Question

Identify the correct sequence of steps in the formation of root nodules in legumes:
[a.] Formation of infection thread
[b.] Curling of root hair
[c.] Stimulation of cell division in cortex and pericycle
[d.] Release of sugars and amino acids by legume roots
[e.] Release of bacteria into cortical cells

• A. e, d, a, b, c
• B. c, d, a, b, e
• C. b, d, a, c, e
• D. d, b, a, e, c

Hint:

Root nodule formation begins with chemical attraction (sugars, amino acids) and ends with cortical cell division for nodule development.

Answer 1

The Correct Option is D

The formation of root nodules in leguminous plants is a multi-step process involving chemical signaling and physical changes in root tissues:
1. (d) The legume root releases flavonoids, sugars, and amino acids into the rhizosphere. These act as chemical signals to attract Rhizobium bacteria.
2. (b) In response, Rhizobium induces curling of root hairs, creating a trap for bacterial entry.
3. (a) Infection threads are formed — tubular structures through which bacteria enter into the plant root.
4. (e) The bacteria are then released into cortical cells from the infection thread.
5. (c) Finally, the plant stimulates cell division in the cortex and pericycle, leading to nodule formation.
This sequence ensures successful colonization and symbiotic nitrogen fixation.

Answer 2

Identify the correct sequence of steps in the formation of root nodules in legumes:

The process of root nodule formation in legumes occurs in the following sequence:

1. d. Release of sugars and amino acids by legume roots – The legume roots secrete nutrients that attract nitrogen-fixing bacteria.
2. b. Curling of root hair – The root hairs curl around the bacteria, trapping them.
3. a. Formation of infection thread – An infection thread develops in the root hair through which bacteria enter the root.
4. e. Release of bacteria into cortical cells – Bacteria are released from the infection thread into the root cortex cells.
5. c. Stimulation of cell division in cortex and pericycle – This leads to the formation of root nodules where nitrogen fixation occurs.

Thus, the correct order is: d, b, a, e, c.

Correct Answer: d, b, a, e, c