This chapter lends itself well to outside reports. Some report topics could include protozoan diseases, protistan roles in agriculture and ecology, life cycles of slime molds, protistan roles in the food chain, and plankton species diversity. The list is virtually endless.
You may be tempted to reduce this chapter to a mere collection of facts -- and it certainly is a fact-filled chapter! I caution you not to succumb to this temptation. Strive to make the delineation of the protists logical and interesting. You can do this with anecdotes about specific species. Anecdotes will help the organisms come alive. Certain anecdotes are included in the text; I have added a few more in the Hints section below.
Because there are so many facts given in this chapter, I urge you to re-visit your course and chapter objectives. What do your students need to know and why do they need to know it?
The classification schemes given in the Lewis book are not universally accepted. No scheme is universally accepted! Some of your students may have learned a different phylogeny. Accept that by stating that any scheme is simply a method of organizing material. Since not everything is known about these organisms, there are bound to be different approaches to classifying them.
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.
An interesting way to introduce the section on protozoans is to ask the students to write down 5 points they know about protozoans. The standard answers will include about 3 points, one each on the Amoeba, the Paramecium, and the Euglena. Someone may have something about a protozoan disease, such as malaria. In general, students do not have a particularly good background in protozoan biology, although they tend to think they do. They tend to think the field is much simpler than it is.
Begin the whole section on algae by asking the class how many have eaten algae. Unless you are in a school in Hawaii or on one of the Pacific Islands, most of your students will honestly believe they have never eaten algae and that even the thought is a bit unnerving.
- I. Some books discuss "animal-like", "plant-like", and "fungal-like" protists. Without using those terms, that is approximately what Lewis does in grouping the protistan types.
Lewis makes a good point by stating that most protistans are unicellular. Most is an important word here, particularly when dealing with some of the algae and slime molds. Often instructors make a point of stressing protistans as unicellular and then begin talking about Volvox.
I suggest you make good use of the opening vignette. In addition to the places mentioned, foraminiferan shells are the basis for the chalk beds in Georgia and Arkansas. These were formed when the Cretaceous Sea covered the central part of the United States during the Mesozoic era.
- II. Note that Lewis has defined phyto as meaning plant. It would be good for you to stress this to your class. Tell them that phyto and phyta always indicate plant and can be used as prefixes or suffixes or as insertions within other words.
- II.A. There are numerous ways to classify the protozoans. Lewis is working from a developing refinement of several different classification schemes. This structure will continue to be refined but it is at present the most solid way of grouping the protozoans.
In the past, locomotion was the sole criterion used for classifying protozoans. Some older books still use this criterion. Some students may come to you from high schools where this concept was taught.
The statement is made in the first paragraph that Pneumocystis carinii causes pneumonia in people with AIDS. Some students may wonder if it ever causes pneumonia in people without AIDS. The answer is , "Yes, but it is quite rare. If a person without AIDS comes down with this type of pneumonia, that person probably has a compromised immune system."
You might ask your class if protozoan conjugation is really sexual reproduction -- or if it is really reproduction at all. Of course, this is a matter of semantics, but it should get the students thinking about what really is meant by reproduction.
- II.B. As stated, the protozoan phyla are still in a state of flux.
- II.B.1. The Sarcomastigophora used to be classified as two distinct phyla, Mastigophora and Sarcodina. These are now considered to be subphyla or the phylum Sarcomastigophora.
- II.B.5. You might ask your students why "whirling disease" would be a problem.
- II.B.7. The Ciliophora look like spaghetti balls when viewed with a scanning electron microscope. Also, the only ciliated protozoan pathogenic to humans is Balantidium coli. It causes balantidiasis, a dysentery-type disease rare except in the Philippines. It is transmitted by cysts in the fecal matter.
- II.C. This section is especially interesting. Lewis does a very nice job of explaining these diseases, especially malaria (Biology in Action 23.1). Your students might be interested in researching some of these diseases for regular or extra credit.
- III. The last sentence in this section is important because some of your students will have learned that the brown and red algae should be classified as plants. We may never have total agreement on this point.
- III.A. In this section is a list of criteria for classifying algae. We discussed pigments briefly back in Chapter 8. Notice that they appear again here. Some of your students will need to be reminded about what pigments are.
Notice the flagella in Figure 23.7. Some of your students will have difficulty relating movement to photosynthetic organisms. There may be a mind-set problem with how movement relates to being a forerunner of "real" plants.
- III.B. Algal blooms are mentioned in several places. Algal blooms can actually occur with any type of algae, though the ones mentioned in the text are certainly the most interesting!
To demonstrate the problems connected with algal blooms, draw this hypothetical body of water:
Now put a fish and some plants in the water. Sketch some algae growing on the top. If your class is good at thinking things through, ask what is happening. Draw out of them that as the surface algae grow, oxygen below the surface is going to decrease because of diffusion and also because the surface algae will decrease the amount of sunlight available to the plants below the surface. The fish will die or move away. Since the sub-surface plants cannot grow, they will die. The bottom layers of algae from the bloom will also die. The decaying material will cause a shift in the microbial population from aerobic to anaerobic. And the story continues.
- III.B.1. The last sentence in this section about Volvox possibly being the bridge between the unicellular and multicellular way of life is important. Ask the class what types of specialization Volvox has had to demonstrate for such a statement to be made.
- III.B.4. The term Pyrrhophyta means "fire plant" or "fire algae." Although the Pyrrhophyta cause the "red tides", they should not be confused with the red algae.
Red tides can occur very quickly. Some Biblical scholars believe that when Moses turned the water to blood, the blood was actually a red tide of Pyrrophyta.
- III.B.5. The world of diatoms is indeed fascinating. Be sure to compose at least an oral list of all the uses of diatoms in the world today. If you have time, assign a student to report on reproduction in diatoms. This information can be found in any microbiology book.
- III.B.6. Some of these giant kelps -- brown algae -- have been known to kill swimmers because the swimmers become entangled in them.
- III.B.7. Make at least an oral list of the uses of the Rhodophyta. This is where you can really prove to the students that they all have indeed eaten algae!
Note that agar is listed in this section. I discussed the history of agar in the Chapter 22 of this Instructor's Manual.
- IV. It is good to say that the chytrids, water molds, and slime molds are classified more by what they are not than by what they are. This is a good opportunity for you to tell the class that changes in this classification system may be in the offing here as more and more is discovered about what these organisms are (instead of what they aren't).
- IV.C. One interesting point about the acellular slime molds is their synchronous mitosis. All the nuclei in a given "glob" of Physarum go through mitosis simultaneously, and at predictable intervals. If you have some Physarum with a 6 hour life cycle and some more Physarum with a 12 hour life cycle and you mix the two together, the resultant mass will have a 9 hour life cycle. So far no one has been able to figure out exactly what happens.
