Reviewing a science book for high-school honors courses

Human Biology
1995. 527 pages + appendices. ISBN: 0-534-20208-X.
Wadsworth Publishing Company, 10 Davis Drive, Belmont,
California 94002.

This Book Forces Students
to Depend on Memorization

William T. Mosenthal

In this review I shall concentrate on the book's predominant segment, dealing with anatomy and physiology. Here I find flaws that greatly detract from the book's value as an educational instrument. Before I analyze those flaws, however, I have a preliminary comment. If a student attempts to use this book without having taken a course in basic, general chemistry, the student will surely founder. Such a course should be decreed as a prerequisite at the very beginning of the book, but neither the preface nor the introduction says anything about this.

In the preface, some lofty goals are set forth. The reader is told to expect "engaging writing" in a book that will "clearly explain key concepts," will be "interesting to read," and will shun "confusing jargon" and "distracting digressions." That is exactly how any textbook should behave! Unfortunately, it just doesn't happen in Human Biology.

The text of Human Biology abounds with unexplained terms and with unsupported statements, so students must rely on memorization without comprehension. The value of a book that fosters this type of "learning" is pretty low. Students' grasp of the subject matter will be second-rate, and even the most eager students will lose interest and will regard reading their textbook as a chore. Let these examples suffice to show how the writers of Human Biology require students to accept statements on faith and to dodge around gaps in reasoning:

• Page 79: The writers mention "about 2.5 million sweat glands, which are controlled by sympathetic nerves." Such kindly nerves have not been described previously, nor are they described here.

• Page 99: In a two-paragraph section on "How Muscles and Bones Interact," the final sentence states: "In addition, the nervous system uses signals from stretch receptors in tendons or muscles to coordinate the contractions." Stretch receptors? Coordinate the contractions? The writers' remark goes unexplained, and the student who has been climbing laboriously up the didactic hill suddenly slides back down to the bottom.

• Page 150: In describing the cardiac cycle, the writers say three times that the semilunar valves close. The mechanism of closure is not explained, however. The valves just close -- take it or leave it!

• Page 156: "Epinephrine triggers vasoconstriction or vasodilation." Here's a statement that badly needs explanation! Yet the writers provide none, and the student must simply accept and memorize the bald claim that the same hormone can induce two opposite effects.

• Page 157: "In the intrinsic clotting mechanism, a plasma protein becomes activated . . . ." Please, what activates it?

• Page 278: "Oxytocin has roles in reproduction in both males and females. For example, it triggers muscle contractions in the uterus during labor and causes milk to be released when a mother nurses her infant." But nothing is said, here or anywhere else, to support the statement that oxytocin also functions in males.

Another serious obstacle to understanding is the omission of essential context. For instance, it is impossible to understand the human nervous system without a résumé of its evolution. Without an evolutionary perspective, the student can merely memorize, not comprehend, the seemingly strange fact that "Most axons of the optic nerves lead into the thalamus, which passes on information to the visual cortex" (page 270). Such roundabout routing of visual signals is a vestige of evolution. In the ancient vertebrates that were our ancestors, the thalamus itself handled visual matters; in modern mammals, this function has been transferred to the cerebral cortex (an elaborate new structure that has provided us with new switchboards, integration centers and memory banks), but visual impulses still travel to the thalamus first, before they go to the cortex's visual centers.

The omission of context and of "the big picture" recurs throughout the book, and the neophyte is expected to learn reams of information without seeing the meaning of it all. Homeostasis, one of the most important concepts that biology has to offer, is briefly mentioned on page 4, where it seems to have something to do with "maintaining a constant internal environment." Then it appears again on pages 81 and 82, in a section that includes an attempt to explain what feedback mechanisms are; here the writers use some strange examples (involving kissing and parturition), and they fail to show that homeostasis is an all-important phenomenon which affects all cellular activity. They should have developed homeostasis as a major concept, and they should have emphasized it repeatedly as their book unfolded.

The writers drop many hints about DNA before they finally describe it in chapter 19 ("DNA Structure and Function"). Yet DNA is so fundamental, and so necessary for understanding other topics, that it belongs near the front of the book. The basic chemistry of DNA (and an outline of the DNA-replication mechanism) must be established before, not after, students attempt to learn about protein synthesis, cell division, and so forth. A more detailed treatment can be reserved for a late chapter, but the basics cannot.

• Page 96: In describing the carpal tunnel syndrome, the writers make no mention of its anatomical basis: A narrow, indistensible tunnel houses all the flexor tendons and the median nerve as well.

• Page 96: "A triangular kneecap, the patella, helps protect the knee joint." A far more important function of the patella is to afford mechanical advantage to the tendons that extend the joint.

• Page 117: In discussing the cause of peptic ulcer, the writers do not say one word about hyperacidity.

• Pages 142 and 144: The writers tell that a red blood cell assumes the form of a biconcave disk (due to the expulsion of the cell's nucleus), but they do not explain that this shape is advantageous in exposing the contained hemoglobin to gases.

