Q.3:- Explain with examples: macronutrients, micronutrients, beneficial nutrients, toxic elements and essential elements.
Macronutrients : Those elements which are generally present in plant tissues in large amounts (in excess of 10 mmole Kg-1 of dry matter) and are involved in the synthesis of organic molecules and development of osmotic potential are called macronutrients or macroelement, e.g. carbon, hydrogen, oxygen, nitrogen, sulphur, potassium, calcium and magnesium etc.
Micronutrients : Those elements which are required by plants in’very small amounts (less than 10 mmole Kg-1 of dry matter) are called micronutrients, e.g. iron, zinc, manganese, boron, copper, molybdenum, chlorine and nickel. These elements are mostly involved in the functioning of enzymes as cofactor or metal activators.
Beneficial nutrients : Those elements which are required by higher plants along with the macro and micronutrients are called beneficial nutrients, e.g. cobalt, silicon, sodium and selenium.
Toxic elements : Any mineral element if supplied to plant tissue in such concentration that it reduces the dry weight of tissues by about 10 percent, is called toxic element. e.g. manganese toxicity leads to the appearance of brown spots surrounded by chlorotic veins. Excess of manganese induces deficiency of iron, magnesium and calcium.
Essential elements : Any element required by living organisms to ensure normal gfbwth, development, maintenance, metabolism and causes deficiency symptoms if not supplied to the plant from external medium is called essential element, e.g. C, H, O, N, P, K, S, Mg, Ca, Mn, Cu, Mo, Zn, B, Cl, etc. Potassium plays an important role in opening and closing of stomata, protein synthesis etc. Magnesium is found in chlorophyll and phosphorus in ATP. Mg2+ is an activator for both ribulose bisphosphate carboxylase-oxygenase and phosphsenol pyruvate carboxylase.Zn2+ is an activator of alcohol dehydrogenase and Mo of nitrogenase during nitrogen metabolism.