Question

The smallest organelle in a cell is

• A. Lysosome
• B. Spherosome
• C. Peroxisome
• D. Ribosome

Hint:

Ribosomes are so small that they can only be resolved using an electron microscope.
They are non-membrane-bound complexes of RNA and protein found in both prokaryotic ($70\text{S}$) and eukaryotic ($80\text{S}$) cells.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Cells contain numerous organelles specialized for different physiological processes.
These structures vary widely in size, from large membrane-bound organelles like the nucleus to sub-microscopic non-membrane-bound ribonucleoprotein complexes.

Step 2: Detailed Explanation:
Let us compare the approximate sizes of the listed cell organelles:
- Lysosomes: These are membrane-bound vesicular organelles containing hydrolytic enzymes, with a typical diameter ranging from $0.1$ to $1.2\,\mu\text{m}$.
- Spherosomes: These are small, single-membrane-bound organelles in plant cells involved in lipid synthesis, measuring about $0.5$ to $1.0\,\mu\text{m}$.
- Peroxisomes: These are microbodies involved in oxidative reactions, typically having a diameter of $0.1$ to $1.0\,\mu\text{m}$.
- Ribosomes: These are non-membrane-bound macromolecular complexes composed of ribosomal RNAs and proteins.
They measure only about $20$ to $30\,\text{nm}$ in diameter ($0.02$ to $0.03\,\mu\text{m}$).
Because of their sub-microscopic size, ribosomes are significantly smaller than any membrane-bound organelle.

Step 3: Final Answer:
Therefore, the ribosome is the smallest organelle in a cell, making option (D) the correct choice.