1. PHOTOSYNTHESIS
PLANTS. Feeding, clothing, sheltering and medicating the world for millions of years.

2. Photosynthesis
A biochemical pathway where autotrophs use energy from sunlight (light energy) to produce organic compounds (chemical energy)
6CO2 + 6H2O -> C6H12O6 + 6O2
2 stages:
1. Light reactions
2. Calvin cycle

6. Visible Spectrum
White light is composed of a variety of colors – visible spectrum
Pigments absorb light
Light that is not absorbed is reflected

8. Pigments Chlorophyll (a and b)
Plants are green because green wavelengths of light are REFLECTED
Chlorophyll a is responsible for absorbing the energy from sunlight
Chlorophyll b is an accessory pigment; also carotenoids (yellow, orange and brown)

9. Photosynthesis depends upon green pigment CHLOROPHYLL (absorbs light in the blue-violet and orange-red and reflects light in green region
Accessory pigments help harvest light energy

13. CHLOROPLAST STRUCTURE
Surrounded by double membrane
PLUS an inner membrane system:
THYLAKOIDS – flattened sacs
GRANA – stacks of thylakoids
Light harvesting pigments embedded in thylakoid membrane
Surrounding thylakoids, liquid: STROMA

16. LIGHT DEPENDENT RXNS
Visible light (traveling in “photons”, packets of energy) is changed into chemical energy
H2O is split into O2 and H
PS I and II absorb light energy
This light energy is transferred to reaction center, a Chlorophyll a that donates e- to electron carriers

17. At end of electron flow, electrons combine with NADP+ to form NADPH
Lost e- from PSII is replaced by e- from H2O
As electrons flow along electron transport chain, protons build up inside thylakoids
These built up protons will diffuse down concentration gradient through ATP synthase

18. TAH-DAH!! ATP is made!!! PRODUCTS: O2, ATP and NADPH!!!!
ATP and NADPH area both needed for the Calvin Cycle

19. Chemiosmosis
Electrochemical gradient exists between the stroma and the thylakoid interior
As protons diffuse through ATP Synthase, ATP is made
Where do these protons come from?

22. f,'-carotene
H1 CH3
C "
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I I I I I I I I I I H3C CHJ
H1C C C C C C C C C C C /C"
/c, /C"", /c""' /C, /C, /C""' /c, /C"", /c~ /c, /c" /CH1
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"/, C1
H3C H

24. CALVIN CYCLE Requires ATP and NADPH from light rxns Occurs in stroma
1 molecule of CO2 combines with RuBP (5 carbon compound) = “carbon fixation”
Resulting 6C molecule splits into 2- 3 carbon molecules of PGA

25. Each PGA, using 1 ATP and 1 NADPH makes one PGAL
Each PGAL converted into various 4, 5 and 6 carbon sugars
RuBP is recycled
3 turns of the cycle -> 6 PGAL, 5 -> RuBP, 1 for other sugars
Rubisco is the enzyme which catalyzes rxn that fixes CO2
Calvin cycle AKA C3 cycle

26. Photosynthesis depends upon green pigment CHLOROPHYLL (absorbs light in the blue-violet and orange-red and reflects light in green region
Accessory pigments help harvest light energy

27. CALVIN CYCLE CO2 converted to G3P; ATP and NADPH are consumed
To make one molecule of G3P, three turns of the cycle + 3 CO2 molecules
CO2 is fixed to RuBP by rubisco – produces unstable intermediate -> 3-phosphoglycerate

28. 3-phosphoglycerate is phosphorylated -> 1,3-diphosphoglycerate
NADPH reduces 1,3-phosphoglycerate to glyceraldehyde-3-phosphate
RuBP is regenerated – one per each trip through the cycle
Uses 9 ATP and 6 NADPH

29. C4 FIXATION
First carbon compound formed has 4 carbons instead of three
Bundle sheath cells – grouped around veins
CO2 added to PEP (a 3-C compound) phosphoenolpyruvate to form oxaloacetate (catalyzed by PEP carboxylase)
Oxaloacetate exported to bundle sheath cells, which break it down into CO2 molecules
CO2 then converted to carbs through Calvin cycle (occurs only in bundle sheath cells)

30. CAM Photosynthesis Adaptation to hot dry climates
Stomates open at night and closed during day to minimize water loss
CO2 taken in at night, converted to various organic molecules and stored in vacuoles
In morning, stomates close and plants release CO2 for normal photosynthesis

31. Rate of Photosynthesis
4 limiting factors:
Light intensity, temperature, [CO2], [O2]
Active site of Rubisco can bind to O2 or CO2: Photorespiration – results in release of previously fixed CO2 that would otherwise remain in organic form

32. RATES OF PHOTOSYNTHESIS
As light intensity increases, so does rate of photosynthesis
Levels off at a max rate, when all electrons are excited
Same thing for CO2 levels
Temperature increase, rate increases to a point; then, enzymes denature and stomates close to prevent water loss, thus decreasing rate at high temperatures