Today's experiment was done with simple test strips of PTC paper. PTC stands for "phenylthiocarbamide," and PTC is a molecule that triggers one of the receptor molecules humans possess to taste bitter flavors, the TAS2R38 gene product. Each of us has many bitter flavor receptors, so if you don't have the TAS2R38 receptor that tastes this particular bitter molecule, you have other bitterness receptors instead. But if you do have the TAS2R38 gene, or better yet have two copies of the gene, you'll notice the bitterness right away. And among our trio of experimentalists today, we ran the spectrum from non-taster, to mild taster, to “supertaster,” to great effect! PTC papers are available online from many retailers.
At its core, science is a system for asking and answering questions in a reliable way, and it follows a set of steps that humans naturally engage in. To demonstrate this principle, Dr. Bob does an experiment on a sugar-like substance, and in doing so, taps into the curiosity that drives science and demonstrates that science helps us understand the present and make predictions about the future.
“How does that work?” This key question is asked by children and adults alike; only the subject matter changes. Children wonder about their toys. Teenagers wonder about their peers. Adults wonder about their jobs. In each case, you wonder how something works, think up an idea that might be true, gather information that tests the idea, and if the new information doesn’t support the idea, you update the idea. In the end, our ideas are informed by the information – the evidence – we gather, and the best ideas are the ones supported by the most evidence. This is the process of science, and since we all do it every day, Dr. Bob argues we are all scientists.
How does science help us? Science methodically tests our ideas about how the natural world works. Experiments in the present help us make predictions about how things might work in the future. Science follows the same steps we all use every day: Think of an idea you believe is true based on what you know – scientists call this idea a “hypothesis”. Gather information that tests the idea – scientists call this information “data” and they gather it through experimentation. Keep the idea or update it – scientists use data to support or refute a hypothesis. In this way, the best ideas about how things work rise to the top because they are supported by the best evidence. And by following these steps, we all follow the scientific method, and we are all scientists!
The testing phase for today’s experiment was done with crystals of sodium polyacrylate that I released from baby diapers, but it takes a LOT of diapers to release just a LITTLE bit of crystals! I found it much easier to buy the crystals in bulk. Sodium polyacrylate is available from many online sources for about $20 per pound. Just search for “sodium polyacrylate absorbant polymer.”
The small volume demonstration I did with Joy and Wayne involved adding drops of food coloring to 300 ml (1 1/4 cup) of water then pouring that water straight on top of 10 g (1/3 oz) of dry sodium polyacrylate. Distilled water works best.
The large volume demonstration I did with Joy and Wayne involved adding 3 L (about a gallon) of distilled water straight on top of 80 g (3 oz) of dry sodium polyacrylate in a 4 L beaker. Because the sodium polyacrylate will absorb 200-300x its weight in water, you can use less of the crystals, but it will not solidify instantly. And the instant absorption is really cool to see!