Microorganisms


Q1.Describe the classification of microorganisms.

Ans: Classification of Microorganisms

Microorganisms are diverse microscopic organisms that can be unicellular, multicellular, or acellular. They are primarily classified into five major groups based on their cellular structure, morphology, and biological characteristics.

1. Bacteria

Bacteria are single-celled prokaryotic organisms. They lack a defined nucleus and membrane-bound organelles.

  • Characteristics: They possess a cell wall made of peptidoglycan.
  • Shapes: Classified into Cocci (spherical), Bacilli (rod-shaped), Spirilla (spiral), and Vibrio (comma-shaped).
  • Examples: Escherichia coli, Lactobacillus.

2. Fungi

Fungi are eukaryotic organisms that can be unicellular (yeasts) or multicellular (molds and mushrooms).

  • Characteristics: They are heterotrophic (cannot produce their own food) and have cell walls made of chitin.
  • Examples: Saccharomyces cerevisiae (Yeast), Penicillium.

3. Protozoa

Protozoa are unicellular eukaryotic organisms that exhibit animal-like behaviors, such as motility and predation.

  • Characteristics: They lack a cell wall and are often found in aquatic environments or as parasites.
  • Examples: Amoeba, Paramecium, Plasmodium.

4. Algae

Algae are plant-like eukaryotic organisms that contain chlorophyll and perform photosynthesis.

  • Characteristics: They can be unicellular or multicellular and usually live in moist or aquatic habitats.
  • Examples: Chlamydomonas, Spirogyra.

5. Viruses

Viruses are unique because they are considered on the borderline between living and non-living things.

  • Characteristics: They are acellular and consist of genetic material (DNA or RNA) enclosed in a protein coat. They can only replicate inside the living cells of a host organism.
  • Examples: Influenza virus, Bacteriophage, SARS-CoV-2.

Question 1: Structure and function of bacteria

Ans : Bacterial Structure and Function

Bacteria are single-celled prokaryotic organisms. Their structure is simple yet highly efficient for survival in diverse environments.

1. Structural Components

  • Cell Wall: Composed of peptidoglycan, it provides structural support and protection. It determines the shape of the bacterium (cocci, bacilli, etc.).
  • Plasma Membrane: A lipid bilayer that regulates the transport of molecules into and out of the cell.
  • Cytoplasm: A gel-like substance where metabolic reactions occur.
  • Nucleoid: A region containing the circular DNA molecule. Bacteria lack a membrane-bound nucleus.
  • Ribosomes: Sites of protein synthesis (70S type).
  • Plasmids: Small, circular, extra-chromosomal DNA that often carry genes for antibiotic resistance.
  • Flagella and Pili: Flagella are whip-like structures used for locomotion, while pili (or fimbriae) help in attachment to surfaces and conjugation.
  • Capsule: A protective outer layer found in some bacteria that helps evade the host immune system.

2. Functions

  • Reproduction: Primarily through binary fission, an asexual process where one cell divides into two identical daughter cells.
  • Metabolism: Bacteria can be autotrophs (producing their own food via photosynthesis or chemosynthesis) or heterotrophs (decomposers or parasites).
  • Decomposition: They play a vital role in nutrient cycling by breaking down organic matter.


Question 2: What are viruses? Describe their characteristics.

Ans: Understanding Viruses

Viruses are submicroscopic infectious agents that replicate only inside the living cells of an organism. They are considered to be at the edge of life, as they possess genetic material but lack a cellular structure.

Characteristics of Viruses

  • Acellular Nature: They do not have a cytoplasm, organelles, or a cell membrane. They are essentially genetic material wrapped in a protein coat.
  • Obligate Intracellular Parasites: They cannot reproduce or carry out metabolic activities outside a host cell.
  • Genetic Material: They contain either DNA or RNA, but never both. This genetic material can be single-stranded or double-stranded.
  • Capsid: The nucleic acid is protected by a protein shell called a capsid, made of subunits called capsomeres.
  • Envelope: Some viruses (like Influenza or HIV) have an outer lipid envelope derived from the host cell membrane.
  • Host Specificity: Viruses are highly specific to the hosts they infect (e.g., bacteriophages infect only bacteria).
  • Size: They are much smaller than bacteria, typically ranging from 20 to 300 nanometers, and can only be seen under an electron microscope.
  • Inert Outside Host: Outside a living cell, a virus exists as an inactive particle called a virion.


Previous Year Questions (As per INC & ANC Syllabus)

 Long Questions

* Define microorganisms. Explain the classification of microorganisms.
* Describe the morphology and structure of bacteria.
* Explain the characteristics of viruses with examples.
* Discuss the classification and importance of fungi.
* Explain protozoa and diseases caused by protozoa.
* Describe parasites and parasitic infections.
* Explain the growth and reproduction of bacteria.
* Discuss beneficial and harmful effects of microorganisms.
* Explain pathogenicity and virulence of microorganisms.
* Describe the life cycle of parasites.
* Explain transmission and prevention of microbial diseases.
* Discuss the role of microorganisms in health and disease.
* Explain bacterial spores and their importance.
* Describe the differences between bacteria and viruses.
* Explain the economic importance of microorganisms.


 Short Notes

* Bacteria
* Virus
* Fungi
* Protozoa
* Parasites
* Cocci
* Bacilli
* Spirilla
* Spores
* Pathogenic microorganisms
* Non-pathogenic microorganisms
* Normal flora
* Amoebiasis
* Malaria parasite
* Ringworm
* Yeast
* Helminths
* Transmission of microorganisms
* Microbial growth
* Virulence

 Very Short Questions 

* Define microorganisms.
* Name different types of microorganisms.
* What are bacteria?
* Define virus.
* What are fungi?
* Define protozoa.
* What are parasites?
* Name one bacterial disease.
* Name one viral disease.
* Name one fungal disease.
* Name one protozoal disease.
* What are cocci?
* Define bacilli.
* What are spores?
* What is virulence?
* Define pathogenicity.
* What is normal flora?
* Name one parasite.
* What is infection?
* Define helminths.

 MCQs Previous Year Type)

*Bacteria are:
  a) Multicellular organisms
  b) Unicellular organisms
  c) Viruses
  d) Parasites
  Ans: b) Unicellular organisms

* Malaria is caused by:
  a) Bacteria
  b) Virus
  c) Protozoa
  d) Fungus
  Ans: c) Protozoa

* Ringworm is caused by:
  a) Bacteria
  b) Fungus
  c) Virus
  d) Parasite
  Ans: b) Fungus

* AIDS is caused by:
  a) Fungus
  b) Protozoa
  c) Virus
  d) Bacteria
  Ans: c) Virus

* Round-shaped bacteria are called:
  a) Bacilli
  b) Spirilla
  c) Cocci
  d) Vibrios
  Ans: c) Cocci

* Rod-shaped bacteria are called:
  a) Cocci
  b) Bacilli
  c) Spirilla
  d) Spores
  Ans: b) Bacilli

* Organisms causing disease are known as:
  a) Non-pathogens
  b) Pathogens
  c) Flora
  d) Saprophytes
  Ans: b) Pathogens

Tuberculosis is caused by:
  a) Virus
  b) Fungus
  c) Bacteria
  d) Protozoa
  Ans: c) Bacteria


 Important Repeated Questions for Exam

* Define microorganisms and explain their classification.
* Describe structure and morphology of bacteria.
* Explain characteristics of viruses.
* Differentiate bacteria and viruses.
* Write short note on fungi and protozoa.
* Explain pathogenic microorganisms.
* Describe transmission of microbial diseases.
* Discuss beneficial and harmful effects of microorganisms.