Photosynthesis reaction efficiency

The first chapter introduces the theoretical framework for constructing predictive knowledge models leading to the calculation of the volumetric and surface rates of biomass production, and the thermodynamic efficiency of the process. Here, the main assumption is that photosynthesis reaction is limited by radiative transfer only. First, the predictive determination of the scattering and absorption properties of photosynthetic microorganisms of... 

Solar chemical refers to a number of possible processes that harness solar energy by absorbing sunlight in a chemical reaction in a way similar to photosynthesis in plants but without using living organisms. Metals, such as zinc, have been shown to drive photoelectrolysis of water. Transition metal compounds, such as titania, titanates, niobates, and tantalates, exhibit very low efficiency photoelectrolysis of water. Man-made photosynthesis reactions could also convert solar energy and CO2 into useful chemicals. 

Lower photosynthesis in plants under red LEDs may be associated with lower stomatal conductance, for stomata have been shown to be controlled more by blue than by red light. It has also been suggested that the narrow peak emission of red LEDs leads to an imbalance of photons available to photosystem I and photosystem II, thus altering the ratio of cycle to whole chain reaction transport, and causing a reduction in net photosynthesis. Moreover, red LEDs produced less nonphotosynthetic radiation than conventional lamps, which implicates differences in photosynthesis utilization efficiency of photons emitted from LEDs relative to broad-spectrum lamps. 

Oceanic surface waters are efficiently stripped of nutrients by phytoplankton. If phytoplankton biomass was not reconverted into simple dissolved nutrients, the entire marine water column would be depleted in nutrients and growth would stop. But as we saw from the carbon balance presented earlier, more than 90% of the primary productivity is released back to the water column as a reverse RKR equation. This reverse reaction is called remineralization and is due to respiration. An important point is that while production via photosynthesis can only occur in surface waters, the remineralization by heterotrophic organisms can occur over the entire water column and in the underlying sediments. 

Studies (see, e.g., (101)) indicate that photosynthesis originated after the development of respiratory electron transfer pathways (99, 143). The photosynthetic reaction center, in this scenario, would have been created in order to enhance the efficiency of the already existing electron transport chains, that is, by adding a light-driven cycle around the cytochrome be complex. The Rieske protein as the key subunit in cytochrome be complexes would in this picture have contributed the first iron-sulfur center involved in photosynthetic mechanisms (since on the basis of the present data, it seems likely to us that the first photosynthetic RC resembled RCII, i.e., was devoid of iron—sulfur clusters). 

In photosynthesis, the reaction involves eight photons for each oxygen molecule, each with an energy of about 1.8 eV (175kJ/mol). Hence the efficiency of... 

Photoinduced ET at liquid-liquid interfaces has been widely recognized as a model system for natural photosynthesis and heterogeneous photocatalysis [114-119]. One of the key aspects of photochemical reactions in these systems is that the efficiency of product separation can be enhanced by differences in solvation energy, diminishing the probability of a back electron-transfer process (see Fig. 11). For instance, Brugger and Gratzel reported that the efficiency of the photoreduction of the amphiphilic methyl viologen by Ru(bpy)3+ is effectively enhanced in the presence of cationic micelles formed by cetyltrimethylammonium chloride [120]. Flash photolysis studies indicated that while the kinetics of the photoinduced reaction,... 

P is crucial for several aspects of plant metabolism, especially the energy and sugar metabolism, and several enzymatic reactions, including photosynthesis. Plants have therefore developed mechanisms for the uptake and efficient use of P. Maize plants recycled N quicker from old to young tissue when P is deficient, leading to earlier leaf senescence (Usuda 1995). P-deficient plants invest more resources into root development and therefore have an increased root-to-shoot biomass ratio compared to well-nourished plants. Furthermore, they accumulate more carbohydrates in leaves and allocate more carbon to the roots (Hermans et al. 2006). 

A potentially more serious problem than that of low efficiency is the requirement that the photochemical absorber operate without any significant side reactions. For example, if the quantum yield for side reactions were 1%, then after only 100 cycles the concentration of the absorber would have decreased to 37% of its original concentration. It is interesting that in photosynthesis each chlorophyll molecule processes at least 10 photons in its lifetime in a leaf. This means that the quantum yield for reactions leading to the degradation of chlorophyll must be less than 10-5 ... 

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