Question
Classify essential minerals into macronutrients and micronutrients. Describe the deficiency symptoms for key minerals in plants.
Solution — Step by Step
flowchart TD
A[Essential Mineral Elements - 17] --> B[Macronutrients - needed in large amounts]
A --> C[Micronutrients - needed in trace amounts]
B --> B1[C, H, O, N, P, K, Ca, Mg, S]
C --> C1[Fe, Mn, Cu, Zn, Mo, B, Cl, Ni]
B --> D[Structural and Metabolic roles]
C --> E[Enzyme cofactors and activators]Plants need 17 essential elements. Macronutrients (9 elements: C, H, O, N, P, K, Ca, Mg, S) are needed in concentrations above 10 mmol/kg of dry matter. Micronutrients (8 elements: Fe, Mn, Cu, Zn, Mo, B, Cl, Ni) are needed in concentrations below 10 mmol/kg. Both are equally essential — “micro” refers to quantity needed, not importance.
Nitrogen (N): Chlorosis (yellowing) of older leaves first (N is mobile — it moves from old to new leaves). Stunted growth. Phosphorus (P): Purple/dark green leaves, poor root development. Potassium (K): Marginal scorching (brown edges) of older leaves, weak stems. Calcium (Ca): Death of growing tips (meristems), distorted young leaves. Magnesium (Mg): Interveinal chlorosis of older leaves (Mg is part of chlorophyll).
Iron (Fe): Interveinal chlorosis of young leaves (Fe is immobile). Zinc (Zn): Little leaf disease, shortened internodes. Manganese (Mn): Interveinal chlorosis with small necrotic spots. Boron (B): Death of apical meristems, hollow stem in cauliflower. Molybdenum (Mo): Whiptail disease in cauliflower (leaf blade fails to develop).
Why This Works
The pattern of deficiency symptoms depends on mobility of the element. Mobile elements (N, P, K, Mg) move from older leaves to newer ones when deficient — so older leaves show symptoms first. Immobile elements (Ca, Fe, Mn, B) cannot be redistributed — so younger leaves and growing tips show symptoms first. This mobility rule helps identify which element is deficient.
Alternative Method
| Element | Mobile/Immobile | Deficiency Symptom | Affected Part |
|---|---|---|---|
| N | Mobile | Chlorosis | Older leaves |
| P | Mobile | Purple colour | Older leaves |
| K | Mobile | Marginal necrosis | Older leaves |
| Mg | Mobile | Interveinal chlorosis | Older leaves |
| Ca | Immobile | Meristem death | Growing tips |
| Fe | Immobile | Interveinal chlorosis | Young leaves |
| B | Immobile | Hollow stem, tip death | Growing tips |
Common Mistake
Students confuse iron and magnesium deficiency because both cause interveinal chlorosis. The key difference is where it appears: Mg deficiency shows on older leaves (Mg is mobile). Fe deficiency shows on younger leaves (Fe is immobile). NEET tests this distinction frequently.