• Direct the ensuing discussion to the comparison, evaluation, and extension of the offered answers rather than simple validation or refutation of right and wrong answers.

  • Pose a second or follow-up question to continue the exploration.

Biochemistry, Genetics, and Molecular Biology at Stanford University

Professor: Sharon Long

Enrollment: 400 students

Even a small-scale demonstration can work in a large class if it uses an everyday object that students recognize, and especially if it is something the students can find and use on their own. My favorite example is to use a telephone cord to demonstrate supercoiling of DNA. The phone cord has its own intrinsic helicity, as does DNA, though usually phone cords are left handed whereas DNA is most often discussed in its right handed B form.

Who doesn't have the experience of having the coiled headset cord of a telephone show supercoils (twists around itself)? This presents the students with the chance to play at home, where they can convince themselves that the direction (handedness) of the supercoils depends on the direction of the original helix, and on whether the cord was underwound or overwound before the headset was replaced (constraining the ends). Students learn both an important principle for understanding nucleic acids and a handy practical tip that lets them predict the easiest way to get the kinks out of the phone cord! They get the chance to test their understanding by making predictions and doing trials-exactly what one hopes for in active scientific learning.

A professor's questions should build confidence rather than induce fear. One technique is to encourage the student to propose several different answers to the question. The student can then be encouraged to step outside the answers and begin to develop the skills necessary to assess the answers. Some questions seek facts and simply measure student recall; others demand higher reasoning skills such as elaborating on or explaining a concept, comparing and contrasting several possibilities, speculating about an outcome, and speculating about cause and effect. The type of question asked and the response given to students' initial answers are crucial to the types of reasoning processes the students are encouraged to use. Several aspects of questions to formulate them, what reasoning or knowledge is tested or encouraged, how to deal with answers-similar for dialogue and for testing. Chapters 5 and 6 contain more information on questions as part of assessment, testing, and grading.


Demonstrations can be very effective for illustrating concepts in class, but can result in passive learning without careful attention to engaging students. They can provoke students to think for themselves and are especially helpful if the demonstration has a surprise, challenges an assumption, or illustrates an otherwise abstract concept or mechanism. Demonstrations that use everyday objects are especially effective and require little preparation on the part of faculty (see sidebar). Students' interest is peaked if they are asked to make predictions and vote on the most probable outcome. There are numerous resources available to help faculty design and conduct demonstrations. Many science education periodicals contain one or more demonstrations in each issue. The ''Tested Demonstrations" column in the Journal of Chemical Education and the "Favorite Demonstration" column in the Journal of College Science Teaching are but two of the many examples. The American Chemical Society and the University of Wisconsin Press have published excellent books on chemical demonstrations (Shakhashiri, 1983, 1985, 1989, 1992; Summerlin and Ealy, 1985; Summerlin et al., 1987). Similar volumes of physics demonstrations have been published by the American Association of Physics Teachers (Freier and Anderson, 1981; Berry, 1987).

You should consider a number of issues when planning a demonstration (O'Brien, 1990):

  • What concepts do you want the demonstration to illustrate?

  • Which of the many demonstrations on the selected topic will generate the greatest enhancement in student learning?

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