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Ch. 2 Light and Photosynthesis (Ps)
Sunflecks: Bad
• Sunflecks & drought stress
• Ex, regeneration Abies magnifica (CA
red fir)
Sunflecks
• Ex, regeneration Abies magnifica (CA red fir)
• Seedling pattern determined by
Chasing Sun: heliotropism
• Move leaf (heliotropism): rotate
• Diaheliotropism: blade ______________ sun
Chasing the sun: heliotropism
• Diaheliotropism ex:
• Dicoria canescens: annual plant. Death Valley
National Park CA
– Eureka Dunes: 680 ft. tall!
Chasing the sun: heliotropism
• Dicoria canescens: Germinates after rains
• Diaheliotropism maximizes
Chasing the sun: heliotropism
• Local example (crop)?
Chasing the sun: heliotropism
• Ex, cotton (Gossypium hirsutum)
Ch. 2 Photosynthesis (Ps) and Light
Ps: Importance
• 1) Energy to
• 2) C to
• 3) O2 for aerobic respiration (Rs)
Photosynthesis: Importance
• Mitochondria and chloroplasts
Photosynthesis: Importance
• Mitochondria and chloroplasts
• T/F: Plants have only chloroplasts in their cells (no
mitochondria)
Photosynthesis (Ps) vs. Respiration (Rs)
• Basics:
• Net Ps = CO2 uptake/release
• Net Ps = Gross Ps (Ps rate) – Rs
Photosynthesis (Ps) vs. Respiration (Rs)
• Basics:
• Net Ps = CO2 uptake/release
• Net Ps = Gross Ps (Ps rate) - Rs
– Net Ps negative in dark
• Compensation point: light intensity where net Ps
How measure it?
• Net Ps: IRGA (Infrared Gas Analyzer)
– Measure CO2 before/after
– Difference: net Ps
Net Ps = Gross Ps - Rs
IRGAs
How measure it?
• Net Ps: IRGA (Infrared Gas Analyzer)
– Measure CO2 before/after air flows
– Difference: net Ps
• How determine Gross Ps?
Net Ps = Gross Ps - Rs
IRGAs
Photosynthesis (Ps)
• 3 patterns:
– C3 Ps
– C4 Ps
– CAM Ps
• Leaf anatomy
• Chemical reactions
BIOL 3060 review!
Leaf anatomy C3 plant
• 2 layers (w/
chloroplasts)
– Palisade
mesophyll
– Spongy
mesophyll
Leaf anatomy C3 plant
• 2 layers (w/
chloroplasts)
– Palisade
mesophyll
– Spongy
mesophyll
• Vein: bundle
sheath (small
cells, usually
chloroplasts)
C3 Ps Overview
• C uptake & Ps day
• Night: no light, no Ps. Stomata closed
Mesophyll cell
BIOL 1020 review!
C3 Ps Overview
• 2 major stages:
• 1) Light reactions: light energy to
• 2) Calvin cycle (dark reactions): CO2 to
BIOL 1020 review!
C3 Ps Overview
• 1) Light reactions
– Make high-energy:
• ATP
• NADPH: high-energy electron carrier.
Involves photolysis: split water,
BIOL 1020 review!
C3 Ps Overview
• 2) Calvin Cycle
– C (CO2 ) energized (use ATP & NADPH)
– Make C-H bonds (reduces C)
– Sugar (glucose) made
BIOL 1020 review!
C3 Ps Overview
• 2) Calvin Cycle
• 2 main stages
– Fix CO2 (C inorganic to organic), C fixation
step
– Energize C (make C-H bonds)
BIOL 1020 review!
C3 Ps Overview
• 5-C molecule (RuBP)
starts
• Rubisco (enzyme)
adds 1 C, makes 2
3-C pieces (PGA)
• Why called C3 Ps?
Fig. 2.3
BIOL 1020 review!
C3 Ps Overview
• C reduced
(energized) by ATP +
NADPH
• 6 CO2 makes 1
glucose.
Fig. 2.3
Fatal Flaws of Fotosynthesis!
Fatal Flaws of Fotosynthesis!
• 1) Water loss/CO2 gain conundrum (=dilemma)
Fatal Flaws of Fotosynthesis!
• 1) Water loss/CO2 gain conundrum (=dilemma)
• To gain C: open stomata, will lose water!
Fatal Flaws of Fotosynthesis!
• 2) Photorespiration
• Not respiration in mitochondria (aerobic respiration)
Fatal Flaws of Fotosynthesis!
• 2) Photorespiration begins chloroplast
• RuBP + O2, catalyzed by Rubisco!
Box 2A
Fatal Flaws of Fotosynthesis!
• 2) Photorespiration
• Makes PGA (3 C) and glycolate (2 C)
• Glycolate: 1 C to amino acids, the other to CO2
Glycolate
Box 2A
Fatal Flaws of Fotosynthesis!
• 2) Photorespiration
• Net result: LOSS C (NOT C gain)
• What drives photorespiration?
Fatal Flaws of Fotosynthesis!
• 2) Photorespiration
• What drives photorespiration? Increases as:
– 1) light intensity increases
Fatal Flaws of Fotosynthesis!
• 2) Photorespiration
• What drives photorespiration? Increases as:
– 1) light intensity increases
– 2) leaf temperature increases
Fatal Flaws of Fotosynthesis!
• 2) Photorespiration
• What drives photorespiration? Increases as:
– 3) ratio O2:CO2 increases
• More CO2, lots Ps
• Less CO2, less Ps
Atmosphere:
0.04% CO2
21% O2