Biological Classification (NEET Biology Class 11): Five Kingdoms, Monera to Animalia
Classification through History & the Five Kingdoms
🎯 NEET priority: High-yield. 5–7 questions every year. NCERT is asked almost line-for-line here — every kingdom, every example organism, every special term is fair game. Learn it all.
How do you sort millions of living things into a system that makes sense? That single question drives this chapter — and NEET loves testing every twist in the answer.
From two kingdoms to five
Aristotle was the earliest to attempt a scientific classification, sorting plants into trees, shrubs and herbs, and animals by whether they had red blood.
Linnaeus gave the Two Kingdom system — Plantae and Animalia. Its fatal flaw: it lumped prokaryotes with eukaryotes, and photosynthetic with non-photosynthetic organisms, so it was abandoned.
R.H. Whittaker (1969) proposed the Five Kingdom Classification — Monera, Protista, Fungi, Plantae, Animalia — using cell structure, body organisation, mode of nutrition, reproduction and phylogenetic relationships.
The Five Kingdoms at a glance (memorise this grid)
Character | Monera | Protista | Fungi | Plantae | Animalia |
Cell type | Prokaryotic | Eukaryotic | Eukaryotic | Eukaryotic | Eukaryotic |
Cell wall | Non-cellulosic | Present in some | Chitin | Cellulose | Absent |
Nuclear membrane | Absent | Present | Present | Present | Present |
Body organisation | Cellular | Cellular | Multicellular/loose | Tissue/organ | Organ system |
Nutrition | Auto/Hetero | Auto/Hetero | Heterotrophic | Autotrophic | Holozoic |
The three-domain system — know the answer NEET wants
Later, Carl Woese proposed the three-domain system. It splits Kingdom Monera into two domains — Archaea (the archaebacteria) and Bacteria (the eubacteria) — and groups all eukaryotes into a third domain, Eukarya. So the three domains are Archaea, Bacteria and Eukarya. Splitting Monera this way also yields a six-kingdom classification: Archaebacteria, Eubacteria, Protista, Fungi, Plantae and Animalia. NCERT keeps this brief, but remember the proposer (Woese) and the three domain names — that is exactly what gets asked.
Exam trap: the flaw the five-kingdom system fixed was classifying organisms by a single character — "having a cell wall" — which wrongly lumped prokaryotic bacteria and blue-green algae together with eukaryotic plants and fungi.
Kingdom Monera — the Bacteria
Monera contains the bacteria — the most abundant micro-organisms on Earth, found everywhere from hot springs to deep oceans. They are all prokaryotic.
Bacterial shapes & nutrition
Four shapes by form: Coccus (spherical), Bacillus (rod), Vibrium (comma), Spirillum (spiral).
Bacteria show the most extensive metabolic diversity of any group — autotrophic (photosynthetic or chemosynthetic) or, in the vast majority, heterotrophic.
Archaebacteria — the extremophiles
Live in the harshest habitats, thanks to a different cell wall structure: halophiles (extreme salt), thermoacidophiles (hot springs), methanogens (marshy areas).
Methanogens live in the gut of ruminants (cows, buffaloes) and produce methane (biogas) from dung.
Eubacteria, cyanobacteria & mycoplasma
Cyanobacteria (blue-green algae) have chlorophyll a and are photosynthetic; some fix atmospheric nitrogen in specialised cells called heterocysts — e.g. Nostoc and Anabaena. They form blooms in polluted water.
Chemosynthetic bacteria oxidise inorganic substances (nitrates, nitrites, ammonia) and help recycle nitrogen, phosphorus, iron and sulphur.
Bacteria reproduce mainly by fission; under stress they form spores.
Mycoplasma completely lack a cell wall, are the smallest living cells known, and can survive without oxygen.
Kingdom Protista — Single-Celled Eukaryotes
Protista holds all single-celled eukaryotes — the link between Monera and the higher kingdoms. Every protist has a true nucleus and membrane-bound organelles.
