Photosynthesis reducing agent

The bulk of root products are C compounds derived from products of photosynthesis. The root products that are not C compounds are few (H", inorganic ions, water, electrons) but nevertheless are deemed to be highly significant. Both H and electrons may be secreted as C compounds in the form of undissociated acids and reducing agents, respectively. 

Photosynthesis in green plants occurs in two basic processes. In the dark (the Calvin cycle) carbon dioxide is reduced by a strong reducing agent, the reduced form of nicotinamide adeninedinucleotide phosphate, NADPH2, with the help of energy obtained from the conversion of ATP to ADP ... 

The Z scheme is a mechanism whereby electrons are transferred from water to NADP +. This process produces the reducing agent NADPH required for fixing carbon dioxide in the light-independent reactions of photosynthesis. Removal of the electrons from water also results in the production of oxygen. As electrons flow from PSII to PSI, protons are... 

We already know from our earlier mapping of the path of carbon in photosynthesis that we need not only a reducing agent for the reduction of carbohydrate but also, in addition, a rather specific type of chemical. Since we know the exact steps for carbon reduction, we were able to... 

Gyanobacteiia were apparently the first organisms that developed the ability to use water as the ultimate reducing agent in photosynthesis. As we have seen, this feat required the development of a second photosystem as well as a new variety of chlorophyll, chlorophyll a rather than bacteiiochlorophyll in this case. Ghlorophyll b had not yet appeared on the scene, as it occurs only in eukaryotes. The basic system of aerobic photosynthesis was in place with cyanobacteria. As a result of aerobic photosynthesis by cyanobacteria, the Earth... 

In an alternative approach to mimic tyrosinase activity a copper(I)-copper(n) redox couple and a hydroquinone-quinone redox couple were incorporated in one complex (scheme 17). The hydroquinone moiety should act as an electron shunt between an external reducing agent, i.e. ascorbic acid, zinc or electrochemical reduction, and the copper ions. Catalytic oxygenation by monooxygenases is usually accompanied by the formation of water, with the aid of an external electron and proton source.35 46 Activation of O2 by dinuclear copper(I) complex 58 results in superoxo- or p-peroxo-dicopper(II) complex 59, which oxygenates an external substrate molecule. Internal electron transfer to quinone dicopper(II) complex 60 is followed by quinone to hydroquinone reduction. The electron transfer system shown here is reminiscent of the quinone based systems found in the primary photochemical step of bacterial photosynthesis, and in (metallo)porph3nin-quinone electron transfer systems.In contrast to expectation, the hydroquinone dinuclear copper(II) complex 60 (L = (2-pyridylethyl)formidoyl, scheme 17), designed to mimic step c in this cycle, is a stable system in which the hydroquinone moiety is not oxidized to a quinone structure 61. 

Identify the oxidizing agent and the reducing agent in the photosynthesis reaction. 

---