Reviewing a science book for high-school honors courses

All in All, It Does a Good Job
of Teaching the Fundamentals

Charles S. Nicoll

Overall, Human Biology is a very good introductory textbook. It is broad in scope, it is up-to-date in most areas, it shows few errors, and it devotes reasonable amounts of space to most of the topics it covers. The artwork is excellent, and the illustrations generally are well integrated with the text (though I shall cite some exceptions below).

For the most part, the organization of topics is good. I believe, however, that the chapters on the nervous and endocrine systems come too late. They appear in Part Six (titled "Regulation and Integration"), after the authors have dealt with everything else except reproduction and heredity. I have always found it more logical to discuss control systems before examining the systems that are controlled. For example: Since it is impossible to understand renal function without acknowledging antidiuretic hormone or aldosterone, students need to know something about hormones, including the general mechanisms of action of peptide and steroid hormones, before they tackle the task of learning how the urinary system functions.

A significant strength of Human Biology is its emphasis upon health and disease -- subjects of interest to everyone who has a human body. This emphasis is explained by the authors, on page 95:

In the chapters that follow, we will describe the most important diseases of each organ system. In doing this, we will take an objective, scientific, and sensitive approach to diseases. We want you to discover two things: (1) how knowledge of normal structure and function is applied to understanding the abnormal and (2) how reliable general information can be useful in your personal life, family life, and career.

I believe that the authors have achieved their aims. Besides placing a section about "Diseases and Disorders" in nearly every chapter, they have pointed to some connections between diseases and essential physiological processes. (On page 55, for example, in a section about the transporting of ions through ion channels, they note that "The inherited disease cystic fibrosis is believed to be caused by a defective channel protein.") They also have provided eight "Spotlight on Health" articles dealing with topics that are sure to be of interest, such as cancer, exercise, AIDS, alcohol abuse, and sexually transmitted diseases. Of course, many textbooks have such features. What sets Human Biology apart, to my mind, is that it also devotes two entire chapters to disease processes and the body's tactics for fighting them. These chapters -- "Microbes, Diseases, and Health" (chapter 12) and "Body Defenses: The Lymphatic System and Immunity" (chapter 13) -- tackle difficult and complex material in an unusually clear way. Given this foundation, the extensive discussion of AIDS in a later "Spotlight on Health" article is all the more meaningful.

When, for example, the authors tell of "the Arrangement Common to All Atoms," they make these statements about electron shells: "Each shell can hold only a limited number of electrons. For the atoms of living cells, this number is usually 8, and this represents a stable condition (see Figure 1.4)." Unfortunately, the figure illustrates argon -- hardly an important atom in living cells!

A few paragraphs later, the authors note that radioactive isotopes can be used to "tag" molecules, and that "The condition of your thyroid gland can be examined by injecting a small amount of ¹³¹I into the blood (Figure 1.6)." Figure 1.6 shows a drawing of a thyroid gland, along with autoradiographs produced by a normal thyroid and by a cancerous one. Those are fine illustrations, but nowhere have the authors mentioned the significance of iodine in thyroid physiology. A short explanation of the role of iodine in thyroid hormones, and of what those hormones do, would have made this example useful rather than frustrating.

In the next section, diagrams of compounds that contain double bonds are shown on page 22 -- two pages before double bonds are mentioned in the text.

In writing about the attraction between positive and negative ions, the authors first cite NaCl. This makes sense, for the authors already have told about the single positive charge on a sodium ion and the single negative charge on a chloride ion. Their next example, however, involves calcium phosphate -- Ca₃(PO₄)₂ -- even though they do not offer any discussion of multiple charges on atoms, do not consider the concept of valence, and do not show the obvious calculations which explain why three calcium ions would combine with two phosphates.

Perhaps the greatest failing of this chapter about "Chemistry and the Human Body" lies in the section called "Biological Molecules and Their Roles," for the authors apparently assume that the reader already is knowledgeable in biochemistry. They begin with a short passage about proteins, then they quickly introduce the concept of an enzyme, and they present a figure that depicts enzyme-substrate and enzyme-product interactions at an enzyme's "active site" -- a term which is not explained. All this comes before any mention of protein structure! A naive reader could not be faulted for failing to find any sense in this material.

The other important classes of compounds are treated just as poorly. The ring structure of monosaccharides is presented but is not explained. Cholesterol is depicted in two different ways, but these are not explained either. The section on nucleic acids will be comprehensible only to a reader who already is familiar with nucleic-acid chemistry. And in the last paragraph of the chapter, the authors awkwardly aver that "In modern biology, proteins and protein synthesis are very important." What does this mean? That proteins and protein synthesis were not important in earlier times?

