Aristotle’s classification It included the unicellular and the multicellular organisms
- Aristotle was the earliest to attempt a more scientific basis in same group. E.g. Chlamydomonas and Spirogyra were
for classification of organisms. placed under algae.
- He classified plants to trees, shrubs & herbs and animals It did not differentiate between the heterotrophic fungi and
into 2 groups- those with red blood & without red blood. the autotrophic green plants. Fungi have chitinous cell wall
Linnaeus’s Two-kingdom classification while the green plants have cellulosic cell wall.
- Linnaeus (1758) classified organisms into Two Five Kingdom Classification
Kingdoms- Kingdom Plantae & Kingdom Animalia. - It is proposed by R.H. Whittaker (1969).
Drawbacks of 2-kingdom classification: - It includes Monera, Protista, Fungi, Plantae & Animalia.
Prokaryotes (Bacteria, cyanobacteria) and eukaryotes - This is based on cell structure, thallus organization, mode
(fungi, mosses, ferns, gymnosperms & angiosperms) were of nutrition, reproduction and phylogenetic relationships.
included under ‘Plants’ based on the presence of cell wall. Three-domain system: It divides Kingdom Monera into two
But they are widely differed in other characteristics. domains. Eukaryotic kingdoms are included in third domain.
Thus it is six-kingdom classification.
Characteristics of the five kingdoms
Characters Monera Protista Fungi Plantae Animalia
Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic
Non-cellulosic (poly- Present (Chitin & Present
Cell wall Present in some Absent
saccharide + amino acid) polysaccharides) (Cellulose)
Nuclear membrane Absent Present Present Present Present
Multicellular, Tissue/organ/
Body organisation Cellular Cellular Tissue/organ
loose tissue organ system
Autotrophic (photosynthetic
Autotrophic Heterotrophic Heterotrophic
& chemosynthetic) and Autotrophic
Mode of nutrition (photosynthetic) (saprophytic or (holozoic,
heterotrophic (photosynthetic)
and heterotrophic parasitic) saprophytic etc.)
(saprophyte/parasite)
1. KINGDOM MONERA (BACTERIA)
- Bacteria are the most abundant microorganisms. II. Eubacteria (‘true bacteria’)
- Hundreds of bacteria are present in a handful of soil. - They have a rigid cell wall and a flagellum (if motile).
- They also live in extreme habitats such as hot springs, - They include Autotrophs (photosynthetic and
deserts, snow & deep oceans. Many are parasites. chemosynthetic) and Heterotrophs.
- Based on shape, bacteria are 4 types: Coccus (Spherical),
a. Photosynthetic autotrophs (E.g. Cyanobacteria):
Bacillus (Rod-shaped), Vibrium (Comma-shaped) &
- They have chlorophyll a similar to green plants.
Spirillum (Spiral).
- Cyanobacteria (blue-green
algae) are unicellular,
colonial or filamentous,
marine or terrestrial algae.
- The colonies are generally
surrounded by gelatinous
- Some bacteria are autotrophic (synthesize food from sheath.
inorganic substrates). Majority are heterotrophs (they do - They often form blooms in
not synthesize food but depend on other organisms or on polluted water bodies.
dead organic matter for food). - Some of them fix
I. Archaebacteria atmospheric nitrogen in
- They live in harshest habitats such as extreme salty areas specialized cells (heterocysts). E.g., Nostoc & Anabaena.
(halophiles), hot springs (thermoacidophiles) and marshy b. Chemosynthetic autotrophs:
areas (methanogens). - They oxidize inorganic substances such as nitrates, nitrites
- Archaebacteria have a different cell wall structure for their & ammonia and use the released energy for ATP production.
survival in extreme conditions. - They help in recycling nutrients like nitrogen,
- Methanogens are present in the guts of ruminant animals phosphorous, iron and sulphur.
(cows, buffaloes etc). They produce methane (biogas) c. Heterotrophic bacteria:
from the dung of these animals. - They are the most abundant in nature.
