What is the nature of a virus?

A virus is an acellular (non-cellular) infectious particle that can reproduce only inside the living cells of a host organism. Unlike living cells, viruses do not have cytoplasm, organelles, or a cell membrane. They are extremely small—much smaller than bacteria—and cannot perform any metabolic activities on their own.

A typical virus consists of two main parts:

1. 
   

   Genetic material – either DNA or RNA, but never both. This carries the instructions for making new viruses.

   
   


2. 
   

   Protein coat (capsid) – a protective layer that surrounds the genetic material and helps the virus attach to host cells.

   
   

Some viruses also have an additional lipid envelope derived from the host cell membrane, as seen in influenza and HIV viruses.

Viruses are unique because they display characteristics of both living and non-living things. Outside a host, they behave like non-living particles — they do not move, grow, or reproduce. But once inside a living cell, they use the host’s machinery to multiply, which makes them appear “alive.” This is why scientists consider viruses to be at the borderline between living and non-living organisms.

Viruses can infect almost all living things — animals, plants, fungi, and even bacteria (these are called bacteriophages). Diseases such as influenza, measles, COVID-19, polio, and AIDS are all caused by viruses.

Let’s analyze the options:

• 
  

  A) Unicellular – Has one cell; viruses have none.

  
  


• 
  

  B) Multicellular – Has many cells; not applicable to viruses.

  
  


• 
  

  C) Acellular – ✅ Correct. Viruses are not made of cells.

  
  


• 
  

  D) None of these – Incorrect.

  
  

Hence, the correct answer is that viruses are acellular, meaning they lack a cellular structure and depend entirely on host cells for reproduction.

✅ Correct Answer: C) Acellular