If I were using Human Biology as my teaching text, I would supplement the first chapter with material from the 1998 edition of Vander, Sherman and Luciano's Human Physiology (another textbook published by McGraw-Hill). Even though the latter book is aimed at a more advanced audience, its chapter about chemistry is very clear and is suitable for students in a high-school honors course.

In chapter 2, dealing with cell structure and function, the authors do not introduce the term cytosol (to denote the intracellular fluid). Instead, they let the word cytoplasm designate both the cytosol and the material that lies inside of the plasma membrane but outside of the nucleus. This blurring is unfortunate and unnecessary, and it later will cause confusion for students.

Another difficulty appears, in the same chapter, when the authors broach the topic of facilitated diffusion. The text is acceptable (even though it suggests that carriers merely speed the transport of glucose across membranes, rather than being necessary for such transport to occur at all). But the accompanying illustration (figure 2.8) is very confusing: A nameless ion is bound directly to a carrier protein on one side of a membrane while another nameless ion is being released from a carrier protein on the other side of the membrane; there is a glucose molecule on each side of the membrane, but the glucose is not interacting with a carrier; and the legend says, "Molecules such as glucose and some ions cross the membrane by facilitated diffusion, using membranes that change position on binding to a specific molecule or ion."

This depiction is troublesome for two reasons. First, I do not know of any ions that are transported by themselves -- ions are moved after they have been incorporated into secondary active-transport mechanisms, but the authors do not mention such mechanisms. Second, the facilitated diffusion of glucose does not, to my knowledge, involve the binding of ions to the carrier protein. Looking at the figure, one gets the impression that carrier proteins lack specificity, and that they shuttle glucose one moment and ions the next.

I was somewhat disappointed, too, by the chapter about the heart and circulation. The authors make no attempt to tell how, during exercise, the autonomic nervous system can alter cardiac output and the distribution of blood flow. Nor do they discuss the feedback mechanisms which operate in response to a decrease in blood pressure (during hemorrhage, for example).

Finally, I wish that these authors had told something about the growth factors (such as insulin-like growth factor I), which are known mitogens and which mediate the response of cartilage cells and muscle cells to pituitary growth hormone (GH). The text merely says that GH "influences the metabolism of cells in ways that promote the growth of body tissues," that it stimulates protein synthesis, and that it encourages the utilization of fat as an energy source. GH does indeed have these direct effects on cells, but they are secondary to the effects of growth factors. (The importance of growth factors is demonstrated by the pygmies, who have a hereditary deficiency of one of these factors.)

Too Much Is Attempted,
and Too Little Is Taught

William T. Mosenthal

Each chapter opens with a useful, concise statement of intent that focuses the reader's attention. Each chapter includes succinct, boxed summaries that are appropriately placed and do not disrupt the flow of the text. In most instances, the chapter ends with sections that show how, by using biological facts which have just been presented in the text, we can understand some processes of aging ("Life Span Changes") or some aspects of disease.

Closer inspection reveals that the authors have included commendable phonetic instructions for the pronunciation of new terms -- home-ee-oh-stay-sus, for example. (How nice it would be if they had also included some etymology: Greek homoi-, same + stasis, standing. Knowing the derivations of words is a tremendous aid to learning, remembering and understanding!)

So far, very good. But when we begin a systematic reading of the book, we run into difficulties. In their preface, the authors state that "Human Biology is written for nonscience students who have little or no background in the sciences." However, I do not believe that even the most brilliant student, unless he already has received formal instruction in chemistry, can be expected to understand chapter 1 ("Chemistry and the Human Body") or the complex chemistry that appears later in chapter 7 ("Nutrition and Metabolism") and in chapter 11 ("The Urinary System"). The student may accumulate a chemical vocabulary by reading these chapters -- but without the drill and conceptual development provided by a course in chemistry, he will have no real understanding and will acquire only a warped and sophomoric sort of learning.

I say to these authors: Leave out the bewildering detail, and learn to explain general chemical principles in general terms. Otherwise, change the preface and declare outright that the student must have a knowledge of chemistry before using the book.

• Page 145: The patella is described as a pulley. In fact, it acts chiefly as a fulcrum that greatly increases the leverage available to the anterior thigh muscles. This could have been explained easily to the reader.

• In the chapter "The Digestive System," the authors accord respect to the beneficial bacteria that normally dwell in the large intestine. Then, in a later chapter, the authors describe how antibiotics kill bacteria that are pathogenic. Any discerning student will wonder what happens to "good" bacteria when an antibiotic is turned loose to suppress pathogenic ones, but the authors do not consider this matter.

