Assertion (A):In the early history of biology, the discipline remained primarily as a "natural history" for a long time. Reason (R): Before experimental biology and physiology were established, naturalists described only the diverse forms of life through naked eyes or simple magnifying lenses.
Before experimental biology or physiology was established, naturalists described biology through observations of gross structural features. Thus biology remained a natural history for a long time, and the reason correctly explains the assertion.
Question 252 of 300
📘 CLASS XI
Assertion (A): Detailed morphological descriptions of life forms were utilized in later-day reductionist biology. Reason (R): Detailed descriptions of structures became highly meaningful and helpful in framing research questions in physiology and evolutionary biology.
Both statements are true. The detailed descriptions compiled by naturalists were utilized in reductionist biology and also became valuable in framing questions in physiology and evolutionary biology. However, the reason states their utility rather than explaining why they were utilized.
Question 253 of 300
📘 CLASS XI
Assertion (A): Katherine Esau's book Plant Anatomy, published in 1954, brought about a worldwide revival of the discipline of plant structure. Reason (R): The book took a dynamic, developmental approach designed to enhance one's understanding of plant structure.
Katherine Esau's book had an enormous impact worldwide because it adopted a dynamic developmental approach to understanding plant structure. Therefore, the reason correctly explains the assertion.
Question 254 of 300
📘 CLASS XI
Assertion (A): Direct elongation of the radicle in a mustard plant leads to the formation of a taproot system. Reason (R): Mustard is a dicotyledonous plant where the primary root and its lateral branches constitute the taproot system.
In dicotyledonous plants such as mustard, direct elongation of the radicle forms the primary root, whose lateral branches together constitute the taproot system.
Question 255 of 300
📘 CLASS XI
Assertion (A): In wheat plants, the primary root developed from the radicle is short-lived. Reason (R): Wheat is a monocotyledonous plant where the primary root is replaced by a large number of roots originating from the base of the stem.
In monocotyledonous plants like wheat, the primary root is short-lived and is replaced by numerous roots arising from the base of the stem, forming the fibrous root system.
Question 256 of 300
📘 CLASS XI
Assertion (A): Root hairs are delicate, thread-like structures that emerge from the region of maturation. Reason (R): Epidermal cells proximal to the region of elongation differentiate and mature to form the region of maturation.
Both Assertion and Reason are true. The cells of the elongation zone gradually differentiate and mature to form the region of maturation. From this maturation region, some of the epidermal cells develop into root hairs. However, differentiation of cells into the maturation zone does not explain why root hairs are formed or why they are thread-like; it only describes the developmental origin of the zone from which they arise.
Question 257 of 300
📘 CLASS XI
Assertion (A): If the region of maturation is completely removed from a root-tip, the plant's capacity to absorb water and minerals from the soil is severely compromised. Reason (R): Root hairs, which absorb water and minerals, develop exclusively from the epidermal cells of the region of maturation.
Root hairs are the primary structures responsible for absorbing water and minerals from the soil, and they arise exclusively as outgrowths of the epidermal cells of the region of maturation. Removal of this region prevents root hair formation and greatly reduces water and mineral absorption. Therefore, Reason (R) correctly explains Assertion (A).
Question 258 of 300
📘 CLASS XI
Assertion (A): The stem develops from the plumule of the embryo of a germinating seed. Reason (R): Stems bear nodes and internodes, whereas roots do not bear these structures.
Both Assertion and Reason are true. The stem develops from the plumule of the embryo, and stems are characterized by the presence of nodes and internodes, unlike roots. However, the presence of nodes and internodes does not explain the embryonic origin of the stem.
Question 259 of 300
📘 CLASS XI
Assertion (A): The region of a stem where leaves are borne is called an internode. Reason (R): Internodes are the portions of the stem lying between two successive nodes.
Assertion (A) is false because leaves are borne at the nodes, not the internodes. Reason (R) is true because an internode is the portion of the stem between two successive nodes.
Question 260 of 300
📘 CLASS XI
Assertion (A): Young stems are generally green and photosynthetic, but they may later become woody and dark brown. Reason (R): Stems conduct water, minerals, and photosynthates and spread out branches bearing leaves, flowers, and fruits.
Both Assertion and Reason are true. Young stems are green and photosynthetic and often become woody and dark brown with age. Stems also conduct water, minerals, and photosynthates while supporting branches, leaves, flowers, and fruits. However, these functions do not explain the colour and structural changes during ageing.
