Question

Which of the following is an acellular organism?
(a) Bacteria
(b) Fungi
(c) Protozoa
(d) Virus

Answer 1

Hint: It is a microscopic infectious agent that replicates only inside the living cells of an organism. It is both living and non- living and infuses all types of life forms, from animals and plants to microorganisms.

Complete answer:
Viruses are non- cellular, microscopic organisms. They are infectious agents, which can only replicate inside a host cell. They possess certain defining characteristic features of living organisms and nonliving entities. That is why they cannot be classified as either a living organism or non- living.
In brief, a virus is a non- cellular, infectious entity made up of genetic material and protein that can invade and reproduce only within the living cells of bacteria, plants, and animals. For example, a virus cannot replicate itself outside the host cell, because they lack the required cellular machinery. Therefore, it enters and attaches itself to a specific host cell, injects its genetic material, reproduces by using the host genetic material, and finally, the host cell splits open, releasing the new viruses.
So, the correct answer is ‘Virus’.

Additional information:
The other characteristics of Viruses are:
- They are non- cellular organisms, which are enclosed in a protective envelope.
- The presence of spikes helps in attaching the viruses to the host cell.
- These viruses do not grow, neither respire nor metabolize, but they reproduce.
- They are surrounded by a protein coat – capsid and have a nucleic acid core comprising DNA or RNA.
- These viruses cause several infections and reproduce within the host cell by using the enzymes and raw materials.

Note: The Baltimore classification is the most commonly used for studying the system of virus classification. This system was developed by an American biologist David Baltimore in the 1970s, for which he was awarded the Nobel Prize.