What are Microorganisms? Definition, History, Characteristics, Importance

A microorganism, in simple terms, is a tiny living organism that is too small to be seen with the naked eye. These organisms include bacteria, viruses, fungi, and protists.

Microbes: A broader term that encompasses microscopic organisms including bacteria, viruses, fungi, and protists, as well as certain non-living entities such as prions and viroids.

Microorganisms: Specifically refers to living microscopic organisms such as bacteria, viruses, fungi, and protists. These are organisms that carry out life processes and can reproduce.

Introduction to Microorganisms:

  • Microbes existed much earlier than humans, and the fossil record shows that microbes existed on Earth as early as 3.2 billion years ago. 

  • According to the "five kingdoms" of biology, organisms can be divided into prokaryotes, protists, fungi, plants, and animals. The microorganism is a collective term for the first three.

  • Although human beings cannot see these small lives with the naked eye, they are always accompanied by human beings and have a huge impact on human life and production.

  • Leeuwenhoek is called "the pioneer of microbiology", Pasteur is called "the founder of microorganisms", and Koch is called "the founder of bacteria"

  • Leeuwenhoek used a self-made single-type microscope with a magnification of about 200 times to observe individuals of microorganisms such as bacteria, and described the morphology of some microorganisms, 

  • Their common feature is that they are small in size, but they are an important part of nature and ecosystems and are closely related to humans.

What are Microorganisms? Definition, History, Characteristics, Importance
What are microorganisms pic

Definition of Microorganisms:

  • Microorganisms are small organisms that cannot be seen through the naked eye and can only be seen under a microscope are called microorganisms or microbes. 

  • A microbe is a prokaryotic living thing that is too small to be seen with the naked eye and can only be seen under a microscope.

What are Microorganisms?

  • Microbes are the general term for all small organisms that are invisible to the naked eye.

  • Prokaryotic microbes include bacteria, actinomycetes, cyanobacteria, mycoplasma, rickettsia, and chlamydia, etc.

  • Eukaryotic microbes are included in fungi, protozoa, and microscopic algae, as well as viruses and subviruses belonging to the acellular type.

  • The study of microbes is known as Microbiology 

  • Microbes are much simpler than plants and animals, which have similar characteristics and an elementary biological organization.

  • Microbes can be categorized into two types pathogenic and non-pathogenic microorganisms.

  • Pathogenic are those that are capable of causing disease while non-pathogenic are entirely harmless and some of the microscopic life that lives inside the human body.

Discovery of Microorganisms:

  • The discovery and morphological observation of microorganisms began with the invention of the microscope by Antoni van Leeuwenhoek.
  • He clearly saw bacteria and protozoa with a microscope that could magnify 50 to 300 times. 
  • Antoni van Leeuwenhoek's discovery and description revealed a new biological world for the first time. 
  • The study microbial world is called Microbiology. 
  • It has epoch-making significance in the development history of microbiology.
  • In the 19th century, Pasteur in France and Koch in Germany advanced the study of microbes from morphological description to the stage of physiological research, revealing that microorganisms are the cause of spoilage fermentation and human and animal diseases, and established A series of unique microbial technologies such as isolation, culture, inoculation, and sterilization. 
  • This laid the foundation of microbiology and opened up branch disciplines such as medical and industrial microbiology. Pasteur and Koch were the founders of microbiology.
  • The outstanding work of Pasteur and Koch made microbiology begin to form as an independent discipline, and various branches established by them appeared, such as bacteriology (Pasteur, Koch, etc.), disinfection surgery Technology (J. Lister), Immunology (Pasteur, Metchnikoff, Behring, Ehrlich, etc.), Soil Microbiology (Beijernck Winogradsky, etc.), Virology (Ivanowsky, Beijerinck, etc.), Phytopathology and Mycology (Bary, Berkeley, etc.), etc.), brewing (Hensen, Jorgensen, etc.), and chemotherapeutics (Ehrlich, etc.). 

Characteristics of Microorganisms?

  • They are small in size and can't be seen with the naked eye.
  • They perform metabolic reactions.
  • They need water to metabolize.
  • They have short generation periods.
  • They produce through asexual reproduction.
  • They can alter the environment in which they are found.
  • They are essential for life on the planet.
  • They are present everywhere like soil, water, and air.

Why microorganisms are important?

