I recommend a good generalized sexual life cycle. The one below can be used for any sexually reproducing organism from a pine tree to a human or a mushroom, or anything in between. Notice that a time frame is not included. Thus, you can augment the cycle to meet any situation from zygotic meiosis to long term seed dormancy.
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.
This chapter lends itself well to the student-generated annotated outline. The information is straight forward and easily assimilated. You can require such an outline to be handed in before you begin discussing the topics in class. This will allow you to concentrate on the overriding concepts without dwelling on material already known to the students.
Your real areas of concern will be the specific sexual variations between the three groups of organisms mentioned. Concentrate on those points.
Determine in advance how much emphasis you are going to put on the various aspects of "alternation of generations." Some of your students will see this immediately; some will have a great deal of difficulty with the concepts. Part of the problem is that many believe that a full-grown, adult organism must necessarily be a diploid. It really shatters their belief system that something like a moss could be a haploid individual.
If you are going to spend time with the alternation of generations concept, work from Figures 28.3, 28.4, and 28.5. Understand these figures thoroughly yourself. Have a good feel for the relative sizes of the different stages of the plants involved. Ask your class for examples they may be familiar with. Many will have seen the moss sporophyte and probably everyone will be familiar with the pine cone. Quite a few of your students will know something about ferns. Ask if any of them have seen the tiny gametophyte. Keep in mind that the sizes and shapes of many of the structures shown are species specific.
The most important thing you can do with this chapter is stress commonalities. Start with a the commonality of sexual function. Then show how each process is merely an adaptive variation on that commonality.
- II. Students often do not realize the many dimensions of asexual reproduction. I suggest you use class input to generate a list. Include new plants from roots, stems, and leaves. Also include ideas generated from Biology in Action 28.1. Ask if grafting is asexual reproduction. (The answer will depend on the definition and is, therefore, often a matter of semantics.)
- IV. Another point students often do not realize is that a pollen grain (as in the annual pollen counts and sneeze factors) is actually a microspore (gymnosperm or angiosperm).
- V.A. Most of your students will have had the parts of the flower at some time in their academic careers. If you are going to spend time with the flower, bring in a complete flower and pull it apart to demonstrate the different anatomical components. Use a projector so everyone can see.
- V.C. Students are generally fascinated by the methods of pollination. With a good general botany book you can augment the pollination methods listed in the text. Stress the concepts of coevolution and the intricacies of ecological balance.
- V.H. Students are also usually fascinated by the methods of fruit and seed dispersal.
- V.J. The last paragraph in this section begins, "A plant produces its first chloroplasts and begins photosynthesizing...." This may be confusing for some of the students who may have a knowledge of the endosymbiont theory. Chloroplasts develop from plastids. Either the proplastid or the chloroplast itself is present from the beginning in all plant cells. In some instances, this organelle is well developed and capable of photosynthesis as is; in other cases, further development of the plastid is necessary. This differentiation may include further development of the grana. The exact requirements are species specific.