• Page 213: If the draining of urine through the urethra is inhibited, the writers say, "bacterial growth can trigger infection." They do not point out that this exemplifies a general principle which, if properly elucidated, could help the student to comprehend the basis of many infections. Bacteria are everywhere, and bacterial overgrowth is a common result when an obstruction creates a mass of stagnant fluid in any organ -- the urinary bladder, the gall bladder, a sinus, a salivary gland, et cetera.

• Page 240 offers a masterpiece of understatement: "The activities of the cerebellum appear to be quite important in coordinating voluntary movements." In fact, there would be no coordination at all without the cerebellum!

In describing circulation of the blood, the writers fail to point out that the volume of the capillary beds is far greater than the volume of the blood. Arteriolar sphincters are vital in distributing the available blood to the beds where it is needed, and the failure of these sphincters (or a substantial loss of blood through hemorrhage) results in true shock, a collapse of blood pressure, and death. This is a fairly important concept!

The factual information presented in the text and illustrations is accurate, in general, but there are some disturbing errors too. For example:

• Page 7: "Liver cells step up their secretion of insulin." Liver cells do not secrete insulin; they use it. Insulin is produced by the islets of the pancreas.

• Page 73: "Adipose tissue has a rich supply of blood vessels." Actually, adipose tissue -- in comparison with most other tissues -- has a scanty supply of blood vessels.

• Page 96: "A pair of coxal bones . . . curve forward to meet at the pubic arch." They actually meet in the pubic symphysis.

• Page 113: "Thickened regions of muscle occur in the wall at either end of the stomach and at other specialized locations. These muscular regions serve as one-way valves called sphincters, . . . ." That is incorrect. By definition, a sphincter is a ring-shaped muscle that surrounds a channel or aperture. There is no anatomic sphincter at the proximal end of the stomach, and there is no demonstrable region of thickening. However, the muscles at the proximal end do perform a sphincter-like action, preventing the backflow of stomach acid into the esophagus.

• Page 158: The writers' Rh story is erroneous. Sensitization of the Rh-negative mother occurs only if breaking or tearing of the placenta allows fetal red cells to enter the maternal blood. Fetal cells do not pass through an intact, normal placenta.

• Page 266: "A clear fluid (aqueous humor) bathes both sides of the lens, . . . ." No, only the anterior side. The lens is in the posterior wall of the eye's anterior chamber, and there is no aqueous humor behind it.

• Figure 4.6: The structure labeled "hyoid bone" is really the zygomatic arch, and the zygomatic arch has nothing to do with supporting the tongue.

• Figure 10.14 is titled "The major nerves in the nervous system," but it's really a picture of spinal segmental nerves exiting the spinal cord. The only "major nerves" that it shows are the ulnar and the sciatic.

• Figure 10.20: The image titled "Activity in auditory cortex (hearing)" actually shows activity in the speech area of the frontal lobe.

• Figure 11.6: This picture of "Regions of referred pain" is inaccurate, fanciful and misleading. Referred-pain areas aren't discrete and circumscribed, but this illustration indicates that they are.

For all these reasons -- the frequent failure to explain terms and statements, the dependence on rote memorization, the omission of important background and context, and the recurrent failure to emphasize truly basic concepts -- I find Human Biology to be a difficult, uninspiring book. I do not recommend it for use by high-school students.

A Hasty, Disjointed Text
That Has Too Many Gaps

Ben E. Coutant

All of the human body's major systems are surveyed, at least in part, and the book's factual errors are generally subtle, but Human Biology is not always easy to read. It seems to be a condensed version of a more advanced book, abbreviated in ways which have left too many gaps that beginning students will find difficult to bridge. In biology, it is extremely important for students to see both the "forest" and the "trees," and to see how they are integrated, but Human Biology doesn't favor this result. It has too many paragraphs that contain short sentences which lack logical connections, and there are too many gaps between information presented in illustrations and information presented in text. The writers should have paid more attention to making their book flow logically, even if this would have required making the book bigger.

A prime example of how this textbook skimps on anatomical information is provided by Chapter 4, titled "Musculoskeletal System: Support and Movement." On page 92, the beginning paragraph under "Skeletal System" correctly mentions that there are 206 bones in a typical human body, but this statement is not developed or supported. Relatively few of the bones are covered in the subsequent text or figures, and virtually nothing is said about any bone's structural details. Joints are covered in a half-page of text and one page of figures, which is insufficient for enabling a student to understand either the structural diversity of joints or the multitude of movements that joints make possible.

In the same chapter, the section titled "Muscular System" begins with the correct statement that there are "more than 600 muscles, arranged as pairs or groups." But in the entire section, only 16 muscles are ever depicted and identified in illustrations. A student will get little understanding of musculoskeletal anatomy from this chapter.

• Acids are defined as substances that release hydrogen ions in water, and bases are said to be substances that release hydroxide ions. These definitions are certainly inadequate for understanding the chemistry of biological systems, and the writers should at least have mentioned the Lowry-Brönsted concept, in which acids are proton donors and bases are proton acceptors. Without that concept, how can students understand the actions of such important bases as ammonia, amines and bicarbonate?

