1. Photosynthesis
Chapter 6

2. Autotrophs Sustain themselves without eating other organisms
Produce organic molecules
Photoautotrophs
Light
Photosynthesis
Plants, protists and prokaryotes
Chemoautotrophs
Chemical

3. Chloroplasts Found in leaves, stems, unripen fruit Chlorophyll
Green pigment inside chloroplasts
Absorbs energy
Drives synthesis of food
Found in mesophyll
Tissue part of the inside of leaves

4. Nutrient pathway Stomata Veins Openings on leaves Water absorbed
Allows O2 to enter and CO2 to exit
Veins
Water absorbed
Export sugar to roots and other parts of the leaves

5. Mesophyll cell 30 – 40 chloroplasts Stroma Thylakoid Dense fluid
Interconnected system of compartments
Encloses lumen
Stacked into columns
Called grana

6. Leaf cross section
Chloroplasts
Vein
Mesophyll
Stomata
CO2 O2
Chloroplast
Mesophyll cell
Outer membrane
Thylakoid
Intermembrane space
Stroma
Granum
20 m
Thylakoid space
Inner membrane
1 m

7. Pathway of photosynthesis
6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O
Two stages

8. Light Reaction Solar energy into chemical energy
Electrons and hydrogen from H2O to NADP+
Water is split
Gives off O2
Reduced NADP to NADPH
addition of an electron pair and H+
Photophosphorylation
ADP + phosphate group > ATP
Light energy initially transformed to chemical energy
Occurs in thylakoids

9. Calvin Cycle Carbon Fixation Reduces fixed carbon into carbohydrate
Incorporates Co2 into organic molecules
Reduces fixed carbon into carbohydrate
Produces sugar
Reduced by NADPH
Energizes electrons
Needs both NADPH and ATP
Don’t need light directly
Mostly occurs in daylight
Light reaction needed for NADPH and ATP production
Occurs in the stroma

11. Sunlight Electromagnetic energy Wavelength Spectrum
380nm – 750 nm = visible light
Spectrum

12. Light Reaction Photon Atmosphere only allows visible light through
Interactions of light with matter
Light particles
Quantity of energy
Atmosphere only allows visible light through
Drives photosynthesis

13. Light Absorption Can only use absorbed light wavelengths
Light seen is light reflected
Pigments differ in absorption spectrum

14. Engelmann’s experiment Action spectrum
Rate of photosynthesis at different wavelengths
Not = absorption spectrum
Only chlorophyll directly participates
Accessory pigments can give energy collected from different wavelengths to Ca
Chlorophyll b
Carotenoids
Photo protection
Absorb and dissipate excess potentially harmful energy

15. Excited electrons Absorbing photons Electron excited to next orbital
More potential energy
Return to original orbital
Release light or heat
Excited state
Heat e
Photon (fluorescence)
Ground state
Photon
Chlorophyll molecule
Energy of electron
Excitation of isolated chlorophyll molecule

16. Photosystem Light harvesting unit Antenna complex Reaction center
Collection of chloroplast a, chloroplast b and carotenoids
Deliver energy to chloroplast a
Reaction center
Location of specialized chlorophyll a
Only functions properly within a photosystem
Starts light reaction
Primary electron acceptor
Reduced by chlorophyll a

17. Chloro- phyll a
Chlorophyll b
Absorption of light by chloroplast pigments
Carotenoids
(a)
Absorption spectra
400
500
600
700
Wavelength of light (nm)
Rate of photosynthesis (measured by O2 release)
(b) Action spectrum
400
500
600
700
Aerobic bacteria
Filament of alga
Engelmann’s experiment
(c)
400
500
600
700

18. Types of photosystems Photosystem I Photosystem II
P700 center
Photosystem II
P680 center
Associated with different proteins

19. THYLAKOID SPACE (INTERIOR OF THYLAKOID)
Photosystem
STROMA
Photon
Light- harvesting complexes
Reaction- center complex
Primary electron acceptor
Chlorophyll
STROMA e
Thylakoid membrane
Thylakoid membrane
Transfer of energy
Special pair of chlorophyll a molecules
Pigment molecules
Protein subunits
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
THYLAKOID SPACE
(a) How a photosystem harvests light
(b) Structure of photosystem II

20. Noncyclic electron flow
Uses photosystems I and II
Generates ATP and NADPH
Equal amounts
Electrons pass from H2O to NADPH

21. Electron transport chain
Primary acceptor
Primary acceptor 4 7
Electron transport chain Fd Pq e 2 e 8 e e
H2O
NADP
2 H
Cytochrome complex
NADP reductase
+ H + 3
1/2 O2
NADPH Pc e e
P700 5
P680
Light 1
Light 6
ATP
Pigment molecules
Photosystem I (PS I)
Photosystem II (PS II)

22. Steps Photosystem II absorbs light
Chlorophyll a oxidized
Enzyme used electrons from water to replace Ca’s e-
Splits water and adds O together > O2
Electron transferred to photosystem I
Electron transport chain
Noncyclic photophosphorylation
Chemiosmosis
Uses energy produced by ETC to power ADP > ATP
Powers the Calvin Cycle

23. Steps Electron is supplied to chlorophyll a in Photo I
Electron collected by primary electron acceptor undergoes the ETC
NADP+ reductase transfers electron to NADP+
NADPH used in Calvin Cycle
Reducing agent

24. Cyclic electron flow Simpler pathway Only uses photosystem I
Chemiosmosis
Cyclic photophosphorylation
Generates ATP
Calvin cycle uses more ATP than NADPH
NADPH concentration might regulate which pathway is used

25. Chemiosmosis in chloroplasts
H+ pumped into Thylakoid space
Proton gradient
H+ used by ATP synthase to drive combination of ADP and a phosphate group
Pumped back into the stroma

26. Calvin Cycle Uses ATP and NADPH to convert CO2 to sugar In stroma
3 CO2 > sugar
Glyceraldehyde – 3 – phosphate
Cycles 3 times to fix carbon thrice

27. Calvin Cycle Carbon fixation Reduction Regeneration of Rubisco
Enzyme rubisco attaches CO2 to 5 carbon sugar
6 carbon intermediate > 3 phosphoglycerates
Reduction
Phosphoglycerate + phosphate group from ATP > bisphosphoglycerate
Reduced by NADPH
3 CO2 makes 6 G3P
Regeneration of Rubisco
5 G3P rearranged into 3 RuBP
Uses 3 ATP
Uses CO2

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

29. Net gain 3 CO2, 9 ATP and 6 NADPH > G3P
Transferred into other metabolic pathways
glucose + other carbs
Both light and dark reactions needed for sugar production

30. Labs Leaf photosynthesis Sodium bicarbonate = carbon source
With photosynthesis the leaves would produce oxygen within its mesophyll
Decrease density
30 cm away
Float
Dark for half of the exposure time
Fewer disks floating
Water/soap control = no carbon source
All sink
50 cm away