Question

Arrange the following micro-organisms in ascending order on the basis of their size:
(A). Parvovirus
(B). Clostridium tetani
(C). Mycoplasma gallisepticum
(D). Balantidium coli
Choose the correct answer from the options given below:

• A. (A), (C), (B), (D).
• B. (B), (A), (C), (D).
• C. (C), (A), (B), (D).
• D. (D), (B), (A), (C).

Hint:

To remember size hierarchies:
\[ \text{Viruses (nm)} < \text{Mycoplasmas (fraction of }\mu\text{m)} < \text{Bacteria (few }\mu\text{m)} < \text{Protozoan parasites (tens of }\mu\text{m)} \] Balantidium is a massive ciliate and is visible even under low magnification.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
This question tests the comparative size differences among different classes of microorganisms, ranging from tiny viruses and atypical bacteria to typical rod-shaped bacteria and large protozoans.
To arrange these in ascending order, we must list them from the smallest physical size to the largest.

Step 2: Detailed Explanation:
Let us analyze the dimensions of each microorganism to understand their scale of measurement:
- (A) Parvovirus:
Parvoviruses are extremely small, non-enveloped, single-stranded DNA viruses.
They measure only \( 18 \text{ to } 26 \text{ nm} \) in diameter, which is at the nanometer scale.
- (C) Mycoplasma gallisepticum:
Mycoplasmas are atypical bacteria that lack a cell wall, making them highly pleomorphic.
They are widely recognized as the smallest self-replicating prokaryotes, with cell diameters ranging from \( 0.25 \text{ to } 0.5\ \mu\text{m} \) (\( 250 \text{ to } 500 \text{ nm} \)).
- (B) Clostridium tetani:
This is a typical, spore-forming, rod-shaped (bacillus) Gram-positive bacterium.
The vegetative cells of Clostridium tetani measure about \( 0.5\ \mu\text{m} \) in width and \( 2 \text{ to } 5\ \mu\text{m} \) in length.
- (D) Balantidium coli:
This is a large, ciliated, unicellular protozoan parasite that infects the intestines of pigs and humans.
It is the largest protozoan parasite affecting humans, with trophozoites measuring \( 50 \text{ to } 200\ \mu\text{m} \) in length and \( 40 \text{ to } 70\ \mu\text{m} \) in width.
Converting all measurements to a uniform scale (such as micrometers, where \( 1\ \mu\text{m} = 1000 \text{ nm} \)):
1. Parvovirus: \( \sim 0.02\ \mu\text{m} \)
2. Mycoplasma gallisepticum: \( \sim 0.3\ \mu\text{m} \)
3. Clostridium tetani: \( \sim 3\ \mu\text{m} \)
4. Balantidium coli: \( \sim 100\ \mu\text{m} \)
Thus, the correct ascending order of size is:
\[ \text{Parvovirus (A)} < \text{Mycoplasma gallisepticum (C)} < \text{Clostridium tetani (B)} < \text{Balantidium coli (D)} \] This sequence matches the order (A), (C), (B), (D), which corresponds to Option (A).

Step 3: Final Answer:
The correct ascending order is (A), (C), (B), (D).
Therefore, the correct choice is Option (A).