Explain nodule formation and diagrammatically show the steps of nitrogen fixation biologically. (3marks)
The formation of root nodules involves multiple steps. The process may be summarized as follows:
1) Rhizobium, a bacteria divides itself to form colonies which gets attached to the root hair and the epidermal cells of the plant.
2) The bacteria invades the root hair making the roots hair to curl.
3) An infection thread is then formed which carries the bacteria into the cortex of the root.
4) The bacteria gets itself modified into rod shaped bacteroids.
5) Then the cells present inside the cortex and pericycle divide resulting in the formation of root nodules.
6) The root nodules then formed gets connected with the vascular tissues of the plant leading to nutrient exchange by the roots.
Biological Nitrogen Fixation can be represented as -
NH2 + 8H+ + 8e- + 16ATP = 2NH3 + H2 + 16 ADP + 16 Pi
This reaction is carried out by the enzyme Nitrogenase.
The enzyme is composed of two proteins - an Iron protein and an Molybdenum-Iron protein
The overall Nitrogen Fixation can be demonstrated as -
