I made ScienceFix.com to share my favorite demos that I do in my middle school science classes.  

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Video Demo: Rainbow pH

This demo comes from Flinn Scientific. Flinn provides a Chem Fax! service, which are free demos that Flinn emails you. This demo demonstrates the changing color of an indicator when pH changes. Here is the procedure:

1. 100 ml of a 0.1 M NaOH solution is added to 350 ml of distilled water in a 500 ml graduated cylinder.
2. 10 ml of universal indicator solution is added, which turns the solution dark purple, indicating a highly basic solution.
3. An Alka-Seltzer tablet is added, which results in carbon dioxide bubble being produced. The carbon dioxide gas causes carbonic acid production, thus lowering the pH (more acidic). The solution starts turning green, then to yellow.
4. When the Alka-Seltzer tablet rises to the top (due to the attached carbon dioxide gas bubbles lowering the tablet’s density), add 10 ml of vinegar to the solution. This will cause a bright red color to be produced at the top, indicating high acidity (low pH).


Video Demo: Strikeless Matches

Activation energy is the minimum amount of energy needed to start a chemical reaction. Many chemical reactions don’t need a lot of energy to react. A classic example when baking soda mixes with vinegar. The heat energy that is in the environment is enough to start this chemical reaction. Other chemical reactions need a higher amount of energy. A match lighting is one example. When a match strikes, the friction produces heat energy. This heat energy is the activation energy that starts the chemical reaction. In the following demo three matches are tied together with thread and placed into a flask that is covered with a piece of aluminum foil. The bottom part of the matches touches the bottom of the flask. The flask is placed on a hot plate on the high setting. The hot plate provides the energy to start the chemical reaction between the matches and oxygen that is in the flask.


Video Demo: Yeast Cellular Respiration

This demo demonstrates that yeast do cellular respiration. When sugar (glucose) and oxygen are present, yeast mitochondria will make those chemicals react and release energy as well as the products water and carbon dioxide. Bromothymol blue solution will change to yellow in the presence of carbon dioxide. If there is no more oxygen, then yeast cells will shift to fermentation.


Video Demo: Whiteboard Protein Synthesis Demo

Protein synthesis is the process that the cell goes through to make a protein from the information stored in the DNA. The video below shows a demonstration that you can do in your classroom to show how protein synthesis works. This demonstration emphasizes the following points:

1. DNA contains the information to make a specific protein.
2. The DNA is in the nucleus of the cell.
3. The DNA cannot leave the nucleus.
4. The ribosomes make the protein from the information.
5. The ribosomes are in the cytoplasm and cannot go into the nucleus.

The metaphor that I use in class is that the DNA is like a series of recipe books in the library. These books cannot be checked out/taken out of the library. The only way to get the information that is in the books out of the library is to make a copy. mRNA is the copy of the information that can leave the nucleus and go into the cytoplasm so that the ribosome can read and make the protein. Watch the video to see how it comes all together.

Teaching tips: Place the amino acids around the classroom (cytoplasm). Assign students to be specific tRNA’s. They will get the specific amino acid and bring it to the ribosome for you.


Biology Christmas Connection

Well here is the connection between Christmas and biology that I could make. I showed the students this candy cane and told them if they could name the shape that the red stripes make they would all get one. Most of them raised their hands and when I called on one, he said "double helix". We built DNA paper models this week and they learned its shape.