Answer:
The purpose of these nodules is that they contain bacteria whcih has the ability to convert atmospheric nitrogen into ammonia.
Step-by-step explanation:
A small buldged like part present in the roots of leguminous plant due to symbiosis association of root with the nitrogen fixing bacteria such as rhizobium is called as root nodules.
It is composed of protein and nitrogen fixing bacteria. Under nitrogen deficient condition, the legemunous plant with help of root nodules traps the atmospheric nitrogen and fixes it with the help of nitrogen fixing bacteria present in them.