Photosynthesis, trees importance

Photosynthesis (Scheme 1.2) is the source of food and fossil fuel and has played an important role in the origin of life.a A fully grown beech tree assimilates about 10 m3 of C02 (contained in 4 x 104 m3 of air) on a sunny day, producing the same amount of 02 and 12 kg of carbohydrates. Globally, photosynthesis stores about 2 x 10121 of C02 in biomass per year, the equivalent of 2 x 1019kJ, most of which, however, is eventually returned to the atmosphere by reoxidation. 

The second line of evidence relates to more recent metabolic innovations such as photosynthesis. LUCA, it seems, could not photosynthesize. No form of photosynthesis based on chlorophyll is found in any archaea. A completely different form of photosynthesis, based on a pigment called bacteriorhodopsin, similar to the photoreceptor pigments in our eyes, is practised by the so-called halobacteria, archaea that live in high-salt conditions. This mode of photosynthesis is not found in any bacteria. These disparate forms of photosynthesis presumably evolved indepen-dently in bacterial and archaeal lineages some time after the age of LUCA, and subsequently remained tied to their respective domains. If a metabolic innovation as important as photosynthesis did not cross from one domain to another, there is no reason to think that other forms of respiration would have done so. We should certainly be wary of postulating that respiratory genes crossed domains unless we have evidence that they did so and the evidence from evolutionary trees suggests that they did not. 

Critical loads to forest soils have been proposed for the deposition of total nitrogen, total sulfur, and total acidity. Critical loads models assume that indirect effects occur on trees via changes in soil chemistry. However, there exist important direct and indirect impacts of wet and dry deposition on leaves and needles with regard to photosynthesis, nutrient leaching, stomatal function, and leaf surface properties. The values for critical loads are influenced by precipitation, elevation, soil texture, and base cation deposition. 

The importance of heterocycles in life was recognized as the nascent stage of organic chemistry two centuries ago with isolation of alkaloids such as morphine from poppy seeds, quinine from cinchona barks, and camptothecin from the Chinese joy tree. Today, heterocycles are found in numerous fields of biochemical and physiological such as photosynthesis, amino acids, DNA bases, vitamins, endogenous neurotransmitters, and so on. 

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