Question

How atmospheric nitrogen is fixed by symbiotic system?

Answer 1

Hey user ...

The fixation of free nitrogen of air by microorganisms living symbiotically inside the plants (roots) is called symbiotic nitrogen fixation.
The symbiotic system consists of bacteria of the genus Rhizobium together with many members of the family Leguminosae, such as peas, beans, clovers etc. to form nitrogen fixing co-operative.
The actual site of nitrogen fixation is the nodules formed on the roots of the legume plants as a "result of the penetration of Rhizobium. Neither organism alone is able to fix nitrogen. Rhizobial genes responsible for nodule formation are termed as nod genes. In the initial stage, host cells recognise the correct strain of symbiotic bacteria. The roots of leguminous plants secrete some growth factors. As a result the bacteria accumulate in the vicinity of plant roots.
The bacteria, then, either penetrate the relatively soft root hair tip or invade damaged or broken root hairs and progress in as an infection thread.
The infection thread intrudes, settles and liberates its contents in a cortical cell which is usually a tetraploid. The Rhizobia are liberated either individually or in small groups enclosed by a membrane bound vacuole and enter the plant cell. The vacuoles are termed as symbiosomes.
The bacterial cells induce the certical cells to divide which ultimately result in the formation of nodules on the surface of roots. The bacterial cell divides and attain enlargement to fix nitrogen in this area. At this stage the bacteria arfi called endosymbionts or bacteriods.
The nodules grow rapidly, pushing its way to the surface of the root. The module contains a red pigment leghaemoglobin which combine with oxygen. The development of leghaemoglobin and nitrogen fixing capacity are outcome of symbiotic Fig-3-5- Pea plant showing root nodules, interaction. The mature nodules remain connected with the
root via vascular tissues through which exchange of fixed nitrogen of the bacteriods and the nutricn of host takes place.

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Answer 2

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Atmospheric Fixation.
The enormous energy of lightning breaks nitrogen molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides.
These dissolve in rain, forming nitrates, that are carried to the earth.

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