Lewis/Life - Teaching Techniques

Chapter 19 - Teaching Techniques

A. General Tips
I suggest you begin your preparation of this chapter by reading the Summary on page 401. Most of the material is relatively easy to work with. By going over this summary, you will gain a perspective and you will be able to determine how much emphasis you wish to place on which concepts. Keep in mind all of your course objectives.
In general, this is a straight forward, easy to understand chapter. Some students may have a little trouble with some of the vocabulary. A few will become confused with the sections on common DNA and common protein sequences. These should not be major problems.
To help with molecular confusion, put up on the board a simple chromosome. Circle a region and call it a "common or conserved" region. Refer back to this as needed. Ask the students to recall what DNA codes for. When they tell you, "protein," tell them that your hypothetical region codes for a common protein. Simplifying this material may seem quite simplistic to your students who have excellent backgrounds, but to many of your students, this type of simplification is exactly what is needed to gain a firm foundation on these concepts. (For some of your students, your class is a first exposure to some of these ideas. And some of these ideas are not easily understood the first time around.)
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
The material in this chapter -- actually in the whole unit -- lends itself well to the annotated outline. Such an outline could be assigned to be handed in before you lecture on the material. That way the students would have a perception of the sequence of events under consideration and the lecture itself could be used to focus on a conceptual or developmental understanding of the information (rather than on a straight chronology).
A good way to begin this chapter is with a non-quiz. Ask such questions as: 1) What are fossils? 2) What is molecular evolution? 3) If you were going to study whether or not organisms were related (at the molecular level), what types of things might you look at?
Most of the students will do fairly well with a non-quiz like this. Those who do have problems will readily see the answers and you will then have a firm foundation for covering as much or as little of the rest of this material as you see fit -- in keeping with the objectives of your course. Keep the molecular part very simple until the students have a solid foundation.
C. Hints Related to Specific Chapter Topics
- I. Distinguish between phylogenies and cladistics. Students often confuse these terms.
- II.A. Stress the definition that a fossil is any evidence of an organism. Some students mistakenly believe that fossils must be actual remains of an organism. They need to be prodded into believing that shell impressions and dinosaur footprints are also fossils.
  Toward the end of page 390 the term "recent relatives" is used. Ask the class to define "recent relatives." You will probably find a bit of confusion here. This confusion is based on our inability to comprehend the time frames of paleontology.
- II.B. Radiometric dating can be a real problem for students. The overriding concept is simple enough but invariably they have trouble with the idea of half-life.
  After you have explained half-life to your class, ask them to compute a simple half-life problem. For instance, "Substance X has a half-life of 6 months. Three years ago you had 100 grams. How much do you have now?" Very few will come up with 1.5625 grams. Show the class on the board how you arrived at the answer:
  
  3 years ago 100 g
  2-1/2 50 g
  2 25 g
  1-1/2 12.5 g
  1 6.25 g
  1/2 3.125 g
  today 1.5625 g
  
  (The students who see this exponentially will have gotten the correct answer to start with.)
- III.A. Lewis states that determining whether structures are homologous or analogous is sometimes difficult. This is certainly true! Be certain the students understand the overall concept, but, for the sake of those having trouble with the minutia, do not dwell on it.
  Spend some time with Figures 19.5 and 19.6.
- III.B. Students generally like the section on vestigial organs. But, as a point of interest, the human appendix is no longer considered vestigial. The human appendix, replete with lymphoid tissue, is now considered an important part of the immune system. Research is presently under way at the National Institutes of Health to determine the exact functions of the appendix.
  Spend some time with Figures 19.5 and 19.6.
- III.C. The outgrowth of Haeckel's thinking became Ontogeny recapitulates phylogeny.
- IV. A word of explanation about the terms "highly conserved" and "synteny" would be in order here.
- IV.B. Remind the students of the overview of protein synthesis.
- IV.E. The concept of molecular clocks is difficult for some students. Spend a few extra minutes with the idea of parsimony. Use the board or overhead projector to show this.
- IV.F. This section ties this whole chapter together. You may wish further to expand on what is said here and relate it back to concepts in Chapters 17 and 18 and ahead to concepts in Chapter 20.

3 years ago	100 g
2-1/2	50 g
2	25 g
1-1/2	12.5 g
1	6.25 g
1/2	3.125 g
today	1.5625 g