1. How Cells Acquire Energy
Chapter 6

2. (see next slide) leaf’s upper surface photosynthetic cells
two outer layers of membrane
inner membrane system (thylakoids,
all interconnecting bychannels)
(see next slide)
Fig. 6.3a, p. 94
stroma

3. Organelles of photosynthesis
Chloroplasts
Organelles of photosynthesis

4. Photosynthesis Equation
LIGHT ENERGY
12H2O + 6CO2
6O2 + C2H12O6 + 6H2O
water
carbon dioxide
oxygen
glucose
water

5. 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

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

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

8. Wavelength (nanometers)
Pigments
Light-absorbing molecules
Absorb some wavelengths and transmit others
Color you see are the wavelengths NOT absorbed
chlorophyll a
chlorophyll b
Wavelength (nanometers)

9. Pigment Structure
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

10. Excitation of Electrons
Excitation occurs only when the quantity of energy in an incoming photon matches the amount of energy necessary to boost the electrons of that specific pigment
Amount of energy needed varies among pigment molecules

11. Pigments in Photosynthesis
Bacteria
Pigments in plasma membranes
Plants
Pigments embedded in thylakoid membrane system
Pigments and proteins organized into photosystems
Photosystems located next to electron transport systems

12. Photosystems and Electron Transporters
water-splitting complex
thylakoid
compartment
H2O
2H + 1/2O2
P680
P700
acceptor
acceptor
PHOTOSYSTEM II
pool of electron transporters
stroma
PHOTOSYSTEM I

13. Light-Dependent Reactions
Pigments absorb light energy, give up e- which enter electron transport systems
Water molecules are split, ATP and NADH are formed, and oxygen is released
Pigments that gave up electrons get replacements from splitting water

14. Electron Transport System
Adjacent to photosystem
Acceptor molecule donates electrons from reaction center
As electrons flow through system, energy they release is used to produce ATP and, in some cases, NADPH

15. Cyclic Electron Flow e– e– ATP e– e– electron acceptor
electron transport system e–
ATP e– e–

16. Machinery of Noncyclic Electron Flow
H2O
photolysis e– e–
ATP SYNTHASE
NADP+
NADPH
ATP
PHOTOSYSTEM II
PHOTOSYSTEM I
ADP + Pi

17. Potential to transfer energy (voids)
Energy Changes
second
transport
system e–
NADPH
first e–
transport
system e–
Potential to transfer energy (voids) e–
(PHOTOSYSTEM I)
(PHOTOSYSTEM II)
H2O
1/2 O2 + 2H+

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

19. 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
12NADP+ 10
PGAL 12
PGAL 2
PGAL Pi P
glucose

20. animation

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