State  in brief about the Macronutrients 

Each element is specific in its function in plant metabolism, however, the exact functions for a number of them are still not known. These essential elements exist as structural components of a cell, maintain cellular organisations, function in energy transformations and in enzyme reactions.  

Carbon, hydrogen and oxygen form about 94% of the dry mass of plants.  These elements are obtained from carbon dioxide and water which are converted to carbohydrates photochemically and ultimately  transformed to protein and protopl asm. Besides their structural role, they provide energy required for the growth and development of plants by oxidative breakdown during cellular respiration. These elements, however, are not considered to be mineral nutrients.