Arrange the following events during nitrogen fixation in correct sequence. 

A. Infection thread formation

B. Curling of root hairs

C. Differentiation of nitrogen fixing cells 

Solution:

The various steps in a sequence during root nodule formation in legumes are:

1. Multiplication and colonisation of Rhizobia at root surroundings.
2. Attachment of Rhizobia to epidermal cells or root hairs of root.
3. Curling of root hairs.
4. Infection thread formation which carries the bacteria into the cortical cells.
5. Initiation of root nodule formation in root cortical cells.
6. Release of bacteria from infection thread into root cortical cells.
7. Differentiation of Rhizobia and cortical cells as specialised nitrogen fixing cells.
8. Establishment of vasculature between the root and nodule.