1. How Cells Acquire Energy
Chapter 7

2. Photoautotrophs
Capture sunlight energy and use it to carry out photosynthesis
Plants
Some bacteria
Many protistans

3. Figure 10.2 Photoautotrophs
(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. Linked Processes Photosynthesis Aerobic Respiration
Energy-storing pathway
Releases oxygen
Requires carbon dioxide
Aerobic Respiration
Energy-releasing pathway
Requires oxygen
Releases carbon dioxide

5. Figure 10.3 Zooming in on the location of photosynthesis in a plant
Leaf cross section
Vein
Mesophyll
Stomata
CO2 O2
Chloroplast
Mesophyll cell
Outer
membrane
Figure 10.3 Zooming in on the location of photosynthesis in a plant
Thylakoid
Intermembrane
space
5 µm
Stroma
Granum
Thylakoid
space
Inner
membrane
1 µm

6. Chloroplast Structure
two outer membranes
stroma
inner membrane system
(thylakoids connected by channels)
Figure 7.3d, Page 116

7. Photosynthesis Equation
LIGHT ENERGY
12H2O + 6CO2
6O2 + C2H12O6 + 6H2O
Water
Carbon Dioxide
Oxygen
Glucose
Water
In-text figure Page 115

8. Where Atoms End Up Reactants 12H2O 6CO2 Products 6O2 C6H12O6 6H2O
In-text figure Page 116

9. Two Stages of Photosynthesis
sunlight
water uptake
carbon dioxide uptake
ATP
LIGHT-DEPENDENT REACTIONS
ADP + Pi
LIGHT-INDEPENDENT REACTIONS
NADPH
NADP+ P
glucose
oxygen release
new water
In-text figure Page 117

10. Electromagnetic Spectrum
Shortest Gamma rays
wavelength X-rays
UV radiation
Visible light
Infrared radiation
Microwaves
Longest Radio waves
wavelength

11. Visible Light Wavelengths humans perceive as different colors
Violet (380 nm) to red (750 nm)
Longer wavelengths, lower energy
Figure 7.5a Page 118

12. Photons Packets of light energy
Each type of photon has fixed amount of energy
Photons having most energy travel as shortest wavelength (blue-violet light)

13. Pigments Color you see is the wavelengths not absorbed
Light-catching part of molecule often has alternating single and double bonds
These bonds contain electrons that are capable of being moved to higher energy levels by absorbing light

14. Light Reflected light Chloroplast Absorbed Granum light Transmitted
Fig. 10-7
Light
Reflected
light
Chloroplast
Figure 10.7 Why leaves are green: interaction of light with chloroplasts
Absorbed
light
Granum
Transmitted
light

15. Variety of Pigments
Chlorophylls a and b
Carotenoids
Xanthophils

16. Wavelength absorption (%) Wavelength (nanometers)
Chlorophylls
Main pigments in most photoautotrophs
Wavelength absorption (%)
chlorophyll a
chlorophyll b
Wavelength (nanometers)
Figure 7.6a Page 119
Figure 7.7 Page 120

17. Accessory Pigments Carotenoids, Phycobilins, Anthocyanins
beta-carotene
phycoerythrin (a phycobilin)
percent of wavelengths absorbed
wavelengths (nanometers)

18. Pigments in Photosynthesis
Bacteria
Pigments in plasma membranes
Plants
Pigments and proteins organized into photosystems that are embedded in thylakoid membrane system

19. Arrangement of Photosystems
water-splitting complex
thylakoid
compartment
H2O
2H + 1/2O2
P680
P700
acceptor
acceptor
pool of electron carriers
PHOTOSYSTEM II
stroma
PHOTOSYSTEM I
Figure 7.10 Page 121

20. Light-Dependent Reactions
Pigments absorb light energy, give up e-, which enter electron transfer chains
Water molecules split, ATP and NADH form, and oxygen is released
Pigments that gave up electrons get replacements

21. Photosystem Function: Harvester Pigments
Most pigments in photosystem are harvester pigments
When excited by light energy, these pigments transfer energy to adjacent pigment molecules
Each transfer involves energy loss

