Lewis/Life - Teaching Techniques

Chapter 8 - Teaching Techniques

A. General Tips
One of the biggest problems we face in teaching photosynthesis is that students often do not quite make the connection between this process and "real" carbohydrates such as table sugar and corn starch. How can a gas and some water give you a solid? We, as educators, have already made the leap of faith; our students have not.
There is a lot of good history connected with photosynthesis, and thus many opportunities to explore what people used to think and how the scientific method helped us arrive at our present knowledge of this subject. In addition to the names mentioned in text, some other historical names worth exploring include:
- Jean Senebier who in 1782 identified the gas produced by animals and night plants as CO2.
- N. T. de Saussure who in 1804 showed the uptake of water in photosynthesis.
- Julius Sachs who in 1864 demonstrated that organic matter was a product of photosynthesis.
- C. B. van Niel who in the 1930's discovered the similarities between photosynthesis in plants and photosynthesis in certain bacteria.
- Samuel Ruben and Martin Kamen who in 1941 showed that oxygen came from the splitting of the water.
- Daniel Amon who in 1954 discovered the conversion of ADP and Pi to ATP.
This led to the discovery of photophosphorylation and subsequently to the discovery of the light-dependent and light-independent reactions.
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
In the General Tips I posed the question: How can a gas and some water give you a solid? This would be a good question to ask your class as you begin to teach photosynthesis. Or, another question: What would happen if you set a bucket of water in direct sunlight and then bubbled pure carbon dioxide through it?
The Mastering Concepts questions in this chapter are especially good for students who are having trouble with the different components of photosynthesis. You might consider assigning these (or similar) questions for the students to complete before you lecture on the topic. Your lecture will then become both a method of pulling it all together and an opportunity for the students to ask questions about specific points of confusion.
Table 8.3 is excellent for comparing the different types of photosynthesis. Consider adding this question to the bottom of each column: Where would you find a plant using this type of photosynthesis and why is this type of photosynthesis the most efficient for this plant's particular circumstances?
Table 8.4 is a good summary of the factors controlling photosynthesis.
C. Hints Related to Specific Chapter Topics
- I.A. Reiterate that glucose is a storage molecule in ALL organisms. (Ask why plants make carbohydrates. We humans are secondary; plants make their products for themselves.)
  Stress that the oxygen generated in photosynthesis comes from the splitting of the water and that the water generated in photosynthesis is new water.
- I.B. Some of your students may have learned that heterotrophs "take in" food. We are heterotrophs, as were the first organisms. Students may have also learned that autotrophs make their own food. That is exactly what plants do.
  Biology in Action 8.1 affords an excellent opportunity to examine both the history of an idea and the scientific method in action. As stated, van Helmont concluded the increase in plant matter was due to the plentiful water. He also concluded he had made an error in measurement. In addition, van Helmont (1577-1644) demonstrated that plants do not have the same nutritional needs as animals.
  As another sidelight on this section, note that the percentage of oxygen in the atmosphere has been fluctuating for many millions of years.
- II.B. It is called ultraviolet because its wavelengths are shorter than the low (violet) end of the visible light spectrum. Infrared is beyond the longer (red) end of the visible spectrum. The infrared explanation on page 148 is very nicely done.
- III.A. Chorophyll is really a family of pigments. Notice, for instance, that chlorophyll a is mentioned on page 149 and chlorophyll b is included in the Table on page 150. Chlorophylls c, d, and e are not mentioned.
- III.B. Logically, the accessory pigments vary with the plant, as well as with the season.
- IV. On page 151 we have an interesting "potential error." Note the word stroma as explained in connection with the chloroplast. Note in Figure 8.6 the word stoma. Stoma is defined on page 159. Take a moment and point out how similar -- yet how different -- these two words are.
- V. In other words, the light-dependent reactions produce the energy for the light-independent reactions. Table 8.2 gives an excellent summary of the basic requirements for the light-dependent reactions. In some ways, the light-dependent reactions could be called "Photosynthesis, part I."
- V.A. Recall the functions of the photosystems. Note, too, the reference to oxidative phosphorylation in mitochondria at the end of this section. This is a good time to remind the students that plants have mitochondria too.
- V.B. The last sentence on page 155 is a reiteration of the key to the whole of the light- dependent reactions -- to produce the power to drive the light-independent reactions.
- VI. The light-independent reactions could be called "Photosynthesis, Part II."
- VI.A. The Calvin Cycle is sometimes called the Calvin-Benson Cycle.
- VI.B. Note the use of the scientific method in the delineation of the Calvin Cycle. Even so, some of your students will probably have trouble with this section. Be clear in your own mind exactly what your students will be responsible for.
- VII. You might consider asking the students about the significance of the numbers listed in this section. The numbers and the percentages can actually be quite mind-boggling.
- VII.A. As you begin this topic, some of the students will have forgotten the meaning of C3. Recall PGA. You might ask how photorespiration and photosynthesis are alike and how they are different.
- VIII. Recall negative feedback controls. The same principles apply.