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Photosynthesis and Heliotropism in Plants

This article explores the importance of photosynthesis in plants and how they respond to sunlight through heliotropism. It discusses the different patterns of photosynthesis, leaf anatomy, and the challenges faced by plants in the process.

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Photosynthesis and Heliotropism in Plants

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  1. Ch. 2 Light and Photosynthesis (Ps)

  2. Sunflecks: Bad • Sunflecks & drought stress • Ex, regeneration Abies magnifica (CA red fir)

  3. Sunflecks • Ex, regeneration Abies magnifica (CA red fir) • Seedling pattern determined by

  4. Chasing Sun: heliotropism • Move leaf (heliotropism): rotate • Diaheliotropism: blade ______________ sun

  5. Chasing the sun: heliotropism • Diaheliotropism ex: • Dicoria canescens: annual plant. Death Valley National Park CA • Eureka Dunes: 680 ft. tall!

  6. Chasing the sun: heliotropism • Dicoria canescens: Germinates after rains • Diaheliotropism maximizes

  7. Chasing the sun: heliotropism • Local example (crop)?

  8. Chasing the sun: heliotropism • Ex, cotton (Gossypium hirsutum)

  9. Ch. 2 Photosynthesis (Ps) and Light

  10. Ps: Importance • 1) Energy to • 2) C to • 3) O2 for aerobic respiration (Rs)

  11. Photosynthesis: Importance • Mitochondria and chloroplasts

  12. Photosynthesis: Importance • Mitochondria and chloroplasts • T/F: Plants have only chloroplasts in their cells (no mitochondria)

  13. Photosynthesis (Ps) vs. Respiration (Rs) • Basics: • Net Ps = CO2 uptake/release • Net Ps = Gross Ps (Ps rate) – Rs

  14. 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

  15. How measure it? • Net Ps: IRGA (Infrared Gas Analyzer) • Measure CO2 before/after • Difference: net Ps Net Ps = Gross Ps - Rs IRGAs

  16. 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

  17. Photosynthesis (Ps) • 3 patterns: • C3 Ps • C4 Ps • CAM Ps • Leaf anatomy • Chemical reactions BIOL 3060 review!

  18. Leaf anatomy C3 plant • 2 layers (w/ chloroplasts) • Palisade mesophyll • Spongy mesophyll

  19. Leaf anatomy C3 plant • 2 layers (w/ chloroplasts) • Palisade mesophyll • Spongy mesophyll • Vein: bundle sheath (small cells, usually chloroplasts)

  20. C3 Ps Overview • C uptake & Ps day • Night: no light, no Ps. Stomata closed Mesophyll cell

  21. BIOL 1020 review! C3 Ps Overview • 2 major stages: • 1) Light reactions: light energy to • 2) Calvin cycle (dark reactions): CO2 to

  22. BIOL 1020 review! C3 Ps Overview • 1) Light reactions • Make high-energy: • ATP • NADPH: high-energy electron carrier. Involves photolysis: split water,

  23. BIOL 1020 review! C3 Ps Overview • 2) Calvin Cycle • C (CO2 ) energized (use ATP & NADPH) • Make C-H bonds (reduces C) • Sugar (glucose) made

  24. 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)

  25. 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

  26. BIOL 1020 review! C3 Ps Overview • C reduced (energized) by ATP + NADPH • 6 CO2 makes 1 glucose. Fig. 2.3

  27. Fatal Flaws of Fotosynthesis!

  28. Fatal Flaws of Fotosynthesis! • 1) Water loss/CO2 gain conundrum (=dilemma)

  29. Fatal Flaws of Fotosynthesis! • 1) Water loss/CO2 gain conundrum (=dilemma) • To gain C: open stomata, will lose water!

  30. Fatal Flaws of Fotosynthesis! • 2) Photorespiration • Not respiration in mitochondria (aerobic respiration)

  31. Fatal Flaws of Fotosynthesis! • 2) Photorespiration begins chloroplast • RuBP + O2, catalyzed by Rubisco! Box 2A

  32. 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

  33. Fatal Flaws of Fotosynthesis! • 2) Photorespiration • Net result: LOSS C (NOT C gain) • What drives photorespiration?

  34. Fatal Flaws of Fotosynthesis! • 2) Photorespiration • What drives photorespiration? Increases as: • 1) light intensity increases

  35. Fatal Flaws of Fotosynthesis! • 2) Photorespiration • What drives photorespiration? Increases as: • 1) light intensity increases • 2) leaf temperature increases

  36. Fatal Flaws of Fotosynthesis! • 2) Photorespiration • What drives photorespiration? Increases as: • 3) ratio O2:CO2increases • More CO2, lots Ps • Less CO2, less Ps • Atmosphere: • 0.04% CO2 • 21% O2

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