These notes are provided from studifysuccess
Chapter- 2
Biological classification
Classification of living organisms has a long history, which was initially based on practical needs such
as food, shelter, and clothing.
Aristotle made early attempts at classification, using simple morphological characteristics to
categorize plants and animals.
Later, Linnaeus developed a Two Kingdom system (Plantae and Animalia), but it was limited and did
not account for prokaryotes, unicellular organisms, and differences in their nutrition and habitat.
Earlier classification systems included bacteria, blue-green algae, fungi, mosses, ferns, gymnosperms,
and angiosperms under one kingdom 'Plants' due to the presence of a cell wall in their cells. This
grouping brought together organisms with widely differing characteristics, such as prokaryotic
bacteria and eukaryotic blue-green algae (cyanobacteria).
It also grouped unicellular and multicellular organisms, like Chlamydomonas and Spirogyra,
respectively under the category of 'algae.'
However, this classification did not differentiate between heterotrophic fungi and autotrophic green
plants, even though they had differences in cell wall composition (fungi had chitin, green plants had
cellulose).
Classification systems had to evolved over time, with changing criteria like cell structure, nutrition,
reproduction, and evolutionary relationships.
R.H. Whittaker proposed a Five Kingdom Classification in 1969: Monera, Protista, Fungi, Plantae, and
Animalia. His criteria included cell structure, body organization, mode of nutrition, reproduction, and
phylogenetic relationships. This five-kingdom classification is also known as the “Modern
Classification.”
As a result, fungi were placed in a separate kingdom called 'Kingdom Fungi.'
Prokaryotic organisms were grouped under 'Kingdom Monera,' and unicellular eukaryotic organisms
were placed in 'Kingdom Protista.'
'Kingdom Protista' brought together organisms like Chlamydomonas, Chlorella (earlier placed in
Algae within Plants), with Paramecium and Amoeba (which were earlier placed in the animal
kingdom, lacking cell walls).
Modern classification aims to consider not only morphological, physiological, and reproductive
similarities but also phylogenetic relationships based on evolutionary history.
1. Kingdom Monera:
Bacteria are the sole members of the Kingdom Monera.
Bacteria are the most abundant micro-organisms found almost everywhere.
https://www.studifysuccess.com/ MADE BY – ERA KASHYAPP
, These notes are provided from studifysuccess
They are found in various habitats, including hot springs, deserts, snow, and deep oceans, where
few other life forms can survive.
Bacteria are grouped into four categories based on their shape: cocci (spherical), bacilli (rod-
shaped), vibrio (comma-shaped), and spirilla (spiral).
Despite their simple structure, bacteria exhibit complex behaviour.
Some bacteria are Autotrophic bacteria, i.e., they can synthesize their own food from inorganic
substrates, either through photosynthesis or chemosynthesis whereas the vast majority of
bacteria are heterotrophic, depending on other organisms or dead organic matter for food.
(a) Archaebacteria:
• Archaebacteria live in extreme and harsh habitats, including halophiles (salty areas),
thermoacidophiles (hot springs), and methanogens (marshy areas).
• Archaebacteria differ from other bacteria due to their unique cell wall structure, which also
contributes to their survival in extreme conditions.
• Methanogens are a type of archaebacteria found in the gut of ruminant animals such as
cows and buffaloes. They are helpful for the production of methane (biogas) from the dung
of these animals.
(b) Eubacteria:
• commonly known as 'true bacteria.'
• Eubacteria are characterized by the presence of a rigid cell wall and, if motile, a flagellum is
present for mobility.
• Cyanobacteria (Blue-Green Algae): They are a type of eubacteria that have chlorophyll a
similar to green plants, making them photosynthetic autotrophs. They can be unicellular,
colonial, or filamentous and are found in freshwater, marine, or terrestrial environments.
They often form colonies surrounded by a gelatinous sheath and can create blooms in
polluted water bodies.
• Some cyanobacteria can fix atmospheric nitrogen in specialized cells called heterocysts, e.g.,
Nostoc and Anabaena.
• Chemosynthetic Autotrophs: These bacteria oxidize various inorganic substances such as
nitrates, nitrites, and ammonia, using the released energy for ATP production. They play a
crucial role in recycling nutrients like nitrogen, phosphorus, iron, and sulfur.
• Heterotrophic Bacteria: They bacteria are the most abundant in nature and serve as
important decomposers. They have various impacts on human affairs, from curd production
to antibiotic synthesis. Some can fix nitrogen in legume roots, while others are pathogens
causing diseases in humans, crops, farm animals, and pets (e.g., cholera, typhoid, tetanus,
citrus canker).
• Bacteria primarily reproduce by fission but can produce spores under unfavourable
conditions. They can also engage in sexual reproduction by adopting a primitive form of DNA
transfer from one bacterium to another.
Mycoplasma: They are a group of organisms that completely lack a cell wall. They are the smallest
known living cells and can survive without oxygen. Many mycoplasma species are pathogenic in both
animals and plants.
