Nitrogen assimilation during photosynthesis

During photosynthesis nutrients, including nitrogen, are assimilated into organic matter and molecular oxygen is produced, depicted schematically by... 

Mineral nitrogen in any form accepted by plants cannot be directly incorporated into proteins, however, it needs first to be transformed via keto acids into molecules of amino acids. All these processes are anabolic and endothermic and thus, they require energy, which is mainly released by the oxidation of organic substances produced during photosynthesis and CO2 assimilation. 

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