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) O 2 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 = CO 2 uptake/release Net Ps = Gross Ps (Ps rate) – Rs

Photosynthesis (Ps) vs. Respiration (Rs) Basics: Net Ps = CO 2 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 CO 2 before/after –Difference: net Ps IRGAs Net Ps = Gross Ps - Rs

How measure it? Net Ps: IRGA (Infrared Gas Analyzer) –Measure CO 2 before/after air flows –Difference: net Ps How determine Gross Ps? IRGAs Net Ps = Gross Ps - Rs

Photosynthesis (Ps) 3 patterns: –C 3 Ps –C 4 Ps –CAM Ps Leaf anatomy Chemical reactions BIOL 3060 review!

Leaf anatomy C 3 plant 2 layers (w/ chloroplasts) –Palisade mesophyll –Spongy mesophyll

Leaf anatomy C 3 plant 2 layers (w/ chloroplasts) –Palisade mesophyll –Spongy mesophyll Vein: bundle sheath (small cells, usually chloroplasts)

C 3 Ps Overview C uptake & Ps day Night: no light, no Ps. Stomata closed Mesophyll cell

C 3 Ps Overview 2 major stages: 1) Light reactions: light energy to 2) Calvin cycle (dark reactions): CO 2 to BIOL 1020 review!

C 3 Ps Overview 1) Light reactions –Make high-energy: ATP NADPH: high-energy electron carrier. Involves photolysis: split water, BIOL 1020 review!

C 3 Ps Overview 2) Calvin Cycle –C (CO 2 ) energized (use ATP & NADPH) –Make C-H bonds (reduces C) –Sugar (glucose) made BIOL 1020 review!

C 3 Ps Overview 2) Calvin Cycle 2 main stages –Fix CO 2 (C inorganic to organic), C fixation step –Energize C (make C-H bonds) BIOL 1020 review!

C 3 Ps Overview 5-C molecule (RuBP) starts Rubisco (enzyme) adds 1 C, makes 2 3-C pieces (PGA) Why called C 3 Ps? Fig. 2.3 BIOL 1020 review!

C 3 Ps Overview C reduced (energized) by ATP + NADPH 6 CO 2 makes 1 glucose. Fig. 2.3 BIOL 1020 review!

Fatal Flaws of Fotosynthesis!

1) Water loss/CO 2 gain conundrum (=dilemma)

Fatal Flaws of Fotosynthesis! 1) Water loss/CO 2 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 + O 2, 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 CO 2 Box 2A Glycolate

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 O 2 :CO 2 increases More CO 2, lots Ps Less CO 2, less Ps Atmosphere: 0.04% CO 2 21% O 2