Which is the smallest of all microorganisms?

Which is the smallest of all microorganisms?

• A. Virus
• B. Bacteria
• C. Fungi
• D. Parasites

Answer: (A)

Size is the key factor. Viruses are the tiniest microorganisms because they are acellular particles made of genetic material wrapped in a protein shell (sometimes with a lipid envelope), and they range from about 20 nanometers up to a few hundred nanometers. Bacteria are single-celled organisms with their own metabolic machinery and cell structures, typically about 0.2 to 2 micrometers in size, which is larger than most viruses. Fungi, including yeasts and molds, are eukaryotic and generally even larger, often micrometers to tens of micrometers. Parasites cover a broad group, from single-celled protozoa that are usually larger than bacteria to multicellular worms that are much larger still. Because of their acellular, nanoscale size, viruses are the smallest among these microorganisms.

Size is the key factor. Viruses are the tiniest microorganisms because they are acellular particles made of genetic material wrapped in a protein shell (sometimes with a lipid envelope), and they range from about 20 nanometers up to a few hundred nanometers. Bacteria are single-celled organisms with their own metabolic machinery and cell structures, typically about 0.2 to 2 micrometers in size, which is larger than most viruses. Fungi, including yeasts and molds, are eukaryotic and generally even larger, often micrometers to tens of micrometers. Parasites cover a broad group, from single-celled protozoa that are usually larger than bacteria to multicellular worms that are much larger still. Because of their acellular, nanoscale size, viruses are the smallest among these microorganisms.