Lewis/Life - Teaching Techniques

Chapter 29 - Teaching Techniques

A. General Tips
This will be an interesting chapter for your students. Most of them will like it because they have never really thought about the defined actions and reactions of plants.
There are numerous topics in this chapter that could be assigned for outside research. Also, numerous scientists whose work could be studied are mentioned. Encourage your students to look into some of these outside areas.
Any of the extra topics in this chapter could be assigned for required or extra credit work.
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
If you plan ahead, there are a number of very simple experiments you can do to enhance this chapter. Several such experiments involve radish seeds. These in-class experiments can be especially valuable if your class does not have a corresponding lab. Radish experiments are good because these hardy plants will grow in paper towels for extended periods of time. Also, if you do not have some type of projector, you can pass the radish packages around the room and the plants do survive handling by numerous student.
-- Start this experiment several class periods before your discussion on this chapter. Prepare several packages by taking some radish seeds and wrapping them in dark paper towels. Wet thoroughly and keep the packages moist. Keep some of the packages in the dark and some in the light. After two or three days, open a "dark" package and a "light" package. Note any differences.
-- After another two days, open a "dark" package and allow it to continue germination in the light. Note any color changes over the next few days. -- Allow a "light" package to begin leaf development and then put it in total darkness.
-- Open a package and put a shield completely over half of it. Allow that half access to normal background light. Off to the side of the other half, however, put a bright light source. Keep this light source on for extended periods of time.
-- Allow certain plants to begin to develop. After a few days of growth, turn them upside down.
-- If you have access to any plant hormones, design some simple experiments to observe the hormonal action.
-- Design a few more mini-experiments that can be used in your lecture room.
C. Hints Related to Specific Chapter Topics
- II-IV. Show how section two relates to sections three and four. Compare and contrast sections three and four.
  Note in Table 29.2 that there are more tropisms and nastic movements listed than are explain in the text. Point out that "-tropism" and "-nasty" could be applied to numerous other specific responses too.
- II.D. Lewis brings out the chemical reason why "one bad apple spoils the whole batch." Ask the class why this is an energy efficient move in leaf ripening.
  Another interesting point is that in the absence of ripe fruit (or ethylene), unripe fruit can be ripened by burning a kerosene lamp nearby. You might ask why that is.
- IV. If you have a sense of humor, you could make a few jokes about "nasty movements" --just to help students remember the term.
- V.A & B. Most students find this information quite interesting and most have never heard it before. Sometimes a question about the length of time of the flash of light. As might seem logical, the critical time for the flash of light varies with the plant species; some species are more sensitive than others. The important thing is the uninterrupted period of darkness.
- VI.B. Students are often surprised to learn that the temperature of some seeds must drop below a certain level before dormancy can be broken. "Protecting plants from the cold" seems to be a mind-set of many.
  You might also mention that fire is required for certain seeds to break dormancy. How does this relate to the mind-set that all forest fires are bad?