Jane

Hi Jane,

Yeast will grow on various agar plates including: YED agar or on Nutrient agar + glucose agar plates (see links below for more info and preparation instructions). You may be able to order these plate pre-poured.

See the links below for examples of how to conduct this type of experiment. There are tips for growing and storing cultures in some of these web sites.

Here are some good sites for you to have a look at:

Common baker's yeast, Saccharomyces cerevisiae
Background info:
http://www.phys.ksu.edu/gene/a1.html

Culture media:
http://biology.clc.uc.edu/fankhauser/La ... _Count.htm
http://www.sas.org/E-Bulletin/2002-01-1 ... /body.html

Experimental methods:
http://www.accessexcellence.org/LC/OP/RAY/
http://www.scienceteacherprogram.org/bi ... hah04.html
http://www.usc.edu/CSSF/History/2004/Projects/S1316.pdf
http://www.accessexcellence.org/AE/AEPC ... using.html

Have a look at the information available on these websites and feel free to get back to us with any specific questions you may have. I hope this helps!

Good luck!

Mary

Thank you for the help. I am grateful because you gave me a lot of sites I could gain information at. The background information about the baker's yeast was very useful. My science partner and I plan to use that site to write out the information we found while researching along with other sites we found. I see there are many ways to go about doing this experiment. I think some of the materials needed for this experiment will be very easy to find, but I don't know where to get some of the other materials. For example, where can we obtain the goggles the site[s] were talking about (the sites under the "Experimental Methods" section)? My teacher can most likely help out by letting us borrow safety goggles, but I think some of the sites said that we needed goggles that also protected the sides of our eyes. Also, can we just use regular safety goggles for this experiment or do we need a certain type to be safe from the UV light? Another thing I'm wondering about is what type of sugar we are supposed to use in order to make the yeast dilution? There was a site that mentioned how to make an inexpensive UV box and said there were instructions on how to make the box in a book. I'm not sure if I can get the book. Do you know how to make an inexpensive UV box? Another thing I'm confused about is this...how do we get an incubator for the petri dishes?? A lot of the sites I went on mentioned that they incubated the petri dishes. Is incubating the same thing as storing? Does it have to be a specific type of incubator? If we're not able to buy an incubator, how to we make it? I'm sorry I had so many questions, but I hope I can get a response quickly. I don't want to buy things that I don't necessarily need for the project if there's a less expensive way of getting/making it. Thank you once again for replying! It was a great help!

Jane--

An incubator is a bit like an oven. It heats up, and you put the petri dishes inside it and leave them there overnight to let the bacteria grow. Unfortunately, I don't know whether you can make an incubator, and I don't think I would suggest using your oven as a replacement.

You can store the bacteria in your refrigerator (although you might want to check with your parents if this is okay!). The cold will preserve the bacteria and keep them from growing.

I have used normal safety goggles with a UV lamp. As long as you don't look directly into the bulb, you should be fine.

Science Buddies has a page that discusses what yeast eat:
https://www.sciencebuddies.org/mentorin ... ?from=Home
Especially if you are using bread yeast, you should be able to use normal table sugar (which contains glucose) for your dilutions.

Good luck!
Sonia

Hi Jane,

Here are a few suggestions:

-you may want to use sunglasses (the kind that filter UV) as safety glasses, or ask your teacher what kind of safety glasses he/she could provide you with (ask if they protect against UV) or go to your local hardware store and check out what kind of safety glasses are available

-as for what kind of sugar to use – regular table sugar should be just fine

-as for making a UV box – you may just be able to use a regular cardboard box, just cut a hole in it that will allow your UV light source to fit in

-incubate means to keep under conditions favorable for development, so in your case you want to put the yeast on the appropriate agar media and put them at a temperature that will favor their growth

-you first need to determine what temperature you need to incubate your yeast at (look on some of the previous websites provided), the simplest case would be room temperature (about 25 degrees Celsius), in this case you could just leave your plates in a container in the ambient air

-if you need to incubate at a higher temperature, for example 37 degrees Celsius, you will need to find an incubator to do this in – I would suggest talking to your teacher and see if he/she could help you locate a lab with an incubator (most likely you don’t want to purchase an incubator as these are generally expensive pieces of equipment)

Hope this helps! Please post again if you have more questions.

Mary