Oxygen in photosynthesis

We cover each of these types of examples in separate chapters of this book, but there is a clear connection as well. In all of these examples, the main factor that maintains thermodynamic disequilibrium is the living biosphere. Without the biosphere, some abiotic photochemical reactions would proceed, as would reactions associated with volcanism. But without the continuous production of oxygen in photosynthesis, various oxidation processes (e.g., with reduced organic matter at the Earth s surface, reduced sulfur or iron compounds in rocks and sediments) would consume free O2 and move the atmosphere towards thermodynamic equilibrium. The present-day chemical functioning of the planet is thus intimately tied to the biosphere. 

OXII is responsible for the production of molecular oxygen in photosynthesis. A manganese complex, probably with four atoms of manganese, is attached to a protein molecule. It reduces OXjj which is recycled for use by another excited chlorophyll molecule in PS-II. In the redox reaction the manganese shuttles between two oxidation states with each manganese atom... 

R Emerson and W Arnold (1932) The photochemical reaction in photosynthesis. J Gen Physiol 16 191-205 Govindjee (1999) On the requirement of minimum number of four versus eight quanta of light for the evolution of one molecule of oxygen in photosynthesis A historical note. Photosynthesis Res 59 249-254 RE Fenna, BW Mathews, JM Olson and EK Shaw (1974) Structure of a bacteriochlorophyll-protein from the green photosynthetic bacterium Chlorobium limicola crystallographic evidence fora trimer. J Mol Biol 84 231 -240... 

Green plants make glucose and oxygen in photosynthesis, a redox process shown below. (Chapter 16)... 

Copper is one of the twenty-seven elements known to be essential to humans (69—72) (see Mineral nutrients). The daily recommended requirement for humans is 2.5—5.0 mg (73). Copper is probably second only to iron as an oxidation catalyst and oxygen carrier in humans (74). It is present in many proteins, such as hemocyanin [9013-32-3] galactose oxidase [9028-79-9] ceruloplasmin [9031 -37-2] dopamine -hydroxylase, monoamine oxidase [9001-66-5] superoxide dismutase [9054-89-17, and phenolase (75,76). Copper aids in photosynthesis and other oxidative processes in plants. 

An extensive source of natural pollutants is the plants and trees of the earth. Even though these green plants play a large part in the conversion of carbon dioxide to oxygen through photosynthesis, they are still the major source of hydrocarbons on the planet. The familiar blue haze over forested areas is nearly all from the atmospheric reactions of the volatile organics... 

Heavy isotopes endow the compounds in which they appear with slightly greater masses than their unlabeled counterparts. These compounds can be separated and quantitated by mass spectrometry (or density gradient centrifugation, if they are macromolecules). For example, O was used in separate experiments as a tracer of the fate of the oxygen atoms in water and carbon dioxide to determine whether the atmospheric oxygen produced in photosynthesis arose from HgO, COg, or both ... 

Elements of photosynthesis elucidated by J. Ingenhousz green plants in daylight use CO2 and evolve oxygen in the dark they liberate CO2. 

About 8(1 percent of the electric energy used in the United States is derived from stored energy in coal. The stored energy has its origin in photosynthesis. Coal is the end product of the accumulation of plant matter in an oxygen-deficient environment where burning is thwarted. Formation takes millions of years. Proven reseiwes of coal in the United States are upwards of 500 billion tons, a reserve so great that even if coal continues to be burned at a rate of over one billion tons per year, the reserves will last for hundreds of years. 

This result shows that the oxygen produced in photosynthesis comes from the water molecules, not the carbon dioxide molecules. 

A small fraction (less than 1%) of the fixed carbon produced by photosynthesis is buried and physically removed from any potential reaction with oxygen (until the buried material is brought to the surface - at a much later time). Thus, the oxygen in our contemporary atmosphere is the consequence of many millions of years of fixed carbon burial. More details on this topic can be found in Chapters 8 and 11. 

Fig. 1. (a) Schematic representation of the three types of anoxygenic ([1] and [2]) and oxygenic ([3]) photosynthesis found in plants and bacteria, (b) Phylogenetic tree based on 16S-rRNA sequence comparisons featuring only photo synthetic phyla. 

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... 

Fourthly living things do not just respond to the climate—they affect it as well. Plants consume carbon dioxide and produce oxygen through photosynthesis. Earthbound plants take carbon dioxide directly from the air drifting photosynthetic micro-organisms called phytoplankton use carbon dioxide dissolved in water. 

A study of photosynthetic organisms other than green plants has revealed that certain bacteria, such as the purple sulfur bacteria, utilize H2S instead of H20 as a reductant in photosynthesis. The product obtained is elemental sulfur instead of oxygen ... 

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