Calcium and sulphur.

Increase of mineral nutrients more than the normal concentration causes toxicity. A concentration, at which 10% of the dry weight of tissue is reduced, is considered as toxic.

Biological chelating agents produced by bacteria are called siderophores. They are iron chelating agents which chelate Ferric iron from environment and host.

Plants grown in alkaline soil when supplied with all nutrients will show Iron deficiency. This can be rectified by making Iron into a soluble complex I by adding a chelating agent like EDTA (Ethylene Diamine Tetra Acetic acid) to form Fe-EDTA.

Fertilizers containing Nitrogen, Phosphate with Potassium in different proportions are called NPK fertilizers.

(i) Yes. Nitrogen cannot be directly absorbed by plants but they are essential for normal growth and functioning of a plant. Hence they are fixed by bacteria and some fungi.
(ii) It can be utilised only in the form of nitrates (NO₃^-) and nitrites (NO₂^-).

This technique was developed by Soifer Hillel and David Durger. It is a system where roots are suspended in air and nutrients are sprayed over the roots by a motor driven rotor.

Amon and Stout gave criteria required for essential minerals:
1. Elements necessary for growthand development.
2. They should have direct role in the metabolism of the plant.
3. It cannot be replaced by other elements.

(i) Nitrogen fixation process requires Nitrogenase enzyme complex, Minerals (Mo, Fe and S), anaerobic condition, ATP, electron and glucose 6 phosphate as H⁺ donor.
(ii) Nitrogenase enzyme is active only in anaerobic condition.
(iii) To create this anaerobic condition a pigment known as leghaemoglobin is synthesized in the nodules which acts as oxygen scavenger and removes the oxygen.

Ammonia Assimilation : 
Ammonia is converted into amino acids by the following processes:
1. Reductive amination :
Glutamic acid or glutamate is formed by reaction of ammonia with a ketoglutaric acid.

2. Transamination: Transfer of amino group (NH₃⁺) from glutamic acid to keto group of keto acid. Glutamic acid is the main amino acid from which other amino acids are synthesised by transamination. Transamination requires the enzyme transaminase and co enzyme pyridoxal phosphate (derivative of vitamin B6 -pyridoxine)
3. Catalytic Amination:(GS/GOGAT Pathway) Glutamate amino acid combines with ammonia to form the amide glutamine.

Glutamine reacts with \(\alpha\) ketoglutaric acid to form two molecules of glutamate.

(GOGAT - Glutamine - 2 Oxoglutarate aminotransferase)

Nitrogen cycle and nitrogen metabolism
I. Nitrogen cycle : This cycle consists of following stages:
Nitrogen Fixation :
(i) Di-nitrogen molecule from the atmosphere progressively gets reduced by addition of a pair of hydrogen atoms to form Ammonia.
(ii) Nitrogen fixation process requires Nitrogenase enzyme complex, Minerals (Mo, Fe and S), Anaerobic condition, ATP, e^- and H⁺ donor glucose 6 phosphate.
(iii) Nitrogenase enzyme is active only in anaerobic condition. To create this anaerobic condition a pigment known as leghaemoglobin is synthesized in the nodules which acts as oxygen scavenger and removes the oxygen.
(iv) Nitrogen fixing bacteria in root nodules appears pinkish due to the presence of this leghaemoglobin pigment.
Overall equation:
N₂ + 8e^-+ 8H + 16ATP  \(\rightarrow\) 2NH₃+H₂+16ADP+16 P_i
2. Nitrification :
(NH₃⁺) Ammonia is converted into Nitrite
(NO₂^-) by Nitrosomonas bacterium. Nitrite
(NO₂^-)is then converted into Nitrate (NO₃^-) by Nitrobacter bacterium
2 NH₃⁺ + 3O₂ \(\overset { Nitrosomonas }{ \longrightarrow } \) 2 NO₂^- + 2H⁺ + 2H₂ O
2 NO₂^- + O₂ \(\overset { Nitrobacter }{ \longrightarrow } \)2 NO₃^-
3. Nitrate Assimilation :
The process by which nitrate is reduced to ammonia is called nitrate assimilation and occurs during nitrogen cycle.
NO₃^- \(\overset { Nitrate\ reductase }{ \underset { Mo }{ \longrightarrow } } \)NO₂^-
NO₂^- \(\overset { Nitrate\ reductase }{ \underset { Mo }{ \longrightarrow } } \) NH₃⁺
4. Ammonification :
Decomposition of organic nitrogen from dead plants and animals into ammonia is called ammonification. organisms involved in this process are Bacillus ramosus and Bacillus vulgaris.
5. Denitrification:
Nitrates in the soil are converted back into atmospheric nitrogen by a process called denitrification. Bacteria involved in this process are Pseudomonas; Thiobacillus and Bacillus subtilis.
Nitrate \(\overset { Pseudomonas }{ \longrightarrow } \) Molecular Nitrogen
(NO₃^-)                                   (N₂)

Plants which are growing in nitrogen deficient areas develop insectivorous habit to resolve nitrogen deficiency.
a. Nepenthes (Pitcher plant): Pitcher is a modified leaf and contains digestive enzymes. Rim of the pitcher is provided with nectar glands and acts as an attractive lid. When insect is trapped, proteolytic enzymes will digest the insect.
b. Drosera (Sundew): It consists of long club shaped leaves with tentacles which secrete sticky digestive fluid which looks like a sundew and attracts insects.
c. Utricularia (Bladder wort): Submerged plant in which leaf is modified into a bladder to collect insect in water.
d. Dionaea (Venus fly trap): Leaf of this plant modified into a colourful trap. Two folds of lamina consist of sensitive trigger hairs and when insects touch the hairs it will close and traps the insects.