CH. 8 - PHOTOSYNTHESIS
I. INTRODUCTION
A. ELECTROMAGNETIC ENERGY SPECTRUM (p.151)
1. Photons – energy particles that travel in waves – excites e- (p. 21)
2. Psyn uses only a fraction of visible light.
3. Short wave - high energy (blue light 400 nm)
4. Long wave - low energy (red light 650 nm)
5. Light energy used to split H2O (Oxidized) è H + O
a. H added to CO2 è CH2O (Reduced)
b. O2 released as waste
B. ABSORPTION SPECTRUM - absorption pattern of a pigment (p. 152)
1. Chlorophyll A.
a. absorbs blue & red, REFLECTS green!
b. green pigment in all plants.
2. Accessory/Antenna pigments
a. absorbs other wavelengths of light
b. often masks chl. a
c. Carotenes, xanthophylls, chl. b, c, etc.
3. Ultraviolet screened by O2, O3
4. Infrared screened by H2O, CO2
II. CHLOROPLAST STRUCTURE - (p. 148)
A. OUTER & INNER MEMBRANES
B. THYLAKOIDS - light-dependent rxns; GRANA - thylakoid stacks
C. STROMA - light-independent rxns
III. 2 STAGES OF PSYN - (p. 149)
A. LIGHT DEPENDENT/ENERGY CAPTURING RXNS (p. 159)
Makes: ATP, NADPH & O2
Location: thylakoids
1. PS I - 2 pathways
a. Noncyclic photophosphorylation - makes NADPH
1. Light strikes chl a, e- excited to higher energy level (p. 21)
2. e- passed to rxn cntr P700
3. e- passed to primary e- acceptor
4. e- passed down ETC in redox rxns to NADPH
5. energy used to make NADPH
6. e- is lost; NONCYCLIC = “e- hole” in PS I
7. e- replaced with e- from PS II
b. Cyclic photophosphorylation - makes ATP
1-3 same
4. e- shunted to ETC from PS II
5. energy used to make ATP
6. e- returns to chl a in PS I
7. e- is not lost; CYCLIC
2. PS II
a. Noncyclic photophosphorylation - makes ATP
1-3 same, except P680 is rxn center
4. e- passed down ETC to make ATP
5. e- fills "e- hole" in PS I.
6. e- is lost; NONCYCLIC
7. e- replaced from splitting H2O in HILL RXN:
b. Hill Rxn:
2H2O ==========> 4e- + 4H+ + O2
1. 4e- to P680
2. 4H+ to proton pump for chemiosmosisè ATP (p. 159)
3. O2 released as waste
3. Summary of Light-Dependent Rxns:
a. Products: 1. ATP 2. NADPH 3. O2
b. NADPH is final e- acceptor
c. ATP & NADPH used to drive/power dark rxns
d. Occurs in thylakoids
e. Solar è electrical è chemical energy
B. LIGHT-INDEPENDENT/DARK/CALVIN CYCLE/CARBON FIXING/C3
Makes: glucose using CO2 & ATP & NADPH from Light Rxns
Location: Stroma
1. Introduction:
a. carbohydrate/sugar synthesis
b. chemical energy è chemical energy
c. CO2 + ATP+ NADPH + RuBP è GLUCOSE
d. occurs in the stroma.
e. independent (mostly) of light
2. Steps: (p. 161)
a. CO2 (1C) + RuBP (5C) è 2 PGA (3C)
b. 2PGA + ATP + NADPH è2PGAL(G3P) 1st stable end-product of psyn
c. G3P/PGAL used to form more RuBP
d. 3 "Turns" = 6G3P/PGAL è 5 to make more RuBP, 1 G3P left over
e. 6 "Turns"=12 G3P/PGALè10 to make more RuBP, 2 G3Pè 1 glucose!
3. C4 Pathway (p. 165)
a. PEP binds to CO2 instead of RuBP Oxaloacetic acid (4C)
b. Uses CO2 more efficiently with less H20 loss
c. Hi light, hot, dry climates
d. Corn, sugercane, sorghum
C. SUMMARY OF PSYN:
6 CO2 + 12 H2O + light energy è Glucose + 6 O2 + 6H2O
D L D L
1. LIGHT è ATP, NADPH, O2 - IN THYLAKOIDS
2. DARK è G3P (GLUCOSE) - IN STROMA
D. PSYN & RESP LINKED (p. 162)