Microorganisms: An Introduction

  • Microorganisms, or microbes, are minute organisms that cannot be seen with the naked eye due to their extremely small size.
  • They occur virtually everywhere - in air, soil, water, food, and within and on our bodies.
  • Microbes include a wide variety of organisms such as bacteria, viruses, protozoa, algae, and fungi.
  • Most microorganisms are harmless, but some can cause disease, known as pathogens.


  • Bacteria are single-celled prokaryotic organisms. They have a simple cell structure without a nucleus and other membrane-bound organelles.
  • They reproduce asexually by binary fission, a process where one cell divides into two identical cells.
  • Bacteria play a vital role in nitrogen fixation in the soil, making nitrogen available to plants.
  • Numerous bacteria are involved in the fermentation process which is used in food production like in making yoghurt, cheese, and alcoholic beverages.


  • Viruses are non-living entities that can only reproduce within a host cell.
  • They infect all types of life forms, from animals and plants to bacteria.
  • Viruses have a simple structure of genetic material (either DNA or RNA) enclosed in a protein coat.
  • They can cause diseases including flu, HIV/AIDS, and COVID-19.


  • Protozoans are single-celled eukaryotic organisms with complex structures.
  • They can move using various methods such as through pseudopodia, cilia, and flagella.
  • Some species are parasites and can cause diseases including malaria and sleeping sickness.


  • Algae are a diverse group of photosynthetic organisms, ranging from single-celled to multicellular forms.
  • They form the base of the aquatic food chain and help in oxygen production in the atmosphere.
  • Economically important as they can be used to produce biofuels, food additives, and are sources of certain medicines.


  • Fungi are eukaryotic organisms that include multicellular moulds and single-celled yeasts.
  • They are important decomposers, playing an essential role in nutrient cycling.
  • They can also cause plant and animal diseases, but also have uses in the production of bread, beer, and antibiotics.