1. Photosynthesis
BioA-ch10-106
國防醫學院 生物及解剖學科
藍心婕

2. Overview: The process that feeds the biosphere
Photosynthesis光合作用 : the process that converts solar energy into chemical energy
Plants and other autotrophs自營are the producers of the biosphere
Plants are photoautotrophs光合自營they use the energy of sunlight to make organic molecules from water and carbon dioxide
Other organisms also benefit from photosynthesis.

3. Figure 10.2
Photosynthesis occurs in plants, algae, certain other protists原生生物 and some prokaryotes原核生物
Heterotrophs異營obtain their organic material from other organisms are the consumers消費者of the biosphere
(a) Plants
(b)
Multicellular alga
Figure 10.2 Photoautotrophs.
(d) Cyanobacteria
40 m
(c)
Unicellular protists
10 m
(e)
Purple sulfur bacteria
1 m 3

4. 10.1 Photosynthesis converts light energy to the chemical energy of food
Leaf cross section
Chloroplasts
Vein
Chloroplasts葉綠體: The sites of photosynthesis in plants
The leaves of plants are the major sites of photosynthesis
Chloroplasts are the organelles in which photosynthesis occurs, contain thylakoids類囊體and grana葉綠層
Mesophyll
Stomata
CO2 O2
Chloroplast
Mesophyll
cell
Outer
membrane
Thylakoid
Intermembrane
space
Thylakoid
space
Stroma
Granum
20 μm
Inner
membrane
1 μm

5. i. Intermembrane space ii. Thylakoid space iii. stroma(基質)
Chloroplasts are divided into three functional compartments by a system of membranes:
Outer membrane
Intermembrane space
Inner membrane
1 m
Thylakoid space
Thylakoid
Granum
Stroma
Chloroplast
i. Intermembrane space
ii. Thylakoid space
iii. stroma(基質)

6. Tracking atoms through photosynthesis: Scientific inquiry
Photosynthesis is summarized as:
6 CO H2O+ Light —> C2H12O6 + 6O2 + 6 H2O
energy
The splitting of water: Chloroplasts split water into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules
Photosynthesis as a redox process: Water is oxidized, carbon dioxide is reduced
Reactants:
Products:
6 CO2
6 H2O
6 O2
12 H2O
C6H12O6

7. The two stages of photosynthesis: A preview
Photosynthesis consists of two processes: light reactions光反應and the Calvin cycle卡爾文循環
The light reactions: occur in the grana, split water, release oxygen, produce ATP, and form NADPH. The light reactions power the addition of a phosphate group to ADP in a process called photophosphorylation光合磷酸化
The Calvin cycle: occurs in the stroma forms sugar from carbon dioxide, using ATP for energy and NADPH for reducing power
Light
Thylakoid
Stroma
Chloroplast
LIGHT
REACTIONS
NADP+
ADP
P i +
H2O
[CH2O]
(sugar)
CALVIN
CYCLE
CO2
NADPH
ATP O2

8. 10.2: The light reactions convert solar energy太陽能 to the
chemical energy of ATP and NADPH
The Nature of Sunlight
Light: a form of electromagnetic energy電磁能, which travels in waves波
Wavelength: is the distance between the crests of waves and determines the type of electromagnetic energy
Electromagnetic spectrum 電磁光譜: the entire range of electromagnetic energy, or radiation輻射
Visible light spectrum可見光譜: includes the colors of light we can see and includes the wavelengths that drive photosynthesis
Visible light
Gamma
rays
X-rays UV
Infrared
Micro-
waves
Radio
380
450
500
550
600
650
700
750 nm
Shorter wavelength
Higher energy
Lower energy
Longer wavelength
10− 5 3
1 nm 10 6 9
(10
nm)
1 m m

9. Photosynthetic pigments色素: The light receptors受體 or 受器
Pigments: are substances that absorb visible light, reflect light, which include the colors we see
Chloroplast
Light
Reflected light
Absorbed light
Transmitted light
Granum

10. Determining of an absorption spectrum
Spectrophotometer光電比色計: is a machine that sends light through pigments and measures the fraction of light transmitted at each wavelength
White
light
Refracting
prism
Chlorophyll
solution
Photoelectric
tube
Galvanometer
Slit moves to pass light
of selected wavelength.
Green
Blue 1 2 3 4

11. Chloro- phyll a
Chlorophyll b
Carotenoids
Wavelength of light (nm)
Absorption of light by chloroplast pigments
Rate of photosynthesis (measured by O2 release)
Aerobic bacteria
Filament of alga
400
500
600
700
1. Absorption spectrum吸收光譜: is a graph plotting light absorption versus wavelength
2. The absorption spectra of chloroplast pigments provide clues to the relative effectiveness of different wavelengths for driving photosynthesis
3. The action spectrum 作用光譜: is a pigment profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesis
4. The action spectrum for photosynthesis was first demonstrated by Theodor W. Engelmann
Which wavelengths of light are most effective in driving photosynthesis?

