Biophysical considerations activity

Isoprene (2-methyl-1,3-butadiene, C5H8) is unique among the biogenic hydrocarbons in its relationship to photosynthetic activity in a plant. It is emitted from a wide variety of mostly deciduous vegetation in the presence of photosynthetically active radiation, exhibiting a strong increase in emission as temperature increases. Not only do the isoprene and terpenoid emissions vary considerably among plant species, but the biochemical and biophysical processes that control the rate of these emissions also appear to be quite... 

The quantum yield is expressed as the number of moles of O2 evolved (or CO2 fixed) per mole absorbed quanta of photosynthetically active radiation (400-700 nm). Obviously the quantum yield is constrained by biophysical/biochemical processes. Healthy leaves of C3 plants show almost identical quantum yields for O2 evolution at a saturating partial pressure of C02f irrespective of taxa and habitats of the materials, which approach the theoretical maximum of around 0.11 mol O2 mol absorbed quanta (2,3). Compared with this, the quantum yield is considerably lower at the CO2 partial pressure of around 350 bar due to photorespiration. Nevertheless, variation in the quantum yield among various C3 plants remains small also at this CO2 partial pressure. Thus, initial slopes of the light response curves are not markedly different among "healthy C3 plants. 

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