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 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.'"
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.