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- Aristotle was the earliest to attempt a more scientific basis in same group. E.g. Chlamydomonas and Spirogyra were
for classification of organisms. placed under algae.
- He classified plants to trees, shrubs & herbs and animals It did not differentiate between the heterotrophic fungi and
into 2 groups- those with red blood & without red blood. the autotrophic green plants. Fungi have chitinous cell wall
Linnaeus’s Two-kingdom classification while the green plants have cellulosic cell wall.
- Linnaeus (1758) classified organisms into Two Five Kingdom Classification
Kingdoms- Kingdom Plantae & Kingdom Animalia. - It is proposed by R.H. Whittaker (1969).
Drawbacks of 2-kingdom classification: - It includes Monera, Protista, Fungi, Plantae & Animalia.
Prokaryotes (Bacteria, cyanobacteria) and eukaryotes - This is based on cell structure, thallus organization, mode
(fungi, mosses, ferns, gymnosperms & angiosperms) were of nutrition, reproduction and phylogenetic relationships.
included under ‘Plants’ based on the presence of cell wall. Three-domain system: It divides Kingdom Monera into two
But they are widely differed in other characteristics. domains. Eukaryotic kingdoms are included in third domain.
Thus it is six-kingdom classification.
Characteristics of the five kingdoms
Characters Monera Protista Fungi Plantae Animalia
Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic
Non-cellulosic (poly- Present (Chitin & Present
Cell wall Present in some Absent
saccharide + amino acid) polysaccharides) (Cellulose)
Nuclear membrane Absent Present Present Present Present
Multicellular, Tissue/organ/
Body organisation Cellular Cellular Tissue/organ
loose tissue organ system
Autotrophic (photosynthetic
Autotrophic Heterotrophic Heterotrophic
& chemosynthetic) and Autotrophic
Mode of nutrition (photosynthetic) (saprophytic or (holozoic,
heterotrophic (photosynthetic)
and heterotrophic parasitic) saprophytic etc.)
(saprophyte/parasite)
1. KINGDOM MONERA (BACTERIA)
- Bacteria are the most abundant microorganisms. II. Eubacteria (‘true bacteria’)
- Hundreds of bacteria are present in a handful of soil. - They have a rigid cell wall and a flagellum (if motile).
- They also live in extreme habitats such as hot springs, - They include Autotrophs (photosynthetic and
deserts, snow & deep oceans. Many are parasites. chemosynthetic) and Heterotrophs.
- Based on shape, bacteria are 4 types: Coccus (Spherical),
a. Photosynthetic autotrophs (E.g. Cyanobacteria):
Bacillus (Rod-shaped), Vibrium (Comma-shaped) &
- They have chlorophyll a similar to green plants.
Spirillum (Spiral).
- Cyanobacteria (blue-green
algae) are unicellular,
colonial or filamentous,
marine or terrestrial algae.
- The colonies are generally
surrounded by gelatinous
- Some bacteria are autotrophic (synthesize food from sheath.
inorganic substrates). Majority are heterotrophs (they do - They often form blooms in
not synthesize food but depend on other organisms or on polluted water bodies.
dead organic matter for food). - Some of them fix
I. Archaebacteria atmospheric nitrogen in
- They live in harshest habitats such as extreme salty areas specialized cells (heterocysts). E.g., Nostoc & Anabaena.
(halophiles), hot springs (thermoacidophiles) and marshy b. Chemosynthetic autotrophs:
areas (methanogens). - They oxidize inorganic substances such as nitrates, nitrites
- Archaebacteria have a different cell wall structure for their & ammonia and use the released energy for ATP production.
survival in extreme conditions. - They help in recycling nutrients like nitrogen,
- Methanogens are present in the guts of ruminant animals phosphorous, iron and sulphur.
(cows, buffaloes etc). They produce methane (biogas) c. Heterotrophic bacteria:
from the dung of these animals. - They are the most abundant in nature.
1
