Most of us develop a sort of intuitive logic about how the natural world works. Unfortunately, a lot of that informal reasoning turns out to be wrong, which complicates scientific education. But as students make their way through the science education pipeline, they should gradually start moving beyond the informal reasoning of their earlier years. Or at least that's what we'd like to think; instead, a new survey of college students, some in advanced biology classes, indicates that most end up with a confused mix of formal and informal reasoning.
The clearest example of the chasm between a typical intuition and scientific reasoning comes from the world of physics. Imagine a marble rolling around a curved track that comes to a sudden end. Physics tells us that, as soon as the marble is off the track, it'll continue moving in a straight line until it runs into something else. But many people use informal reasoning and conclude that the marble will continue to follow a circular path even after it escapes the track. In other contexts, it involves an interventionist view of the world. As the people behind the survey put it, "When using informal reasoning, students look for 'actors' that drive 'events' and are aided by 'enablers.'"
Scientific education, then, needs to convince people to move past their intuitions (at least if they want a more accurate picture of how the world operates).
The new survey tested for informal reasoning in the biological sciences, using over 500 students at a variety of colleges, enrolled in classes ranging from introductory biology to advanced ecology. The results show that, even as the students are immersed in things like trophic pyramids and the Calvin cycle, they don't always come to grips with basic things like conservation of matter and energy.
For example, most students could describe how the process of photosynthesis involves removing carbon dioxide from the atmosphere and combining it with water to form carbohydrates, which then get used to build the cellulose that forms most of the plant's bulk. But, when asked to actually trace what's going on on the organismal scale, many students have problems recognizing that a substantial proportion of a tree's solid bulk originated from a gas, instead suggesting that most of it was brought up from the soil.
The problems work in the opposite direction, too. When respiration breaks down solid matter, most of it is released in gaseous form, as carbon dioxide and water vapor. But the students often had a problem with recognizing that a solid compound could be chemically converted into a gas.
In the same way, they seem to believe that every leaf contains a miniature Mr. Fusion, since they think that some of a plant's mass comes from the transformation of one atom into another. Nearly 70 percent "chose 'sunlight' as a possible source of atoms in chlorophyll molecules," according to the results. They had problems with other aspects of energy, too, not recognizing that moving up a trophic level in an ecosystem generally entailed the loss of energy to the environment—"only 44 percent of students thought the top of a food web would have 'less available energy than the trophic levels below it.'"
Other problems noted by the authors include the use of energy as a fudge factor to make things balance out, and a tendency to substitute a wall of scientific terminology for actual understanding.
In all, the majority of the students used a mix of scientific and informal reasoning on the surveys, with about 20 percent using informal reasoning alone. More depressing still, the authors designed a short course to help introduce formal scientific logic, but it didn't help much. The course shifted more people towards relying on scientific reasoning, but the percentage of students who relied on it exclusively rarely exceeded 30 percent, and was sometimes in the neighborhood of 20, depending on the topic (on average, it went from 12 to 27 percent).
What's the root of this problem? The authors ascribe a lot of it to language. It's quite common to hear people describe fat as just melting away or vanishing, which doesn't encourage anyone to try to balance the books on where all those atoms actually go to, much less get them thinking in terms of their release as carbon dioxide and water vapor. The same problem persists in the language commonly used by biologists. We frequently refer to energy as "lost" when it's no longer available to an organism, but that doesn't mean it's not still there, typically in the form of heat.
The end result, the authors conclude, is that "faculty are unknowingly speaking a different language from their students." They think that when they mention lost energy, the students know what they're talking about, or that their students' poor choice of wording doesn't represent a failure of logic. As a result, they see little reason to speak more carefully or devote instructional time to clearing up misconceptions. And, even if they wanted to, most biology textbooks consider principle-based reasoning beyond their scope.
But, even if instructors and textbooks were ready, the limited improvements that resulted in the targeted interventions used in this study show that overcoming the tendency towards informal reasoning can be a significant challenge. And the authors don't necessarily know what to suggest beyond starting the process early and keeping it a consistent focus of the education system.
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