Answer: Macronutrients are needed in large amounts (>0.1% dry weight); micronutrients are needed in trace amounts (<0.1%).
- A Macronutrients are mostly organic compounds; micronutrients are mostly inorganic ions in form under most conditions encountered
- B Macronutrients are needed in large amounts (>0.1% dry weight); micronutrients are needed in trace amounts (<0.1%)
- C Macronutrients consist mainly of nitrogen, phosphorus, and potassium ions specifically as frequently observed in practice
- D Micronutrients can become toxic to most plant species at unusually high concentrations in many documented cases
Correct answer: B. Macronutrients are needed in large amounts (>0.1% dry weight); micronutrients are needed in trace amounts (<0.1%)
Explanation: Macronutrients (needed >0.1% dry weight): C, H, O, N, P, K, Ca, Mg, S. Micronutrients (needed <0.01% dry weight): Fe, Mn, Zn, Cu, Mo, B, Cl, Ni. Essential for specific enzymatic and structural functions.
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.