Microorganisms – Complete Biology Notes for OTET, CTET, OSSTET, B.Ed & Competitive Exams

MICROORGANISMS – COMPLETE BIOLOGY NOTES

Biology Study Material
Topic: Microorganisms
Useful for OTET, CTET, OSSTET, B.Ed, Junior Teacher, Odisha Constable and other competitive examinations.

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1. Meaning of Microorganisms

Microorganisms are very small living organisms that cannot usually be seen with the naked eye. They are also called microbes.

• They are found in air, water and soil.
• They are present in hot springs, deserts and extremely cold regions.
• Some microorganisms are useful, while others cause diseases.
• They play an important role in decomposition and nutrient cycling.

2. Major Groups of Microorganisms

The major groups commonly studied are:

1. Bacteria
2. Fungi
3. Protozoa
4. Algae
5. Viruses (acellular infectious agents)

3. Bacteria

Bacteria are microscopic, single-celled prokaryotic organisms. They do not have a true membrane-bound nucleus.

Characteristics

• Mostly unicellular organisms.
• Do not possess a membrane-bound nucleus.
• Reproduce mainly by binary fission.
• May be autotrophic or heterotrophic.
• Some bacteria are useful and some cause diseases.

Shapes of Bacteria

Shape	Name
Spherical	Coccus
Rod-shaped	Bacillus
Spiral-shaped	Spirillum
Comma-shaped	Vibrio

Useful Bacteria

• Lactobacillus: Converts milk into curd.
• Rhizobium: Fixes atmospheric nitrogen in association with legume roots.
• Acetobacter: Used in vinegar production.
• Streptomyces: Produces several antibiotics.

4. Fungi

Fungi are eukaryotic organisms that obtain nutrients by absorption. Most fungi are multicellular, but yeast is unicellular.

• They lack chlorophyll.
• They cannot prepare their own food through photosynthesis.
• Their cell wall generally contains chitin.
• They commonly reproduce by spores.
• Yeast reproduces mainly by budding.

Examples

• Yeast – Used in baking and fermentation.
• Rhizopus – Bread mould.
• Penicillium – Source of penicillin.
• Agaricus – Mushroom.

5. Protozoa

Protozoa are mostly unicellular, eukaryotic organisms. Many are free-living, while some are parasites.

Protozoan	Important Feature
Amoeba	Moves using pseudopodia.
Paramecium	Moves using cilia.
Plasmodium	Causes malaria.
Trypanosoma	Causes sleeping sickness.
Giardia	Causes giardiasis.

6. Algae

Algae are photosynthetic organisms, mostly aquatic, that contain chlorophyll.

• They may be unicellular or multicellular.
• They prepare their own food through photosynthesis.
• They are important producers in aquatic ecosystems.
• They release oxygen through photosynthesis.

Examples

• Chlamydomonas – Unicellular green alga.
• Spirogyra – Filamentous green alga.
• Volvox – Colonial green alga.
• Ulothrix – Filamentous green alga.

7. Viruses

Viruses are acellular infectious agents. They can reproduce only inside living host cells.

• They contain genetic material: DNA or RNA.
• They are surrounded by a protein coat called capsid.
• Some viruses also possess an outer lipid envelope.
• They infect plants, animals and microorganisms.
• Antibiotics do not work against viral infections.

Examples of Viral Diseases

• Common cold
• Influenza
• COVID-19
• Polio
• Rabies
• Dengue
• Measles
• AIDS (caused by HIV)

8. Useful Microorganisms

A. In Food Production

• Lactobacillus converts milk into curd.
• Yeast is used in bread making.
• Yeast helps in the fermentation of sugar.
• Some bacteria and fungi are used in cheese production.

B. In Medicine

• Penicillium produces the antibiotic penicillin.
• Streptomyces produces several antibiotics.
• Some microorganisms are used to manufacture vaccines.

C. In Agriculture

• Rhizobium fixes atmospheric nitrogen in leguminous plants.
• Blue-green algae (cyanobacteria) help in nitrogen fixation.
• Microorganisms improve soil fertility.

D. In Environment

• Decompose dead plants and animals.
• Recycle nutrients in nature.
• Help in sewage treatment.
• Some microbes are used in bioremediation.

9. Harmful Microorganisms

Microorganisms that cause diseases in humans, animals and plants are called pathogens.

