Ever wondered how scientists make sense of the incredible diversity of life on Earth?
From tiny bacteria to giant elephants, how do we group them all? That’s where
biological classification steps in. Think of it as organizing your wardrobe — grouping
clothes by seasons, types, or colours. Similarly, biologists classify organisms to
understand their relationships, structure, evolution, and roles in ecosystems.
Classification makes it easier to study organisms. Instead of remembering millions of
individual species, students and researchers can study groups with shared
characteristics. It also helps in identifying organisms, predicting characteristics, and
understanding evolutionary links.
Need for Five Kingdom Classification
Back in the day, organisms were split into just two kingdoms — Plantae and
Animalia. But scientists soon realized that this system was too simplistic. Many
organisms didn’t fit neatly into these two categories. Enter Robert Whittaker. In 1969,
he proposed the Five Kingdom Classification, a revolutionary system that brought
clarity to the biological world.
The five kingdoms — Monera, Protista, Fungi, Plantae, and Animalia — are
based on factors like:
Cell type (prokaryotic or eukaryotic)
Body organization (unicellular or multicellular)
Mode of nutrition (autotrophic or heterotrophic)
Reproduction and habitat
Five Kingdom Classification System
Overview of the Five Kingdoms
Kingdo
m
Cell
Type
Body
Organization Mode of Nutrition
Monera Prokaryoti
c Unicellular Autotrophic/Heterotrophic
Protista Eukaryotic Mostly Unicellular Autotrophic/Heterotrophic
Fungi Eukaryotic Multicellular (mostly) Heterotrophic (absorptive)
Plantae Eukaryotic Multicellular Autotrophic
(photosynthesis)
Animalia Eukaryotic Multicellular Heterotrophic (ingestive)
Each kingdom groups organisms that share fundamental biological traits, helping
students approach complex questions with ease.
Criteria for Classification
The classification is based on:
- Cell Type – Prokaryotic or Eukaryotic
- Cell Wall Composition – Present or Absent; Made of Peptidoglycan,
Cellulose, or Chitin - Nuclear Organization – With or without membrane-bound nucleus
- Body Organization – Unicellular, Colonial, or Multicellular
- Nutrition – Autotrophic (photosynthetic/chemosynthetic) or Heterotrophic
(saprophytic/parasitic/ingestive) - Mode of Reproduction – Asexual, Sexual, Binary Fission, Budding, etc.
Kingdom Monera
Salient Features of Monera
Monerans are the simplest and most ancient forms of life — prokaryotic and
unicellular. They lack a defined nucleus and membrane-bound organelles. Their
genetic material floats freely within the cell in the form of a nucleoid.
Key features include:
Prokaryotic cells
Unicellular organisms
Cell wall present (made of peptidoglycan)
Reproduce asexually (binary fission)
Nutrition varies — autotrophic (photosynthetic/chemosynthetic) and
heterotrophic
Some have flagella for movement
They’re found in diverse environments — from icy glaciers to boiling springs. They
are the pioneers of life and form the foundation of the food chain in many
ecosystems.
Classification of Monera into Archaebacteria and
Eubacteria
Monera is broadly classified into:
Archaebacteria: Unique Features
These are ancient bacteria that thrive in extreme environments — acidic springs,
salty lakes, or deep-sea vents.
Cell wall lacks peptidoglycan
Methanogens (found in guts of ruminants)
Halophiles (salt-loving)
Thermoacidophiles (heat and acid-loving)
Capable of surviving harsh conditions due to unique membrane lipids
They’re important in biotechnology, especially in bio-gas production.
Eubacteria: Types and Characteristics
Also called true bacteria, these are more diverse and commonly found.
Cell wall contains peptidoglycan
Photosynthetic bacteria (like cyanobacteria or blue-green algae)
Chemosynthetic bacteria (derive energy from chemical reactions)
Pathogenic bacteria (cause diseases)
Cyanobacteria are important as they perform oxygenic photosynthesis, playing a
vital role in ecosystems.
Kingdom Protista
Salient Features of Protista
Protista is like the “miscellaneous drawer” of biology. When organisms didn’t fit
neatly into other kingdoms, they landed here. These are mostly unicellular
eukaryotes, meaning they have a well-defined nucleus and other membrane-bound
organelles.
