13505419
Descripción
Fichas por J yadonknow, actualizado hace más de 1 año
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Creado por J yadonknow
hace alrededor de 6 años
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| Pregunta | Respuesta |
| RuBisCO | C3 C Fixation CO2 -> PGA+PGA Photorespiration pathway O2-> PG+PGA |
| Diagram of cycle | aj |
| Concentrating carbon | Concentate co2 around RuBisCO Reduce oxygenase activity reduce E wastage in photorespiration |
| C4 photosynthesis - Spatial separation | btw. where co2 is initially fixed in org compounds and where RuBisCO is acting, so occuring in 2 different cells |
| Specialist anatomy and metabolism for C4 plants | 2 specialised cell types Mesophyll Bundle Sheath |
| C4 mechanism | 1. CO2 is fixed by PEPC into a 4c acid in M. 2. C4 acid moved to the BS. 3. C4 decarboxylated to produce CO2. 4. CO2 used by rubisco in usual calvin cycle 5. C3 acid is recycled back to first cell to start the cycle back again. |
| PEPC | Can discriminate btw. CO2 and O2 Substrate is HCO3- Produces 4c acid |
| Kranz anatomy | Kranz = wreath in german Rubisco only in BS cells So need to maximise BS compounds compared to C3 plants Closer vein spacing BS much bigger BS have suberin in CW to minimise CO2 escape |
| Examples | Maize, sugarcane, miscanthus a large proportion of monocots |
| Water use efficiency of PEPC | PEPC much more efficient at carboxylation than rubisco C4 can maintain a lower stomatal conductance for the same CO2 assimilation rate C4>C3 |
| Why don't all plants use C4? | The regeneration of PEP(C3) costs 2 ATP per CO2 assimilated. |
| Low 'c | At low 'c little photoresp. so C4 is too expensive to run |
| At 20'c | At ~20'c energetic cost of running C4 is equal to photorespiration |
| At high 'C | C4>PhotoR |
| Distribution changes w/ latitude | C4 superior at lower latitude C3 superior at higher latitude |
| CAM Photosynthesis | Crassulacean acid metabolism Temporal separation of initial C fix by PEPC and refix by RuBisCO |
| Process | 1.Stomata open at night when humidity ^ 'c d. 2. PEPC converts CO2->C4 acid 3. Malic aci stored in vacuoles til dawn 4. During day stomata close to conserve water 5. Daytime C4 acid -COOH, releasing CO2 and C3 acid. 6. CO2 then used by Rubisco in calvin cycle. 7. No risk of O2 coming in as stomata are closed 8. If plant cell well supplied w/ water stomata can open to direct fix C3 plants |
| 4 phases of CAM | Phase stomata process enzyme I Night open CO2 capt+stored as m |
| Diagram for this process | a |
| CAM physiology | Other traits to minimise water loss: Thick cuticles Large vacuoles Stomata w/ small apertures |
| Species distribution | Associated with succulent plants in semi-acid environments Trop. rainforests particularly among epiphytes Prickly pear introduced to australia massive success due to CAM |
| CAM switchers | Switch btw. C3 and CAM Use CAM when H2O scarce Switch when H2O available e.g. Ice plant responds to salinity and drought, ^ salinity emulates drought. |
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