Human Diseases

Disease	Causative Microorganism
Tuberculosis	Bacterium – Mycobacterium tuberculosis
Typhoid	Bacterium – Salmonella Typhi
Cholera	Bacterium – Vibrio cholerae
Malaria	Protozoan – Plasmodium
Dengue	Virus – Dengue virus
Polio	Poliovirus
Ringworm	Fungus
Measles	Measles virus
AIDS	HIV

Plant Diseases

Disease	Causative Agent
Citrus canker	Bacterium
Rust of wheat	Fungus
Yellow vein mosaic of bhindi	Virus
Late blight of potato	Oomycete (Phytophthora infestans)

10. Methods of Food Preservation

Food preservation prevents or slows down spoilage caused by microorganisms.

• Salting: Used in preserving fish and meat.
• Sugaring: Used in jams and jellies.
• Oil and vinegar: Used in pickles.
• Refrigeration: Slows microbial growth.
• Heating: Kills many harmful microorganisms.
• Pasteurization: Controlled heating followed by rapid cooling to reduce harmful microbes in milk.
• Drying: Removes moisture required for microbial growth.
• Chemical preservatives: Sodium benzoate is used in some foods.

11. Nitrogen Fixation

Nitrogen fixation is the process of converting atmospheric nitrogen into usable nitrogen compounds.

• Atmospheric nitrogen cannot be directly used by most plants.
• Rhizobium lives in root nodules of leguminous plants.
• Certain cyanobacteria also fix nitrogen.
• Nitrogen fixation helps maintain soil fertility.

12. Vaccination and Antibiotics

Vaccination

• Vaccines stimulate the immune system to develop protection against specific diseases.
• They may contain weakened or inactivated pathogens, their components or genetic instructions.
• Vaccination helps prevent infectious diseases.

Antibiotics

• Antibiotics are medicines used to treat bacterial infections.
• Penicillin was discovered by Alexander Fleming in 1928.
• Antibiotics are not effective against viral infections.
• Misuse of antibiotics can cause antibiotic resistance.

13. Important Scientists

Scientist	Contribution
Antonie van Leeuwenhoek	Early observations of microorganisms.
Louis Pasteur	Germ theory, pasteurization and contributions to vaccination.
Robert Koch	Established the role of specific microbes in diseases; Koch's postulates.
Alexander Fleming	Discovered penicillin.
Edward Jenner	Developed the first successful smallpox vaccine.

14. Difference Between Bacteria and Viruses

Bacteria	Viruses
Cellular organisms.	Acellular infectious agents.
Have cellular structure.	Have genetic material and protein coat.
Can reproduce independently under suitable conditions.	Replicate only inside living host cells.
Some are treated with antibiotics.	Antibiotics are ineffective.

15. Important One-Liners for Competitive Exams

1. Microorganisms are also called microbes.
2. Bacteria are prokaryotic organisms.
3. Yeast is a unicellular fungus.
4. Lactobacillus converts milk into curd.
5. Rhizobium fixes atmospheric nitrogen.
6. Penicillin was discovered by Alexander Fleming.
7. Penicillin is obtained from Penicillium fungi.
8. Malaria is caused by Plasmodium.
9. Malaria is transmitted by female Anopheles mosquitoes.
10. Dengue is transmitted mainly by Aedes mosquitoes.
11. Cholera is caused by Vibrio cholerae.
12. Typhoid is caused by Salmonella Typhi.
13. TB is caused by Mycobacterium tuberculosis.
14. Amoeba moves using pseudopodia.
15. Paramecium moves using cilia.
16. Yeast reproduces mainly by budding.
17. Viruses contain either DNA or RNA as their genome.
18. Viruses reproduce only inside living host cells.
19. Pasteurization is used to reduce harmful microbes in milk.
20. Antibiotics do not cure viral infections.
21. Blue-green algae are actually cyanobacteria.
22. Fungi generally have chitin in their cell walls.
23. Decomposers recycle nutrients in ecosystems.
24. Edward Jenner is associated with the smallpox vaccine.
25. Robert Koch is associated with Koch's postulates.

16. Quick Revision Table

Question	Answer
Curd formation	Lactobacillus
Bread making	Yeast
Malaria	Plasmodium
Penicillin	Penicillium
Nitrogen fixation	Rhizobium
TB	Mycobacterium tuberculosis
Cholera	Vibrio cholerae
Sleeping sickness	Trypanosoma
Antibiotic discovery	Alexander Fleming
Smallpox vaccine	Edward Jenner

EXAM TIP:
Remember these important pairs:
Curd – Lactobacillus
Bread – Yeast
Malaria – Plasmodium
Penicillin – Penicillium
Nitrogen fixation – Rhizobium
TB – Mycobacterium tuberculosis

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Microorganisms Biology Notes OTET CTET OSSTET B.Ed Junior Teacher