Photosynthesis models

As discussed above, the photosynthetic reaction center solves the problem of rapid charge recombination by spatially separating the electron and hole across the lipid bilayer. In order to achieve photoinitiated electron transfer across this large distance, the reaction center uses a multistep sequence of electron transfers through an ensemble of donor and acceptor moieties. The same strategy may be successfully employed in photosynthesis models, and has been since 1983 [42-45]. The basic idea may be illustrated by reference to a triad Dj-D2-A, where D2 represents a pigment whose excited state will act as an electron donor, Di is a secondary donor, and A is an electron acceptor. Excitation of D2 will lead to the following potential electron transfer events. 

A Z-scheme system mimicking the plant photosynthesis model developed with Pt-loaded Ti02 for HER and rutile Ti02 for OER. A IO3 /I shuttle was used as redox mediator. 330... 

Berthon J. F. and Morel A. (1992) Validation of a spectral light-photosynthesis model and use of the model in conjunction with remotely sensed pigment observations. Limnol. Oceanogr. 37(4), 781—796. 

Wemer C., Ryel RJ., Correia O., Beyschlag W. Effects of photoinhibition on whole-plant carbon gain assesed with a photosynthesis model. Plant Cell and Environment 2001 24 27-40. 

Quinones are firmly established in photosynthesis models. But how about vitamins E and K How do quinones work in animals First of all they transport electrons in a similar way as in photosynthesis (Metzler, 1977 Voet, 1990). Second, tocopherol is known to act as an antioxidant or radical quencher. The radical chain starting with the decomposition of unsaturated lipid peroxides, for example, is inhibited by tocopherol, which produces long-lived semiquinone radicals (Scheme 7.2.10). Vitamin E prevents, for example, sterility in rats fed rancid lipids. Vitamin E in connection with carotenes is also used as a stabilizer for diet margarines containing large amounts of essential fatty acids. Another possible activity of tocopherol is participation in oxidative phosphorylation a hydroquinone is mono-esterified with phosphoric acid to form a quinol phosphate and then oxidized to the quinone. The cationic quinone-phosphate adduct then reacts with anionic phosphate to form pyrophosphate (Scheme 7.2.10), (Wang, 1969 Breslow, 1980 Isler and Brubacher, 1982). 

Figure 14 Comparison of photosynthesis models. Parameter values based on highlight acclimated Chlorella sorokiniana Ox=3.5 m moix V s/ph,m = 0.10 mol molph (7s,m = 1.25 X 10 mols moix s - Mx = 24 g moix ...

The variable depends on the photon flux density Iph as discussed in the previous section where the photosynthesis models of Jassby Platt and Blackman were introduced. Consequently, the specific growth rate fi can be written as a function of the photon flux density as illustrated in Fig. 16 ... 

Figure 17 Instantaneous specific growth rate fipi of a microalga as a function of photon flux density /ph and the influence of photoacclimation. The specific growth rate is derived from a substrate balance according to Pirt in combination with the photosynthesis models of Jassby and Platt. Parameter values based on Chlorella sorokiniana ax=3.5 m moix (high light) Ox=7.0 m moix (low light) ...

This observable yield is different from the maximal yield of sugar on photons Ts/ph.m which was defined earlier and which is one of the parameters in the photosynthesis models. This observable yield is a measure of the actual efficiency at which light energy is used in photosynthesis. In Fig. 19 it can be seen that when the photon flux density Jph approaches 0 molph m the maximal yield of 0.10 mols molph is reached. 

PET in artificial photosynthesis model connected by covalent bonding... 

By combining a two-phase flow simulator and the photosynthesis model, Sato et al. [92,93] explored the amount of carbon fixation and the growth curve of microalgae. A similar approach was applied to simulate a tubular recycled PBR for macro-algal cell suspension cultures [49]. This model predicts a critical ceU density at which photosynthetic biomass production switches from a rate-limited process to a CO2 delivery-limited process. Rate-limited growth proceeds only to this critical cell... 

V. Rosenbach-Belkin. The Primary Reactants in Bacterial Photosynthesis Modeling bv in vitro Preparation. Weizmann Institute of Science, Rehovot, Israel (1988)... 

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