Chapter 1, page 11
c <This part of the figure shows a schematic drawing of a heart,
with two arteries emerging from it, one going down and one
upward. Both show exaggerated “ovals” where spurts of
blood are appearing at regular intervals. The arteries then
taper off into capillaries which then lead into smooth veins
that lead back into the heart. Each artery-capillary-vein
system makes a rough schematic oval. >Caption: Arteries must be thick and elastic to accommodate the powerful spurts
of blood sent out by the heart as it pumps. In addition, the elasticity allows the
arteries to close behind each spurt, thus preventing blood traveling upward to the
brain from falling back into the heart. Veins need not accommodate such spurts of
pressure, because the pressure spurts dissipate by the point at which the blood
travels through the capillaries so they are thinner and inelastic.
Understanding
A second essential goal of instruction is student understanding (Duschl & Grandy, 2008; Fennema
& Romberg, 1999; Gardner & Boix-Mansilla, 1994; Mayer, 2005). The goal of learning should not be
simply for students to memorize ideas without understanding them. The goal should be understanding.
Only when students understand ideas can they apply the ideas to solve new problems or to answer new
novel, unfamiliar questions.
An example that highlights the importance of understanding has been described by learning
scientists John Bransford, Ann Brown, and Rodney Cocking (John D. Bransford, Brown, & Cocking,
1999). Their example focuses on the topic of learning about arteries and veins. How would you help high
school students learn that arteries carry blood away from the heart and have thick, elastic walls, whereas
veins carry blood back to the heart and have thin, inelastic walls? I have posed this problem many times to
my own classes; invariably the students come up with teaching devices such as the ones shown in Figure
1.3a and Figure 1.3b. Figures 1.3a and 1.3b are both designed to help students memorize the facts that
arteries have thick, elastic walls and veins have thin, inelastic walls. Neither of these devices explains why
arteries and veins have these properties. And, critically, because there is no explanation, students cannot
use the information about arteries and veins to solve new problems. For example, as Bransford et al. note,
students who have learned only the information in Figures 1.3a and 1.3b would not be able to answer
questions such as these:
Ɣ How would you design an artificial artery? Does it have to be elastic?
Ɣ What are the health implications of hardening of the arteries?
To answer these questions, students need to understand why arteries are thick and elastic. They need to
understand what would happen if arteries were not thick and elastic. They need to understand what the
function of thick, elastic arteries is.
In contrast, consider the explanation provided in Figure 1.3c. This explanation provides an
understanding of why arteries are thick and elastic and veins are thin and inelastic. With the
understanding that is promoted by the explanation in Figure 1.3c, it is possible to generate plausible
answers to the two questions listed above. Does an artificial artery need to be elastic? As the explanation
in Figure 1.3c shows, the elasticity of the arteries functions to accommodate the increased pressure of the