• Page 186: To account for the acid regurgitation associated with esophageal hiatal hernia, the authors invoke the old idea that "the esophageal sphincter gets less support from the diaphragm and consequently may not close completely." This explanation has been discarded. The principal cause of the regurgitation is the negative pressure in the thorax.

• Page 188: "Cirrhosis [of the liver] resulting from alcohol abuse can be corrected by terminating alcohol consumption." No, the truth is that the cirrhosis can only be arrested, not "corrected." Scarring that already has occurred will never go away.

• Page 248: Yes, the semilunar valves close when the ventricles relax (in diastole). However, the student won't understand why this happens, because the authors have not related the action of the valves to the behavior of the aorta and the pulmonary artery. These elastic vessels are stretched and dilated when blood surges into them during systole, but they contract to their resting diameters during diastole -- and as they contract, they generate strong back-pressures that force the semilunar valves to close.

• Page 259: Here the "explanations" of pulmonary edema and peripheral edema do not make sense. The authors attribute pulmonary edema to "reduced cardiac output" in the pulmonary circuit, but the cause of congestive back-up and edema in the lungs is reduced flow from the left ventricle, in the systemic circuit. Conversely, the authors blame peripheral edema on reduced cardiac output "in the systemic circulation," i.e., impaired function in the left heart. The actual cause is impairment of the right heart.

• Page 265: Here the authors state that the C-shaped tracheal cartilages give "a certain flexibility to the trachea wall so that larger than normal volumes of air can be accommodated during strenuous physical activity." This is nonsense! What the cartilages actually impart is rigidity -- rigidity that keeps the trachea from collapsing when there is a difference in pressure across the wall. The trachea remains flexible because the wall is membranous and pliable in the spaces between the cartilages and between the ends of each cartilage.

• Page 285: When discussing nitrogenous wastes, the authors say that "too much urea can be toxic," and "Failure to excrete sufficient urea from the blood produces uremia, a disorder which may cause nausea, vomiting, vertigo, convulsions, and coma." This is misleading. Uremia -- the presence of an abnormally high concentration of urea in the blood -- is an easily recognized symptom of kidney disease, but urea itself does not do the damage that the authors describe. The damage is caused by other catabolic waste products that are retained, along with urea, when the kidneys fail.

• Page 400: These authors make no distinction between the brain-stem pons and the brachium pontis -- two very different structures! The object labeled "pons" in figure 15.5 is actually the brachium pontis, and the student remains unaware of the communication between cerebrum and cerebellum.

• The authors fail to acknowledge that we lack explanations for some prominent phenomena. For instance, a student will surely wonder why motor and sensory fibers cross as they pass to and from the brain, and the authors should inform him that there is no known reason for this. They should not leave the student swinging.

• In describing the physiology of the intestinal tract, why not point to its marvelous performance in conserving fluids? More than seven liters of body fluids flow into the tract every day -- in the form of saliva, liver bile, and secretions from the stomach, the pancreas and the intestines themselves -- yet only a cupful leaves the body in the feces. A truly remarkable achievement!

• The discussion of the central nervous system would be much more interesting and sensible if it related the human CNS to the nervous systems of some of our old ancestors. Show that the cerebellum is much smaller in a "hind-brain" animal than in a human, and that this allows us to do things that are impossible for a "hind-brainer." Point out that our brain retains structures that are old, in evolutionary terms, but these structures are now integrated and controlled by newer, higher centers. Show that this enables us to perform complex behaviors that go far beyond reflexive reactions -- but the old, reflexive reactions are manifested if the higher centers are damaged and integrative control is lost.

• Relate the chemical composition of our intercellular fluid to the composition of seawater. The two fluids are similar, and each displays a constancy of composition that is crucial to the life which the fluid supports.

To conclude: I feel that Human Biology has serious defects as an introductory text for "nonscience students." Too much is attempted, and too little is taught, while basic biological truths are obscured. Finally, I object to the authors' practice of touting commercial products, and citing them by their brand names, in some of the passages about health and disease. Plugs for Accutane, Zantac, Tagamet, Acyclovir, Condylox, Alferon, Clotrimazole, Femstat, Monistat, Vagistat, and other such proprietary products do not belong here.

Charles S. Nicoll is a professor in the Department of Integrative Biology at the University of California at Berkeley. His teaching includes courses in comparative physiology, human physiology and human reproduction, and his research focuses on the regulation of growth in various animal species.

William T. Mosenthal, a surgeon, is a professor of anatomy and surgery, emeritus, at 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 classes 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).

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