Question

The smallest living organism that causes diseases is
A. Ants
B. Virus
C. Bacteria
D. Lice

Answer 1

Hint: A disease is an abnormal condition of the body that affects the structure and function of an organism. It is caused by pathogens which are mostly microorganisms that cannot be seen with the naked eye. The smallest living organisms are the same organisms that cause AIDS, dengue, corona, etc.

Complete answer: An organism is said to be living if it can undergo replication, carry out other biological processes and can synthesise their own proteins. The smallest living organisms are microorganisms like bacteria, fungi and viruses that are able to replicate and can also cause several life-threatening diseases.
a) Bacteria: The size of bacteria is one-tenth of that of the eukaryotic cell. The size ranges from 0.5-5 micrometre in length. They are capable of self-replication and can synthesise their own proteins. Diseases caused by bacteria include tuberculosis, typhoid, etc.
b) Virus: A virus is the smallest living organism that remains inert outside the cell but is capable of replicating and synthesising its protein only inside the living host. They are much smaller than bacteria and are sub-microscopic with a size around 20 nanometers. Diseases caused by viruses are influenza, common cold, HIV, etc.
c) Ants: The size of ants vary from 6-12 mm in size. These are small organisms which can be easily seen with naked eyes. The ants are terrestrial organisms that mainly carry the bacteria called Salmonella sp.
d) Lice: Lice are wingless parasitic insects that feed on the human blood. They can easily be seen with the naked eye.
Thus, the correct answer is option B.

Note: Virus infects all types of cell starting from bacteria to plants, animals and human beings. The diseases caused by viruses are not easily cured. Many viral diseases can be prevented through vaccines. Its symptoms can only be reduced.