1. (a) Excitation of isolated chlorophyll molecule (b) Fluorescence
Fig
Excited
state e–
Heat
Energy of electron
Photon
(fluorescence)
Photon
Figure Excitation of isolated chlorophyll by light
Ground
state
Chlorophyll
molecule
(a) Excitation of isolated chlorophyll molecule
(b) Fluorescence

2. (INTERIOR OF THYLAKOID)
Fig
Photosystem
STROMA
Photon
Primary
electron
acceptor
Light-harvesting
complexes
Reaction-center
complex e–
Thylakoid membrane
Figure How a photosystem harvests light
Pigment
molecules
Transfer
of energy
Special pair of
chlorophyll a
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)

3. Linear Electron Flow
During the light reactions, there are two possible routes for electron flow: cyclic and linear
Linear electron flow, the primary pathway, involves both photosystems and produces ATP and NADPH using light energy
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4. Electron transport chain
Fig
Electron
transport
chain
Primary
acceptor
Primary
acceptor 4 7
Electron transport chain Fd Pq e– 2 e– 8 e–
H2O e–
NADP+
+ H+
Cytochrome
complex
2 H+
NADP+
reductase + 3
1/2 O2
NADPH Pc e– e–
P700 5
P680
Light 1
Light 6 6
ATP
Figure How linear electron flow during the light reactions generates ATP and NADPH
Pigment
molecules
Photosystem I
(PS I)
Photosystem II
(PS II)

5. ATP NADPH Mill makes ATP Photosystem II Photosystem I e– e– e– e– e–
Fig e–
ATP e– e–
NADPH e– e– e–
Mill
makes
ATP
Photon
Figure A mechanical analogy for the light reactions e–
Photon
Photosystem II
Photosystem I

6. H+ Diffusion Electron transport chain ADP + P
Fig
Mitochondrion
Chloroplast
MITOCHONDRION
STRUCTURE
CHLOROPLAST
STRUCTURE H+
Diffusion
Intermembrane
space
Thylakoid
space
Electron
transport
chain
Inner
membrane
Thylakoid
membrane
Figure Comparison of chemiosmosis in mitochondria and chloroplasts
ATP
synthase
Matrix
Stroma
Key
ADP + P i
ATP
Higher [H+] H+
Lower [H+]

7. Fig. 10-17 STROMA (low H+ concentration) Cytochrome complex
Photosystem II
Photosystem I
4 H+
Light
NADP+
reductase
Light Fd 3
NADP+ + H+ Pq
NADPH e– Pc e– 2
H2O 1
1/2 O2
THYLAKOID SPACE
(high H+ concentration)
+2 H+
4 H+ To
Calvin
Cycle
Figure The light reactions and chemiosmosis: the organization of the thylakoid membrane
Thylakoid
membrane
ATP
synthase
STROMA
(low H+ concentration)
ADP +
ATP P i H+

8. Concept 10.3: The Calvin cycle uses ATP and NADPH to convert CO2 to sugar
The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle
The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9. Figure 10.18 The Calvin cycle
Input 3
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco 3 P P
Short-lived
intermediate 3 P P 6 P
Ribulose bisphosphate
(RuBP)
3-Phosphoglycerate 6
ATP
6 ADP
3 ADP
Calvin
Cycle 6 3 P P
ATP
1,3-Bisphosphoglycerate 6
NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+ 6 P i
Figure The Calvin cycle 5 P
G3P 6 P
Glyceraldehyde-3-phosphate
(G3P)
Phase 2:
Reduction 1 P
Glucose and
other organic
compounds
Output
G3P
(a sugar)

10. The closing of stomata reduces access to CO2 and causes O2 to build up
Concept 10.4: Alternative mechanisms of carbon fixation have evolved in hot, arid climates
Dehydration is a problem for plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis
On hot, dry days, plants close stomata, which conserves H2O but also limits photosynthesis
The closing of stomata reduces access to CO2 and causes O2 to build up
These conditions favor a seemingly wasteful process called photorespiration
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11. Photorespiration: An Evolutionary Relic?
In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound
In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle
Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

12. C4 Plants
C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells
This step requires the enzyme PEP carboxylase
PEP carboxylase has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low
These four-carbon compounds are exported to bundle-sheath cells, where they release CO2 that is then used in the Calvin cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

13. CAM Plants
Some plants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon
CAM plants open their stomata at night, incorporating CO2 into organic acids
Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

14. (a) Spatial separation of steps (b) Temporal separation of steps
Fig
Sugarcane
Pineapple C4
CAM
CO2
CO2
Mesophyll
cell 1
CO2 incorporated
into four-carbon
organic acids
(carbon fixation)
Night
Organic acid
Organic acid
Figure C4 and CAM photosynthesis compared
Bundle-
sheath
cell
CO2
CO2
Day 2
Organic acids
release CO2 to
Calvin cycle
Calvin
Cycle
Calvin
Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps

15. You should now be able to:
Describe the structure of a chloroplast
Describe the relationship between an action spectrum and an absorption spectrum
Trace the movement of electrons in linear electron flow
Trace the movement of electrons in cyclic electron flow
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

16. Describe the role of ATP and NADPH in the Calvin cycle
Describe the similarities and differences between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts
Describe the role of ATP and NADPH in the Calvin cycle
Describe the major consequences of photorespiration
Describe two important photosynthetic adaptations that minimize photorespiration
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings