1. AN OVERVIEW OF PHOTOSYNTHESIS
Copyright © 2009 Pearson Education, Inc.

2. Light energy Glucose Oxygen gas Photosynthesis6
CO2
+ 6
H2O
C6H12O6
+ 6 O2
Carbon dioxide
Water
Glucose
Oxygen gas
Photosynthesis

3. Photosynthesis
Chloroplasts are the major sites of photosynthesis in green plants
Chlorophyll, light absorbing pigment in chloroplasts, is responsible for the green color of plants
absorbs all colors of the visible spectrum except green and yellow
Chlorophyll absorbs light energy and drives the synthesis of organic molecules.
Teaching Tips
1. The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters.
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 to the extensive folding of the thylakoid membranes.
Copyright © 2009 Pearson Education, Inc.

4. Light Reflected light Chloroplast Absorbed light Thylakoid Transmitted
Figure 7.6B The interaction of light with a chloroplast.
Chloroplast
Absorbed
light
Thylakoid
Transmitted
light

5. Photosynthesis continued…
stomata are tiny pores in the leaf that allow carbon dioxide to enter and oxygen to exit
stroma- the dense fluid within the chloroplast
thylakoids- a system of interconnected membranous sacs that separate the stroma from another compartment, the thylakoid space
Grana- thylakoids are concentrated in stacks called
Chlorophyll resides in the thylakoid membranes.
Teaching Tips
1. The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters.
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 to the extensive folding of the thylakoid membranes.
Copyright © 2009 Pearson Education, Inc.

6. Leaf Cross Section Leaf Mesophyll Vein Stoma CO2 O2 Mesophyll Cell
Figure 7.2 The location and structure of chloroplasts.
Chloroplast

7. Chloroplast Outer and inner membranes Thylakoid Intermembrane space
Stroma
Granum
Thylakoid
space
Figure 7.2 The location and structure of chloroplasts.

8. Figure 7.3A Oxygen bubbles on the leaves of an aquatic plant.

9. Photosynthesis Equation:
6CO2 + 6H2O = C6H12O6 + 6O2
oxygen
carbon dioxide
sugar (glucose)
water
Reactants
“what is used”
Products
“what is made”

10. Reactants: 6 CO2 12 H2O Products: C6H12O6 6 H2O 6 O2
Figure 7.3C Fates of all the atoms in photosynthesis.

11. Light-Dependent Reaction Light-Independent Reaction (Calvin Cycle)
Photosynthesis
Light-Dependent Reaction
Light-Independent Reaction (Calvin Cycle)
- sunlight is required
O2 is produced from water
e- (light energy) fuel the reactions
-sunlight is NOT required
Glucose is produced from CO2

12. 7.4 Photosynthesis
Photosynthesis, like respiration is an oxidation-reduction process
Water molecules are split apart by oxidation, which means that they lose electrons along with hydrogen ions (H+)
Then CO2 is reduced to sugar as electrons and hydrogen ions are added to it
The simple sugar produced in photosynthesis is glucose, using a number of energy-releasing redox reactions.
Teaching Tips
1. 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.
Copyright © 2009 Pearson Education, Inc.

13. Reduction 6 CO2 + 6 H2O C6H12O6 + 6 O2 Oxidation
Figure 7.4A Photosynthesis (uses light energy).

14. 7.4 Photosynthesis continued…
In photosynthesis, electrons gain energy by being boosted up an energy hill
light energy is converted to chemical energy, which is stored in the chemical bonds of sugar molecules
The sugar produced in photosynthesis is stored for later use or as raw material for biosynthesis of new plant material.
Teaching Tips
1. 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.
Copyright © 2009 Pearson Education, Inc.

15. The two stages of photosynthesis
Photosynthesis occurs in two stages:
Stage 1: Light reactions
In the light reactions
light energy is converted in the thylakoid membranes to chemical energy and O2
Water is split to provide the O2 as well as electrons
The two metabolic stages are the light reactions and the Calvin cycle.
Student Misconceptions and Concerns
1. 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.
Teaching Tips
1. 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.
2. Figure 7.5 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure demonstrates 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.
Copyright © 2009 Pearson Education, Inc.

