NEET 2025 Zoology Question 153 Solution

A typical microsporangium is bounded by four distinct concentric wall layers: epidermis, endothecium, middle layers, and tapetum:

• • The tapetum is the innermost nutritive somatic layer in direct contact with the sporogenous tissue.
• • Tapetal cells are physiologically active, possessing dense cytoplasm and abundant organelles (mitochondria, ribosomes, endoplasmic reticulum).
• • During early development, tapetal nuclei undergo endomitosis (karyokinesis without cytokinesis) or polyteny, resulting in cells that generally have more than one nucleus (binucleate or multinucleate).
• • Therefore, Assertion (A) is completely TRUE.

Connecting nuclear multiplicity to functional efficiency:

• • The primary physiological role of the tapetum is to provide continuous nutrition to developing microspore mother cells (MMCs) and maturing pollen grains.
• • The presence of multiple nuclei (or polyploidy) increases gene dosage and elevates transcription rates for critical enzymes (such as callase, which dissolves callose walls of microspore tetrads) and precursors of sporopollenin (pro-Ubisch bodies).
• • This amplifies the metabolic capacity and nutritive throughput of the tapetum.
• • Therefore, Reason (R) is scientifically and biologically TRUE.

Reason (R) provides the definitive functional adaptation explaining why tapetal cells undergo endomitosis to become multinucleate. Hence, Reason (R) is the correct explanation of Assertion (A).