Q.14 Which of the following is not a part of endomembrane system?
- Golgi body
- Lysosome
- Ribosome
- Vesicles
Ribosome is not a part of the endomembrane system, as it is a non-membranous structure free in cytosol or on rough ER, unlike the membrane-bound organelles listed.
Question Analysis
This question tests knowledge of the endomembrane system—a network of interconnected, membrane-bound organelles handling protein/lipid modification, sorting, and transport via vesicles.
Option Breakdown
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Golgi body: Central hub; receives ER-derived vesicles, modifies proteins/lipids (glycosylation), sorts them to lysosomes, plasma membrane, or secretion.
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Lysosome: Derived from Golgi; contains hydrolytic enzymes for intracellular digestion (autophagy, endocytosis); acidic interior from proton pumps.
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Ribosome: Protein synthesis machinery (rRNA + proteins); lacks membrane, operates in cytosol (free ribosomes for cytoplasmic proteins) or bound to rough ER (for secretory proteins)—not part of endomembrane flow.
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Vesicles: Membrane-bound carriers shuttling cargo between ER, Golgi, lysosomes, plasma membrane; essential for system connectivity.
Answer: Ribosome—excluded due to absence of membrane.
Introduction to Endomembrane Network
The question “not a part of endomembrane system” highlights ribosome’s exclusion from this membrane trafficking pathway. The system coordinates ER-Golgi-lysosome functions for cellular logistics.
Core Components Explained
Golgi modifies and packages; lysosomes degrade waste; vesicles enable transport. Ribosomes synthesize proteins but aren’t membranous or vesicle-derived, marking them as outsiders.
Option Membrane-Bound? Role in Endomembrane Flow Golgi body Yes Protein modification hub Lysosome Yes Degradation compartment Ribosome No Protein synthesis only Vesicles Yes Cargo transport Why Ribosome Stands Out
Ribosomes dock on rough ER transiently but aren’t system components—mitochondria/chloroplasts similarly excluded. Key for distinguishing membranous vs. free organelles in exams.
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