22. Photosystem Function: Reaction Center
Energy is reduced to level that can be captured by molecule of chlorophyll a
This molecule (P700 or P680) is the reaction center of a photosystem
Reaction center accepts energy and donates electron to acceptor molecule

23. (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)

24. Electron Transfer Chain
Adjacent to photosystem
Acceptor molecule donates electrons from reaction center
As electrons pass along chain, energy they release is used to produce ATP

25. Cyclic Electron Flow Electrons Electron flow drives ATP formation
are donated by P700 in photosystem I to acceptor molecule
flow through electron transfer chain and back to P700
Electron flow drives ATP formation
No NADPH is formed

26. Primary acceptor Primary Fd acceptor Fd NADP+ Pq + H+ NADP+ reductase
Fig
Primary
acceptor
Primary
acceptor Fd Fd
NADP+
+ H+ Pq
NADP+
reductase
Cytochrome
complex
NADPH Pc
Figure Cyclic electron flow
Photosystem I
Photosystem II
ATP

27. Noncyclic Electron Flow
Two-step pathway for light absorption and electron excitation
Uses two photosystems: type I and type II
Produces ATP and NADPH
Involves photolysis - splitting of water

28. Machinery of Noncyclic Electron Flow
H2O
second electron transfer chain
photolysis e– e–
ATP SYNTHASE
first electron transfer chain
NADP+
NADPH
ATP
PHOTOSYSTEM II
PHOTOSYSTEM I
ADP + Pi
Figure 7.13a Page 123

29. 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)

30. Potential to transfer energy (volts)
Energy Changes
second
transfer
chain e–
NADPH
first e–
transfer
chain
Potential to transfer energy (volts) e– e–
(Photosystem I)
(Photosystem II)
H2O
1/2O2 + 2H+
Figure 7.13b Page 123

31. Chemiosmotic Model of ATP Formation
Electrical and H+ concentration gradients are created between thylakoid compartment and stroma
H+ flows down gradients into stroma through ATP synthesis
Flow of ions drives formation of ATP

32. Chemiosmotic Model for ATP Formation
H+ is shunted across membrane by some components of
the first electron transfer chain
Gradients propel H+ through ATP synthases;
ATP forms by phosphate-group transfer
Photolysis in the thylakoid compartment splits water
H2O e–
acceptor
ATP SYNTHASE
ATP
ADP + Pi
PHOTOSYSTEM II
Figure 7.15 Page 124

33. 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+

34. Light-Independent Reactions
Synthesis part of photosynthesis
Can proceed in the dark
Take place in the stroma
Calvin-Benson cycle

35. Calvin-Benson Cycle Overall reactants Overall products Carbon dioxide
ATP
NADPH
Overall products
Glucose
ADP
NADP+
Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

36. unstable intermediate6
CO2 (from the air)
Calvin- Benson Cycle
CARBON FIXATION 6 6
RuBP
unstable intermediate 12
PGA
6 ADP 12
ATP 6
ATP 12
NADPH
4 Pi
12 ADP
12 Pi
12 NADP+ 10
PGAL 12
PGAL 2
PGAL Pi
Figure 7.16 Page 125 P
glucose

37. The C3 Pathway
In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA
Because the first intermediate has three carbons, the pathway is called the C3 pathway

38. Photorespiration in C3 Plants
On hot, dry days stomata close
Inside leaf
Oxygen levels rise
Carbon dioxide levels drop
Rubisco attaches RuBP to oxygen instead of carbon dioxide
Only one PGAL forms instead of two

39. C3 and C4 plant structure compared

40. C4 Plants Carbon dioxide is fixed twice
In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate
Oxaloacetate is transferred to bundle-sheath cells
Carbon dioxide is released and fixed again in Calvin-Benson cycle

41. CAM Plants Carbon is fixed twice (in same cells) Night Day
Carbon dioxide is fixed to form organic acids
Day
Carbon dioxide is released and fixed in Calvin-Benson cycle

42. i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH
Fig
H2O
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
[CH2O]
(sugar) O2

43. Satellite Images Show Photosynthesis
Atlantic Ocean
 Photosynthetic activity in spring
Figure 7.20 Page 128