• Figure 1.15 shows the ring structures of glucose and fructose, including the hydroxyl groups, followed by a diagram in which glucose and fructose form a molecule of sucrose through a dehydration synthesis. During the synthesis, all the hydroxyl groups mysteriously disappear. This is bound to confuse students who aren't familiar with saccharide chemistry.

• The only picture pertaining to steroids is a diagram of the four-ring "steroid backbone." There are no pictures of any specific steroid molecules, so students cannot appreciate how the actions of different steroids depend on subtle differences in structure.

Chapter 10, about the nervous system, has several errors in its discussion of action potentials. For instance, the writers imply that the sodium-potassium pump has to act before a "membrane region" can recover from a single action potential. (In actuality, experiments in which the sodium-potassium pump was blocked have shown that millions of action potentials can be triggered before the ion gradients are reduced enough to render a neuron incapable of responding to stimulation.) The writers also err when they state:

The sheathed regions [of myelinated axons] hinder the flow of ions across the membrane, which forces the ions to flow along the length of the axon until they can exit at a node and generate a new action potential there. The node-to-node hopping in myelinated neurons is called saltatory conduction, after a Latin word meaning "to jump."

If ions really had to "flow" in that way, the propagation of an action potential down an axon wouldn't be called saltatory. An electrical current is propagated by charge displacements, not bythe "flow" of individual charged particles. (If I may be forgiven a mechanical analogy, a conductor is somewhat like a long tube that is completely filled with marbles. If you push a new marble into one end of the tube, all the other marbles are immediately displaced, and the marble at the far end is immediately ejected; but the displacement experienced by any one marble is minuscule, and no marble "flows" along the entire length of the tube.)

The discussion of chemical synapses between cells also appears inadequate. The writers correctly tell that "Depending on the type of channels being opened up, a neurotransmitter may either excite or inhibit the membrane . . . ." But they do not elaborate on how the opening of channels (and the associated, unmentioned movements of ions) actually alter the membrane potential.

The section on brain anatomy (starting on page 241) has some factual difficulties. For example, the tectum of the midbrain is described as a site where "visual and auditory sensory input converges before being sent on to higher brain centers." While the tectum is a major relay station for auditory input, it is -- in humans -- only a minor pathway for visual input.

The paragraph about the forebrain says that the forebrain's major structures include "a pair of olfactory lobes." Some vertebrates have discrete olfactory lobes, but humans process olfactory inputs in several evolutionarily ancient regions of the cerebral cortex. I've never seen a reputable neuroanatomy text refer to human "olfactory lobes," and I suspect that the writers of Human Biology may be less familiar with the neuroanatomy of mammals than with the neuroanatomy of other animals.

In some sections the writers attempt to treat physiological functions in an advanced way, but most of these efforts, unfortunately, are wasted: The writers do not provide enough context to allow students to assimilate the information that is presented. An example is figure 11.17, which endeavors to explain the processing of visual input in the occipital cortex. There is not enough information in the figure and the accompanying text to give the reader a clear idea of the occipital cortex's functional organization.

On page 38, a section on "The Nature of Cells" begins with this statement: "Cells are amazingly diverse in structure and function." The accompanying figure, however, shows only two types -- a smooth muscle cell and a motor neuron.

Tissues are considered in a little more detail, but many important types are not pictured. I can only assume that students are expected to flip pages and attempt to find appropriate pictures of these tissues in other parts of the book.

Figure 4.3 includes a micrograph of an osteon, but the part labeled "osteocytes" is just a smudge. It seems to be a lacuna (one of the spaces in which osteocytes reside) that is not in the plane of focus. To avoid misleading the student, the illustrator should have put his label on one of the sharply focused lacunae that appear elsewhere in the image.

Figure 10.20 is a series of PET-scan images of the brain, and one of them, showing activity in the frontal lobe, is titled "Activity in auditory cortex (hearing)." But as the accompanying drawing correctly shows, the auditory cortex is in the temporal lobe.

In summary, Human Biology seems to be a poorly condensed version of some other book. Its thin treatment of anatomy, its lack of clarity, and its failure to integrate information make it a poor choice for teaching human anatomy and physiology to high-school students.

William T. Mosenthal, a surgeon, is a professor of anatomy and surgery, emeritus, at the Dartmouth Medical School (Hanover, New Hampshire). He has given courses in anatomy, neuroanatomy and surgical principles at that institution, and he has taught introductory anatomy and physiology at a nearby community college. He is the author of A Textbook of Neuroanatomy with Atlas and Dissection Guide, issued in 1995 by the Parthenon Publishing Company (Pearl River, New York).

Ben E. Coutant is an assistant professor in the School of Natural and Health Sciences at Barry University (Miami Shores, Florida), where he teaches courses in physiology, anatomy, neuroanatomy and general biology.

return to top go to Home Page read our Index List, which shows all the textbooks, curriculum manuals,      videos and other items that are considered on this Web site subscribe to The Textbook Letter order back issues of The Textbook Letter support the work of The Textbook League contact The Textbook League by e-mail The Textbook Letter is published, copyrighted and distributed by The Textbook League (P.O. Box 51, Sausalito, California 94966)