Q.Essential macroelements are ............

Plants absorb roughly 36 to 40 elements of the periodic table from soil, air and water, taken up mainly as dissolved ions (e.g. PO4, CO3, SO4) through the roots. Carbon comes from atmospheric CO2, hydrogen from water, and oxygen from air and water -- so C, H and O are not of mineral origin -- while nitrogen is derived from the soil. Elements are judged truly essential by the Arnon and Stout (1939) criteria: necessary for normal growth and reproduction, having a specific irreplaceable function, and directly involved in nutrition. Minerals are informally grouped into macroelements (C, H, O, N, P, K, S, Ca, Mg, Fe -- required in large amounts, mainly structural/nutritive) and microelements (Zn, Cu, Mn, B, Mo, Cl -- required only in trace amounts, mainly as enzyme cofactors), though this quantity-based scheme, like the older essential/non-essential one, is now considered a simplification and minerals are classified today by biochemi …