In many science classes, students’ only introduction to the nature of science is “the magical” scientific method—a method usually portrayed as a series of three, five, or seven steps all scientists are said to follow when conducting investigations.
A couple of problems exist with this scenario, however. Most importantly, it is inaccurate. Have you ever heard scientists themselves discussing which step of the scientific method they are currently working on? Have you ever seen a chart outlining the steps of the scientific method in a research lab? Scientists do not follow a single method to arrive at certain knowledge. Scientists follow scientific methods with common characteristics, but no single path leads to certainty.
Scientific knowledge is tentative and open to revision. This sense of tentativeness, or changeability, is missing in the way textbooks and teachers often portray the nature of science (NOS). Instead, students are left with the impression that the scientific method produces sure knowledge and that they can uncritically accept the knowledge because it was created—or discovered—via the scientific method.
So, what is the alternative? How can science be portrayed more accurately, especially in today’s climate, which demands that students understand and are assessed on increasing amounts of content? Certainly, many activities and strategies exist that can help illustrate how science actually functions, as teachers can see by reviewing the other articles in this issue of The Science Teacher. Equally important, however, is for teachers to accurately and consciously portray NOS in almost everything they do when working with students. To illustrate this point, this article looks specifically at how laboratories can help students better understand NOS.
The way students learn common lab activities can have a huge impact on their view of science. One example is a moderately open-ended exercise similar to the chromatography activity in the Lawrence Hall of Science’s Great Explorations in Math and Science series (Barber 1985).
In the first part of the original activity, students follow a somewhat structured procedure to learn what paper chromatography is and how it works (see sidebar, “Chromatography” ). The second part of the original activity is more open-ended as students try to determine the source of a “mystery” signature (via chromatography, of course). I usually make the first part of the activity slightly more open-ended than the original instructions indicate to let students experiment and investigate with a variety of ink sources, including indelible ink, which does not separate at all with chromatography. Before beginning this lab, students should already be accustomed to working in a somewhat open-ended lab environment.
Students put about 1.5 cm of water inside a glass. They take a strip of filter paper—or cut a coffee filter into a strip—and place a thick mark with a black magic marker–style pen, or other water-soluble ink, at 5 cm from the bottom of the strip. Now students carefully place the strip vertically into the beaker containing the water so that only the marked end is submerged. The mark should not be in the solution but rather be about 2.5 cm above the water.
Students should make sure that the end of the paper is in the water. Students watch the water as it moves up the strip of paper, and see what happens as it comes in contact with the black mark. The strip is left in the solution until the water has climbed well past the black mark. This will take several minutes, so students may want to hold the filter paper in place by taping it to a pencil (or stirring rod) that’s placed across the beaker’s top. Different inks produce distinct patterns.
In this activity students perform tests on unknown white powders. Dozens of choices exist, but common powders include salt, sugar, baking soda, cornstarch, plaster, and talc. Students first test the powders individually, then see if they can use their knowledge to determine the contents of an unknown made of one or more of the white powders. Typical tests include looking at the powders through a magnifying glass, and seeing how the powders individually respond to a few drops of water, iodine, vinegar (weak acid), baking soda solution (weak base), and heat. Kotar (1989) and Phillips (1981) discuss other powders and tests available to teachers.
Chromatography is particularly well-suited to inquiry investigations because the materials are relatively inexpensive and safe to handle. Teachers who need guidance on how to make lab activities more open-ended may want to read Colburn (1997) or Colburn and Clough (1997).
One student in each pair (or group) is charged with the task of writing down everything that group says, does, or thinks during the activity. Teachers can tailor the chromatography activity to their students. For example, depending on class size, teachers can determine what size to make the groups, which student would make the best group “journalist,” the extent to which lab reports are individual efforts, and how to share journals.
Teachers also have the power to shape student experiences during the activity via the kinds of questions asked. Some examples of questions or comments for this chromatography activity include:
- What sorts of things have you noticed so far?
- Tell me about what you’re thinking, or Tell me about what you’re thinking when you see [insert observation here].
- What do you think would happen if you…
- used a different marker?
- let the filter paper with an ink spot sit in the water even longer?
- used a different solvent, like alcohol?
- used warmer water? (Any of these questions could be followed by: How could you find out?)
- How confident are you in your conclusion?
- What would it take for you to be more confident?
- Why do you think that is?
- How could you explain that?
If students come up with testable explanations, teachers can then help them make predictions and test their explanations.
The first two bulleted statements provide good starting points when talking to individuals or small groups of students. The questions are nonthreatening—any honest response is an acceptable answer and provides the teacher with information to determine what students do and do not understand. The questions give teachers the chance to respond in ways custom tailored to help students learn.