Chrysophytes (diatoms & golden algae): microscopic plankton; diatoms have silica cell walls that fit like a soap-box and are indestructible — their deposits form diatomaceous earth. Diatoms are the chief producers in the oceans.
Dinoflagellates: mostly marine, photosynthetic, with stiff cellulose plates. Red dinoflagellates (e.g. Gonyaulax) multiply to cause red tides; their toxins can kill fish.
Euglenoids: freshwater; no cell wall but a protein pellicle; mixotrophic (photosynthetic in light, heterotrophic in dark). e.g. Euglena.
Slime moulds: saprophytic; form an aggregation called a plasmodium; spores have true walls and resist adverse conditions.
Protozoans are heterotrophic predators/parasites in four groups: amoeboid (pseudopodia; Amoeba, Entamoeba), flagellated (Trypanosoma → sleeping sickness), ciliated (Paramoecium, with a gullet), and sporozoans (Plasmodium → malaria).
Exam trap: diatomaceous earth (polishing/filtration), red tides (Gonyaulax), and "which protist causes which disease" are classic NEET one-liners.
Kingdom Fungi — the Four Classes
The four protist groups — match-the-pair reference
Group | What it is | Locomotion / feature | The NEET hook |
Chrysophytes | Diatoms and golden algae | Float passively as plankton | Indestructible silica walls fit like a soapbox; leave diatomaceous earth |
Dinoflagellates | Marine, photosynthetic protists | Two flagella — one longitudinal, one transverse | Gonyaulax multiplies into red tides and releases toxins |
Euglenoids | Freshwater, no cell wall | Two flagella, one long one short | Pellicle instead of a wall; photosynthetic in light, heterotrophic in dark |
Slime moulds | Saprophytic protists | Aggregate into a plasmodium | Form resistant spores under unfavourable conditions |
Protozoans | Heterotrophic, predator or parasite | Pseudopodia, cilia or flagella | Amoeboid, flagellated, ciliated and sporozoan — Plasmodium is a sporozoan |
Exam trap. Euglena is the classic "both plant and animal" organism — it has chlorophyll and photosynthesises in sunlight, but feeds heterotrophically in the dark, and it has no cell wall, only a protein-rich pellicle.
Fungi are heterotrophic eukaryotes with chitin cell walls. Except unicellular yeasts, their body is a network of thread-like hyphae called a mycelium. Multinucleate tubes without cross-walls are coenocytic hyphae.
Most are saprophytes (absorb dead organic matter); others are parasites or symbionts (with algae as lichens, with roots as mycorrhiza). The sexual cycle runs plasmogamy → karyogamy → meiosis (giving haploid spores), sometimes via an intervening dikaryon (n+n) stage.
The four classes
Phycomycetes: aquatic/decaying wood; aseptate, coenocytic mycelium; asexual zoospores/aplanospores; sexual zygospore. e.g. Mucor, Rhizopus (bread mould), Albugo (mustard parasite).
Ascomycetes (sac-fungi): septate mycelium; asexual conidia; sexual ascospores in sac-like asci. e.g. Penicillium (antibiotics), yeast (Saccharomyces), Aspergillus, Neurospora (used in genetics).
Basidiomycetes: mushrooms, rusts, smuts; sexual basidiospores on a basidium. e.g. Agaricus (mushroom), Ustilago (smut), Puccinia (rust).
Deuteromycetes (imperfect fungi): only asexual/vegetative phase known; reproduce by conidia; many are decomposers. e.g. Alternaria, Trichoderma, Colletotrichum.
Kingdoms Plantae & Animalia
The fungal classes — the one table that answers most fungus questions
Class | Common name | Hyphae | Sexual spore | Examples |
Phycomycetes | Algal fungi | Aseptate, coenocytic | Zoospores / aplanospores | Mucor, Rhizopus (bread mould), Albugo |
Ascomycetes | Sac fungi | Septate, branched | Ascospores in an ascus | Aspergillus, Penicillium, Neurospora, yeast, morels |
Basidiomycetes | Club fungi | Septate | Basidiospores on a basidium | Mushrooms, bracket fungi, puffballs, rusts, smuts |
Deuteromycetes | Fungi imperfecti | Septate | None known — only conidia | Alternaria, Colletotrichum, Trichoderma |
Exam trap. Deuteromycetes are called 'imperfect' because only their ASEXUAL phase is known — once a sexual stage is discovered, the fungus is moved to Ascomycetes or Basidiomycetes. Also remember Neurospora is an ascomycete widely used in genetics, and that only Phycomycetes have aseptate (coenocytic) hyphae.
These two kingdoms are detailed in later chapters, but NEET tests their defining features here.
Plantae: all eukaryotic, chlorophyll-containing organisms with cellulose walls — algae, bryophytes, pteridophytes, gymnosperms, angiosperms. A few are heterotrophic: insectivorous Bladderwort and Venus flytrap, and the parasite Cuscuta.
Plant life cycles show alternation of generations — a diploid sporophyte alternating with a haploid gametophyte.
Animalia: heterotrophic, multicellular eukaryotes that lack a cell wall, store glycogen/fat, and have a holozoic mode of nutrition (ingestion). Higher forms show sensory/neuromotor systems and locomotion.
Viruses, Viroids, Prions & Lichens
Whittaker's five kingdoms leave out the acellular agents and lichens — NCERT covers them at the end, and NEET asks about them often.
Viruses
Non-cellular, inert crystalline structures outside the host; obligate parasites that hijack host machinery to replicate.
Ivanowsky (1892) found microbes causing tobacco mosaic disease; Beijerinck (1898) named the fluid Contagium vivum fluidum; Stanley (1935) showed viruses can be crystallised.
Genetic material is RNA or DNA, never both. Plant viruses → usually ss-RNA; bacteriophages → usually ds-DNA. The protein coat is the capsid, made of subunits called capsomeres.
Viroids, Prions & Lichens
Viroids: Diener (1971) found free RNA without a protein coat, causing potato spindle tuber disease.
Prions: abnormally folded infectious proteins causing mad cow disease (BSE) and CJD.
Lichens: symbiotic associations of an alga (phycobiont, autotroph) and a fungus (mycobiont, heterotroph); excellent pollution indicators.
Why this matters for NEET
Pure recall chapter: "which kingdom / which class / which example" questions dominate — the example organisms (Nostoc, Gonyaulax, Paramoecium, Rhizopus, Puccinia) are as testable as the concepts.
Favourite traps: Mycoplasma (no wall, smallest), diatoms (silica wall), RNA-or-DNA-never-both, viroid = RNA only, and the scientist–discovery matches (Ivanowsky/Stanley/Diener).
Test Yourself: MCQs, PYQs & Active Recall
Answer these, then close the article and do an Active Recall. Reveal each answer only after you commit to one.
Practice Questions
Q1. Who proposed the Five Kingdom Classification?
(a) Linnaeus
(b) Ernst Haeckel
(c) Aristotle
(d) R.H. Whittaker
Show answer
Answer: (d) — R.H. Whittaker proposed it in 1969, using cell structure, body organisation, nutrition, reproduction and phylogeny.
Q2. Which kingdom contains only prokaryotic organisms?
(a) Fungi
(b) Monera
(c) Protista
(d) Plantae
Show answer
Answer: (b) — Monera (bacteria) is the only entirely prokaryotic kingdom; the other four are eukaryotic.
Q3. The smallest living cells, lacking a cell wall, are:
(a) Archaebacteria
(b) Diatoms
(c) Mycoplasma
(d) Cyanobacteria
Show answer
Answer: (c) — Mycoplasma completely lack a cell wall, are the smallest known living cells, and survive without oxygen.
Q4. Diatoms are characterised by cell walls made of:
(a) Silica
(b) Peptidoglycan
(c) Chitin
(d) Cellulose
Show answer
Answer: (a) — Diatom walls are embedded with indestructible silica, forming soap-box-like overlapping shells; their deposits make diatomaceous earth.
Q5. Red tides in the sea are caused by:
(a) Dinoflagellates
(b) Chrysophytes
(c) Slime moulds
(d) Euglenoids
Show answer
Answer: (a) — Rapidly multiplying red dinoflagellates (e.g. Gonyaulax) cause red tides; their toxins can kill marine animals.
Q6. Which protozoan causes malaria?
(a) Paramoecium
(b) Entamoeba
(c) Plasmodium
(d) Trypanosoma
Show answer
Answer: (c) — Plasmodium is a sporozoan with an infectious spore-like stage; it causes malaria. Trypanosoma causes sleeping sickness.
Q7. Nitrogen-fixing cyanobacteria carry out fixation in specialised cells called:
(a) Heterocysts
(b) Pellicle
(c) Asci
(d) Conidia
Show answer
Answer: (a) — Heterocysts are the specialised nitrogen-fixing cells of cyanobacteria such as Nostoc and Anabaena.
Q8. The bread mould Rhizopus belongs to which class of fungi?
(a) Deuteromycetes
(b) Ascomycetes
(c) Basidiomycetes
(d) Phycomycetes
Show answer
Answer: (d) — Rhizopus (bread mould) is a phycomycete — aseptate, coenocytic mycelium, forming zygospores.
Q9. Which statement about viruses is correct?
(a) They contain both RNA and DNA
(b) They are obligate parasites with a protein capsid
(c) They have a cellulose cell wall
(d) They reproduce by binary fission
Show answer
Answer: (b) — A virus has either RNA or DNA (never both), is an obligate parasite, and its nucleic acid is protected by a protein capsid of capsomeres.
Q10. Viroids differ from viruses in that they:
(a) Have only DNA
(b) Are larger than bacteria
(c) Have a thick protein coat
(d) Are free RNA without a protein coat
Show answer
Answer: (d) — Diener (1971) found viroids to be free, low-molecular-weight RNA lacking the protein coat that viruses have.
Q11. Which class of fungi is characterised by aseptate, coenocytic hyphae?
(a) Basidiomycetes
(b) Deuteromycetes
(c) Ascomycetes
(d) Phycomycetes
Show answer
Answer: (d) — Only Phycomycetes — the algal fungi such as Mucor, Rhizopus and Albugo — have aseptate hyphae, meaning multinucleate tubes with no cross-walls. All three other classes are septate.
Q12. Deuteromycetes are called 'fungi imperfecti' because:
(a) Only their asexual or vegetative phase is known
(b) They lack a cell wall
(c) They are always parasitic
(d) They cannot reproduce at all
Show answer
Answer: (a) — Only the asexual stage is known — hence 'imperfect'. If a sexual stage is later discovered, the fungus is reclassified into Ascomycetes or Basidiomycetes, so the class is effectively a holding bay.
Q13. Red tides in the sea are caused by the rapid multiplication of:
(a) Diatoms
(b) Euglena, a euglenoid
(c) Slime moulds
(d) Gonyaulax, a dinoflagellate
Show answer
Answer: (d) — Gonyaulax is a red dinoflagellate that multiplies so rapidly it turns the sea red, releasing toxins that can kill fish and other marine animals.
Q14. Which organism has characteristics of both plants and animals?
(a) Amoeba
(b) Paramecium
(c) Euglena
(d) Plasmodium
Show answer
Answer: (c) — Euglena is photosynthetic in sunlight like a plant, yet feeds heterotrophically in the dark like an animal — and it has no cell wall, only a protein-rich pellicle.
Q15. Diatomaceous earth, used in polishing and filtration, is formed from the cell walls of:
(a) Blue-green algae
(b) Slime moulds
(c) Diatoms (chrysophytes)
(d) Dinoflagellates
Show answer
Answer: (c) — Diatom cell walls are made of indestructible silica and overlap like a soapbox. