Question

Some bacteria live in the roots of plants like soybeans and peas.

Bacteria growing on plant roots.
What is the role of these bacteria in the nitrogen cycle?

to absorb nitrogen-containing compounds from the soil
to release free nitrogen into the atmosphere
to break down nitrogen-containing compounds in dead organisms
to convert free nitrogen into usable nitrogen

Answer 1

to convert free nitrogen into usable nitrogen

Explanation: Legume root bacteria (e.g., Rhizobium) fix atmospheric N2 into ammonia/nitrogen compounds the plant can use, in a mutualistic relationship in root nodules.