Problem 53 - Objective Biology for NEET

Question

The sequential stage for principal stages of nodule formation are (1) Rhizobia multiply and colonies the surrounding roots. (2) Rhizobia attached to epidermal and root hair cells. (3) Root hair curl and bacteria invades root hair. (4) Initiation of nodule formation in cortex. (5) Infection thread is produced carrying bacteria to cortex. (6) Bacteria released from thread into cells and causes their differentiation in specialized nitrogen fixing cells. (7) Nodule formed is establish, a direct vascular connection with the host for exchange of nutrient. (a) $\mathrm{I} \rightarrow \mathrm{VII} \rightarrow \mathrm{II} \rightarrow \mathrm{VI} \rightarrow \mathrm{III} \rightarrow \mathrm{V} \rightarrow \mathrm{IV}$ (b) II $\rightarrow \mathrm{III} \rightarrow \mathrm{IV} \rightarrow \mathrm{I} \rightarrow \mathrm{VII} \rightarrow \mathrm{V} \rightarrow \mathrm{VI}$ (c) VII $\rightarrow \mathrm{VI} \rightarrow \mathrm{IV} \rightarrow \mathrm{I} \rightarrow \mathrm{III} \rightarrow \mathrm{V} \rightarrow \mathrm{II}$ (d) $\mathrm{I} \rightarrow \mathrm{II} \rightarrow \mathrm{III} \rightarrow \mathrm{V} \rightarrow \mathrm{IV} \rightarrow \mathrm{VI} \rightarrow \mathrm{VII}$

Step-by-Step Solution

Answer

The correct answer is option (d) I -> II -> III -> V -> IV -> VI -> VII.

Step 1 Analysis

Look closely at each stage and get an understanding of the process. It starts with Rhizobia multiplying and ends with the nodule being established:

Step 2 Analyzing options

Examine each of the given options and check which one is in accordance with the given stages.

Step 3 Comparing options with stages

The correct sequence of stages is Rhizobia multiply and colonies the surrounding roots, Rhizobia attached to epidermal and root hair cells, root hair curl and bacteria invades root hair, infection thread is produced carrying bacteria to cortex, Initiation of nodule formation in cortex, bacteria released from thread into cells and causes their differentiation in specialized nitrogen fixing cells and finally, Nodule formed is establish, a direct vascular connection with the host for exchange of nutrient. So, the correct sequence is I -> II -> III -> V -> IV -> VI -> VII.

Step 4 Selecting the correct option

After interpreting the correct sequence of stages, it becomes clear that the correct answer is option (d) I -> II -> III -> V -> IV -> VI -> VII.