The third group of bullets represents the kind of investigations students can complete during the more open-ended part of the activity. From a NOS perspective, the investigations illustrate a key aspect of science: Science demands and relies on empirical evidence. What one thinks is “right” is only as important or valid as the data supporting the conclusion. The fourth group of bullets, asking students about what it would take for them to feel even more confident in their conclusions, illustrates another aspect of NOS: No one way exists to directly and definitively prove a scientific explanation. Explanations are tested deductively via predictions about what would happen if an explanation were assumed to be accurate.
When the activity ends, all students complete a lab report (teachers can use the same lab report format that they usually use in their class). Although the activity discussed here is more open-ended than the classic activity, the content students learn is almost the same, and students can still complete a lab report using the regular lab report format.
In class the next day, teachers can ask students to spend a few minutes comparing their lab reports to the previous day’s journal, which contains everybody’s thoughts and actions. I ask students to highlight parts of the journal that are not in the lab report. We then list, as a class, the kinds of things that were not part of the reports.
If the activity students completed was at least somewhat open-ended, and students are accustomed to completing these sorts of activities, then the generated list will encompass several aspects of “real” science that sometimes receive less attention in school. Teachers cannot predict everything students might say, but the student-generated list generally will help teachers illustrate that, like research in the real world of science, students’ activities showed that
- many scientific ways exist to investigate nature; there is no single, tidy method by which scientific knowledge is created;
- science is creative, messy, and hard to describe, with actions often leading to blind alleys that don’t ultimately pay off with quality data;
- interpreting and even generating data is sometimes a little subjective, requiring judgment on the part of the scientist;
- assumptions underlie the work, and if people hold different assumptions then disagreements about procedure and data can result; and
- science is a social process—success and confidence in one’s conclusions depends on sharing data and interpretations.
Rather than a cookbook lab with preordained results, inquiry investigations like this provide a more accurate view of the scientific endeavor. Any or all of these topics can lead to discussion about how science works, with students now having had a common experience upon which to center the discussion. Students will not learn about NOS simply by doing a lab activity, even an open-ended activity. The combination of the activity and instruction makes the difference.
Students do not have to keep detailed journals during every lab activity. Nor do teachers have to make significant changes in the curriculum to accurately portray NOS. It is only necessary for teachers to constantly be on the lookout for times when students’ thinking or actions demonstrate important aspects of how science works. These times are places in the course where teachers can pause (during or after the activity) to tell students about how their experiences are mimicking those of research scientists.
In the classic “mystery powders” activity, which fits well with forensic science units, students examine the properties of several white powders (see sidebar, “Mystery powders”). Students usually test the powders to see what, if any, reaction they have with liquids such as water, iodine, weak acids and bases, and heat. Afterward, students use this knowledge to figure out which powders were mixed together in an unknown or “mystery” mixture. The activity is similar to elementary qualitative analysis. For a sample activity about investigating mystery powders, teachers can reference Kotar (1989) or Phillips (1981).
Scientists apply their knowledge when addressing related questions and solving mysteries of their own. For this reason, the activity itself illustrates important aspects of NOS. For example, at one point students might heat each of their powders over a low flame, investigating how the different powders react to heat. Some students find that their data for one of the powders may differ from their neighbor’s data, some find that the powder melts and bubbles, and others find that the powder smokes and turns dark brown or black.
This is a great moment for teachers to stop class and ask, “How can it be that these groups, composed of bright and capable students, can do the same thing and get different results?” Teachers should solicit student responses, and feel free to explain their “suspicion” that students were not doing exactly the same thing—even though both groups were following the directions they were given.
Confirming these suspicions, though, requires evidence. Science requires evidence, rather than just pronouncements from experts. This is another important aspect of NOS that can be modeled frequently. So, teachers should ask students about how they heated their powders. Teachers should find evidence from students that supports a conclusion that one group applied more heat to their powders than the other group, for example, by holding their sample closer to the heat source or heating the sample for a longer time.
This in-class example illustrates why it is important for scientists to keep careful notebooks. Scientists are sometimes literally not allowed to remove their notebooks from the lab because they are so important to the process of conducting science. If procedures are carefully noted, then students (scientists) can compare their work later when trying to explain their data.
The example also helps illustrate the social NOS. Gone are the days, if they ever existed, of the mythical scientist working in the basement, all alone, making a major discovery, shouting “Eureka!” and instantly changing the world. Instead, scientific work must be examined, scrutinized, and ultimately discussed by colleagues before being accepted as “true.” Even the most independent of scientists must eventually discuss their work with others and publish their results.
