Nitrogen-fixing bacteria are associated with which of the following plant families?

Leghaemoglobin helps in

Which of the following is a recently discovered Gram-positive,non-leguminous,nitrogen-fixing bacterium?

The nitrogen-fixing symbiotic organism present in $Azolla$ is:

Rhizobium lives symbiotically with root nodules and fixes atmospheric nitrogen. It provides nitrogenous compounds to the host and in turn takes food from the host. This food taken by the bacterium is:

Trace the events starting from the coming in contact of Rhizobium to a leguminous root till nodule formation. Add a note on the importance of leghemoglobin.