Thursday, January 28, 2010

General Science: Iodine as Indicator

This week the kids learned how to use an INDICATOR, a compound that changes color when it comes in contact with a particular substance. The kids were given around 10 different foods to test using iodine, an indicator that changes from orange to black on contact with starch. As they made their way through the food samples (testing them, not eating them), they were able to refine guesses about what starches have in common. Finally, we concluded that starches come from plants and are how plants store simple sugars.

Afterward we discussed how simple sugars are connected by chemical bonds to make complex sugars and conversely, how the chemical bonds within complex sugars are broken to produce simple sugars. Try chewing on a cracker for a few minutes (works best with unsalted ones), and you'll notice a sweet taste in your mouth that results from your saliva breaking down the starch into simple sugars.

Monday, January 25, 2010

Biology: DNA: Recipe for life

This week's topic was DNA, so naturally we made 3 batches of chocolate chip cookies. Confused?
Let me explain. We started by reviewing a recipe, and then the kids were divided into 3 groups, each of whom was given a slightly different version. Some of the differences involved spelling mistakes, some were missing parts of or entire words, and some had slightly different measurements. We baked cookies from each of these recipes and discussed what if any effects these different versions produced. With the recipes the kids used, the cookies all came out pretty much the same. This in itself was an interesting result. In addition, we agreed that certain typos would have yielded significantly different cookies, like say adding 1 teaspoon of flour instead of 1 cup, or adding 2 legs in place of 2 eggs.

DNA is essentially the recipe for life. How this recipe gets translated into different kinds of "cookies" (personally, I prefer oatmeal) will be our topic for the next few weeks.

FYI: I sent home each kid with a baggie of some of the unused dough, so check their bags before this evolves into an entirely different experiment.

Monday, January 18, 2010

Biology: Sensational Skin

This week we investigated a type of cell called the sensory receptor. These receptors are found in our skin and allow us to feel pressure, pain, heat, and cold. The kids made pressure probes (see photo), which were used to test 4 different areas of the body: fingertip, forearm, cheek, and calf. The idea was to GENTLY (In this particular experiment we were investigating pressure NOT pain) poke these areas with the probe, gradually decreasing the distance between the 2 toothpicks until the subject could only feel 1 prick. The area with the smallest 2-point discrimination was the area that was most sensitive and was assumed to contain the highest number of sensory receptors for pressure. The kids were surprised to find quite a great deal of variation. Subjects could distinguish 2 distinct pricks at an average of 7 cm on their fingertips, while the 2-point discrimination was much larger for the calf - as much as 30-40 cm.

Friday, January 15, 2010

General Science: It's a gas!

For our experiment this week, we did an oldie but a goodie...
what happens when you mix baking soda and vinegar?

Having some experience with making volcanoes or otherwise messing around in the kitchen, the kids guessed correctly that the combination would produce, in their words, "AN EXPLOSION!!!" (Aren't you glad this happens at my house and not yours?!)

This week we took it one step further to show that the combination of baking soda and vinegar produces a gas that can put out a fire. Passing a lit candle over baking soda had no effect on the flame. Same deal for the vinegar, but when you combine the two, and you get your EXPLOSION (i.e. bubbles), passing the candle over extinguishes the flame. Why does this happen? Mixing baking soda and vinegar is a chemical reaction, and as such, produces something new, carbon dioxide. That's what the bubbles are, and they have the property of putting out a fire and that's why they carbon dioxide in an actual fire extinguishers. Cool, huh!?

Physics: Good Vibrations

This week we started a new topic: SOUND. We talked about what a sound is and experimented with sounds produced by different materials. The kids made oboe-like straws, plucked rubber bands of different widths and lengths across shoe boxes, bounced wooden sticks off the side of tables, and struck water-filled glass jars, noting in each case how different changes affected the pitch. Finally, the kids used their observations to created their own instruments, and then we had a concert!

Wednesday, January 6, 2010

Physics: Making magnets

A couple weeks back the kids discovered that iron-containing metals can themselves become magnets if they are rubbed by a magnet. We used this observation to build compasses in 3 easy steps:
  1. Rub a light-weight iron needle with a magnet (always in the same direction) 50 times.
  2. Stick it through a thin piece of Styrofoam.
  3. Set the whole business afloat in a bowl of water and observe how try as you might, you cannot prevent the needle from pointing along a north-south axis.

Afterward, the kids built electromagnets. In an electric circuit, the movement of electrons creates a magnetic field, but because it is so weak, you might not notice it. However, if you build a circuit with MANY loops of wire, all in the same direction, each loop reinforces the strength of the magnetic field.

Tuesday, January 5, 2010

Biology: What do yeast like to eat best?

Following our discussions on cell transport, we spent some time this week on cellular respiration, that's fancy talk for the breakdown of food within a cell to release energy. This process produces carbon dioxide as a byproduct.

We focused on yeast, a single-celled fungus. Some of the yeast we fed flour, some sugar, and of course some unlucky yeast got nothing at all. To get an idea of which food was eaten most heartily by each sample of yeast, we covered each bottle with a balloon. Then we sat back and watched the show. The samples of yeast fed sugar were the happiest, i.e. the balloons were the most inflated because of the greater production of carbon dioxide. The flour came in second place, and not surprisingly, the yeast fed nothing did nothing.

We related this experiment to earlier discussions comparing the size of different carbohydrates. Flour is an example of a starch, and as such is LARGE and must be broken down first before entering the cell. That takes time. Sugar, on the other hand is smaller, and can be broken down more easily.

Next week we'll be making bread and butter, so send your kids with an appetite.