12. The absorption spectra of three types of pigments in chloroplasts
Chlorophyll a: the main photosynthetic pigment
Chlorophyll b: is an accessory pigment
Other accessory pigments: absorb different wavelengths of light and pass the energy to chlorophyll a, ex. Carotenoids類葫蘿蔔素 have phtotprotection function

13. Excitation 激發of chlorophyll by light
When a pigment absorbs light it goes from a ground state 基態to an excited state激態, which is unstable
If an isolated solution of chlorophyll is illuminated it will fluoresce發螢光, giving off light and heat
Excited state
Heat e
Photon (fluorescence)
Ground state
Photon
Chlorophyll molecule
Energy of electron
(a) Excitation of isolated chlorophyll molecule
(b) Fluorescence

14. A Photosystem光系統: A reaction Center complex作用中心複合體associated with light-harvesting complexes
A photosystem is composed of a reaction-center complex surrounded by a number of light-harvesting complexes.
The light-harvesting complexes consist of pigment molecules bound to particular proteins and funnel the energy of photons光子 of light to the reaction center
When a reaction-center chlorophyll molecule absorbs energy one of its electrons gets bumped up to a primary electron acceptor

15. (b) Structure of photosystem II
Thylakoid membrane
Chlorophyll
STROMA
Protein subunits
THYLAKOID SPACE

16. There are two types of photosystems in the thylakoid membrane
Photosystem II (PS II) functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of 680 nm (so called P680)
Photosystem I (PS I) is best at absorbing a wavelength of 700 nm (so called P700)

17. A. Linear Electron Flow 線性電子流
The thylakoid membrane is populated by two types of photosystems I (PSI-p700) and II (PS II -p680)
A. Linear Electron Flow 線性電子流
Cytochrome complex
Primary acceptor
H2O O2
2 H +
1/2
P680
Light
Pigment molecules
Photosystem II (PS II)
Photosystem I (PS I) Pq Pc
ATP 1 2 3 5 6 7 8
Electron transport chain
Electron transport chain
P700
+ H
NADP
NADPH
NADP reductase Fd e 4
Pq: plastoquinone
Pc: plastocyanin
Fd: ferredoxin

18. Linear Electron Flow
Noncyclic electron flow: the primary pathway of energy transformation in the light reactions produces NADPH, ATP, and oxygen.
A mechanical analogy for the light reactions

19. Cyclic Electron Flow循環電子流
Under certain conditions, photoexcited electrons take an alternative path
In cyclic electron flow only photosystem I is used, only ATP is produced
Primary
acceptor Fd
Cytochrome
complex Pc Pq
Photosystem II
Photosystem I
NADP+
+ H+
reductase
NADPH
ATP
Summary of light reactions:
During noncyclic electron flow, the photosystems of the thylakoid membrane
transform light energy to the chemical energy stored in NADPH and ATP.
2. During cyclic electron flow, electrons ejected from P700 reach ferredoxin and
flow back to P700, Produces ATP but doesn’t produce NADPH or O2.

20. Electron transport chain
Comparison of chemiosmosis in chloroplasts and mitochondria
Mitochondrion
Chloroplast
MITOCHONDRION STRUCTURE
CHLOROPLAST STRUCTURE
Intermembrane space
Inner membrane
Matrix
Thylakoid space
Thylakoid membrane
Stroma
Electron transport chain H
Diffusion
ATP synthase
ADP  P i
Key
Higher [H ]
Lower [H ]
ATP
Generate ATP by the same basic mechanism: chemiosmosis
Use different sources of energy to accomplish this: light and chemical energy
Different spatial organization 空間結構of chemiosmosis
In both organelles 胞器redox reactions of electron transport chains generate a H+ gradient across a membrane
ATP synthase ATP合成酶 : uses this proton-motive force to make ATP

