Functions of nitrogen: 

(a) Nitrogen is an essential component of several metabolically active compounds and it plays vital role in plant metabolism. 

(b) Nitrogen is an integral part of chlorophyll, which harvest solar energy through photosynthesis process. 

(c) As a constituent of nucleic acids, it transfers genetic information and regulates cellular metabolism of amino acids and proteins. 

Deficiency of nitrogen: 

(a) Plants containing less than 1 % nitrogen are considered deficient in nitrogen. 

(b) Symptoms of nitrogen deficiency first appear in the older leaves as nitrogen mobilize from older to young leaves. A pale yellow chlorosis develops near the tip of the leaf blade and the chlorosis advances towards the base in V- Shape pattern along the leaf margins until the whole leaf blade turns yellow. The leaf turns from yellow to brown and necrosis occurs at the leaf tip. 

(c) Nitrogen deficient plants show stunted growth and produce less flowers and shrivelled grains. 

(d) The nitrogen deficient plants have slender and woody stems due to the buildup of excess carbohydrates. 

(e) Example: In cauliflower, young leaves turn pale yellow and old leaves become orange. In the case of coffee, Veins becomes yellow and new leaves are very small. 

Functions of phosphorus: 

(a) Phosphorus plays important function as a structural component of the cell membrane system, chloroplast and mitochondria. 

(b) Phosphorus is an important constituent of nucleic acids, nucleoproteins, phospholipids, co-enzymes, energy rich adenosine diphosphate (ADP) and adenosine triphosphate (ATP). 

(c) It plays vital role in energy transfer, metabolic processes, transformation of sugars and starch and physiological processes like photosynthesis. 

(d) It is essential for cell division, stem and root growth, fruit and seed development. 

Deficiency symptoms of phosphorus: 

The phosphorus concentration below 0.1% in plants causes deficiency and the plants exhibit deficiency symptoms. 

(a) Phosphorus deficient plants develop poor root system and the plants remain stunted. 

(b) Since phosphorus ismobile in plants and at times of deficiency, phosphorus mobilizes from older leaves to new leaves or active meristematic regions. The older leaves develop characteristic symptoms of blue-green colouration starting from the leaf tip to the base. The colour changes to reddish brown in the later stages. The leaves may be malformed and contain small necrotic spots which are dead tissues. 

(c) Under the condition of severe deficiency, the plants develop spindly growth and reddish purple colour is observed in the nodes and internodes which shows formation of anthocyanin.