Key features:
Eukaryotic and mostly unicellular
Some multicellular forms (like algae)
Aquatic in nature
Photosynthetic, heterotrophic, or mixotrophic
Reproduce sexually or asexually
Protists are the bridge between prokaryotic Monera and multicellular kingdoms like
Plantae and Animalia. Some protists behave like plants (autotrophs), some like
animals (heterotrophs), and some like fungi.
They play a crucial ecological role as primary producers and form the base of
aquatic food chains. Some, however, like Plasmodium (causes malaria), are
harmful pathogens.
Classification of Protists
The kingdom Protista is classified into the following groups based on nutrition and
form:
Chrysophytes, Dinoflagellates, Euglenoids
Chrysophytes (e.g., diatoms, golden algae): Have silica in cell walls; form
diatomaceous earth; major photosynthetic organisms in oceans.
Dinoflagellates (e.g., Gonyaulax): Mostly marine, have two flagella, show
red tides due to rapid multiplication; may release toxins.
Euglenoids (e.g., Euglena): Unique because they are mixotrophic
(photosynthesize in sunlight, ingest food in dark); have no cell wall, but a
protein-rich pellicle.
Slime Moulds and Protozoans
Slime moulds: Fungal-like protists; feed on decaying organic matter; have
plasmodium stage (multinucleated mass); reproduce via spores.
Protozoans: Animal-like protists; heterotrophic; classified based on
locomotion:
o Amoeboid protozoans (e.g., Amoeba) – pseudopodia
o Flagellated protozoans (e.g., Trypanosoma) – flagella
o Ciliated protozoans (e.g., Paramecium) – cilia
o Sporozoans (e.g., Plasmodium) – non-motile
Kingdom Fungi
Salient Features of Fungi
Fungi are strange yet fascinating organisms. Neither plants nor animals, they live
mostly as saprophytes, breaking down dead organic matter. From mushrooms to
molds to yeasts, fungi are everywhere — in your bread, soil, and even in antibiotics.
Salient features:
Eukaryotic and mostly multicellular (except yeast)
Cell wall made of chitin
Heterotrophic (absorptive nutrition)
Reproduce sexually and asexually
Body made of hyphae (network forms mycelium)
Can be saprophytic, parasitic, or symbiotic
Phycomycetes
Fungi play key ecological roles: decomposers in nature, food sources, and producers
of medicines (like penicillin from Penicillium).
Classification of Fungi into Major Groups
Based on reproduction and structure, fungi are classified into four major groups:
Found in aquatic habitats and moist soils.
Asexual reproduction by zoospores, sexual reproduction by zygospores.
Example: Rhizopus (bread mould), Mucor.
Ascomycetes (Sac Fungi)
Unicellular (yeasts) to multicellular (morels, truffles).
Asexual spores – conidia; sexual spores – ascospores in ascus.
Examples: Aspergillus, Saccharomyces (baker’s yeast), Neurospora (used in
genetics).
Basidiomycetes (Club Fungi)
Mostly terrestrial, include mushrooms, bracket fungi.
Asexual spores usually absent; basidiospores formed on basidium.
Examples: Agaricus, Puccinia (rust fungus).
Deuteromycetes (Imperfect Fungi)
Called imperfect because sexual reproduction is unknown.
Reproduce only by asexual conidia.
Many are pathogens or decomposers.
Examples: Alternaria, Trichoderma, Colletotrichum.
Understanding fungal groups with examples is critical for NEET, especially questions
on industrial uses or diseases caused by fungi.
Lichens
Symbiotic Nature
Lichens are a classic example of symbiosis — a mutual relationship between two
organisms. They consist of a fungus and an alga or cyanobacterium living
together.
Fungus provides structure, shelter, and absorbs water
Alga performs photosynthesis to produce food
The two partners live so closely that they appear as one organism. Lichens grow on
rocks, trees, and soil, often in extreme environments.
Ecological Importance
Lichens are crucial bioindicators of air quality. They’re highly sensitive to air
pollution, especially sulphur dioxide. Their absence in an area may indicate
pollution.
They’re also:
Pioneers in ecological succession
Used in dyes, perfumes, and traditional medicines
Viruses and Viroids
Nature and Structure of Viruses
Viruses are a biological paradox — they exist at the boundary of living and non-
living. Outside a host, they’re inert; inside, they hijack the host’s machinery to
reproduce.
