Despite the presence of about 21 %O2 in the atmosphere,organs of plants and mammals are inevitably subject to lower O2 ten-sions(pO2) due to high O2 demand in metabolic active cells and limited O2 transport efficiency.In humans,for example,the pO2 decreases from the ambient 21 %(160mm Hg) of the inhaled air to 2 %-9 %in the internal organs(Brahimi-Horn and Pouyssegur,2007).
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