Each year I change the unknown samples a little, depending on how challenging they are for the students. I try to have one sample that is water; but I color it so that the students do not initially think it is water. I try to have another sample that consists of simple sugars (Jello), one that has starch in it (corn), one that is made of lipids (oil), and one that is a mixture of biological molecules. This year, I used a slice of pizza that had been pureed. In the past, I have used cheeseburgers, deli sandwiches, and stew. I think the pizza was a good choice, as students usually get close with their hypothesis based on the smell and color.
One thing that I did differently this year and would certainly keep for the future was the beginning of the lab where I asked them to make some initial observations using only their basic senses. I gave them a blank chart on which they were to decide what observations they would make and then record their results:
Most of the students came up with the same things- like color and smell. Some surprised me with things like viscosity and transparency.
After making their initial observations, they were to design a procedure where they used various indicator solutions; Biuret's solution, Lugol's iodine, and Benedict's solution. As a class, we discussed each and what they were used for. They also had to be aware of the initial color of each solution and what color it would change to if it were positive for a particular substance.
The biggest problem I encountered in this part of the lab is one that I struggle with consistently throughout the year. Students will write out a procedure, but often leave out the details that are necessary. I usually tell my students to write the procedure in a very detailed manner, so that anyone could read it and conduct the same experiment. I give them tips like to have their groupmates read over it and look for missing instructions. As a class, I will get a range of procedures. Some will be almost too detailed, while others will be severely lacking. Here are two examples below:
In the first sample, the group had the right idea to test all unknown samples of food with each indicator solution, but they were not specific about amounts of unknown food or amounts of indicator solutions. The second sample paper was much more detailed and considered these factors.
Lastly, my students were asked to record their results and write a conclusion. I gave them some guidance on how to write their conclusion. They were asked to specifically discuss the unknown samples, the major biological molecules, and the indicator solutions. I also prompted them to discuss their initial hypothesis, possible errors, how to make their procedures better, and any errors. A good group would have another group or outsider look over their procedure to see what could have been done better. Here is a sample of recorded results and conclusion:
This group did address their hypotheses, and even mentioned that they should have been more specific in their procedure. Although the initial procedure was not perfect. I was glad they addressed this in their conclusion. What this tells me is that the next time I have them design an experiment, they will probably do a better job with the procedure, having noticed their deficits on this assignment.
Using this particular template was helpful for me. I realize that this experiment is extremely important in my class as it gives students the ability to conduct an inquiry-based lab. Dr. Randy Bell discussed the importance of teaching our students the various skills needed in science (Laureate Education Inc., 2010). My students are able to make detailed observations, make inferences based on their data, and provide evidence as to why they made their conclusions.
If time and supplies are running short, there is website I can utilize to do this lab in a virtual format. It is a very messy lab that requires a lot of setup and supplies. For new teachers, they sometimes opt for the virtual version of the lab to get comfortable with what is being done before they dive into the real thing. While this is okay to start, it does not give the students the ability to design a procedure. They are still solving problems and coming to conclusions, but lose the control of designing the experiment.
References:
Banchi, H., & Bell, R. (2008). The many levels of inquiry. Science and Children, 46(2), 26–29.
Laureate Education, Inc. (Executive Producer). (2010). Video Nine. Interview with an expert: Dr. Randy Bell.. The Nature of Science. Baltimore, MD: Author.
