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Biology

Building Blocks of Life - DNA Extraction

Every living thing on Earth has DNA, but DNA is normally so tightly wrapped and so small that we cannot see it. It’s our code for life and most of the time, we seem to ignore its existence. Yet, there are ways to bring it out so that students can touch and see DNA with their own eyes. For our students we used split peas to show how easy it actually is to extract DNA from an organism.

Split Pea Extraction from www.decodedscience.com (Mendel’s Peas: A DNA Experiment to do at Home by Erin Connelly)

Materials

  • 1 C of Peas
  • 1/4 Tsp Salt
  • 2 C ice cold water
  • Blender
  • Strainer
  • 4 Tbs Liquid Laundry Detergent
  • Meat Tenderizer
  • Chilled Rubbing Alcohol (isopropyl or ethyl alcohol)
  • Something to collect the DNA with (wooden stirring stick, straw, or glass rod)

Instructions

  1. Combine the peas, salt, and cold water in the blender. Blend well.
  2. Strain the pea mixture to remove the solids from the solution. Add the laundry detergent to the remaining solution and gently swirl the mixture and then let it sit for 10 minutes. (This step allows the detergent to break down the cell membrane and nucleus to release the DNA.)
  3. Add a pinch of meat tenderizer to break down the proteins to which the DNA is bound to. Stir the solution very gently. Stirring too hard will break up the DNA.
  4. Tilt your container to about a 45 degree angle and slowly add the rubbing alcohol to the solution, running it down the side of the container. You’ll want to see the alcohol float on your solution.
  5. The DNA will precipitate were your pea solution and alcohol layers meet. Using your stick, straw, or glass rod, remove the DNA from the solution. Sometimes this takes some time (up to an hour), but it should happen fairly quickly.

Building Blocks of Life - Licorice DNA

A good precursor to the DNA extraction lab is to have students build their own DNA strands so they have some concept of what DNA looks like. It is even better when these models are edible.

Materials

  • Licorice
  • Multi-colored mini marshmallows
  • Toothpicks

Instructions

  1. Pick four colors of the mini marshmallows and assign each of those four colors on of the nucleic acids (cytosine, guanine, thymine, and adenine).
  2. Use two licorice strands (you’ll want the big twizzler-type strands) for the phosphate ‘spines’, begin building your DNA on the toothpicks. Cytosine pairs with guanine, thymine with adenine. You’ll want to only have two marshmallows on each toothpick.
  3. The toothpicks will go into the licorice strands. The students then twists the strands to imitate the double helix structure of DNA.
Licorice DNA

Evolution - Survival of the Fittest with Rice Krispies

Here is another edible science experiment that is perfect for the classroom because rice krispies avoid most common allergies and gluten when made from scratch. The purpose of this experiment is to make several different kinds of rice krispies, some will have lots of salt or too much marshmallow and too little rice krispies and some will have m&ms or oreos and the perfect ratio. Students will then be asked to sample all of the rice krispies and take a vote on which rice krispy was their favorite. The favorite rice krispy is the krispy with the least chance of survival in the environment of your classroom. The least favorite rice krispy would have the best chance of surviving and creating offspring if it were an animal.

Evolving Rice Krispies

Here are some of the rice krispy recipes for you to use (courtesy of http://www.ricekrispies.com/recipes/the-original-treats):

Rice Krispy #1

  • 3 Tbs butter
  • 1 package (40 marshmallows) marshmallows or 4 C. mini marshmallows
  • 6 C Rice Krispies

In a microwave-safe bowl heat butter and marshmallows on HIGH for 3 minutes, stirring after 2 minutes. Stir until smooth. Add the rice krispies and stir until the cereal is coated. Using a spatula, press the mixture into a 13 X 9X 2 inch pan. Cool.

Rice Krispy #2

  • 3 Tbs butter
  • 1 package of marshmallows
  • 5 C Rice Krispies
  • 1 Package Oreo Bits

Follow the instructions for Rice Krispies #1, adding the oreos with the rice krispies.

Rice Krispy #3

  • 3 Tbs butter
  • 1 package of marshmallows
  • 6 C Rice Krispies
  • 3 Tbs salt

Follow the instructions for Rice Krispies #1, adding the salt with the rice krispies cereal.

Rice Krispy #4

  • 3 Tbs butter
  • 1 package marshmallows
  • 3 C Rice Krispies

Follow the instructions for Rice Krispies #1

Microbiology - Bacteria Around Us

Many students will probably be familiar with the term ‘germophobe’ and most of these germs are actually bacteria left on surfaces we use everyday, such as keyboards, stair railings, and faucets. There are even bacteria that live in our mouths. A great way to show students all the different bacteria that live with us, around us, and in us is to make agar and have students collect bacteria samples and see what grows in the petri dishes.

Agar Recipe (courtesy of http://www.umsl.edu/~microbes/pdf/homemademedia.pdf

Materials

  • 4 envelopes of plain gelatin
  • water
  • sugar
  • beef bouillon granules
  • foil muffin cups
  • muffin pans
  • measuring spoons
  • sandwich bags

Instructions

  1. In a saucepan, mix the envelopes of gelatin with 4 C. of cold water, 8 tsp sugar, and 4 tsp of bouillon granules or 4 bouillon cubes.
  2. Bring slowly to a boil, stirring constantly.
  3. Cool slightly and fill about 1/3 - 1/2 full with hot gelatin solution either 1. sterile disposable petri dishes 2. foil muffin cup liners in muffin pans for support
  4. Cool until the gelatin is solid (refrigerate if possible)
  5. Remove foil muffin cup liners from muffin pan and store in plastic zip-lock bags in the fridge - be careful not to touch the surface of the gelatin.
  6. Use within 2-3 days.
  7. Have students use swabs to go and collect bacteria from surfaces. Make sure they only touch one end of the swab and that isn’t the end they want to test.
  8. Using the swab, drag it in a zig-zag pattern over the agar before covering it and labeling it.
  9. Wait a few days to see what bacteria you have growing.

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