NEET 2025 Zoology Question 140 Solution

The endomembrane system functions as an integrated secretory conduit:

• • Proteins and lipids synthesized in the rough and smooth endoplasmic reticulum (RER and SER) must be post-translationally modified, sorted, and routed.
• • The Golgi apparatus principally performs the function of packaging these materials into membrane-bound vesicles, targeting them either to specific intracellular destinations (e.g., lysosomes) or secreting them extracellularly via exocytosis.
• • Therefore, Assertion (A) is completely TRUE.

Structural and functional polarity of Golgi cisternae:

• • Golgi cisternae are concentrically arranged near the nucleus with distinct polarity: a convex forming face (*cis* face) and a concave maturing face (*trans* face).
• • Vesicles transport synthesized proteins/lipids from the ER and fuse with the *cis* face.
• • As these cargo molecules transit through the medial cisternae, they undergo crucial biochemical modifications (e.g., glycosylation into glycoproteins and glycolipids).
• • Finally, the modified molecules are pinched off in secretory vesicles from the *trans* face.
• • Therefore, Reason (R) is completely TRUE.

Reason (R) describes the exact mechanistic basis of how the Golgi apparatus functions as the cell's packaging and distribution center for ER products. Hence, Reason (R) is the correct explanation of Assertion (A).