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Chapter 10: Photosynthesis


Class Activities

Chapter 10: Photosynthesis

1. Relevance of Topic

All plant growth on the earth relies on photosynthesis to produce energy.

Plants are the major food source for animal life on the planet, and they are responsible for the conversion of carbon dioxide to oxygen.

News stories on the issue of deforestation have been prominent for several years now, and the problem is worsening. Related to this, there are concerns that if deforestation is not controlled, the greenhouse effect from carbon dioxide will worsen, affecting the entire planet and climates around the globe.

Ocean pollution is another concern, since it kills off plant life there, and these plants are the major source of oxygen for the earth's atmosphere, as well as being a major food source for ocean life.

2. Continuity

Respiration, covered in the previous chapter, is the reverse chemical reaction from photosynthesis.

An understanding of how plants convert energy and produce food for animals is critical in later chapters where plant structure and function, and studies in ecology are presented.

3. Demonstration Activities

Text section 10.1

1. Figure 10.1 takes the student from macro to micro levels, from the leaf cross section down to the organelle level and the thylakoid membrane.

2. Show a color photograph of a plant cell showing the chlorophyll in the chloroplasts.

3. Use Elodea leaves under a microscope to show cytoplasmic streaming of chloroplasts.

Text section 10.2

1. Figure 10.3 illustrates the spectrum of electromagnetic radiation, including that of visible light. This is useful in showing that plants appear green to us because they absorb in the red and blue wavelength range and reflect in the green range.

2. A discussion of microwaves used in cooking, with wavelengths from 1 mm to 1 m, can be used to present an example of electromagnetic radiation with wavelengths outside the visible range.

3. Figure 10.5 shows the absorption spectra for chlorophyll a and b and carotenoids; this is another graphical illustration of how we visualize these pigments.

4. Another demonstration of absorption spectra could be done by flame tests with solutions of sodium, strontium, potassium, lithium, copper, iron, chromium, and a host of other salts, all of which release energy in a specific range and show flames of specific colors (consult a chemistry text for guidance).

Text section 10.3

1. Figure 10.6 compares the chemical structure of chlorophyll a, beta-carotene, and retinol (the major visual pigment that absorbs light in the human eye). Coupled with this, show a carrot, sweet potato, yellow squash, or other vegetables high in beta-carotene, and talk about why these are "good for your eyes."

2. Show a color photograph of leaves changing color (in autumn) to illustrate the chlorophyll becoming inactive and revealing other pigments such as carotenoids and xanthophylls.

3. Using paper chromatography, do a demonstration on separation of pigments with a spinach leaf slurry. Let this run over the course of the class, and separation of pigment by color front should occur.

Text sections 10.5, 10.6, and 10.7

1. Figures 10.11 and 10.12 summarize the mechanism of photosystems I and II, and illustrate the path of electrons through both systems.

 

Text section 10.8

1. Figures 10.15 and 10.16 illustrate the key reaction in the Calvin cycle.

Text section 10.9

1. Figure 10.17 illustrates structural differences in the leaves of C3 and C4 plants.

2. Show color photographs of fields of C4 plants, such as corn and sugarcane, and discuss how the photosynthetic systems of these plants are well-adapted to their warm, arid environments.

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