Ascending Order of Xylem Strands in Roots

To arrange the given plants in ascending order based on the number of xylem strands in their roots, we need to understand the characteristics of each plant and their root structures. Xylem strands are responsible for transporting water and minerals from the roots to the rest of the plant. The more xylem strands a plant has, the more efficient it is in water and nutrient uptake.

Let's analyze each plant and their root structures to determine the correct order:

(I) Trapa:
Trapa, commonly known as water chestnut, is an aquatic plant. It has a complex root system consisting of numerous fine roots. The primary roots of Trapa do not have a well-developed xylem structure. Therefore, Trapa likely has the lowest number of xylem strands among the given plants.

(II) Pisum:
Pisum, also known as pea, is a herbaceous plant. It has a taproot system with a main root (primary root) and several lateral roots. The primary root of Pisum contains xylem strands that branch out into the lateral roots. However, the number of xylem strands is generally lower than in plants with a well-developed taproot system.

(III) Castanea:
Castanea, commonly known as chestnut, is a tree. It has a deep taproot system with a primary root that extends vertically into the soil. The primary root of Castanea is well-developed and contains a significant number of xylem strands to support the growth and water uptake of a tree.

(IV) Nicotiana:
Nicotiana, also known as tobacco, is a herbaceous plant. It has a fibrous root system with numerous adventitious roots arising from the stem base. The fibrous roots of Nicotiana do not have a well-defined taproot, and the number of xylem strands is generally lower compared to plants with a taproot system.

Based on the above analysis, we can arrange the plants in ascending order of xylem strands in their roots as follows:

b) IV, III, I, II
- Nicotiana (IV) has the lowest number of xylem strands, as its fibrous root system is less developed than the taproot systems of the other plants.
- Castanea (III) has a well-developed taproot system with a significant number of xylem strands to support its growth as a tree.
- Trapa (I) has a complex root system with numerous fine roots, but the primary roots do not have a well-developed xylem structure, resulting in a lower number of xylem strands.
- Pisum (II) has a taproot system with a main root and lateral roots, but the number of xylem strands is generally lower than in plants with a well-developed taproot system like Castanea.

By arranging the plants in this order, we have considered the root structures and the efficiency of water and nutrient uptake based on the number of xylem strands.

Right answer is option (a)...