Science Fair Project: Growing Microbes on Potato Sucrose Gelatin

Where do Microbes Live? What do they Look Like?

Where are microbes? What do they look like? Were the questions my 1st grade daughter had been asking my biologist husband. So when it came time for her first ever school science fair, we came up with this original project which uses potato sucrose gelatin (original recipe included) as a food for microbes. Using petri plates or any other closed sterilized container makes this experiment safe. We looked at microbes growing in the soil by spreading a little soil on top of the gelatin.

For more information about how to help your child do a science project and how to put your board together, check out Great Science Fair Projects.

Original Science Project Idea: Good for 4th-8th Grade

This experiment was the first one our family ever did, and it was frankly a bit ambitious for a 1st grade project. However, since our school science fair was not competitive, so we decided to use this project to help teach our daughter. The process of the project was really too complicated for a 1st grade project, but my daughter was able to assist with all the steps (see notes for what she did), but a 4th to 8th grade student could do this project on their own. An older student might end up doing more evaluation of the microbes which they find growing by looking them up online. Furthermore, they may also want to design the experiment to find out something, for example the microbes in soils that are known not to be good for plants vs. soil that is good for plants (could be soils in the neighborhood or even in your own garden).

Questions:

1. What do microbes look like?
2. Do different microbes grow in different places?
3. Can you kill microbes?

Materials

Potato Sucrose Gelatin (recipe follows)

Petri plates (or other secure, sterilized container)

Digital camera and printer

Microscope and slides

Purpose

The purpose of this project is to see what microbes look like and find out where they grow.I also want to see whether different microbes grow in different places.I wondered how I could kill microbes.

Method:

April 28:I learn about microbes from my Dad ( a professor of biology).He explains to me that we can find out whether microbes are on something by putting a piece of it on a plate of potato sucrose gelatin and seeing if anything grows.He says that we have to first kill all of the microbes in the gelatin by using heat. We will test to see if we have done a good job by using some controls (plates that have tap water, boiled water and nothing on them).

He tells me there are three kinds of microbes: fungi, yeast and bacteria.He says that looking with my eyes fungi will look fuzzy and both yeast and bacteria will look slimy.He says that you need to use a microscope to see whether the slimy stuff is yeast or bacteria. We walk around the yard looking for things we want to put on our Petri plates.

April 30:We make potato sucrose gelatin and pour into Petri plates.

Potato Sucrose Gelatin

Dad remembered that when he was a student, he had made a potato dextrose agar for growing bacteria and fungi.We decided to see if we could come up with a homemade version.Since we couldn’t find a recipe anywhere, we came up with our own version using Dad’s knowledge of what was needed to make things grow and mom’s knowledge of how to can foods and make them sterile.Maggie did all of the steps which did not require her to handle hot liquids.In parenthesis we show what each person did.

• Step 1:Cut up three potatoes into cubes (Maggie)
• Step 2: Put potatoes in a pot and cover with distilled water (Maggie)
• Step 3: Boil potatoes until water is light brown (Mom and Maggie)
• Step 4: Drain water into a canning jar (Mom)
• Step 5: Add ¼ cup sugar and 1 package of unflavored jello and stir until dissolved (Maggie)
• Step 6: Cover jar with canning lid and put into boiling water bath for 20 minutes to kill all bacteria (as you would in canning fruits or vegetables) (Mom)
• Step 7: Take jar out of water bath and carefully pry lid open but leave it on the jar. (Dad).
• Step 8: Pour the Gelatin into the Petri plates (Dad and Maggie)
• Step 9: Put the plates in the refrigerator until they are set (Maggie)

March 1:We gather all of the things we want to look at.We are careful to lift the lid of the plate just a little and to put the material on quickly so we don’t let any other microbes in the air on to our plates.Here are the things we put on the Petri plates:

• China Berries—small pieces put on plate
• Black Spots on Seed Pods—small piece put on plate
• Acorn—rolled across the plate
• White fuzz on bark small piece put on plate
• Jasmine flower petal—pressed on to plate
• Black Spots on Rose leaf—small pieces put on plate
• Sand:diluted 1/100 in water
• Sand: diluted 1/10,000 in water
• Garden soil: diluted 1/100 in water
• Garden soil: diluted 1/10,000 in water
• Boiled water Control: boiled to make sterile then cooled it and put some drops on the plate
• Tap water Control:put drops on the plate
• Plain Gelatin control: Plate we didn’t put anything on

March 3:I look at each plate and write down what I see growing.I measure the fuzzy spots and write down the color (see results).

March 4: Everything has grown a lot!I write down what I see and I take pictures.

March 5-15: We put the plates in the refrigerator to slow down the microbes growing and see if the different temperature makes them grow differently.

March 15:Dad shows me how the microscopes work and how to make slides.I made a slide by putting a few drops of water on it first.Then I used a toothpick and took a piece off something growing on a plate.I put that piece on the slide in the water.Then I put a piece of glass on top.Then I looked at it under the microscope.

I look at some of the fuzzy microbes and some of the slimy ones.The fuzzy ones are easier to see. Some of the slimy ones are small dots.Dad says those are probably yeast.I can’t see some of the slimy ones.Dad says that those are probably bacteria and we would need a more powerful microscope to see those.

Results: (We had Maggie draw pictures of what she saw in the microscope and we also took pictures of the petri plates. In her original project, we also had a table which showed when each plate started growing and described what was on each plate).

I think the one that had the most microbes in it was the flower press and the white fuzzy bark.The microbes in the flower press had eaten up all of the gelatin.I noticed that the slimy microbes ate up the gelatin but the fuzzy ones didn’t.The black spots on the rose had a lot of neat colors, some white, red and yellow.

Microscope: I saw that fungi is like spider webs or threads.They were different colors like red, yellow or pink.I wondered if the fungi would be the same color as the thing it grew on but it wasn’t.Some of the fungi had spores.The spores looked different.Some of the spores were a whole bunch of little dots inside a ball, sort of like an egg case.Other spores were in small groups of three or four lined up like a ladder.Some spores were all alone.

Conclusion:

I learned that there are microbes in everything and that they are all different. I learned that you can kill microbes by boiling them.I also learned that there aren’t as many microbes in the water we drink as there are in other places.

I learned that there are different microbes in soil and on plants.The soil had mostly slimy microbes and the plants had mostly fuzzy ones. I learned that slimy microbes eat things up faster than fuzzy ones.Slimy microbes are also smaller and harder to see, even with a microscope. Fungi have different colors and different bodies.I learned that they look pretty cool.

Resources: Dad, a biology professor.

Mom, a former elementary school teacher and cook.