Lewis/Life - Teaching Techniques

Chapter 4 - Teaching Techniques

A. General Tips
For those of us who have been around cells for a while, the "cell concept" seems amazingly easy. For some of our students, the trip from cell to organism and back constitutes a giant leap of faith. They have trouble understanding that each cell possesses all the identifying characteristics of the organism and furthermore that it carries on all the life functions of the organism. Even cells that have lost one or more functions (such as red blood cells which have lost their nuclei) in their immature state were indeed totipotent.
Cells are three-dimensional and even the best artistic endeavors cannot totally compensate for the flatness of a piece of paper. Bring in some cell models -- particularly if you class does not have a laboratory component. Show the students where the organelles are. Run a probe around the cell membrane. Show the students where the cell wall would be -- even if it means putting the cell model in a box. Remind students that the organelles within the models are not made to scale. Students sometimes get into the laboratory and wonder why they cannot see mitochondria or lyzosomes.
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
One very interesting way to begin this chapter is with a non-quiz. For a non-quiz, the students write the answers to quiz questions but you do not collect the quizzes. A non-quiz such as this can help the students identify their own misconceptions, because they can see those misconceptions written out on paper.
Non-quiz questions could include: What is the difference between a bacterial cell and an animal cell? What are cellular organelles? What is a virus? This last question is especially interesting because most of your students will firmly believe that virus is synonymous with bacteria.
This idea works well with smaller classes and can be given as an outside assignment. Ask the students to design a project for teaching middle school children about the cell. Tell the students this is to be very visual and that they can use gelatin and any fruits and pastas they wish. As a hint, the plum is a good nucleus because the pit can be the nucleolus and lasagna makes an excellent endoplasmic reticulum. (If the students think they are designing this project for themselves, they may think it sounds a bit juvenile.)
C. Hints Related to Specific Chapter Topics
- I.A. It should probably be noted that there are various versions of the Janssen story -- depending on which reference you use, although the date of 1590 is quite constant.
- I.B. Although Hooke and Leeuwenhoek were the first to see individual cells, the original concept of "cell" was proposed by Aristotle who concluded that there must be an ultimate unit of life.
  Although Leeuwenhoek did not systematically describe and categorize his observations, he did carry on a 50 year correspondence with the Royal Society in London. Some of his observations are only now coming to light.
- I.C. One way to classify light microscopes is as simple (one lens) and compound (more than one lens). A magnifying glass is technically a simple microscope. Somewhat more sophisticated are the simple microscopes of Leeuwenhoek. Most of the microscopes we use today are compound microscopes.
  Magnification with light microscopes is limited by the physical characteristics of glass. Maximum magnification is about 1000x. The two major types of electron microscopes are scanning electron microscope (SEM) and transmission electron microscope (TEM).
- II.B. Prokaryote will be a new term for some of your students. Pro- means "prior to" or "rudimentary" and -karyotos means "with nuts" or "with kernels." "Karyon", a term coined by Robert Brown over 100 years ago, now means nucleus. Thus, a prokaryotic cell is one with the "pre-nucleus." Point out that these two word parts are used over and over in biology. The last sentence in this sections states that protein synthesis is more rapid in the prokaryotic cells than in the more complex cells. You might ask the class what the implications of this are.
- II.C. Eu- means "true." Thus, a eukaryotic cell has a true nucleus.
- II.D. A great deal of new reasearch is presently being done on this new life form. You might consider researching this yourself, or assigning students to dig up some of the latest information on these organisms. You might also consider telling students that outside information found on the archaeans can be used for bonus points on the next test.
  Table 4.1 compares the characteristics of the prokaryotic and eukaryotic cells. You might ask your class to hypothesize about this chart if the archaean cells were to be included.
- III. Keep in mind that the process of making milk as described in this section is a prototype for most cell processes. Extrapolate the concept to almost any cellular/organismal function.
- III.A.2 & 3. It is often helpful to go through this process using a diagram -- such as Figure 4.11. Students can then visualize what is happening. You can also draw a diagram as you speak. This can be very effective because the students see the scenario as it develops. They can see the relationship between one organelle and the next.
- III.B.2. As a point of interest, Christian de Duve, a Belgian cytologist who is cited at the end of this chapter for some of his work with the endosymbiont theory, is the one who named the lysosome the "suicide sac."
- III.B.4. When you mention the chloroplasts, mention that plant cells have mitochondria. For some reason, students think that animal cells have mitochondria and plant cells have chloroplasts. It is worth repeating several times over that plant cells have mitochondria, as do all eukaryotic cells. Stress here and in the last section that the DNA of both the mitochondrion and the chloroplast resembles prokaryotic DNA, rather than eukaryotic DNA.
- IV.A. The biggest favor you can do for your students with this section is convince them that viruses are not bacteria. If you draw a kingdom chart, draw a little circle off to the side and label
  it "V" for virus. You can draw dotted lines to all of the kingdoms to indicate that viruses infect all organisms but that the viruses are not a part of any of the kingdoms. Stress that this is why antibiotics are useless against viruses.
  Plants can also get viral infections. The first virus isolated was the tobacco mosaic virus.
  As an additional point of interest, the units making up the capsid are called capsomeres.
- V. Some texts refer to the endosymbiont theory as the endosymbiotic theory. You might also wish to note that the