  • Microorganisms affect all life and the physical and chemical makeup of our planet. From the origin of life, life without all other organisms is possible, but life without microorganisms is impossible.
  • Microbes are the masters of the biosphere, and our planet is indeed a planet of microbes.
  • Microorganisms are also determinants of human health and a source of critical materials for medical and industrial uses. Therefore, microbiology is as central to the study of life as biochemistry, genetics, evolution, or molecular biology.
  • Microbes are responsible for recycling key elements of life, including carbon, nitrogen, sulfur, hydrogen, and oxygen. 
  • By cycling these elements in the soil, microbes can regulate the availability of plant nutrients to control soil fertility and achieve efficient plant growth that sustains human and animal life.
  • Microbes also play an important role in circulating atmospheric gases, including compounds that cause the "greenhouse effect," which, paradoxically, sustains life on our planet but, through global warming, poses a threat to all living things.
  • Microbes perform more photosynthesis than green plants.
  • Microorganisms are also specialists in recycling, degrading biological waste, and releasing key elements for use by other organisms. 
  • Microorganisms play a big role in daily life, food fermentation, beer brewing, antibiotics, etc.
  • Industrial microorganisms involve food, pharmaceutical, metallurgy, mining, petroleum, leather, light chemical industry, and other industries.

Types of Microorganisms:


  • This term bacteria comes from the Greek “bakteria”, whose meaning refers to a cane, this is due to their morphology.
  • The bacterium is the smallest unicellular organism that exists on Earth. 
  • It belongs to the Kingdom of Monera and is characterized by having a prokaryotic cell.
  • Bacterial size varies between 0.5 and 8 micrometers in length.
  • In bacteria, genetic material is usually found grouped in a nuclear region called nucleoid that lacks its own envelope or membrane.
  • It does not have a nucleus or membrane-bound cellular organelles such as mitochondria, chloroplasts, etc. 
  • They have flagella and pili systems for locomotion.
  • Based on their shape bacteria can be classified into bacilli (elongated or rod-shaped), vibrios (curved), spirilla (spiral), and cocci (rounded). 
  • The latter can occur isolated, in pairs (diplococci), in aligned groups (streptococci), in irregular masses (staphylococci), or in cubic masses (sarcinae).
  • They help break down digested food and others are capable of producing antibiotics and are used in scientific research specifically in biotechnology and genetic engineering.
  • They have wide industrial use in the manufacture of cheese, yogurt, and dairy products, as a result of the lactic fermentation process. 
  • Among the foods that can be derived from microorganisms, are wine, beer, and other alcoholic beverages.


  • A virus is a non-cellular life form that spreads the infection to the cells of living organisms, including bacteria. 
  • The term originated from the Latin word virus, meaning "poison". The origin of viruses is one of the unsolved mysteries of biology. 
  • The number of viruses studied in detail reaches five thousand, but it is believed that their real number exceeds a million.
  • A virus has DNA or RNA as a genetic material protected by a capsid protein shell, in some cases a lipid shell. 
  • Despite the presence of genetic material, viruses cannot reproduce outside a living cell. 
  • Their size is less than one-hundredth of the average bacterium, which is why they are so difficult to study. 
  • The science that studies viruses is called virology.
  • The most common classification of virus species depends on the type of genetic material, that is, DNA-containing and RNA-containing viruses are distinguished. 
  • Most viruses belong to the second class. Some exceptions viruses contain both types of nucleic acid. 
  • Another classification method, proposed by David Baltimore in 1971, also considers the number of nucleic acid chains (one or two) and the method of its replication (synthesis in the nucleus, on ribosomes, or in the cytoplasm).
  • The transfer of viruses can be carried out in various ways: from one organism to another by direct contact, by contact with natural secretions, or by airborne droplets. 
  • Some viruses can infect a wide range of living organisms, others only a certain species. 
  • Human viruses carry a wide variety of infections, ranging from the fairly harmless common cold to diseases such as rabies and AIDS.
  • A great contribution to the study of viruses was made by the domestic microbiologist Dmitry Iosifovich Ivanovsky. In 1892, he discovered that it was a non-cellular life form that was the cause of tobacco mosaic disease and became the discoverer of viruses. 
  • The term was first used in 1898 by his follower, the Dutch microbiologist Martin Beijerinck. 
  • In 2002, American scientists created the first synthetic polio virus.


what are microbes

  • A fungus is a type of eukaryotic organism belonging to the kingdom of Fungi. 
  • Fungi can be unicellular or multicellular For example yeast belongs to unicellular, while mold and mushrooms belong to multicellular fungi.
  • Fungi consist of membrane-bound cell organelles.
  • The cell wall of fungi is made up of chitin.
  • More than 70,000 species of fungi have now been discovered, and it is estimated that only a fraction of all exist. 
  • These are heterotrophic means that cannot synthesize their own food.
  • Yeasts, molds, and mushrooms are some of the important examples of fungi.
  • They decompose dead plants and animals, extracting nutrients from them.
  • Fungi, like bacteria and microbes, are decomposers, that is, organisms that break down the organic matter of dead organisms. 
  • Other fungi are used in food processing, such as yeast for bread and other processing, and brewing also requires fungi.
  • In agriculture, forestry, and animal husbandry, fungi have a harmful side. Fungi can cause a variety of plant diseases, resulting in huge economic losses.
  • Fungi can also cause a variety of diseases in animals, plants, and humans.