16. Photosystems capture solar power
Light behaves as discrete packets of energy called photons
Chlorophyll absorbs light, causing the release of electrons
The electrons jump to a higher energy level—the excited state—where electrons are unstable
The electrons drop back down to their “ground state,” and, as they do, release their excess energy
Student Misconceptions and Concerns
1. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths.
Teaching Tips
1. The authors discuss a phenomenon that most students have noticed: dark surfaces heat up faster in the sun than do lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat.
Copyright © 2009 Pearson Education, Inc.

17. Electron transport chain
Chloroplast
Stroma (low H+
concentration) H+
Light
Light H+
ADP + P
ATP H+
NADP+ + H+
NADPH H+
Thylakoid
membrane
Figure 7.9 The production of ATP by chemiosmosis in photosynthesis: The small diagram on the upper left illustrates the location of the components of the light reactions in a thylakoid membrane. Numerous copies of these components are present in each thylakoid.
H2O H+ H+ 1  2 O2
+ 2 H+ H+ H+ H+ H+ H+ H+
Photosystem II
Electron
transport
chain
Photosystem I H+
ATP synthase H+
Thylakoid space
(high H+ concentration)

18. Light Reactions continued…
An electron transport chain exists in the thylakoid membrane
The splitting of water molecules creates a concentration gradient of H+ ions in the thylakoid
Chemiosmosis occurs and generates ATP in chloroplasts
ATP synthase-enzyme used to produce ATP from ADP and phosphate as H+ ions move
The gradient is produced as the electron transport chain passes electrons down the chain.
Teaching Tips
1. Module 7.9 notes the similarities between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts. If your students have not already read or discussed chemiosmosis in mitochondria, consider assigning Modules 6.6 and 6.10 to show the similarities of these processes. (As noted in Module 7.2, the thylakoid space is analogous to the intermembrane space of mitochondria.)
Copyright © 2009 Pearson Education, Inc.

19. Light reactions continued….
As a result ATP and NADPH are generated
oxygen gas is released
Where did this oxygen and the hydrogen come from?
Teaching Tips
1. The authors develop a mechanical analogy for the energy levels and movement of electrons in the light reaction. Figure 7.8B equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented.
Copyright © 2009 Pearson Education, Inc.

20. Dark Reactions (light-independent reactions)
Stage 2 - Calvin cycle “ light-independent reactions”
occurs in the stroma
requires the products from the light reactions to power the dark reactions
cycle of reactions that build sugar from CO2 and the products of the light reactions
CO2 is incorporated into organic compounds (helps form sugar)
called carbon fixation
The Calvin cycle was named for the Nobel laureate, Melvin Calvin, who traced the path of carbon in the cycle.
Student Misconceptions and Concerns
1. 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.
Teaching Tips
1. 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.
2. Figure 7.5 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure demonstrates 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.
Copyright © 2009 Pearson Education, Inc.

21. H2O CO2 Chloroplast Light NADP+ ADP  P LIGHT REACTIONS CALVIN CYCLE
(in stroma)
(in thylakoids)
ATP
Figure 7.5 An overview of the two stages of photosynthesis that take place in a chloroplast.
Figure 7.5 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.
Electrons
NADPH O2
Sugar

22. Electron transport chain
Provides energy for
synthesis of
by chemiosmosis
NADP+ + H+
NADPH
Photon
Photon
Photosystem II
ATP
Photosystem I 6
Stroma 1
Primary
acceptor
Primary
acceptor 2 e– e–
Thylakoid
mem-
brane 4 5
P700
P680
Figure 7.8A Electron flow in the light reactions of photosynthesis: Both photosystems and the electron transport chain that connects them are located in the thylakoid membrane. The energy from light drives electrons from water to NADPH.
Thylakoid
space 3
H2O 2  1 O2
+ 2 H+

