Which one of the following is the site for active ribosomal RNA synthesis?

Core Logic

• Centrosomes: Non-membrane bound, but found only in animal cells (eukaryotes), not in prokaryotes.
• Ribosomes: Non-membrane bound organelles universally found in all living cells (both prokaryotes and eukaryotes).
• Lysosomes: Single-membrane bound organelles found in eukaryotes.
• Mitochondria: Double-membrane bound organelles found only in eukaryotes.

Step 1: Final Conclusion

Ribosome is the only non-membrane bound organelle present in both cell types.

Pattern Recognition

Prokaryotes lack all membrane-bound organelles. The only structured organelle they possess is the ribosome (70S). Eukaryotes possess ribosomes (80S and 70S) as well.

Chapter Mix

Class 11 Biology: Cell The Unit of Life

Core Logic

Statement A is incorrect because the endomembrane system includes the endoplasmic reticulum, Golgi complex, lysosomes, and vacuoles, but does not include mitochondria. Statement E is incorrect because the mitochondrion is a double membrane-bound cell organelle, not a single membrane-bound structure. Statements B, C, and D are factually correct descriptions of the RER, semiautonomous organelles, and the cytoskeleton respectively.

Pattern Recognition

Mitochondria and chloroplasts act independently and are NOT part of the coordinated endomembrane system. They are also both double-membrane bound with their own circular DNA.

Chapter Mix

Class 11 Biology: Cell The Unit of Life

Core Logic

Statement C is incorrect for eukaryotes because mesosomes (extensions of plasma membrane into the cell) are found only in prokaryotes. Eukaryotes lack such structures. Statement E is incorrect in this context as the distinct glycocalyx layer described typically forms the outermost layer of the cell envelope in prokaryotes, though eukaryotes have glycoproteins/glycolipids. Statements A, B, and D correctly describe the eukaryotic cell membrane (e.g., human RBC membrane has ~52% protein and ~40% lipids; lipid bilayer with hydrophobic tails inside).

Step 1: Final Conclusion

Hence, only statements A, B, and D are correct.

Pattern Recognition

Mesosomes = prokaryotes. Eliminate any option with C for eukaryotes.

Chapter Mix

Class 11 Biology: Cell The Unit of Life