Long answer type questions.
Why were micronutrients discovered later than macronutrients? With one example each, mention the physiological role and deficiency disease caused by (i) nitrogen, (ii) phosphorus, (iii) copper, and (iv) iron.

Functions:

(i) It is the major constituent of proteins, purines, pyrimidines, vitamins, chlorophyll and hormones, It is also present as a component of coenzymes like FAD, NAD, NADP etc., Older leaves when turning yellow, their nitrogen passes to younger parts in the form of amines and amides.

Deficiency Symptoms:

(i) Stunted growth due to reduced cell division and dormant lateral buds. Chlorosis (yellowing of leaves), Suppressed or late flowering, Increase in starch content but the decrease in protein content, Wrinkling of cereal grains, Purple coloration appears in shoot axis.

Functions:

Deficiency Symptoms:

Purple or red pigmentation on leaves, Premature fall of leaves and floral buds

Iron is involved in the production of chlorophyll, and iron chlorosis is easily recognized on iron-sensitive crops growing on calcareous soils. Iron also is a component of many enzymes associated with energy transfer, nitrogen reduction and fixation, and lignin formation. Iron is associated with sulfur in plants to form compounds that catalyze other reactions. Iron deficiencies are mainly manifested by yellow leaves due to low levels of chlorophyll. Leaf yellowing first appears on the younger upper leaves in interveinal tissues. Severe iron deficiencies cause leaves to turn completely yellow or almost white, and then brown as leaves die.

Iron deficiencies are found mainly on high pH soils, although some acid, sandy soils low in organic matter also may be iron-deficient. Cool, wet weather enhances iron deficiencies, especially on soils with marginal levels of available iron. Poorly aerated or compacted soils also reduce iron uptake by plants. Uptake of iron decreases with increased soil pH, and is adversely affected by high levels of available phosphorus, manganese and zinc in soils.