Rhizobium is a bacterium that fixes atmospheric nitrogen into organic compounds. Where does Rhizobium live in association with plants?

In the root nodules of legumes

The correct answer is Option (3)- In the root nodules of legumes

Rhizobium is a type of bacterium that forms a symbiotic association with certain plants, especially legumes (plants belonging to the pea family, Fabaceae). This symbiotic relationship benefits both the plant and the bacterium.

When leguminous plants grow in nitrogen-deficient soils, they are unable to obtain sufficient nitrogen for their growth and development. Rhizobium bacteria help solve this problem by converting atmospheric nitrogen (present in the air) into a form that the plants can use - organic compounds like ammonia. This process is called nitrogen fixation.

The process of nitrogen fixation takes place in specialized structures called root nodules, which are formed on the roots of the legume plants. Inside these root nodules, the Rhizobium bacteria live and carry out the conversion of atmospheric nitrogen into organic compounds.

This mutualistic relationship between Rhizobium and leguminous plants is beneficial for both partners, as the plants get a constant supply of nitrogen, and the bacteria receive a source of energy and nutrients. This interaction is essential for maintaining soil fertility and promoting the growth of leguminous crops in agriculture.