Academic journal article The American Biology Teacher

Essential Analogies in Human Anatomy & Physiology

Academic journal article The American Biology Teacher

Essential Analogies in Human Anatomy & Physiology

Article excerpt


Teachers know that learning proceeds from the known to the unknown. Analogies help a student learn abstract material by relating it to his or her known experiences. Gentner (1998, p.107) defines analogies as partial similarities between different situations that support further inferences.

Some analogies are so useful that we call them essential analogies. Here is a topical listing of analogies we have used, some of which we consider essential. This list of analogies will be maintained and updated at You are invited to contribute additional analogies at or

* Homeostasis

Maintaining constant internal conditions is a balancing act for all life. Humans are like the baby bear in Goldilocks in our needs: not too hot, not too cold, not too much water, not too little water.

Positive feedback increases the activity: "Don't laugh at his jokes, you'll only encourage him." Negative feedback decreases the activity, and you can cite American Idol examples. A teeter-totter has positive feedback and is difficult to balance evenly. A rocking chair has negative feedback, and returns to a middle state. Pathology is when the body rocks too far and can't correct itself.

* Chemistry

Chemistry can be very intimidating, especially to returning students. To help explain the unequal sharing of electrons, we use comparisons like these: When the author (Hueftle) shared the TV with his little sister, he watched the game and only during the commercials did she get to watch cartoons. When the author (Sundrud) shared an ice cream cone with his big sister, the ice cream cone spent most of the time in her hand, not his.

An enzyme and its substrate are traditionally compared to a lock and key, so protein/enzyme denaturation is like bending the key: It stops working.

An enzyme can also be compared to a matchmaker (Fiddler on the Roof) in that it is not used up by each reaction catalyzed (or marriage arranged). Heating a solution to increase reaction rates is like giving the matchmaker roller skates so she can work faster.

Emulsification of fats works like crunching a hard candy, thus increasing the surface area and letting it dissolve quickly.

To illustrate monomers and polymers, hydrolysis and synthesis, use large toy pop-together beads as monomers. Folding the chain so that the blocks touch would show hydrogen bonds.

The Hindenburg Disaster of 1937 is an example, not an analogy, but useful in teaching about the periodic table, as the next question is: Why was the Hindenburg flammable, but not the Goodyear blimp? Hydrogen has a vacancy in its outer shell; in Helium, the "No Vacancy" sign is blinking.

* Cells

Most students believe in cells, but don't understand the details. The limitations of the light microscope can be explained by citing television or the comics--putting your nose to the screen doesn't show any additional detail. Using the light microscope to see mitochondria is like wearing boxing gloves while feeling for a dropped pin.

The cell is not like a water balloon with marbles in it. It's more like a baggie of Jell-O fruit salad. The fruits are the organelles, the Jell-O is the cytoplasm, and the baggie is the membrane. Put the baggie in a box to visualize a cell wall.

The cell membrane can also be compared to raisin bread, with the bread being the two layers of phospholipids, and the raisins representing proteins. Big raisins (integral) penetrate the bread and small ones (peripheral) are only on the surface. Wrap the bread around a ball (cytoplasm) to give the three-dimensional aspect.

The Golgi complex looks like a squashed stack of incompletely-cooked pancakes. The lysosome, with its powerful digestive enzymes, can be compared to a "suicide pill," and cytoskeleton microtubules compared to reinforcing rods of concrete. …

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