21. The light reactions and chemiosmosis: the organization
of the thylakoid membrane
There are three steps in the light reactions that contribute to the proton gradient across the thylakoid membrane:
Water is split by Photosystem II on the thylakoid side, releasing protons in the process.
2. As plastoquinone (Pq), a mobile carrier, transfers electrons to the cytochrome 細胞色素complex, it translocates protons from the stroma to the thylakoid space.
3. Protons in the stroma are removed from solution as NADP＋ is reduced to NADPH.
ATP and NADPH are produced on the side facing the stroma, where the Calvin cycle takes place
In summary, light reactions generate ATP and increase the potential energy of electrons by moving them from H2O to NADPH

22. STROMA (low H concentration)
THYLAKOID SPACE (high H concentration)
Light
Photosystem II
Cytochrome complex
Photosystem I
NADP reductase
NADP + H
To Calvin Cycle
ATP synthase
Thylakoid membrane 2 1 3
NADPH Fd Pc Pq
4 H+
+2 H+ H+
ADP + P i
ATP
1/2
H2O O2

23. Concept 10.3: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar
The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH
Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde 3-phospate (G3P)
For net synthesis of 1 G3P, the cycle must take place three times, fixing 3 molecules of CO2
The Calvin cycle has three phases
Carbon fixation (catalyzed by rubisco)
Reduction
Regeneration of the CO2 acceptor (RuBP)

24. H2O CO2 O2 Light NADP+ ADP CALVIN LIGHT CYCLE REACTIONS ATP NADPH
Figure 10.UN03
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
Figure 10.UN03 In-text figure, Calvin cycle schematic, p. 200 O2
[CH2O] (sugar)

25. 10.3 The Calvin cycle uses ATP and NADPH to convert CO2 to sugar
The Calvin cycle: similar to the citric acid cycle, occurs in the stroma
Input 3
(Entering one at a time)
CO2
Phase 1: Carbon fixation
Rubisco P 6
Short-lived intermediate
3-Phosphoglycerate
6 ADP
ATP
1,3-Bisphosphoglycerate
Calvin Cycle
6 NADPH
6 NADP
6 P i
Phase 2: Reduction
Glyceraldehyde 3-phosphate (G3P) 5
G3P
3 ADP
Phase 3: Regeneration of the CO2 acceptor (RuBP)
Ribulose bisphosphate (RuBP) 1
G3P (a sugar)
Output
Glucose and other organic compounds

26. The Calvin cycle has three phases
Carbon fixation 碳固定: each molecule of CO2 is attached to a five-carbon sugar, ribulose biphosphate (RuBP) by an enzyme RuBP carboxlase (rubisco).
Input 3
(Entering one at a time)
CO2
Phase 1: Carbon fixation
Rubisco P 6
Short-lived intermediate
3-Phosphoglycerate
Ribulose bisphosphate (RuBP)

27. Reduction: a two-step process that couples ATP hydrolysis with the reduction of 3-phosphoglycerate to glyceraldehydes phosphate.
Input 3
(Entering one at a time)
CO2
Phase 1: Carbon fixation
Rubisco P 6
Short-lived intermediate
3-Phosphoglycerate
6 ADP
ATP
1,3-Bisphosphoglycerate
Calvin Cycle
6 NADPH
6 NADP
6 P i
Phase 2: Reduction
Glyceraldehyde 3-phosphate (G3P)
Ribulose bisphosphate (RuBP) 1
G3P (a sugar)
Output
Glucose and other organic compounds

28. Regeneration of the CO2 acceptor (RuBP): A complex series of reactions rearranges the carbon skeletons of five G3P molecules into three RuBP molecules
Input 3
(Entering one at a time)
CO2
Phase 1: Carbon fixation
Rubisco P 6
Short-lived intermediate
3-Phosphoglycerate
6 ADP
ATP
1,3-Bisphosphoglycerate
Calvin Cycle
6 NADPH
6 NADP
6 P i
Phase 2: Reduction
Glyceraldehyde 3-phosphate (G3P) 5
G3P
3 ADP
Phase 3: Regeneration of the CO2 acceptor (RuBP)
Ribulose bisphosphate (RuBP) 1
G3P (a sugar)
Output
Glucose and other organic compounds

29. The Calvin cycle
For the net synthesis of one G3P molecule, the Calvin cycle uses the products of the light reactions: 9 ATP molecules and 6 NADPH molecules.
b. G3P produced by the Calvin cycle is the raw material used to synthesize glucose and other carbohydrates.
c. The Calvin cycle uses 18 ATP and 12 NADPH molecules to produce one glucose molecule

