Lewis/Life - Teaching Techniques

Chapter 37 - Teaching Techniques

A. General Tips
** See the General Tips notes in Chapter 30 of this Instructor's Manual.
For your preparation of this chapter, I suggest you have a good anatomy/physiology book or a good nutrition book as a reference. If you are not an anatomy/physiology teacher or a nutrition teacher, you may need such a book for background. I urge you, however, not to try to teach everything you find in your reference books. Since most people are very interested in food, nutrition, and digestive topics, it is especially important that you maintain a perspective based on your original course objectives.
Stress the commonality of the gut, from hydras and insects right on through birds and humans.
Stress also the need for breaking down and building up. Even though the same string of amino acids might be a part of the cow arm muscle and the human arm muscle, the break down and build up must occur.
You might wish to copy and distribute to your students the Overview of Chapter Objectives flowchart found at the beginning of this Instructor's Manual Chapter.
B. Possible Approaches to the Chapter
This chapter is filled with good anecdotes, delightful stories about the food gathering and processing strategies of many non-human vertebrates. I encourage you to make the most of the fact that students will like these explorations.
Because many of your students will have had at least the essentials of human nutrition and digestion in high school, I suggest you begin this material with some sort of evaluation quiz. This may be a non-quiz, or it may be a formal pre-test.
Students have many more problems with nutrition than they do with the essentials of the digestive system. If you have any doubts, ask such non-quiz true or false questions as: Sugar is high in fat. Vegetables do not contain protein. Cows do not need protein. (All three answers are false.)
If your students have a relatively good understanding of the basics, do not beleaguer these concepts. Clear up misunderstandings and work on the non-human nutritional strategies.
One method that has worked quite well for many instructors is to assign for completion outside of class time a summary of the main points of human digestion. This could be in the form of a chart. The chart could include main structures, accessory structures, enzymes, digestive actions, etc. Or the chart could follow the path taken by a bite of a burger with lettuce and tomato straight from one of our fast food gourmet houses.
Another time-honored nutrition teaching method is the food diary. I suggest a week for such a project. During that time, the students write down everything they eat and drink (including quantities!). This should be augmented by an editorial appraisal of their dietary habits. If you have a good rapport with your students, do your own food diary for the same time period.
C. Hints Related to Specific Chapter Topics
- I. Refer back to Chapter 3 for a review of the basic chemistry. Figure 37.2 is especially valuable. Stress the common theme.
  Students are usually interested in baleen whales, as shown in Figure 37.3. Note the reference to the krill. Relate this to Figure 42.1 on page 855.
- I.A. Build a picture; show the rise of heterotrophy. At the same time, you might ask if the earliest organisms really were heterotrophs. Ask, too, if we humans are specialized feeders (as per page 752).
- II.A. It is interesting to note that in some parameciums the food vacuole actually follows a set pathway around the organism and the waste is dumped out of a specific anal pore.
  Some of the students may have heard the term gastrovascular cavity (or GVC) in reference to the digestive systems with a single opening. If you mention the GVC, ask why this is a logical term.
  Stress the last sentence of this section.
- II.B. Mammals do not usually have the enzymes necessary to digest cellulose. This breakdown is normally accomplished by cellulose-degrading bacteria or protistans.
  One advantage of the cud for the ruminates is that the bacteria supply protein for this herbivorous diet. The same is true when the rabbits eat their moist fecal pellets. The term for eating feces is coprophagy. Dogs are not normally coprophages but they will eat fecal material in lieu of starvation. Cats are not fecal diners. For this reason, in malnourished areas of the world you will often find dogs but not cats.
  Although cattle are ruminate animals, horses are not. Which would survive in better health in a nutrient poor field? (Answer: cattle.)
- III. Refer back to Units 1 and 2 as needed. Students who have never had chemistry will have forgotten a great deal of what they learned in those two sections.
  Stress Tables 37.2 through 37.5. Students will find Table 37.3 especially interesting. Encourage them to add to this list.
  In dealing with weight gain and weight loss, a new twist has become slightly more credible in recent years. What about the body's own compensatory mechanisms for increased or decreased food and/or caloric intake?
- IV. Peristaltic waves are generally one way.
- V. As you peruse this section, you will notice quite a few terms. Your students will not be familiar with most of these terms. Decide in advance what they need to know, use the rest as support for the basic concepts.
- V.A. You may have to remind the students that starch is a long chain of glucose molecules.
  Challenge the class to find out whether the muscles of the esophagus are smooth, skeletal, or both. (Upper third is skeletal, middle third is a combination, lower third is smooth.)
- V.C. About 75% of the adult world is lactose intolerant. In most lactose intolerant people, the decline in the ability to digest lactose begins about the age of 4. Some people are only mildly intolerant, meaning they probably do produce a small amount of lactase. In other people, lactase production seems to be inducible. Ask why some people can eat cheap ice cream without any trouble but upon eating rich and expensive ice cream they develop severe gastrointestinal distress.
- V.C. & D. Water absorption is almost entirely the role of the large intestine. The disease cholera is actually a small intestine problem, even though the classic symptom is massive, rice-water diarrhea. The bacteria attack the small intestine causing a loss of cellular integrity. The fluid rushes out and the large intestine, even though it is functioning properly, cannot re-absorb the water fast enough.
- V.E. It is important to point out that the gallbladder is a storage sac. That is why it can be removed without a problem. Cholesterol gallstones are mentioned; other gallstones, such as calcium, can also form.
  Another new and interesting way to treat gallstones today, without removing the gallbladder, is to use sound waves to shatter the stones. Check lithotripsy, as mentioned on page 786 (Chapter 38).
- VI. You might ask the class why most animal species -- other than human -- seem more drawn to what is good for them nutritionally instead of what they "shouldn't eat."
  Yes, the liver can regenerate. Even if most of the liver is lost (or transplanted) a new liver will grow.
  Cirrhosis is often defined simply as a scarring of the liver. It is actually more than that. Cirrhosis is not limited to excessive alcohol intake; it can also be caused by an inflammation of the bile ducts, an overgrowth of hepatic connective tissue, various poisons, nutritional defects, infections, and injury, to name a few.