The free-living nitrogen-fixing cyanobacterium that forms a symbiotic association with the aquatic fern Azolla is ............. .

What is the function of leghemoglobin?

$A$: Bacteria enter only the polyploid cells of the root cortex.
$R$: These cells provide cytokinins to bacteria,which promote bacterial cell division.

Mark the correct sequence of steps for the development of root nodules in legumes:
$a.$ Formation of infection thread.
$b.$ Division of cortical and pericyclic cells.
$c.$ Curling of root hairs.
$d.$ Leghaemoglobin synthesis.

Symbiotic nitrogen fixation in non-leguminous plants is carried out by

Arrange the stages of root nodule formation in the correct sequence:
$I-$ Infection thread is produced.
$II-$ Bacteria are carried to the cortex of the root.
$III-$ Bacteria attach to the root hair.
$IV-$ Bacteria are released from the thread into the cells.
$V-$ Differentiation into nitrogen-fixing cells occurs.