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Ch. 2 Photosynthesis (Ps) and Light

Ch. 2 Photosynthesis (Ps) and Light. Fatal Flaws of Fotosynthesis!. 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: LOSS C ( NOT C gain) What drives?.

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Ch. 2 Photosynthesis (Ps) and Light

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  1. Ch. 2 Photosynthesis (Ps) and Light

  2. Fatal Flaws of Fotosynthesis!

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

  4. Fatal Flaws of Fotosynthesis! • 2) Photorespiration: LOSS C (NOT C gain) • What drives?

  5. Fatal Flaws of Fotosynthesis! • 2) Photorespiration • Increases as: • 1) light intensity increases • 2) leaf temperature increases • 3) ratio O2:CO2increases • More CO2, lots Ps • Less CO2, less Ps

  6. C4 Photosynthesis • 3 patterns: • C3 Ps • C4 Ps • CAM Ps • Minimize FFF • C4 photosynthesis

  7. C4 leaf anatomy • Kranz anatomy (“wreath:” German) • Bundle sheath cells (BSC)

  8. C4 pathway • Mesophyll fix CO2 New enzyme (PEP carboxylase)

  9. C4 pathway • PEP carboxylase: 3 C (PEP) + CO2 = 4 C acid • Acid to BSC Why called C4 Ps?

  10. C4 pathway • BSC: Reaction reversed….CO2 + pyruvate (3 C) • CO2 to Calvin Cycle • Pyruvate to mesophyll, converted to PEP Calvin Cycle (Rubisco) C shuttle!!

  11. C4 pathway • C fixation & Ps separated

  12. C4 pathway • Advantages? FFF?

  13. C4 advantages • Benefits: • 1) PEP Carboxylase fix C • High affinity • No reaction Photorespiration: A FFF!

  14. C4 advantages • Benefits: • 2) CO2 concentrated bundle sheath • O2:CO2 low, low _________ • If photorespiration, CO2 ________

  15. A FFF! C4 advantages • Benefits: • 3) Less • PEP carboxylase hi affinity CO2“Sucks” CO2 well Stoma C4 Good sucker?

  16. C4 advantages • Benefits: • 4) Decrease Rubisco: more Ps w/ less N • High NUE (nitrogen use efficiency): biomass made per _______ Now: CAM

  17. CAM photosynthesis • CAM: Crassulacean Acid Metabolism • Crassulaceae: family succulents • Acid: Leaves acidic Diamorpha smallii (Crassulaceae)

  18. Leaf anatomy • Succulent (fleshy) leaves (or photosynthetic stems)

  19. Leaf anatomy • Succulent (fleshy) leaves (or photosynthetic stems) • Mesophyll not layered • Cells large: large vacuoles • Vascular bundle sheath _____

  20. CAM pathway • Separates C fixation & Ps in time rather than space! Separation in space: C4

  21. CAM pathway • Night: • Stomata _______ • CO2 fixed: PEP carboxylase makes 4 C acid Malic acid

  22. CAM pathway • Acid stored __________ • Leaf pH down @ night (“acid drop”) Acid drop in skateboarding

  23. CAM pathway • Day • Stomata close. • Reaction reversed • Ps: Calvin Cycle

  24. CAM pathway • Separates C fixation & Ps in time (not space!) Day Night

  25. CAM advantages • 1) PEP carboxylase fix C: photorespiration

  26. CAM advantages • 2) Stomata open night.

  27. CAM advantages • 3) Stomata close day. Seal CO2 in, low O2:CO2 ratio = low ____________

  28. CAM variation • Some: CAM when stressed (C3 other times) • CAM & succulence correlated (Fig. 2.14) Aeonium arboreum Fig. 2.14 More succulence, More CAM

  29. CAM • Carbon cycling: capture respiration CO2 night, ________ • Ex, Welwitschia mirabilis (Namib desert) • Gymnosperm Some plants may be 1,000 yr old

  30. Comparing C3, C4, CAM plants • Taxa: most plants (90%) • C4 plants: 3% flowering plants • Exs: • Some grasses: Sugar cane (Saccharum spp.)

  31. Amaizing Facts* • Corn or maize (Zea mays) *another corny Boyd joke.....

  32. Comparing C3, C4, CAM plants • Dicots: • Kudzu (Pueraria montana)

  33. Comparing C3, C4, CAM plants • Typical C4 habitat: • Temperate areas: • winter/spring ___ season • summer ___ season

  34. Comparing C3, C4, CAM plants • % grass flora C4 in N. America Fig. 2.18

  35. Comparing C3, C4, CAM plants • CAM: in 20 families flowering plants (7% all plants) • Exs: many cacti (saguaro, cholla) Saguaro “arms”

  36. Comparing C3, C4, CAM plants • CAM: in 20 families of flowering plants • Exs: Agave species • Economic use??

  37. Comparing C3, C4, CAM plants • Exs: some Crassulaceae (Diamorpha smallii)

  38. CAM and Epiphytes • Epiphytes: plants • Abundant tropical rain forests

  39. CAM and Epiphytes • Spanish moss (Tillandsia usneoides) • CAM plant: pineapple family (Bromeliaceae)

  40. Comparing C3, C4, CAM plants • Exs: many Orchidaceae (esp. epiphytic ones)

  41. Comparing C3, C4, CAM plants • CAM plants: • Succulents (deserts) • Epiphytes (tropical/subtropical areas)

  42. Comparing C3, C4, CAM plants • Trait C3 C4 CAM • Max. Ps rate Fig. 2.12

  43. Comparing C3, C4, CAM plants • Trait C3 C4 CAM • Optimum Ps temp. Fig. 2.11

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