The different steps in a nodule formation are given below
I. A matured nodule establishes a direct vascular connection
II. Root hair curls and the bacteria invade the root hair with the host for exchange of nutrients
III. Rhizobium bacteria contact a susceptile root hair, divide near it
IV. The infection thread is produced carring the bacteria and grows into the cortex of the root
V. The bacteria get modified into rod-shaped bacteroids and cause inner cortical layer and pericycle to divide to form nodule.
The correct sequence is -

Options

A. III, II, IV, I, V.
B. III, II, IV, V, I
C. IV, V, III, II, I
D. I, III, V, II, IV

Answer

To determine the correct sequence of steps in nodule formation, we need to analyze the given steps and arrange them logically based on the biological process involved. Here’s the step-by-step solution:

### Step-by-Step Solution:

1. **Step III: Rhizobium bacteria contact a susceptible root hair, divide near it.**
- This is the initial step where the Rhizobium bacteria find and attach to the root hair of a leguminous plant.

2. **Step II: Root hair curls and the bacteria invade the root hair with the host for exchange of nutrients.**
- After the bacteria contact the root hair, the root hair curls around the bacteria, allowing them to invade and establish a connection for nutrient exchange.

3. **Step IV: The infection thread is produced carrying the bacteria and grows into the cortex of the root.**
- Following the invasion, an infection thread is formed, which transports the bacteria deeper into the root, specifically into the cortex.

4. **Step V: The bacteria get modified into rod-shaped bacteroids and cause the inner cortical layer and pericycle to divide to form nodule.**
- Once inside, the bacteria transform into bacteroids, which stimulate the surrounding cells to divide and form the nodule structure.

5. **Step I: A matured nodule establishes a direct vascular connection with the host.**
- Finally, the matured nodule connects to the plant's vascular system, allowing for the exchange of nutrients between the plant and the bacteria.

### Correct Sequence:
The correct order of steps in nodule formation is: **III → II → IV → V → I.**