Write names of essential elements of plants and write their function, availability, form in which absorbed and deficiency symptoms of any four.

$Potassium$ (K):
It is found in soil insoluble and exchangeable form.
It is absorbed in the form of potassium ion ($K^{+}$).
Potassium is not a component of any biochemical compound and is not a structural element.
It plays an important role in four biochemical reactions viz cation neutralization, transport across the membrane, enzyme activation and osmotic potential regulation.
The best function of potassium is in regulating the opening of stomata.
Deficiency Symptoms:
The first symptom of deficiency of Potassium is marginal chlorosis.
The leaves become mottle due to chlorosis.
Shortening of internodes results in stunted growth and bushy appearance of plants. Necrotic spots appear on the margins of more mature leaves.

$Magnesium$:
Magnesium is found in soil as magnesium carbonate ($MgC{O}_3$​) and is absorbed as magnesium ion ($M{g}^{++}$).
It is an important component of chlorophyll pigment.
This element activates the enzymes of respiration, protein synthesis and photosynthesis. It helps in joining the two subunits of ribosomes.
Deficiency symptoms:
Magnesium deficiency causes extensive interveinal chlorosis.
Leaves show reddish and yellow and orange spots due to the predominance of anthocyanin pigments.

$Sulphur$ (S):
This is absorbed from soil in the form of sulphate ion ($S{O}_4^{++}$​). Besides this sulphur dioxide ($S{O}_2$​) present as an environmental pollutant may also be absorbed by plants.
It is helpful in the synthesis of amino acids such as cysteine, methionine, etc. needed in protein synthesis.
It is also found in vitamin B and coenzyme-A.
It is an important component of protoplasm.
Deficiency symptoms:
Leaves show chlorosis.
Shortage of sulphur-containing amino acids occurs.
Plants become stunted and fail to form fruits.

$Iron$ (Fe):
Plants absorb iron from the soil in the form of ferric ions ($F{e}^{++}$).
It plays an important role in cell division, respiration and different steps of the electron transport system.
It is an important constituent of cytochrome and ferredoxin and acts as an activator of aconitase, catalase, peroxidase and some Krebs cycle enzymes.
It is helpful in chlorophyll synthesis but is not a part of chlorophyll molecules.
Deficiency symptoms:
Young leaves show extensive chlorosis and may become white or yellow-white. The derailment of reactions of photosynthesis, respiration and protein synthesis occurs.
Cell division activity is inhibited.
Plant growth becomes slow.