1. How Cells Acquire Energy

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

5. Chloroplast Structure
two outer membranes
stroma
inner membrane system
(thylakoids connected by channels)

6. Photosynthesis Equation
LIGHT ENERGY
12H2O + 6CO2
6O2 + C2H12O6 + 6H2O
Water
Carbon Dioxide
Oxygen
Glucose
Water

7. Where Atoms End Up
Reactants
12H2O
6CO2
Products
6O2
C6H12O6
6H2O

8. 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

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

10. Visible Light Wavelengths humans perceive as different colors
Violet (380 nm) to red (750 nm)
Longer wavelengths, lower energy

11. 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)

12. Pigments
Color you see is the wavelengths not absorbed

13. Variety of Pigments
Chlorophylls a and b
Carotenoids
Anthocyanins

14. Wavelength absorption (%) Wavelength (nanometers)
Chlorophylls
Main pigments in most photoautotrophs
Wavelength absorption (%)
chlorophyll a
chlorophyll b
Wavelength (nanometers)

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

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

17. 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

18. 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

19. 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

20. Photosystem Function: Reaction Center
This molecule (P700 or P680) is the reaction center of a photosystem

21. Pigments in a Photosystem
reaction center

22. Electron Transfer Chain
Adjacent to photosystem
As electrons pass along chain, energy they release is used to produce ATP

23. 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

24. Synthesis of ATP (chemiosmotic phosphorylation)
second electron transfer chain
photolysis e– e–
ATP SYNTHASE
first electron transfer chain
NADP+
NADPH
ATP
PHOTOSYSTEM II
PHOTOSYSTEM I
ADP + Pi

25. Chemiosmotic Model of ATP Formation
Electrons within the membrane of the chloroplast attract H+ protons
The H+ protons are pumped inside the chloroplast membranes
The Protons are allowed to pass out of the membrane through the CF1 particle that is rich in ADP + P plus phosphorylating enzymes.

26. 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

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

28. 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

29. 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 P
glucose

30. 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

31. Photorespiration in C3 Plants
On hot, dry days stomata close
Inside leaf
Oxygen levels rise
Carbon dioxide levels drop
The plant is in trouble because it does not enough Carbon dioxide to undergo photosynthesis
The plant still needs energy so it taps its own store of glucose

32. C4 Plants Carbon dioxide is fixed twice
In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate
Oxaloacetate is stored as a crystal
When times get bad (drought conditions), the plant can now convert the crystalline form of oxaloacetate back to Carbon dioxide and undergo photosynthesis.

33. 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