1. How Cells Acquire Energy
Chapter 7

2. Carbon and Energy Sources
Photoautotrophs
Carbon source is carbon dioxide
Energy source is sunlight
Heterotrophs
Get carbon and energy by eating autotrophs or one another

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

4. T.E. Englemann’s Experiment
Background
Certain bacterial cells will move toward places where oxygen concentration is high
Photosynthesis produces oxygen

5. T.E. Englemann’s Experiment
Figure 7.1 Page 111

6. Linked Processes Photosynthesis Aerobic Respiration
Energy-storing pathway
Releases oxygen
Requires carbon dioxide
Aerobic Respiration
Energy-releasing pathway
Requires oxygen
Releases carbon dioxide

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

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

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

10. 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

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

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

13. 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)

14. 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

15. Variety of Pigments Chlorophylls a and b Carotenoids Anthocyanins
Phycobilins

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. Pigments in a Photosystem
reaction center
Figure 7.11 Page 122

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. Cyclic Electron Flow e–
electron acceptor
Electron flow through transfer chain sets up conditions for ATP formation at other membrane sites.
electron transfer chain e– e–
ATP e–
Figure 7.12 Page 122

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. 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

30. 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

31. 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

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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. Summary of Photosynthesis
light
6O2
12H2O
CALVIN-BENSON CYCLE
C6H12O6
(phosphorylated glucose)
NADPH
NADP+
ATP
ADP + Pi
PGA
PGAL
RuBP P
6CO2
end product (e.g., sucrose, starch, cellulose)
LIGHT-DEPENDENT REACTIONS
6H2O
LIGHT-INDEPENDENT REACTIONS
Figure 7.21 Page 129

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