Lewis/Life - Teaching Techniques

Chapter 38 - Teaching Techniques

A. General Tips
** See the General Tips notes in Chapter 30 of this Instructor's Manual.
Fortunately, Lewis does not use the terms cold blooded and warm blooded. But, your students might want to use these terms. This is not a good idea. The terminology should be based on the source of heat rather than on the relative temperature.
Students often think of the kidney simply as a vehicle for urine production. I urge you to take some time to discuss the different functions of the kidney and also to discuss the evolution of different types of kidney. How are the structure and function of each kidney type related?
Whether the animal excretes ammonia, urea, or uric acid is based on energy efficiency or cost-benefit trade-offs. Ammonia requires no energy to excrete but it is highly toxic and therefore usually requires an aquatic environment. Uric acid is highly insoluble so, although it requires little water to produce, it does require a great deal of energy. Urea is highly soluble, so it requires a great deal of water to produce, but it is also moderately energy efficient. Urea contains only half as much nitrogen as uric acid. Both urea and uric acid are essentially nontoxic.
It is deceptive to think of nitrogen processing strictly in terms of energy. Some marine organisms retain urea in the blood for osmoregulation. Ruminates recycle urea in the digestive processes. This means the urea is converted to ammonia, which the ruminates' bacteria convert back to microbial protein.
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
Temperature regulation strategies will be an eye-opener for your students. Most will never have thought beyond the fact that people sweat and dogs pant. Most students will be amazed at the retes. Ask why the rete concept is logical.
As far as the kidney is concerned, some students will have difficulty with the sodium/chloride conservation mechanisms. Keep this straight forward and logical. Most will not have any particular problem with the anatomy or the overall principles.
If your course does not have a laboratory exercise related to the kidney, try demonstrating the principle of renal function in the lecture hall. These experiments are written as general observations but if you have time, you can certainly quantify any or all of them.
Put some cornstarch in dialysis tubing. Close both ends and put the sac in some water. Do this at the beginning of class and note the changes at the end of class.
Put some highly concentrated sugar solution in the dialysis tubing and place it in plain water. Prepare a beaker of a highly concentrated sugar solution. Put plain water in a dialysis tubing sac and place this in the sugar solution. At the end of class, note the differences.
If you did any diffusion experiments, refer back to those. Explain how the principles are similar.
C. Hints Related to Specific Chapter Topics
- I. Lewis mentions many marvelous points about the camel. Tell your students that there are even more adaptive mechanisms than are listed here! challenge them to find some of them. For instance, when camels sit, they are actually downloading heat into the ground. Where do they sit? The camel can also withstand greater fluctuations in body temperature than many animals. What adaptations allow this to be so? What else?
- II. If anyone has any trouble with temperature regulation and the shape of proteins, ask what happens to an egg white when it is plopped into a hot frying pan.
- II.A. Ask why your students could outrun a rattle snake. The snake (an ectotherm) doesn't have the cooling mechanisms the student (an endotherm) has.
  It is important to note that all ectotherms have some endothermic characteristics and all endotherms have some ectothermic characteristics. For instance, there is a limit to our own temperature regulation. We can die or heat or cold.
- II.C Another interesting "fish" adaptation is that some fish can live in only a very narrow depth range. This is usually based on temperature.
  Blubber is mentioned. Blubber is quite oily. Oils are better insulators than are solid fats. Consider mink oil.
- II.D. If you want to get into this topic in depth, or challenge your students to do so, there are several books and articles by F. R. Hainsworth, and K. Schmidt-Nielsen that can help you with just about any problem related to body temperature.
- II.D.3. On page 774 Lewis presents an interesting argument in favor of the human's upright stance and relative hairlessness being adaptations to heat. If you have a student who likes to come up with alternate ideas, challenge that student to present the arguments against this paragraph.
- III. Probably the most important phrase in this entire section is "following their concentration gradients." The tendency toward equilibrium is a driving force.
  The term used to describe the areas in the estuaries where salt water and fresh water meet is brackish.
  Some animals have salt glands. Invite the students to investigate these.
  Lewis mentions the metabolic water of the kangaroo rat. Challenge the students to find out how the kangaroo rat's underground domicile aids in its water acquisition and availability.
- IV. Gout is mentioned. If anyone researches this problem, make sure that person is using up to date references.
- IV.A. The nephridia is sometimes called the pre-kidney. Regardless of what it is called, however, it has the same basic function as the more "advanced" Malpighian tubules and kidneys. It is important to stress the common function, common throughout the animal world. Use Figure 38.14 to demonstrate the commonalities between the different types of systems. Read the section under General Tips above about ammonia, uric acid, and urea.
- VII.A. Use pictures liberally throughout this section. Figures 38.16 through 38.18 can be your guide. You may find it advantageous to begin by drawing a nephron in a continuous form, instead of in its folded over form. You can fold it over after the students understand what is happening.
- VIII. You will probably want to use pictures with this section too. You can draw the process quite easily. If you are uncertain of any of the concepts, check an anatomy/physiology book.
  Students are always interested in the alcohol problem, as mentioned on page 785.
- IX.C. Someone may ask you if calcium salts and uric acid are the only substances that form kidney stones. No, but they are the most common.
- IX.D. This kidney failure, or renal shutdown, often occurs also in older dogs and cats. Some students may be interested in researching this with a local veterinarian.