2. Kingdom Protista:
https://www.studifysuccess.com/ MADE BY – ERA KASHYAPP
Chapter- 2
Biological classification
Classification of living organisms has a long history, which was initially based on practical needs such
as food, shelter, and clothing.
Aristotle made early attempts at classification, using simple morphological characteristics to
categorize plants and animals.
Later, Linnaeus developed a Two Kingdom system (Plantae and Animalia), but it was limited and did
not account for prokaryotes, unicellular organisms, and differences in their nutrition and habitat.
Earlier classification systems included bacteria, blue-green algae, fungi, mosses, ferns, gymnosperms,
and angiosperms under one kingdom 'Plants' due to the presence of a cell wall in their cells. This
grouping brought together organisms with widely differing characteristics, such as prokaryotic
bacteria and eukaryotic blue-green algae (cyanobacteria).
It also grouped unicellular and multicellular organisms, like Chlamydomonas and Spirogyra,
respectively under the category of 'algae.'
However, this classification did not differentiate between heterotrophic fungi and autotrophic green
plants, even though they had differences in cell wall composition (fungi had chitin, green plants had
cellulose).
Classification systems had to evolved over time, with changing criteria like cell structure, nutrition,
reproduction, and evolutionary relationships.
R.H. Whittaker proposed a Five Kingdom Classification in 1969: Monera, Protista, Fungi, Plantae, and
Animalia. His criteria included cell structure, body organization, mode of nutrition, reproduction, and
phylogenetic relationships. This five-kingdom classification is also known as the “Modern
Classification.”
As a result, fungi were placed in a separate kingdom called 'Kingdom Fungi.'
Prokaryotic organisms were grouped under 'Kingdom Monera,' and unicellular eukaryotic organisms
were placed in 'Kingdom Protista.'
'Kingdom Protista' brought together organisms like Chlamydomonas, Chlorella (earlier placed in
Algae within Plants), with Paramecium and Amoeba (which were earlier placed in the animal
kingdom, lacking cell walls).
Modern classification aims to consider not only morphological, physiological, and reproductive
similarities but also phylogenetic relationships based on evolutionary history.
1. Kingdom Monera:
Bacteria are the sole members of the Kingdom Monera.
Bacteria are the most abundant micro-organisms found almost everywhere.
https://www.studifysuccess.com/ MADE BY – ERA KASHYAPP
, These notes are provided from studifysuccess
They are found in various habitats, including hot springs, deserts, snow, and deep oceans, where
few other life forms can survive.
Bacteria are grouped into four categories based on their shape: cocci (spherical), bacilli (rod-
shaped), vibrio (comma-shaped), and spirilla (spiral).
Despite their simple structure, bacteria exhibit complex behaviour.
Some bacteria are Autotrophic bacteria, i.e., they can synthesize their own food from inorganic
substrates, either through photosynthesis or chemosynthesis whereas the vast majority of
bacteria are heterotrophic, depending on other organisms or dead organic matter for food.
(a) Archaebacteria:
• Archaebacteria live in extreme and harsh habitats, including halophiles (salty areas),
thermoacidophiles (hot springs), and methanogens (marshy areas).
• Archaebacteria differ from other bacteria due to their unique cell wall structure, which also
contributes to their survival in extreme conditions.
• Methanogens are a type of archaebacteria found in the gut of ruminant animals such as
cows and buffaloes. They are helpful for the production of methane (biogas) from the dung
of these animals.
(b) Eubacteria:
• commonly known as 'true bacteria.'
• Eubacteria are characterized by the presence of a rigid cell wall and, if motile, a flagellum is
present for mobility.
• Cyanobacteria (Blue-Green Algae): They are a type of eubacteria that have chlorophyll a
similar to green plants, making them photosynthetic autotrophs. They can be unicellular,
colonial, or filamentous and are found in freshwater, marine, or terrestrial environments.
They often form colonies surrounded by a gelatinous sheath and can create blooms in
polluted water bodies.
• Some cyanobacteria can fix atmospheric nitrogen in specialized cells called heterocysts, e.g.,
Nostoc and Anabaena.
• Chemosynthetic Autotrophs: These bacteria oxidize various inorganic substances such as
nitrates, nitrites, and ammonia, using the released energy for ATP production. They play a
crucial role in recycling nutrients like nitrogen, phosphorus, iron, and sulfur.
• Heterotrophic Bacteria: They bacteria are the most abundant in nature and serve as
important decomposers. They have various impacts on human affairs, from curd production
to antibiotic synthesis. Some can fix nitrogen in legume roots, while others are pathogens
causing diseases in humans, crops, farm animals, and pets (e.g., cholera, typhoid, tetanus,
citrus canker).
• Bacteria primarily reproduce by fission but can produce spores under unfavourable
conditions. They can also engage in sexual reproduction by adopting a primitive form of DNA
transfer from one bacterium to another.
Mycoplasma: They are a group of organisms that completely lack a cell wall. They are the smallest
known living cells and can survive without oxygen. Many mycoplasma species are pathogenic in both
animals and plants.
2. Kingdom Protista:
https://www.studifysuccess.com/ MADE BY – ERA KASHYAPP
