Let’s Grub on Some Grass Beetles is a natural selection simulation. Natural selection is the “process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common.” In this activity, part 1 involves variations in silver beak loon beak types. There are tweezers, spoon, and knife shaped beaks. The beak best adapted to capturing grass beetles will survive and more chances to reproduce. The tweezers and spoon beaks are best adapted. The population of silver beak loons will change to a majority of tweezers and spoon beaks. Part 2 deals with variations in grass beetle color. The green grass beetles are best adapted to hiding in the grass than the orange or yellow grass beetles. In successive generations the populations of grass beetles will shift to green colors, since they will have the best chance to survive, reproduce and pass the variation to their offspring.
Watch the video and listen to the commentary on how to do the activity. Download handout: Let’s Grub on Some Grass Beetles
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).
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.
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.