  • Protists are simple unicellular eukaryotic organisms that are neither plants nor animals or fungi. 
  • Protists may be autotrophic or heterotrophic.
  • They reproduce mainly through asexual reproduction like binary fission or budding.
  • The name was introduced by Ernst Haeckel in 1866, but in the modern sense, it was first used in 1969 by Robert Whittaker.
  • They consist of only one cell but sometimes there are colonial forms, in which all life processes take place: respiration, nutrition, and reproduction.
  • Some of them are free-living and some are parasites.
  • They vary in size and body shape. Some of them are microscopic, others reach tens of meters in length.
  • Protists live in fresh and marine waters, in moist soil, and on the bark of trees. 
  • Many protists can move with the help of cilia or flagella
  • Examples of protists are amoeba, ciliate shoe, trypanosome.
  • Plant-like protists such as diatoms, and dinoflagellates, animal-like protists such as amoeba, and fungus-like such as slime molds.

Importance of Microorganisms:

  • Microbes are model organisms in the basic research of life sciences. 
  • Promote the development of tissue culture and cell culture technology for higher animals and plants.
  • Microorganisms have an important impact on humans as well as microbial communities. 
  • Microbes are widely involved in many fields such as food, medicine, industry and agriculture, environmental protection, and so on.
  • Bacteria, fungus, molds, and yeast are the most important microorganisms that use in food and food product production.  
  • Many microbes are used in the fermentation process to produce fermented products such as yogurt, wine, beer, ethanol, vitamins, antibiotics, bread, etc.
  • Microorganisms are also used in the Production of Antibiotics, Dairy Products, Alcoholic Beverages, Bread making, Food Yeast, Organic Acids, Vitamins, etc.
  • Microorganisms are used to generate fuels such as ethanol, hydrogen, methane, lipids, and butanol.
  • Microorganisms are used in Scientific research for the study of genomics, biochemistry, and bioinformatics. 
  • Biological techniques use living organisms to remove pollutants and are called bioremediation
  • It may also be used to purify the environment, such as activated sludge and petroleum-degrading bacteria used for the treatment of industrial wastewater.

Frequently Asked Questions on Microorganisms (Microbes): 

1. What are Microbes in biology?
  • Microbe (microorganism) is a collective name for living organisms, the size of which is so small that they cannot be seen with the naked eye. 
  • Microbes include both prokaryotes (non-nuclear) and eukaryotes (nuclear) but do not include viruses and prions.
  • Microbiology is the study of microbes.
  • Microbes live almost everywhere where there is water: on the ground, in the mountains, at the bottom of the oceans, and even deep inside the earth's crust.
  • Microbes participate in the decomposition of organic matter of animal and vegetable origin, carry out the cycle of sulfur, iron, and phosphorus, and provide self-purification of water in reservoirs. 
  • Other microorganisms are not so useful: they carry diseases (pathogenic microbes), deplete the soil with nitrogen, spoil agricultural products, pollute water bodies, and participate in the accumulation of toxins in food.
  • Microorganisms were discovered and first described at the end of the 17th century in Holland by Antoni van Leeuwenhoek, who studied various substances under a microscope. Looking at the water, Leeuwenhoek noticed tiny "animals", which he called "animalcules".

2. How do you define a microbe?
Answer: Microbes are small organisms that cannot be seen through the naked eye and can only be seen under a microscope.

3. What are the main types of microbes?
  • Bacteria: While some bacteria can be good for us, "bad bacteria" can cause disease.
  • Viruses: They can cause outbreaks ranging from the flu to measles and chicken pox.
  • Fungus: Although many fungi do not harm humans, others can cause rashes.
  • Protozoa: Spread through water and can cause intestinal infections.

4. What are microbes and microbiology?
Answer: Microbes are communities of microorganisms that live together in natural habitats that can only be seen with a microscope, and these life forms are called microbes or microbiomes. Microorganisms include bacteria, archaea, viruses, fungi, protozoa, prions, and yeasts as well as microscopic algae.

Microbiology is the study of all living organisms that are invisible to the naked eye. The study of microbiology covers all aspects of these microorganisms, such as their behavior, evolution, ecology, biochemistry, and physiology, as well as the pathology of the diseases they cause. As discussed in the next chapters, microbiology plays a very important role in different streams.

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