There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 6-carbon sugars. For most organisms, the pentose phosphate pathway takes place in the cytosol; in plants, most steps take place in plastids.Similar to glycolysis, the pentose phosphate pathway appears to have a very ancient evolutionary origin.or most organisms, the pentose phosphate pathway takes place in the cytosol; in plants, most steps take place in plastids. Similar to glycolysis, the pentose phosphate pathway appears to have a very ancient evolutionary origin.