Lewis/Life - Teaching Techniques

Chapter 9 - Teaching Techniques

A. General Tips
This is an exciting chapter and the students will generally like it. Most of them have some understanding of mitosis. Your task will be to convince them that mitosis is just one part of the cell cycle. Many of them will have come from high schools where the life of the cell was not really taught and mitosis was the only thing they really needed to worry about.
The students will be especially interested in apoptosis (which will be totally new to most of them) and cancer (which virtually all of them are interested in).
If you need a mnemonic for the cell cycle, try this one, compliments of one of my own students from about 15 years ago: It Probably Means Another Test.
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
I suggest that you teach at least the first part of this material directly from an illustration of the cell cycle. Either have Figure 9.3 in plain view or sketch a similar figure on the board as you begin your discussion. Point out the logic of this cycle and then work your way around it.
Consider drawing an arrow from the junction of the S phase and the G2 phase. Label the arrow "To Meiosis" and tell the class you will pick up meiosis from this point in the next chapter but that you are not going to worry about it now.
It is usually best not to discuss meiosis during this part of the class. Many of the students do not understand meiosis at all, even though they will have had it in high school. Drawing the arrow mentioned in the previous paragraph merely gives a point of reference both for the future, and for recall when you do discuss meiosis.
The discussions on the control of cell division, apoptosis, and cancer are all very interesting. If you are adventuresome, you might wish to start this chapter with control and work backwards.
Table 9.1 is very good, but it may contain more information than you wish your students be responsible for.
Be certain in your own mind exactly how technical you expect your students to be. For instance, chromosomes, chromatids, replicated and unreplicated, centrioles, centrosomes, centromeres, and a myriad of other technical details may overwhelm your students. This is not necessarily bad, but keep in mind your course objectives and be aware of exactly what you want your students to learn from this chapter.
C. Hints Related to Specific Chapter Topics
- II. Many of the students are so inundated with mitosis that they do not see that mitosis is just a part of the cell cycle. Stress that the cell cycle is the whole life-span of the cell.
  Stress too that mitosis is a nuclear event and cytokinesis is a cytoplasmic event. Many of your students will want to say that mitosis is cell division. This is not correct. Mitosis is nuclear division.
  Students often want to use a clock to understand the cell cycle. This is probably because many of the high school texts use clocks. If you use the clock analogy, I urge you not to use a 24 hour clock. Because of transfer misconceptions, it would be better to use a hypothetical 18, or 30, or 42 hour clock.
- II.A. Lewis mentions the old concept that interphase was formerly thought of as the time when the cell is at rest. This idea is not dead! You will find a number of your students still holding on to this mistaken notion.
  As a point of interest, the "G" was originally called "gap" because scientists knew something was occurring during that period but they couldn't identify it. Gradually we are discovering all the events occurring in the "gap" or "growth" periods.
- II.A.1. Lewis mentions cells that may skip the G1 phase. Add to that list the acellular slime molds.
- II.B.1. This section can be overwhelming for your students. Be certain you yourself have a good understanding of how Lewis presents this material.
- II.C. Lewis does a very good job of presenting this material. Urge your students to follow these descriptions Also urge them to note Table 9.2, which covers the stages of mitosis.
- II.C.1. As a point of interest, the nuclear membrane does not break down during yeast mitosis.
- II.D. This section starts with the correct statement that cytokinesis begins during anaphase or telophase. Stress to your students that cytokinesis is a separate event. It is not really a part of mitosis. Besides, mitosis is a continuum and the phases of mitosis are the result of artificial divisions. Therefore, different organisms (or cell types) could logically begin cytokinesis at different points in the cell cycle.
  It is remotely possible that you may have a student who is familiar with the term syncytium as it is used to describe cardiac contraction, or the cells of certain types of sponges or roundworms. If someone brings up one of those (or similar) points, that person is correct. Invite some outside study.
  As a point of interest, the muscle cell, while it is a syncytium, did not become a syncytium by massive karyokinesis without cytokinesis. Rather, the muscle cell is the result of the fusion of uninucleate myoblasts in early development.
- III.A. This discovery is truly a major breakthrough, and one you can use to hype the interests of your students. You can also use it as a pivotal point for discussions on the whole growth process.
- III.B.1. A good example of contact inhibition is what happens when you cut yourself. The local cells on either side of the wound immediately start to proliferate but as soon as they touch, they stop.
- III.B.2. Non-purists might argue about hormones necessarily traveling in the blood stream. It's a matter of semantics and of no importance here.
- IV. Refer back to the first section of this chapter, the balance between cell division and cell death.
  Ask why occasionally someone is born with webbed fingers or webbed toes. The cells in the webbing were suppose to die but there was an error in the programmed cell death. The duck's webbing is not programmed to die away (as per Figure 9.2).
- VI. Stress the differences between the benign and the malignant tumor. This is a much-misunderstood concept in today's world. Bring out that benign tumors can indeed cause problems. Benign tumors within the body (as opposed to malignant tumors) are often encapsulated and the cells maintain their own cellular identity.
  Read this section carefully. Lewis dispels some very prevalent myths about cancer cells. For instance, Lewis has the statement that cancer cells are not necessarily the fastest dividing cells. This fact (and it is correct as stated) is contrary to conventional wisdom.
- VI.A.2. Once a cancerous cell has completed the cell cycle (gone through mitosis) the body no longer recognizes that cell as foreign. Thus, the cell can continue its degenerate ways.
- VII.A. If you are adventuresome, you could discuss the possible viral origin of the oncogenes.
- VII.B. The key is that the genes may be activated or inactivated. This presents an interesting evolutionary problem.