Microorganisms can be divided into prokaryotic and eukaryotic groups. Prokaryotes like bacteria and archaea originated earliest on Earth and initiated an oxygenated atmosphere through endosymbiosis and panspermia, allowing new lifeforms to evolve over billions of years. Microorganisms make up most of Earth's biomass and play crucial roles in ecosystems by producing oxygen, decomposing waste, and nourishing other organisms, though some can cause disease. They are classified into 7 types - bacteria, archaea, fungi, algae, protozoa, viruses, and multicellular animals - based on their cellular structure, genetics, and metabolism.

1. Distribution of microorganisms in
nature - Groups of microorganisms –
Prokaryotic and eukaryotic microbes.
Dr. S. PARTHASARATHY, M.Sc. (Agri)., Ph.D.
Assistant Professor (Plant Pathology)

2. • Life on Earth is thought to have originated from the
oldest single-cell archaea and bacteria.
Microbes and the Origin of Life on Earth
• The proposed mechanisms for the origin of life on Earth
include endosymbiosis and panspermia. Both are
debatable theories.
• In these two theories, bacteria and extremophile archaea
are thought to have initiated an oxygenated atmosphere
creating new forms of life.
• Evolutionary processes over billions of years gave rise to
the biodiversity of life on Earth.

4. Microorganisms make up a large part of the planet’s living
material and play a major role in maintaining the Earth’s
ecosystem.
• Microorganisms are divided into seven types. Each type has a
characteristic cellular composition, morphology, mean of
locomotion, and reproduction.
• Microorganisms are beneficial in producing oxygen,
decomposing organic material, providing nutrients for plants,
and maintaining human health, but some can be pathogenic
and cause diseases in plants, animals and humans.
Types of Microorganisms

5. Microbial Groups
Divided into 7 distinct groups based on phylogeneic,
morphological and physiological characters
• Bacteria
• Archaea (Archaeo bacteria)
• Fungi
• Algae
• Protozoa
• Viruses &
• Multicellular animals

6. Scientists once thought of archaea and bacteria as a single group of organisms. Then in
1977, genetic analysis revealed that archaea had a separate evolutionary history to bacteria
and therefore represent an independent branch of life altogether.

7. Three domains of Microbial Life

8. Three domains of Microbial Life

9. Bacteria

10. This diversity is a mark of
how bacteria have evolved to
thrive in nearly all environments on this planet.
There are more species of bacteria than
any other life form. The most recent
estimate predicts that bacteria
account for over three quarters
of all species of life
on Earth.

11. Archea

12. Fungi

14. Protozoa

15. Algae

16. Viruses

17. Prokaryotes & Eukaryotes
• Prokaryotes- organisms lacking true nucleus and other
organelles like mitochondria, golgi body, endoplasmic
reticulum are referred as prokaryotes.
Eg. Bacteria and archaea.
• Eukaryotes – the organism possessing membrane enclosed
nuclues and other cell organelles are referred as eukaryotes.
Eg. Algae, fungi and protozoa.

18. Size of cell Typically 0.2-2.0 mm in
diameter
Typically 10-100 mm in
diameter
Nucleus No nuclear membrane or
nucleoli (nucleoid)
True nucleus, consisting of
nuclear membrane &
nucleoli
Membrane-
enclosed
organelles
Absent Present; examples include
lysosomes, Golgi complex,
endoplasmic reticulum,
mitochondria &
chloroplasts
Flagella Consist of two protein
building blocks
Complex; consist of
multiple microtubules
Glycocalyx Present as a capsule or
slime layer
Present in some cells that
lack a cell wall
Prokaryotes EukaryotesCharacteristics

19. Cell wall Usually present; chemically
complex (typical bacterial
cell wall includes
peptidoglycan)
When present,
chemically simple
Ribosomes Smaller size (70S) Larger size (80S); smaller
size (70S) in organelles
Mesosomes Present Absent
Chromosome
arrangement
Single circular
chromosome; lacks histones
Multiple linear
chromosomes with
histones
Prokaryotes EukaryotesCharacteristics

20. Extra chromosomal
DNA
Plasmid Mitochondria and
chloroplast
Cell division Binary fission Mitosis
Sexual reproduction No meiosis; transfer of
DNA fragments only
(conjugation)
Involves meiosis
Site for cellular
respiration
Cell membrane Mitochondria
Locomotion Rotating flagella and
gliding
Undulating flagella
and cilia, and also
amoeboid movement
Pili Sex or attachment pili
present
absent
Prokaryotes EukaryotesCharacteristics

21. Prokaryotic vs. Eukaryotic cell