(A) Ribosome

(B) Mitochondria

(C) Endoplasmic reticulum

(D) Centrosome

Endoplasmic reticulum (C) is the organelle enclosed by a single membrane among the given options. Ribosomes, mitochondria, and centrosomes lack this feature, while the endoplasmic reticulum’s continuous single bilayer distinguishes it in eukaryotic cell structure.

Option Analysis

Ribosome (A):
Ribosomes consist of ribosomal RNA and proteins forming two subunits, with no enclosing membrane. They function freely in the cytosol or attach to other organelles for protein synthesis.

Mitochondria (B):
Mitochondria feature a double membrane: an outer membrane and a highly folded inner membrane creating cristae for ATP production. This structure separates matrix functions from the intermembrane space.

Endoplasmic Reticulum (C):
The endoplasmic reticulum (ER) forms a network of tubules and sacs bounded by a single continuous lipid bilayer membrane. Rough ER has ribosomes for protein processing, while smooth ER handles lipid metabolism.

Centrosome (D):
Centrosomes contain paired centrioles surrounded by pericentriolar material but lack any membrane enclosure. They organize microtubules during cell division.

The organelles enclosed by single membrane include key eukaryotic structures like the endoplasmic reticulum, vital for protein and lipid synthesis in cells preparing for CSIR NET Life Sciences exams. This MCQ targets cell biology basics, distinguishing single-membrane organelles from double-membrane or non-membranous ones.

Single vs. Double Membrane Organelles

Single-membrane organelles, such as endoplasmic reticulum, Golgi apparatus, and lysosomes, feature one phospholipid bilayer for selective transport. Double-membrane organelles like mitochondria and chloroplasts enable compartmentalized energy processes.

• Endoplasmic reticulum: Single continuous membrane network.

• Mitochondria: Outer and inner membranes with cristae.

• Non-membranous: Ribosomes and centrosomes operate without boundaries.

Detailed Structures

Endoplasmic Reticulum spans the cytosol as rough (ribosome-studded) or smooth forms, enclosed by one membrane enclosing a lumen for folding and modification.

Mitochondria power cells via oxidative phosphorylation across two membranes. Ribosomes translate mRNA without enclosure, while centrosomes nucleate microtubules via protein complexes.