Question
Classify the essential mineral elements of plants into macronutrients and micronutrients. Describe the deficiency symptoms of major elements.
(NEET, CBSE Class 11 — Mineral Nutrition)
Solution — Step by Step
Required in concentrations greater than 10 mmol/kg of dry matter: C, H, O, N, P, K, Ca, Mg, S. Carbon, hydrogen, and oxygen come from air and water. The remaining six are absorbed from soil.
Required in very small quantities: Fe, Mn, Cu, Zn, B, Mo, Cl, Ni. Despite being needed in traces, they are equally essential — their absence causes specific deficiency symptoms.
- Nitrogen (N): Chlorosis (yellowing) of older leaves first (N is mobile, moves to young leaves)
- Phosphorus (P): Purple/dark green leaves, stunted growth
- Potassium (K): Scorching of leaf edges (necrosis), weak stems
- Calcium (Ca): Death of growing tips (meristems), deformed leaves
- Magnesium (Mg): Interveinal chlorosis in older leaves (Mg is part of chlorophyll)
- Iron (Fe): Interveinal chlorosis in young leaves (Fe is immobile)
- Boron (B): Death of shoot tip, hollow stems
graph TD
A["Essential Minerals"] --> B["Macronutrients<br/>C, H, O, N, P, K, Ca, Mg, S"]
A --> C["Micronutrients<br/>Fe, Mn, Cu, Zn, B, Mo, Cl, Ni"]
B --> D["N deficiency → Chlorosis (old leaves)"]
B --> E["P deficiency → Purple leaves"]
B --> F["K deficiency → Leaf edge necrosis"]
B --> G["Mg deficiency → Interveinal chlorosis"]
C --> H["Fe deficiency → Chlorosis (young leaves)"]
C --> I["B deficiency → Death of shoot tip"]Why This Works
The symptoms depend on whether the element is mobile or immobile within the plant. Mobile elements (N, P, K, Mg) are transported from old leaves to young growing tissues when deficient — so symptoms appear on older leaves first. Immobile elements (Ca, Fe, B, Mn) cannot be redistributed — symptoms appear on younger leaves and growing tips.
This mobility concept is the single most useful framework for predicting deficiency symptoms.
Alternative Method — Group by Function
Structural components: C, H, O, N, S (in proteins). Enzyme activators: Mg, Mn, Zn, Cu, Mo, Ni. Ion balance: K, Ca, Cl. Energy transfer: P (in ATP).
For NEET, the most tested deficiency is chlorosis. If it appears in old leaves — think N, Mg, K (mobile elements). If in young leaves — think Fe, Ca, B (immobile). This old-vs-young distinction is a direct NEET question pattern.
Common Mistake
Students confuse Mg deficiency chlorosis with Fe deficiency chlorosis. Both cause interveinal chlorosis, but Mg deficiency affects older leaves (Mg is mobile) while Fe deficiency affects younger leaves (Fe is immobile). The location of symptoms is the diagnostic clue.