Question

Which one is the smallest organism capable of autonomous growth and reproduction?
A. Virus
B. Viroid
C. Mycoplasma
D. None of the above

Answer 1

Hint: The genetic material of viruses and viroids can be DNA or RNA and they can carry out DNA replication in their host cell. Mycoplasmas have linear and double stranded DNA as its genetic material which can replicate on their own.

Complete step by step answer:
Virus and viroids function as obligate parasites. They cannot exhibit various functions of living organisms like growth and reproduction. They are themselves non living as they cannot carry out DNA replication, etc. by itself. They are only active when they infect and enter the host cell. Also, viruses are not the smallest. So, the smallest is mycoplasma.
 Mycoplasma is the smallest prokaryotic bacteria. They have a diameter of 0.0001 mm. They are present in respiratory mucosa of humans as well as animals. They are living organisms capable of performing various functions like growth, division and reproduction. In unicellular form, mycoplasma reproduces by binary fission whereas if it is in filamentous form, it reproduces through fragmentation. In some cases, mycoplasma cells divide and form tiny cells known as bleb particles which are the elementary bodies. The mycoplasmas do not have a cell wall, therefore their shape changes frequently. This phenomenon of shape changes or shape shifting is also known as pleomorphism.
So, the correct answer is option “C” that is mycoplasma is the smallest organism capable of autonomous growth and reproduction.

Note:
Mycoplasma cells lack cell walls. So, their limiting outer membrane is cell membrane or the plasma membrane which is composed of lipoproteins. Mycoplasmas are parasitic bacteria which are found in the respiratory and genital tracts, waste disposal organs and primate bladder.