30. A. Photorespiration in a C3 plant 光呼吸作用
10.4 Alternative mechanisms of carbon fixation have evolved in hot, arid climates
A. Photorespiration in a C3 plant 光呼吸作用
目的???
Soybeans
Oats
Wheat
Rice

31. Resulting 5-C molecular splits into
On hot dry days, C3 plants close their stomata 氣孔to conserving water but limiting access to CO2 and causing oxygen to build up
Photorespiration 光呼吸: An evolutionary relic?
Photorespiration: O2 substitutes for CO2 in the active site of the enzyme rubisco and the photosynthetic rate is reduced
Rubisco transfer O2 to RuBp
Resulting 5-C molecular splits into
Two-C molecular（glycolate甘醇酸 ) Three-C molecule （3-phosphoglycolate）
Leaves chloroplast & goes to peroxisome Stays in the Calvin cycle
A metabolic pathway begin in the peroxisome
and is completed in the mitochondria
Glycolate is broken down into CO2

32. C4 Plants
C4 plants minimize the cost of photorespiration by incorporating CO2 into four carbon compounds in mesophyll cells葉肉
These four carbon compounds are exported to bundle sheath cells束鞘細胞, where they release CO2 used in the Calvin cycle
C4 leaf anatomy and the C4 pathway
The C4 pathway
Mesophyll cell
PEP carboxylase
CO2
Oxaloacetate (4C)
PEP (3C)
Malate (4C)
Pyruvate (3C)
Bundle- sheath cell
Calvin Cycle
Sugar
Vascular tissue
ADP
ATP
Mesophyll
cell
Bundle-
sheath
Photo-
synthetic
cells of
C4 plant
leaf
Vein
(vascular
tissue)
C4 leaf anatomy
Stoma
Figure C4 leaf anatomy and the C4 pathway. 32

33. CAM Plants
CAM ( crassulacean acid 景天酸metabolism) plants: open their stomata at night, incorporating CO2 into organic acids
During the day, the stomata close and the CO2 is released from the organic acids for use in the Calvin cycle
(b) Temporal separation of steps
CO2
Organic acid
Calvin Cycle
Sugar
Day
Night
CAM
CO2 incorporated (carbon fixation)
CO2 released to the Calvin cycle 2 1

34. The CAM pathway is similar to the C4 pathway
Sugarcane
Mesophyll cell
Bundle- sheath cell C4
CO2
Organic acid
Calvin Cycle
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps
Day
Night
CAM
Pineapple
CO2 incorporated (carbon fixation)
CO2 released to the Calvin cycle 2 1
Differ in that the initial steps of carbon fixation in C4 plants are structurally separate from the Calvin cycle; in CAM plants, the two steps occur at separate times.
Regardless of whether the plant uses aC3, C4 or CAM pathway, all plants use the Calvin cycle to produce sugar from CO2.

35. The Importance of Photosynthesis: A Review
The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds
Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells
Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits
In addition to food production, photosynthesis produces the O2 in our atmosphere

36. REACTIONS: Photosystem II
Figure 10.22a O2
CO2
H2O
Sucrose
(export)
Mesophyll cell
Chloroplast
H2O
CO2
Light
NADP+
ADP
3-Phosphoglycerate
LIGHT
REACTIONS: Photosystem II
Electron transport
chain + P
CALVIN
CYCLE i
RuBP
Figure 10.22a A review of photosynthesis (part 1)
ATP
G3P
Photosystem I
Electron transport
chain
NADPH
Starch
(storage)
Sucrose (export) O2
H2O

37. CALVIN CYCLE REACTIONS
Figure 10.22b
LIGHT REACTIONS
CALVIN CYCLE REACTIONS
Are carried out by molecules in the thylakoid membranes
Take place in the stroma
Use ATP and NADPH to convert CO2 to the sugar G3P
Convert light energy to the chemical energy of ATP and NADPH
Return ADP, inorganic phosphate, and NADP+ to the light reactions
Split H2O and release O2 to the atmosphere
Figure 10.22b A review of photosynthesis (part 2)

38. Global warming and deforestation 全球暖化及去森林化:
Excess CO2 in the atmosphere is contributing to global warming, photosynthesis, which removes CO2 from the atmosphere moderates this warming
The increase in atmospheric carbon dioxide at Mauna Loa, Hawaii, and average global temperatures over land from 1958 to 2004

39. Figure 10.UN06 Appendix A: answer to Figure 10.22 legend question39

40. 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
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