1. Where It Starts – Photosynthesis
Chapter 6
Where It Starts – Photosynthesis

2. Autotrophs = self feeders
Figure 7.1
Autotrophs = self feeders
PHOTOSYNTHETIC AUTOTROPHS
Plants
(mostly on land)
Photosynthetic Protists
(aquatic)
Photosynthetic Bacteria
(aquatic)
Figure 7.1 A diversity of photoautotrophs LM
Forest plants
Kelp, a large, multicellular alga
Micrograph of cyanobacteria
Photoautotrophs – use light energy

3. Properties of Light
Light behaves as waves and discrete packets of energy called photons, fixed quantities of light energy.
A pigment absorbs light of a specific wavelength (chlorophyll a is most common).
Figure 6.1 – Properties of light.
Figure 6-1a p100

4. Properties of Light
Chlorophyll absorbs light in the blue-purple and red-orange wavelengths, but not in the green wavelengths
Figure 7.6

5. WHAT is Photosynthesis?
The simplified equation for photosynthesis. A
chemical transformation of light energy to chemical energy.
Student Misconceptions and Concerns
1. Students often do not fully understand how the burning of fossil fuels contributes to global warming. They might wonder, “How does the burning of fossil fuels differ from the burning of ethanol produced from crops?” Students might not realize that the carbon in fossil fuels was removed from the atmosphere hundreds of millions of years ago, while the carbon in crops was removed much more recently, when the crops were grown. The use of ethanol as an alternative is complicated by the typical reliance upon fossil fuels for ethanol production.
2. Some students do not realize that plant cells also have mitochondria. Instead, they assume that the chloroplasts are sufficient for the plant cell’s needs. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria).
3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants.
4. Students may understand the overall chemical relationships between photosynthesis and cellular respiration, but many struggle to understand the use of carbon dioxide in the Calvin cycle. Photosynthesis is much more than gas exchange.
5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.)
Teaching Tips
1. When introducing the diverse ways that plants impact our lives, consider challenging your students to come up with a list of products made from plants that they encounter regularly. Perhaps you might only list those encountered in a single day of college life. The list can be surprising and help to build up your “catalog of examples.”
2. The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane, the highly branched surfaces of fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes.
3. In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis.
4. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course.
5. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where water and sunlight are used in the thylakoid membranes to generate oxygen, ATP, and NADPH. The second step, in the stroma, reveals the use of carbon dioxide, ATP, and NADPH to generate carbohydrates.
6. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters.
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6. Photosynthesis is a Redox Reaction

7. WHERE does photosynthesis occur?
Figure 4.3-2
WHERE does photosynthesis occur?
Chloroplast
Chloroplast
Figure An idealized animal cell and plant cell (part 2: plant cell)
Plant Cell
In the chloroplasts!

9. Stroma Thylakoids Grana Chlorophyll Thick fluid inside the chloroplast
Connected sacs within the chloroplast
Grana
Stacks of thylakoids
Chlorophyll
Pigment molecules that capture light energy, built into thylakoid membrane
Figure 6.4 {Animated} Zooming in on the site of photosynthesis in a plant cell. The micrograph shows chloroplasts in cells of a moss leaf.
Figure 6-4 p103

10. Photosynthesis has 2 stages:
Light-Dependent Reactions & Calvin-Benson Cycle

11. (a) Absorption of a photon
Figure 7.8-1
Excited state
The electron
falls to its
ground state.
Absorption of a
photon excites
an electron. e
Heat
Light
Light
(fluorescence)
Figure Excited electrons in pigments (part 1: absorption)
Photon
Ground
state
Chlorophyll
molecule
(a) Absorption of a photon

12. Photosystem: group of chlorophyll, accessory pigments, and other molecules

13. Electron Transport Chain
Provides energy for ATP synthesis

14. TWO Photosystems (II and I)

15. Summary of Light-Dependent Reactions
Products = O2 (waste); ATP & NADPH (to C-B cycle)

16. Photosynthesis has 2 stages:
Light-Dependent Reactions & Calvin-Benson Cycle

17. Calvin-Benson Cycle Product = Sugar
Figure 6.8 {Animated} The Calvin–Benson cycle. This sketch shows a cross-section of a chloroplast with the reactions cycling in the stroma. The steps shown are a summary of six cycles of reactions (see Appendix III for details). Black balls are carbon atoms.
1Six CO2 diffuse into a photosynthetic cell, and then into a chloroplast. Rubisco attaches each to a RuBP molecule. The resulting intermediates split, so twelve molecules of PGA form.
2Each PGA molecule gets a phosphate group from ATP, plus hydrogen and electrons from NADPH. Twelve PGAL form.
3Two PGAL may combine to form one six-carbon sugar (such as glucose).
4The remaining ten PGAL receive phosphate groups from ATP. The transfer primes them for endergonic reactions that regenerate the 6 RuBP.
Figure 6-8 p106

18. BioFlix Animation: Photosynthesis
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