Symbiotic hemoglobin (leghemoglobin) is a hemeprotein found in micromolar concentrations in infected cells of legume roots. This is an essential component for nitrogen fixation by legumes. Leghemoglobin is produced as a result of symbiotic association between bacteroid and plant.

Sodium and Iodine  are not required by most of the plants.

Sodium (Na) is required by very limited plants as it helps to concentrate carbon- dioxide, but mostly plants use a trace amount to produce metabolism.

Azotobacter, Beijerinkia are non photosynthetic, non symbiotic and aerobic nitrogen fixing bacteria.

Clostridium is free living, anaerobic nitrogen fixing bacteria.

The ash that is left after burning any dry part of the plant in a crucible, contains only mineral elements and is called plant ash. If dried plant parts are heated in silica crucible at 600$°$C, all organic substance vaporize and the remaining plant ash contains only inorganic substances or absorbed mineral elements.

Lathyrism is a neurological disease causd by khesari dal (Lathyrus odoratus). It carries an ODAP, also known as β-N-oxalyl-amino-L-alanine, or BOAA which is a neurotoxin (glutamate analogue).

Potassium ions are involved in the stomatal movement. Alongwith negative ions, K⁺ ions accumulate in guard cells in response to light. Solute potential become more negative, resulting in entry of water by osmosis and the turgid guard cells. Therefore, the turgidity of guard cell open the stomata.

Molybdenum is a component of nitrogenase and thus brings about fixation of gaseous nitrogen. It also act as enzyme activator of nitrate reductase.

Sulphur is constituent of certain amino acids. The amino acids form the protein by polymerisation. The pulses are rich in protein.

Hydroponics refers to soil-less cultures of plants and growing them on mineral solution

Hydroponics is soil less cultivation of plants by placing the roots in the nutrient solution.