The smallest organism among the following is

The smallest organism among the options provided is the virus. Viruses are much smaller than bacteria, mycoplasma, and yeast. They are submicroscopic infectious agents, ranging in size from about 20 to 300 nanometers. Viruses cannot replicate on their own and must infect a host cell to reproduce. They consist of genetic material (either DNA or RNA) enclosed in a protein coat called a capsid. Some viruses also have an outer lipid envelope. Viruses are known to infect a wide range of hosts, including animals, plants, fungi, and bacteria. Due to their small size and ability to mutate rapidly, viruses pose significant challenges in the development of treatments and vaccines. Despite their small size, viruses play important roles in evolution and the ecosystem, but they can also cause serious diseases in humans, animals, and plants.