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C4 Photosynthesis
C4 Photosynthesis and Evolution
| Question | Answer |
|---|---|
| First appearance of non-vascular land plants | Was 475 mya and triggered a decrease in CO2 levels |
| Causes of increased CO2 levels | 80% burning fossil fuels 20% land-use changes |
| Rubisco Function | CO2 diffuses into the chloroplasts in the leaf, where Rubisco is located. It is the enzyme responsible for assimilating CO2 BUT it can also react with oxygen |
| Carboxylation Reaction | Happens in C3 plants. C5 molecule + CO2 + H2O -> Rubisco -> x2 C3 molecules (used as primary building blocks + fixes CO2 from air) |
| Oxygenation Reaction | C5 molecule + O2 -> Rubisco -> C3 molecule, C2 molecule (waste product) *does NOT fix CO2 Sometimes 2 C2 molecules are converted into a C3 molecule and a CO2, which salvages some carbon but uses lots of energy (photorespiration) |
| Effect of higher temperatures on C3 plants | 1. solubility of CO2 and O2 decreases, but CO2 more (less carboxylation) 2. speed of reactions (Vmax) of Rubisco increases, but more for oxygenation (less carboxylation) 3. lower affinity of Rubisco for both 2, but more for CO2 (less carboxylation) |
| Result of higher temperatures | Higher oxygenation = more waste products = less CO2 assimilation/decreased efficiency |
| C4 plants anatomy | C4 plants have Kranz anatomy (epidermis, mesophyll, bundle sheath cells, vascular bundle) |
| C4 plants function | Very high CO2 concs at site of Rubisco due to pumping mechanisms -> suppresses oxygenation reaction CO2 is drawn in much faster, so conc in the intercellular space is lower (higher conc gradient) so more CO2 flows in oxygenase reaction is NOT favoured |
| C4 plants in hot climates | Enzymes concentrate the CO2, fuelling Rubisco more efficiently. Due to increased efficiency they can close their stomates more, so lose less water while still photosynthesising (they minimise energy loss from photorespiration) |
| Cause of evolution | A drop in CO2 concentrations, which caused strong selection pressures in hotter environments (strong correlation with higher temperatures and abundance of C4 plants). Because C4 plants are more efficient at photosynthesis in warm climates |
| Requirement for evolution | a mutable genome containing genetic templates that can evolve/duplicate to provide the traits necessary for adaptation (recruitment and modification of existing genes) |
| Spread | C4 plants are widely spread and polyphyletic (~7500 species), so it must have been easy to evolve |
| Three types of C4 biochemistry | NAD malic enzyme NADP malic enzyme PEP carboxykinase These are all decarboxylating enzymes that take the CO2 off C4 molecules and transfer to Rubisco. C4 plants produce high levels of at least one of these enzymes |
| Phases | there are 7 phases in the evolution of C4 plants, and plant species exist all the way along the stages |
| Isoforms | Isoforms of enzymes found in C4 plants exist in C3 plants too, but have evolved to become more specialised and abundant |
Created by:
mishm
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