Title Ch-9-Mineral Nutrition.pdf ✅

Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter Contents Chapter 9 Methods to Study the Mineral Requirements of Plants Essential Mineral Elements Mechanism of Absorption of Elements Translocation of Solutes Metabolism of Nitrogen The chemical substances present in food which act as a raw material for body building and maintaining its functions are termed as nutrients. Nutrients can be organic or inorganic in nature. Macromolecules such as carbohydrates, fats and proteins are organic in nature whereas CO2, H2O and mineral ions are inorganic nutrients. Plants require several inorganic nutrients or minerals for their growth, development, structure, physiology and reproduction. The study of source, mode of absorption, distribution and metabolism of various inorganic minerals by the plants is called Mineral nutrition. METHODS TO STUDY THE MINERAL REQUIREMENTS OF PLANTS To determine the essential mineral nutrients, the method is solution culture technique. In this technique, plants are grown directly in a soil-free, defined mineral solution. This solution contains all the essential elements in proper proportion that are required for proper growth and development of plants. First, this technique was demonstrated by a prominent German Botanist, Julius Von Sachs in 1860. He grew plants from seeds to maturity in a defined nutrient solution in absence of soil. This soil-less growth of plants in a nutrient solution is known as Hydroponics. Experimental set-up for Hydroponics In this process, plants are grown in a defined nutrient solution. This nutrient solution is prepared by mixing chemically pure mineral nutrient salts in purified water. The solution is taken in sterilised glass jar or polythene bottles covered with black paper. It minimises the risk of algal contamination and reaction of roots to sunlight. The jars contain split covers or corks with holes for suspending seedling, a funnel for adding solution and a bent tube for aeration. Regular aeration of culture solution is necessary for proper growth and activities of roots. Mineral Nutrition

NEET Mineral Nutrition 75 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Criteria for Essentiality The criteria to determine the essentiality of an element include the following aspects. 1. The element must be absolutely necessary for supporting normal growth and reproduction of plants. In the absence of the element, the plants do not complete their life cycle or set the seeds. 2. The element must be directly involved in the metabolism of the plant. It should form a component of either a structural or functional molecule. 3. The requirement of the element must be specific and not replaceable by another element. 4. Absence or reduced availability of the element causes disorders. 5. The disorders caused by absence or deficiency of an element can be corrected only by the availability of that element. Based upon the above criteria, 17 elements have been found to be essential for plant growth and metabolism. They are C, H, O, N, P, K, Ca, Mg, S, Fe, B, Mn, Cu, Zn, Mo, Cl and Ni. Others are called non-essential elements. Classification of Essential Elements A. On the basis of quantitative requirement : The essential elements (nutrients) are divided into two broad categories based on their quantitative requirements. These are : 1. Macronutrients 2. Micronutrients Differences between Macronutrients and Micronutrients Macronutrients Micronutrients These elements are present in plants in easily detectable quantities. The concentration of a macroelement is above 10 mmole kg of dry matter. They build up the plant body and different protoplasmic constituents. They do not become toxic in slight excess. They include C, H, O, N, P, K, S, Mg and Ca (9 in number). –1 These elements are present in plants in very small amounts or in traces. The concentration of a microelement is less than 10 mmole kg of dry matter. They do not have such a role. They are generally required in the functioning of enzymes. They are toxic in slight excess. They include Fe, Zn, Mn, B, Cu, Mo, Cl and Ni (8 in number). –1 1. 2. 3. 4. 5. 1. 2. 3. 4. 5. In addition to the 17 essential elements named above, there are some beneficial elements such as sodium, silicon, cobalt and selenium. They are required in metabolic activities of higher plants. B. On the basis of Function : Essential elements can also be grouped into four broad categories on the basis of their diverse functions. These categories are : 1. Structural elements : Some essential elements are components of biomolecules and hence are the structural elements of cells. They are carbon, hydrogen, oxygen and nitrogen. For example, (i) C, H and O are components of cellulose and many other biomolecules. (ii) Nitrogen is a constituent of all amino acids, proteins, chlorophyll etc.
76 Mineral Nutrition NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 2. Components of energy-related compounds : Some essential elements become components of energy- related chemical compounds in organisms. For example, (i) Magnesium is a component of chlorophyll that takes part in conversion of light energy into chemical energy. (ii) Phosphorus is a component of ATP which functions as energy currency of the living systems. 3. Enzyme activators or inhibitors : Many essential elements are responsible for activating or inhibiting enzymes. For example, (i) Mg2+ is an activator for both ribulose bisphosphate carboxylase-oxygenase (RuBisCO) and phosphoenol pyruvate carboxylase (PEPCase), both of which are critical enzymes involved in carbon fixation during photosynthesis. (ii) Zn2+ is an activator of alcohol dehydrogenase and Mo is an activator of nitrogenase during the nitrogen metabolism. (iii) Mn2+ is involved in photolysis of water. 4. Maintaining osmotic potential : Most of the osmotic potential of cell sap is due to inorganic salts such as nitrate, Cl–, K+, sulphate etc. Osmotic potential is required for water absorption and maintenance of cell turgidity. Apart from this, mineral elements perform other important functions such as : (i) Movements : Potassium plays an important role in the opening and closing of stomata and other turgor movements. (ii) Buffer activity : Phosphates, weak acids and their salts possess buffer activity against changes in pH. Note : 1. Essential elements can also be categorised as mineral and non-mineral elements on the basis of their source. a. Mineral elements : Elements obtained from soil or crust of the earth are called mineral elements. For example, P, K, S, Mg, Ca, Fe, Zn, Mn, B, Cu, Mo, Cl and N. b. Non-mineral elements : Elements obtained from atmosphere (air) and water are known as non-mineral elements. For example, C, H and O. Carbon is mostly obtained from air as CO2. Hydrogen is obtained from water. Oxygen is obtained from both air and water. C, H and O together constitute about 94% of the total dry weight of the plant. 2. Critical elements : N, P, K 3. Balancing elements : Ca, Mg & K counteract the toxic effects of other minerals. Role of Macro and Micronutrients Let us now study the various forms and functions of essential mineral elements in detail. 1. Nitrogen : Required by plant in the greatest amount. Absorption : Absorbed mainly as NO3 – from the soil. It can also be taken up as NO2 – or NH4 +. Requirement : Nitrogen is required by all parts of a plant, particularly the meristematic tissues and the metabolically active cells.