Root nodules contain

Leghaemoglobin occurs in

Which of the following is correct regarding nitrogen fixation by legumes? They fix nitrogen through:

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.

Which of the following is a symbiotic microorganism?

Identify the $A$ to $D$ correctly in the given diagram of root nodule development and choose the correct option accordingly.