The same point is raised when students are heating their mystery powders. Students can never really understand what’s going on or resolve seeming discrepancies until they talk to one another about what they have done—even if the teacher is moderating the discussion.
Teachers can help students understand these points simply by stopping class for a brief discussion. The key lies in making these brief discussions an important and regular part of the class. By making a few changes in word choice, allowing lab activities to be a little more open-ended, and talking about how the activities mimic the messiness of real science, some significant learning will occur!
The mystery powder lab illustrates another point. When seeing that their data differ from other classmates’ data, some students may explain the discrepancy with the conclusion that they aren’t bright and capable when it comes to science. Differing data among students just supports that conclusion. This is unfortunate because student data are always “right.” Nature always behaves the way nature is supposed to behave. The trick is in explaining why results came out as they did. Real scientific data are often messy, and conclusions are usually approximations. Understanding the true NOS helps students to think better and be better consumers of scientific information, and it can even help them learn to like science more.
Alan Colburn is an associate professor of science education at California State University, Long Beach, Science Education Department, 1250 Bellflower Boulevard, Long Beach, CA 90840; e-mail: firstname.lastname@example.org.
(Used with permission from the JASON Academy.)
Gregor Mendel is one of the most familiar names that students associate with history of science. They know his conclusions, but seldom spend much time thinking about methods.
Mendel found seven pairs of traits that sorted independently in peas. That meant they weren’t linked; each trait was on a different chromosome. Since peas only have seven pairs of chromosomes, that had to be an amazing coincidence!
Or perhaps, Mendel started with a model and then looked for the data that fit his model. That’s the method most science historians believe he used. (Remember, all of Mendel’s notebooks and papers except the single report he sent to the scientific society of Brünn were burned, so we can only speculate.)
That’s a method that students can discuss. Is it “scientific method?” Of course, since there isn’t a single way to do science. It’s much like the method that physicists used to verify Einstein’s model presented in his 1905 papers.
How Close Was He?
Mendel’s model predicted that the ratio of F2 offspring for each of his traits would be 3:1. Here’s his actual data. How close was he?
|Smooth x wrinkled
|Red x white
|Yellow x green
|Inflated x constricted
|Green x yellow
|Axial x terminal
|Long x short
Scientists often reject a model or hypothesis if the margin of error is greater than 5 percent. Should any of Mendel’s cases be rejected?
Ask your students to calculate the statistical significance of Mendel’s results. To do it, they will need to use the chi square statistic. (This is the chitest in Excel, and it’s easy to process.)
Using Chi Square (ChiTest in Excel), and comparing expected (3:1) to actual. (Answer: Significance = .99)
Can You See Like Leeuwenhoek Sees?
Imagine getting this letter from the world’s first microscopist:
|Antoni van Leeuwenhoek to Henry Oldenburg, Secretary of the Royal Society
The first sort by me discover’d in the said water, I after divers times observed to consist of 5, 6, 7 or 8 [very] clear globules, without being able to discern any film [or skin] that held them together or contained them. When these animacula did move, they put forth two little horns, [like a horse’s ears] continually moving themselves. The place between these two horns was flat, though the rest of the body was roundish, sharpening a little towards the end, where they had a tayl, near four times the length of the whole body, of the thickness (by my Microscope) of a Spiders’ web; at the end of which appear’d a globul, of the bigness of one of those which made up the creatures [which were the most wretched ones I ever saw;] if they chanced to light [with the globul[ upon the least filament or string, or other such particle, of which there are many in water especially after it hath stood some days, they stood intangled therein,e xtending their body in a long round, and striving to dis-intangle theyr tayl [by strong extension]’ whereby it came to pass, that their whole body lept back towards the globul of the tayl, which then rolled together Serpent-like, and after the manner of Copper- or Iron- wire that having been wound about a stick, and unwound again, retains those windings and turnings. This motion of extension and contraction continued a while; and I have seen several hundreds of these poor creatures, within the space of a grain of gross sand, lye fast cluster’d together in a few filaments.
What was Leeuwenhoek looking at?
|Rotifer, genus Collotheca by David Walker, www.micscape.org
Used with permission.
Barber, J. 1985. Crime Lab Chemistry: Teacher’s Guide. Berkeley, Calif.: Great Explorations in Math and Science, Lawrence Hall of Science.
Colburn, A. 1997. How to make lab activities more open-ended. CSTA Journal Fall:4–6.
Colburn, A., and M. Clough. 1997. Implementing the learning cycle. The Science Teacher 64(5): 30–33.
Kotar, M. 1989. Demystifying mystery powders. Science and Children 26(6): 25–28.
Phillips, D. 1981. Chemistry for the elementary school. Science and Children (19)2: 8–12.