Question:

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

Updated On: Jul 7, 2022
  • I, II, IV, V
  • III, II, IV, V, I
  • III, II, IV, I, V
  • I, III, V, II, IV
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The Correct Option is B

Solution and Explanation

Answer (b) III, II, IV, V, I
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Concepts Used:

Mechanism of Absorption of Elements

The mechanism of absorption of elements in plants has revealed two major phases of absorption. The first phase and the second phases are passive processes and active processes respectively. The first phase includes a rapid uptake of ions from the soil or atmosphere to the outer or free space of cells known as the apoplast.

  • The first phase includes the movement of elements into the cell wall and intercellular spaces. The absorption of ions takes place through the ion exchange process. The passive movement of ions into the outer space of the plasma membrane usually takes place through ion channels. Cations and anions have the tendency to get occupied in the root cell wall. These ions get switched with the ions in the soil solution. The transmembrane proteins in the ion channel function as fastidious pores.
  • The second phase includes the entry or exit of ions to and from the symplast. This needs energy, it is an active process. The movement of ions from the outer space of the cell to the inner space is in general against the concentration gradient, and hence, requires energy. This happens through the carrier mechanism. The carrier gets operated by the expenditure of energy from the ATP molecule. The activated carrier molecule binds with the ions and passes on them to the cell. The inward movement into the cells is known as influx, and the outward movement is known as efflux.