We can see all the living organisms. But there are some organisms that are very small to be seen through the naked eye. They can only be seen through microscopes and are called microorganisms. Have you seen bread with greyish white patches? What are those patches? Those patches are formed by one of the microorganisms called fungi. Likewise, there are several other groups of microorganisms. To know all the groups of microorganisms, let’s read the full article. This article covers the introduction to microorganisms and various groups of microorganisms.

What do you Mean by Microorganisms?

Microorganisms are organisms that cannot be seen through naked eyes but through microscopes. The study of microorganisms is called microbiology. Microorganisms were first observed by Leeuwenhoek.

Various Groups of Microorganisms

Microorganisms are classified into the following group:-
1. Bacteria
2. Fungi
3. Protozoa
4. Algae
5. Viruses

Fig: Groups of Microorganisms

Habitat of Microorganisms

Microorganisms are found everywhere around us. The air we breathe, the clothes we wear, on our skin, even inside the intestine, everywhere microbes are present. So, it is found everywhere, even inside the body.

Bacteria

Bacteria were the first to appear on earth. They are unicellular prokaryotic organisms.
Habitat: Found everywhere on earth, i.e., in air, soil, water, etc., and even inside the body of organisms.
Structure: A bacterial cell is very simple in structure. They are unicellular structures, have a  cell wall, less organelles, not defined nucleus, i.e., genetic material is naked and not surrounded by the nuclear membrane. In some bacteria, there may be a slimy, gelatinous, protective layer in the form of a capsule.
Shapes: They are of different shapes, namely,
1. Spherical (Cocci)
2. Rod-Shaped (Bacillus)
3. Spiral shaped (Spirillum)
4. Comma shaped (Vibrio)
Sizes: Their size varies. Their length may lie between 0.5–5.0 micrometres.
Locomotion: They have flagella for movement.
Nutrition: They are saprophytic and parasitic in nature. Saprophytic means they feed on the dead and decaying matter, while parasitic means they obtain their nutrition from the host.
Reproduction: Most of the bacteria reproduces by asexual reproduction, i.e., by binary fission. Some other asexual means are seen by budding, conidia formation, cyst formation, etc. Some may reproduce sexually by conjugation, transformation, and transduction.
Examples: Lactobacillus, Nitrosomonas,Rhizobium, etc.

Fig: Bacteria- Different Shapes

Archaebacteria

Archaebacteria are considered the oldest organisms present on earth. It has some characters of eukaryotes and some prokaryotes. It has some unique features too that lead them to be kept in different groups.
Habitat: The unique feature in these archaea is that they can survive in dangerous, extreme, or harsh climates. According to their habitat, they are classified as:-
a. Methanogens- They are methane generating bacteria and are found in the intestines of animals and marshy areas.
b. Halophiles- They are Salt-loving bacteria, so found in high salt concentrations. They are also found in the Dead sea.
c. Thermoacidophiles- They are found at very high temperatures, i.e., they could be near a hot water spring and in a high acidic condition.
Structure: It is a unicellular organism. It has no nucleus and no other complex organelles. The cell membrane is made of branched lipids and hydrocarbons. It has ether-linked lipids in membranes—no peptidoglycan layer in the cell wall. The cell wall is made of pseudo muramic acid, and on that layer, there is ‘S’ or surface proteins.
Locomotion: By flagella
Reproduction: By binary fission. Example: Thermus aquaticus, Halobacterium, Methanopyrus kandleri, etc.

Fungi

They are plant-like organisms but cannot prepare their own food as they do not have chlorophyll.
Habitat: They are found in dark, moist areas with moderate temperatures.
Structure:
a. They are multicellular except yeast which is unicellular.
b. They are eukaryotic.
c. They have a cell wall made of chitin.
d. Most fungi consist of cylindrical thread-like structures called hyphae. Hyphae forms mycelium which is formed by their interconnection.
e. They do not have chloroplast in their cells.
Nutrition: They are heterotrophs, can be saprophytic or parasitic.
Reproduction: Fungi can reproduce both asexually and sexually.
a. Yeast reproduces by budding while molds and mushrooms by spore formation. These are different asexual means.
b. Fungi, in response to adverse environmental conditions, may reproduce sexually in three sequential stages, plasmogamy, karyogamy, and meiosis.
Examples: Yeast, Molds, Mushrooms, etc.

Fig: Fungi

Protozoa

The term “Protozoa” was coined by Georg August Goldfuss in 1818. They are single-celled eukaryotic organisms. Protozoa literally mean “the first animal.”
Habitat: They can be-living, symbiotic, or parasitic.-living is found mostly in moist habitats. In dry environments, they may form resting cysts to remain dormant but can grow again when favourable environments come. Some protozoans live symbiotically with other organisms. At the same time, others are parasitic in nature and can cause disease to the host.
Structure:
a. They are unicellular.
b. Lack a cell wall.
c. In some, the pellicle surrounds the cell, which is a composite membranous envelope around the cell.
Size: It can be 1 micrometer to several millimeters.
Locomotion: They show locomotion by pseudopodia, flagella, or cilia.
Nutrition: Protozoans are heterotrophic, i.e., derive nutrition from others. They can be parasitic, saprophytic, or symbiotic. Except for Euglena, which is autotrophic in nature.
Reproduction:
a. Protozoans can reproduce by asexual means like binary fission or multiple fission, budding, or spore formation.
b. Some can reproduce sexually by conjugation.
Examples: Amoeba, Paramecium, Euglena, etc.

