(i) Why is an element essential? (ii) How many elements are essential? Name them. (iii) Classify as macro and micronutrients. (iv) Name two non-mineral elements.

(i) Criteria of Essentiality:

An element is essential if it has a specific structural or physiological role and without it, plants cannot complete their life cycle.

(ii) Essential Elements:

17 elements are essential: C, H, O, N, P, K, Ca, Mg, S, B, Mo, Mn, Ni, Cl, Fe, Cu, Zn

(iii) Classification:

Macronutrients (9): Required in large quantities (>10 mmol/kg dry matter)

• C, H, O, N, P, K, S, Ca, Mg

Micronutrients (8): Required in trace amounts (<10 mmol/kg dry matter)

• Fe, Mn, Cu, Mo, Zn, B, Cl, Ni

(iv) Non-Mineral Elements:

C, H, O—obtained from air and water, not from soil minerals.