Key features:
Composed of nucleic acid (DNA or RNA) and protein coat (capsid)
Obligate intracellular parasites
Cause diseases like AIDS (HIV), Influenza, Polio, COVID-19
Can infect animals, plants, and bacteria (bacteriophages)
Viruses are not included in the five-kingdom classification due to their acellular
nature.
Viroids: Discovery and Characteristics
Viroids were discovered by T.O. Diener in 1971. They are even simpler than viruses
— composed of naked circular RNA molecules without a protein coat.
Cause plant diseases (e.g., Potato spindle tuber disease)
Smaller than viruses
Can replicate within host cells
Both viruses and viroids are potential NEET MCQ topics due to their unique
biological nature.
Differences at a Glance
Monera vs Protista vs Fungi vs Lichens vs Viruses
Feature Monera Protista Fungi Lichens Viruse
s
Cell Type Prokaryotic Eukaryotic Eukaryotic
Composite
(fungus +
alga)
Acellular
(not truly
cells)
Nucleus Absent Present Present
Present (in
component
s)
Absent
Cell Wall Peptidoglycan
(in most)
Present/Absent
(varies) Chitin Present
(fungal)
Protein
coat
(capsid)
Nutrition Auto/Heterotrop
hic
Auto/Heterotrop
hic
Heterotrophic
(absorptive)
Mutualistic
(fungi+alga
e)
Parasitic
Reproducti
on
Asexual
(mostly)
Sexual &
Asexual
Sexual &
Asexual
Symbiotic
(indirectly)
Host-
depende
nt
replicati
on
Mode of Free- Free- Saprophytic/Para Symbiotic Obligate
Living living/Parasitic living/Parasitic sitic parasite
Habitat Ubiquitous Mostly aquatic Terrestrial/moist
areas
Harsh
environme
nts
Inside
host
cells
NEET Previous Year Questions with Solutions
Monera
Q1. (NEET 2020)
Which of the following are not membrane-bound?
a) Nucleus
b) Ribosomes
c) Lysosomes
d) Mitochondria
Answer: b) Ribosomes
Explanation: Ribosomes are non-membranous structures found in both prokaryotes
and eukaryotes.
Q2. (NEET 2019)
In which group of organisms the cell walls form two thin overlapping shells which fit
together?
a) Euglenoids
b) Dinoflagellates
c) Slime moulds
d) Diatoms
Answer: d) Diatoms
Protista
Q3. (NEET 2021)
Which protists have characteristics of both plants and animals?
a) Dinoflagellates
b) Euglenoids
c) Diatoms
d) Amoeboids
Answer: b) Euglenoids
Explanation: Euglenoids can photosynthesize like plants and ingest food like
animals
Q4. (NEET 2018)
The primitive prokaryotes responsible for the production of biogas from the dung of
ruminant animals include:
a) Halophiles
b) Thermoacidophiles
c) Methanogens
d) Eubacteria
Answer: c) Methanogens
Fungi
Q5. (NEET 2023)
The cell wall of fungi is made of:
a) Cellulose
b) Peptidoglycan
c) Chitin
d) Glycogen
Answer: c) Chitin
Q6. (NEET 2022)
Asexual reproduction in Penicillium occurs by:
a) Zoospores
b) Ascospores
c) Conidia
d) Basidiospores
Answer: c) Conidia
Lichens and Viruses
Q7. (NEET 2017)
Lichens are indicators of:
a) Water pollution
b) Soil pollution
c) Noise pollution
d) Air pollution
Answer: d) Air pollution
Q8. (NEET 2019)
The infectious nucleic acid without protein coat is:
a) Viroid
b) Virus
c) Bacteriophage
d) Plasmid
Answer: a) Viroid
FAQs
Q1. What is the most primitive kingdom in five kingdom classification?
Answer: Monera, because it consists of prokaryotic organisms without a defined
nucleus or organelles.
Q2. Are viruses considered living organisms?
Answer: Only when inside a host cell. Outside, they behave like non-living particles.
Q3. What are lichens a combination of?
Answer: A symbiotic association of fungi and algae or cyanobacteria.
Q4. How is Protista different from Monera?
Answer: Protists are eukaryotic (with a nucleus), while Monerans are prokaryotic.
Q5. What kind of questions are asked from biological classification in NEET?
Answer: Mostly MCQs on examples, differences, cell structure, and characteristics
of kingdoms.