Fig: Protozoa

Algae

Algae are photosynthetic eukaryotes. They are simple plants but lack true roots, stems, and leaves. Algae can be red, brown, and green due to their different chloroplast pigments. Phycology refers to the study of algae. Algae are ecologically important because they add most of the oxygen to the environment. They are a food base for different aquatic organisms.
Habitat: They are found in water bodies, rocks, and snow.
Structure:
a. Eukaryotic organisms
b. Can be unicellular or multicellular.
c. They have a thallus-like body.
d. It contains a nucleus, chloroplast, mitochondria, etc.
e. Lives single or in colonies
Size: 1 micron to several meters. Like giant kelp, which can be 50 meters tall.
Nutrition: Autotrophic in nature as they have chlorophyll.
Reproduction: Algae can reproduce vegetatively, asexually, and even sexually.
a. Vegetatively by cell division, fragmentation, tuber formation, etc.
b. Asexually by the formation of different types of spores in different varieties like that of zoospores, aplanospores, etc.
c. Sexually by isogamy, heterogamy, etc.
Examples: Spirogyra, Chlorella, Prototheca and the diatoms, giant kelp, etc.

Fig: Giant Kelp

Fig: Unicellular algae

Virus

Viruses are smaller than bacteria. These are infectious agents which cannot replicate in a environment but only inside the living organism. Viruses infect not only plants and animals but also some microorganisms like bacteria. The study of viruses is called virology. Viruses can only be seen through a powerful microscope.
Habitat: They are found everywhere on earth. Found in air, water, soil, and living organisms.

Structure:
a. It consists of genetic material as single or double-stranded DNA or RNA.
b. Genetic material is surrounded by a protein coat called a capsid.
Shapes: They can be helical, spherical, polyhedral, or complex structures.
Nutrition: Viruses get nutrition from living hosts.
Reproduction: Viruses cannot reproduce on their own as they lack vital machinery to reproduce. They make multiple copies of themselves but only inside the living host cell.
Examples:  Norovirus and rotavirus, influenza virus, coronavirus, HIV, Bacteriophage, etc.

Fig: Virus- Bacteriophage

Fig: Virus- Coronavirus

Uses of Microorganisms

1. Microorganisms increase soil fertility. Like Rhizobium, bacteria present in the root nodules of leguminous plants help in fixing nitrogen.
2. It helps in cleaning the environment. Bacteria break down raw sewage into harmless and even useful substances which can be used in landfills. Faeces and other organic waste are broken down by bacteria in the absence of oxygen to produce methane gas which is used as fuel for cooking or lightning.
3. Fermentation: It is the process by which bacteria or fungi act on substances like sugars and leads to the production of carbon dioxide and alcohol. Yeast is used to ferment sugars in grapes to make wine. In bakeries, yeast is used to make bread dough.
4. Making antibiotics: Antibiotics are the substances that kill disease-causing microorganisms or stop their growth. Bacteria and fungi secrete antibiotics.
5. Making vaccines: Microbes can be used in the formation of vaccines. Vaccines are made of attenuated microbes, like in the case of Cholera and typhoid vaccines.

Harmful Microorganisms

Microorganisms are harmful in many ways, and some of the microorganisms that cause diseases in human beings, plants, and animals are called diseases causing microorganisms or pathogens. Some are specially adapted to infect and multiply within a host. Microbial diseases that can spread from an infected person to a healthy person through the air, water, food, or physical contact or contact with blood and bodily fluids are called communicable diseases. Examples of such diseases include the common cold, which can spread by sneezing in public without covering the mouth, and likewise, chickenpox spreads through the fluid from the blisters.

Diseases caused by pathogens:

Summary

From the above discussion, we can conclude that there are organisms that cannot be seen through naked eyes but through microscopes called microorganisms, which are divided into the following groups: Bacteria, fungi, protozoa, algae, viruses. Bacteria are unicellular, prokaryotic organisms. They are saprophytic and parasitic in nature. They are found everywhere, even inside our bodies. Fungi are multicellular except yeast which is unicellular. They are eukaryotes.

Fungi cannot prepare their own food, so they are heterotrophs, generally saprophytic or parasitic. Protozoa are unicellular eukaryotes. They are parasitic, saprophytic, or symbiotic, except Euglena, which is autotrophic in nature. Algae are simpler plants having thallus-like structures. They are autotrophic. They can be unicellular or multicellular. Viruses are even smaller than bacteria. They cannot replicate on their own but inside the host cell only. They are the most infectious agents. Microorganisms can be useful and harmful. Harmful microorganisms are called pathogens.

FAQs

Q.1. What are microorganisms?
Ans: Microorganisms are organisms that cannot be seen through naked eyes but through aided eyes like with the help of microscopes.

Q.2. What are the 5 types of microorganisms?
Ans: 5 types of microorganisms are:
a. Bacteria
b. Fungi
c. Protozoa
d. Algae
e. Viruses

Q.3. What are 4 types of bacteria?
Ans: 4 types of bacteria are:
a. Spherical (Cocci)
b. Rod-Shaped (Bacillus)
c. Spiral shaped (Spirillum)
d. Comma shaped (Vibrio)

Q.4. Is algae a bacteria or a plant?
Ans: Algae are simple plants.

Q.5. What are 2 examples of protozoa?
Ans: Amoeba, Paramecium are the two examples of protozoa.

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