Ch 2 Photosynthesis Ps and Light Fatal Flaws
- Slides: 43
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?
Fatal Flaws of Fotosynthesis! • 2) Photorespiration • Increases as: – 1) light intensity increases – 2) leaf temperature increases – 3) ratio O 2: CO 2 increases • More CO 2, lots Ps • Less CO 2, less Ps
C 4 Photosynthesis • 3 patterns: – C 3 Ps – C 4 Ps – CAM Ps • Minimize FFF C 4 photosynthesis
C 4 leaf anatomy • Kranz anatomy (“wreath: ” German) • Bundle sheath cells (BSC)
C 4 pathway • Mesophyll fix CO 2 New enzyme (PEP carboxylase)
C 4 pathway • PEP carboxylase: 3 C (PEP) + CO 2 = 4 C acid • Acid to BSC Why called C 4 Ps?
C 4 pathway • BSC: Reaction reversed…. CO 2 + pyruvate (3 C) • CO 2 to Calvin Cycle • Pyruvate to mesophyll, converted to PEP Calvin Cycle (Rubisco) C shuttle!!
C 4 pathway • C fixation & Ps separated
C 4 pathway • Advantages? FFF?
• Benefits: C 4 advantages – 1) PEP Carboxylase fix C – High affinity – No reaction Photorespiration: A FFF!
• Benefits: C 4 advantages – 2) CO 2 concentrated bundle sheath – O 2: CO 2 low, low _____ – If photorespiration, CO 2 ____
C 4 advantages A FFF! • Benefits: – 3) Less – PEP carboxylase hi affinity CO 2 “Sucks” CO 2 well Stoma C 4 Good sucker?
• Benefits: C 4 advantages – 4) Decrease Rubisco: more Ps w/ less N – High NUE (nitrogen use efficiency): biomass made per _______ Now: CAM
CAM photosynthesis • CAM: Crassulacean Acid Metabolism • Crassulaceae: family succulents • Acid: Leaves acidic Diamorpha smallii (Crassulaceae)
Leaf anatomy • Succulent (fleshy) leaves (or photosynthetic stems)
Leaf anatomy • • Succulent (fleshy) leaves (or photosynthetic stems) Mesophyll not layered Cells large: large vacuoles Vascular bundle sheath _____
CAM pathway • Separates C fixation & Ps in time rather than space! Separation in space: C 4
• Night: CAM pathway – Stomata _______ – CO 2 fixed: PEP carboxylase makes 4 C acid Malic acid
CAM pathway • Acid stored _____ • Leaf p. H down @ night (“acid drop”) Acid drop in skateboarding
• Day CAM pathway – Stomata close. – Reaction reversed • Ps: Calvin Cycle
CAM pathway • Separates C fixation & Ps in time (not space!) Night Day
CAM advantages • 1) PEP carboxylase fix C: photorespiration
CAM advantages • 2) Stomata open night.
CAM advantages • 3) Stomata close day. Seal CO 2 in, low O 2: CO 2 ratio = low ______
CAM variation • Some: CAM when stressed (C 3 other times) • CAM & succulence correlated (Fig. 2. 14) Aeonium arboreum Fig. 2. 14 More succulence, More CAM
CAM • Carbon cycling: capture respiration CO 2 night, ____ • Ex, Welwitschia mirabilis (Namib desert) • Gymnosperm Some plants may be 1, 000 yr old
Comparing C 3, C 4, CAM plants • • Taxa: most plants (90%) C 4 plants: 3% flowering plants Exs: Some grasses: Sugar cane (Saccharum spp. )
Amaizing Facts* • Corn or maize (Zea mays) *another corny Boyd joke. . .
Comparing C 3, C 4, CAM plants • Dicots: – Kudzu (Pueraria montana)
Comparing C 3, C 4, CAM plants • Typical C 4 habitat: • Temperate areas: – winter/spring ___ season – summer ___ season
Comparing C 3, C 4, CAM plants • % grass flora C 4 in N. America Fig. 2. 18
Comparing C 3, C 4, CAM plants • CAM: in 20 families flowering plants (7% all plants) • Exs: many cacti (saguaro, cholla) Saguaro “arms”
Comparing C 3, C 4, CAM plants • CAM: in 20 families of flowering plants • Exs: Agave species – Economic use? ?
Comparing C 3, C 4, CAM plants • Exs: some Crassulaceae (Diamorpha smallii)
CAM and Epiphytes • Epiphytes: plants – Abundant tropical rain forests
CAM and Epiphytes • Spanish moss (Tillandsia usneoides) • CAM plant: pineapple family (Bromeliaceae)
Comparing C 3, C 4, CAM plants • Exs: many Orchidaceae (esp. epiphytic ones)
Comparing C 3, C 4, CAM plants • CAM plants: – Succulents (deserts) – Epiphytes (tropical/subtropical areas)
Comparing C 3, C 4, CAM plants • Trait • Max. Ps rate C 3 C 4 CAM Fig. 2. 12
Comparing C 3, C 4, CAM plants • Trait • Optimum Ps temp. C 3 C 4 CAM Fig. 2. 11
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