23. The two stages of photosynthesis are linked by ATP and NADPH
Use of the light reaction products in the Cavin Cycle:
1. NADPH provides the electrons for reducing carbon
2. ATP provides chemical energy
The Calvin cycle occurs during daytime in most plants when the light reactions are powering the cycle’s sugar assembly line.
For the BioFlix Animation Photosynthesis, go to Animation and Video Files.
For the Discovery Video Trees, go to Animation and Video Files.
Student Misconceptions and Concerns
1. 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.
Teaching Tips
1. 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.
2. Figure 7.5 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure demonstrates 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.
Copyright © 2009 Pearson Education, Inc.

24. THE CALVIN CYCLE: CONVERTING CO2 TO SUGARS
Copyright © 2009 Pearson Education, Inc.

25. 7.10 ATP and NADPH power sugar synthesis in the Calvin cycle
The Calvin cycle makes sugar within a chloroplast
To produce sugar, the necessary ingredients are atmospheric CO2, ATP, and NADPH, which were generated in the light reactions
Using these three ingredients sugar is produced
The Calvin cycle is called a “cycle” because the starting material is regenerated as the process occurs.
Student Misconceptions and Concerns
1. As noted in Module 7.5, the terms light reactions and dark reactions can lead students to conclude that each set of reactions occurs at a different time of the day. However, the Calvin cycle in most plants occurs during daylight, when NADPH and ATP from the light reactions are readily available.
Teaching Tips
1. Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, G3P, as noted in the text, is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students.
Copyright © 2009 Pearson Education, Inc.

26. CO2 ATP NADPH Input CALVIN Output: G3P CYCLE
Figure 7.10A An overview of the Calvin cycle.
Output:
G3P

27. H2O CO2 Chloroplast Light NADP+ ADP + P RuBP CALVIN CYCLE Electron
Photosystem II
RuBP
CALVIN
CYCLE
Electron
transport
chains
3-PGA
(in stroma)
Thylakoid
membranes
Photosystem I
ATP
Stroma
Figure 7.11 A summary of the chemical processes of photosynthesis.
NADPH
G3P
Cellular
respiration
Cellulose
Starch O2
Sugars
Other organic
compounds
LIGHT REACTIONS
CALVIN CYCLE

28. 7.12 EVOLUTION CONNECTION: Adaptations that save water in hot, dry climates evolved in C4 and CAM plants
Some plants have evolved a means of carbon fixation that saves water during photosynthesis
One group can shut its stomata when the weather is hot and dry to conserve water but is able to make sugar by photosynthesis
These are called the C4 plants because they first fix carbon dioxide into a four-carbon compound
Teaching Tips
1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a fine substitute.
2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories.
Copyright © 2009 Pearson Education, Inc.

29. 7.12 EVOLUTION CONNECTION: Adaptations that save water in hot, dry climates evolved in C4 and CAM plants
Another adaptation to hot and dry environments has evolved in the CAM plants, such as pineapples and cacti
CAM plants conserve water by opening their stomata and admitting CO2 only at night
When CO2 enters, it is fixed into a four-carbon compound , CO2 is banked
CO2 is released to the Calvin cycle during the day
For the BLAST Animation Photosynthesis: Light-Independent Reactions, go to Animation and Video Files.
Teaching Tips
1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a fine substitute.
2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories.
Copyright © 2009 Pearson Education, Inc.

30. CALVIN CYCLE CALVIN CYCLE
Mesophyll
cell
CO2
CO2
Night
4-C compound
4-C compound
CO2
CO2
CALVIN
CYCLE
CALVIN
CYCLE
Figure 7.12 Comparison of photosynthesis in C4 and CAM plants: In both pathways, CO2 is first incorporated into a four-carbon compound, which then provides CO2 to the Calvin cycle.
Bundle-
sheath
cell
3-C sugar
3-C sugar
Day
C4 plant
CAM plant