1. Overview: The Process That Feeds the Biosphere
Photosynthesis is the process that converts solar energy into chemical energy
Directly or indirectly, photosynthesis nourishes almost the entire living world

2. Autotrophs
Autotrophs sustain themselves without eating anything derived from other organisms
Autotrophs are the producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules
Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules from H2O and CO2

3. Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes
(a) Plants
Figure 10.2 Photoautotrophs
(c) Unicellular protist
10 µm
(e) Purple sulfur
bacteria
1.5 µm
(b) Multicellular alga
(d) Cyanobacteria
40 µm

4. Heterotrophs
Heterotrophs obtain their organic material from other organisms
Heterotrophs are the consumers of the biosphere
Almost all heterotrophs, including humans, depend on photoautotrophs for food and O2

5. The Two Stages of Photosynthesis: A Preview
Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)
The “light” reactions are in the thylakoids
The Calvin cycle is in the stroma

6. Chloroplast Outer membrane Thylakoid Intermembrane space Stroma Granum
Inner
membrane
Figure 10.3 Zooming in on the location of photosynthesis in a plant
1 µm

7. The “light” reactions overview
Capture light energy using chlorophyll
Split H2O to electrons, protons and oxygen
Release O2
Reduce NADP+ to NADPH
Generate ATP from ADP by photophosphorylation

8. The Calvin cycle overview
begins with carbon fixation, incorporating CO2 into organic molecules
- forms sugars from these organic molecules, using ATP and NADPH (from light reactions)

9. Overview of Photosynthesis 1
Light
NADP+
ADP + P i
Light
Reactions
Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
Chloroplast
Overview of Photosynthesis 1

10. Overview of Photosynthesis 2
Light
NADP+
ADP + P i
Light
Reactions
ATP
Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
NADPH
Chloroplast
Overview of Photosynthesis 2 O2

11. Overview of Photosynthesis 3
CO2
Light
NADP+
ADP + P i
Calvin
Cycle
Light
Reactions
ATP
Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
NADPH
Chloroplast
Overview of Photosynthesis 3 O2

12. Overview of Photosynthesis 4
CO2
Light
NADP+
ADP + P i
Calvin
Cycle
Light
Reactions
ATP
Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
NADPH
Chloroplast
Overview of Photosynthesis 4
[CH2O]
(sugar) O2

13. Chlorophyll is the light-capturing substance
Surrounded by other pigment molecules, enzymes and electron carriers
A “photosystem”
Anchored to thylakoid membranes by proteins

14. Illustration of important properties of chlorophyll
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
If illuminated, a solution of chlorophyll will fluoresce, giving off light and heat

15. (INTERIOR OF THYLAKOID)
Photosynthetic
Energy
Capture
Photosystem
STROMA
Photon
Primary
electron
acceptor
Light-harvesting
complexes
Reaction-center
complex e–
Thylakoid membrane
Figure How a photosystem harvests light
Pigments-chlorophyll
and accessory
Transfer
of energy
Special pair of
chlorophyll a
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)

16. Electron transport chain
“Z-Diagram” of photosynthesis
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)
This illustrates “non-cyclic” electron flow- electrons enter with water and leave with NADPH

17. Primary
acceptor
Primary
acceptor Fd Fd
NADP+
+ H+ Pq
NADP+
reductase
Cytochrome
complex
NADPH Pc
Figure Cyclic electron flow
Photosystem I
Photosystem II
ATP
Cyclic electron flow uses only photosystem I and produces ATP, but not NADPH

18. “Light” reactions of PSI and PSII generate ATP and “reducing power” in the form of NADPH
Reducing power allows the conversion of carbon dioxide to carbohydrate
CO2 to CH2O requires NADPH reducing power

19. Carbon fixation conversion of carbon dioxide to carbohydrate
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
Calvin
Cycle
3 ADP 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
Rubisco is the key enzyme of the cycle
Glyceraldehyde-3-phosphate
(G3P)
Phase 2:
Reduction
Plants that use this cycle exclusively are C3 plants 1 P
Glucose and
other organic
compounds
Output
G3P
(a sugar)

20. Dehydration is a problem for plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis
Plants have evolved two alternate types of carbon fixation
C4 and Crassulean Acid Metabolism (CAM) fixation

21. Electron transport chain C3 Photosynthesis: a review
CO2
Light
NADP+
ADP + P i
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
RuBP
3-Phosphoglycerate
Calvin
Cycle
ATP
G3P
Figure A review of photosynthesis
Starch
(storage)
NADPH
Chloroplast
C3 Photosynthesis: a review O2
Sucrose (export)