Seeding discovery
Yasmin Jayathirtha
As I was considering the experiment detailed here, I also began to think about what motivates me to explore ways of doing experiments. I enjoy chemistry a great deal and when I read about a reaction, my first response is; can I see that? If I search (much easier nowadays with the Internet) I may find links to the experiments. They are usually from college teaching labs, simple enough to do but using chemicals not usually available to us. Many chemistry textbooks at the college and high school level detail a very easy to do experiment to show the formation of nylon by polymerisation. Layer the two monomers in a beaker and as the nylon forms at the interface pull it out. Really simple but… the chemicals are not available easily here. A young friend interested in science also shared his frustration, “All the science activity books show cool experiments, but they casually say ‘get one litre of liquid nitrogen’” It is hard. Nowadays, of course, there is always YouTube, better than nothing but still not the real thing.
Why try so hard to set up experiments? I can think of two reasons. First, most students find chemistry hard, because they are expected to remember details they have not seen. Seeing the reaction acts as an aid to the memory. Second is my learning. As I try to set up and do an experiment, I begin to realize what can be confusing and can be misunderstood. Why are we assuming that what we describe is happening? All this forces me to think about the theory I am trying to teach and, I hope, makes my explanations clearer.
Continuing the theme of the last columns, I wanted to explore digestion of fats, the third food group that students had learnt about. Checking on the web, I found experiments that used Pancreatin (an enzyme) and bile salts. Chemically, the digestion of fats and oils gives fatty acids and glycerine, so a pH meter was used to determine the change in pH. This was where my exploration began. Where can I find lipases (enzymes that digest fats)? Do germinating oil seeds make lipases to break down their food store to grow? Can indicator solution be used instead of a pH meter; will it show enough of a colour change? Will the lipase from groundnuts digest all fats or only groundnut oil?
Here are the results of those experiments and the questions that came up. The first time, I germinated the groundnuts for about three days, till the shoot was quite long. I ground up the seeds and used the extract as the enzyme. I wondered if I could use soap solution as an emulsifier instead of bile salts. The question that came up was, will the soap denature the enzyme. I set up three test tubes; one with heavy cream, one with sunflower oil (all I had at home) and the third with sunflower oil and soap solution. I added the enzyme extract and indicator solution to the tubes and waited. The tubes with oil had changed colour by the next day. The cream had not, but a day later it had also begun to show a colour change. If this had to be a class demonstration, the change had to be faster, so the question was, how long does one germinate? I repeated the experiment, germinating the seeds only till the shoot just started to show. Ground up the seeds and set up the test tubes. As the photographs show, the indicator in the tube containing oil and water only, is green and only in the water layer. The indicator does not dissolve in the oil. The next tube has oil soap solution and the groundnut milk (extract). The indicator has turned yellow and moved into the oil layer. There is a similar reaction in the tube with the enzyme and oil only. The extract alone is mildly acidic (~pH 6). The change occurred within a couple of minutes of mixing the solutions, showing that the concentration of the enzyme was relatively high.
This experiment can now be explored using different oilseeds, different times of germination, different fats and oils, using boiled extract and so on. My questions are: Is the extract acidic because the oil in the seed had already begun to break down? Did the cream take a longer time because it was a different fat or because it was thick and the enzyme did not diffuse? Did it finally change colour because the fat broke down or because it soured? I am sure there will be other questions as I attempt to answer these by doing further experiments. I hope I have given a flavour of the enjoyment that comes with trying to set up experiments. Please experiment!
The author works with Centre for Learning, Bengaluru. She can be reached at yasmin.cfl@gmail.com.
