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Growing Bacteria

based on 34 ratings
Author: Cy Ashley Webb

Grade Level: 4th - 7th; Type: Microbiology

Objective:

The objective of this experiment is to learn how to grow bacteria in a controlled setting. By using simple materials from home instead of Petri dishes students will learn how to perform sterile technique. The outcome of this experiment depends largely upon their ability to keep their equipment sterile. 

Research Questions:

  • What are bacteria? What is mold? What is fungus?
  • How do bacteria reproduce? How do molds reproduce?
  • How successful was your sterile technique? Did anything grow out in dish #2? If your sterile technique was perfect, you should see nothing growing in this dish.
  • How does the control compare to the dish that was exposed to the air? What does this say about the air quality in your kitchen?
  • How do your other dishes compare with one another?

Although they are too small to see, bacteria and mold spores fill the air and come to rest on most surfaces. Although some bacteria and molds cause disease, most organisms you encounter every day are generally harmless unless conditions favor their growth. When you see adults cleaning surfaces in the kitchen that appear to be perfectly clean, the adults are really making sure that there are no bacteria, mold spores or crumbs that could feed these organisms.

This experiment is similar to others often performed using Petri dishes. However, this experiment provides you with the opportunity to practice sterile technique. Surgeons and scientists who do tissue culture practice sterile technique because the introduction of molds or bacteria could hurt the patient or destroy the culture that the scientist is growing.

Bacteria are simple one-celled organisms that reproduce by dividing into two. Molds are similar to bacteria, but they reproduce by generating seed-like spores. One common mold is Mucor mucedo.

Materials:

  • One can of condensed tomato soup
  • Six small custard cups, ramekins or desert dishes. Any dish will do as long as it has a small top no more that 3-4 inches in diameter.
  • Saran Wrap
  • Six rubber bands
  • Kitchen tongs
  • One small saucepan, one large saucepan and one large frying pan that you can boil water in
  • Camera

Experimental Procedure:

  1. Fill the large saucepan with water and bring to a boil. Reduce the heat to a gentle simmer. Place the custard cups and tongs into the boiling water. Simmer for twenty minutes.
  2. Open the can of tomato soup and pour it into the small sauce pan. Add ½ can water and stir. Bring to a boil, cover and let simmer very gently for 20 minutes.
  3. While the tomato soup is simmering, fill the large saucepan with water and bring to a boil. Reduce the heat to a gentle simmer. Place the custard cups, tablespoon, and tongs into the boiling water. Simmer for twenty minutes.
  4. Fill the frying pan with water and bring to a boil. Reduce the temperature so that it is simmering gently.
  5. Cut six squares of Saran Wrap big enough to fit into the frying pan. Be careful not to get the Saran wrap tangled on it. Gently drop the full sheet you cut into the simmering water. It will immediately shrink. Add all squares to the water. You may have to cut additional squares to use in case the Saran Wrap gets tangled.
  6. Make sure that you have a tray next to the stove that has adequate room for all six of the custard cups. Write “Dish #1,” “Dish #2,” “Dish #3,” “Dish #4,” “Dish #5” and “Dish #6” on six 3 x 5 cards. Set the cards down individually with the writing facing up.
  7. Remove the tongs from the boiling water by hooking the handle of a spoon or fork through the handle of the tongs. Carefully rest the tongs so that they are lying flat across a clean glass. Do not let the tongs touch the table or anything else. Do not touch any part of the tongs except for the handle. The object of this step is to keep the tongs sterile until they cool enough for you to handle comfortably.
  8. Once the tongs have cooled, use them to remove the tablespoon from the water. Place the tablespoon across the glad just as you did in step 7. The object here is to keep the spoon sterile while it cools enough for you to comfortably use.
  9. Using your sterile tongs, carefully remove one custard cup from the boiling water and set it on the tray. Using your sterile tablespoon, add two tablespoons of soup to the dish. When you set down your tablespoon or tongs, be sure to set them down across the glass to minimize contamination.
  10. Using your tongs, remove one square of Saran Wrap from the water and place it across the desert cup you prepared in step 9. Set down your tongs across the glass. Secure the Saran Wrap in place using a rubber band. This is dish #1.
  11. Remove a second custard cup from the water and add soup just as you did in step #9. Wait 30 minutes before covering the dish with Saran Wrap just as you did to dish #1 in step 10. This is dish #2.
  12. Remove a third custard cup from the water and add soup just as you did in step #9. Since you have very clean hands, get a brother, sister, parent or friend to stick a dirty finger across the tomato soup. Immediately cover the dish with Saran Wrap and secure with a rubber band just as you did in step 10. This is dish #3.
  13. Repeat step 9 with dishes #5 and #6. For dish # 5, run a finger across the kitchen floor before introducing it to the tomato soup. Immediately cover dish #5, just as you did in step 10.   For dish #6, sprinkle a few break crumbs across the tomato soup and cover promptly.
  14. Create a table with seven columns so that you have one column for the date and one for each of your six dishes. In the far left column, you will enter the time and date. Write down your observations for each dish. Continue making observations twice a day for a week.

Terms/Concepts: Bacteria; Microbiology; Bacterial growth; Sterile technique; Bacterial reproduction; Mold spores; Mucor mucedo

References:

  • Oetting, Judy and Tad Herr. Germs (Rookie Readers) Children’s Press (2007)
  • Cole,Joanna, Jon Speirs, and Bruce Degan. The Magic School Bus Inside Ralphie: A Book About Germs. Scholastic Paperbacks, 1995
  • DiConsiglio, John. There’s a Fungus Among Us: True Stories of Killer Molds. Children’s Press (2007).
  • Viegas, Jennifer. Fungi and Molds (Germs! the Library of Disease-Causing Organisms). Rosen Publishing Group (2004)
  • http://kidshealth.org/kid/talk/qa/germs.html

 

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