Mineral nutrition is the study of source, mode of absorption, distribution and metabolism of various inorganic substances (minerals) by plants for their growth, development, structure, physiology and reproduction. Hydroponics is the technique of growing plants in nutrient solution in complete absence of soil. Plants obtain their inorganic nutrients from the soil, water, and air. They absorb a wide variety of mineral elements, but not all are absorbed. The elements that are required in large quantities are referred to as macronutrients whereas those required in lesser quantities are termed as micronutrients. The role of essential elements, their major deficiency symptoms, and the mechanism of absorption of these essential elements. This unit also briefly introduces students to the significance and mechanism of biological nitrogen fixation.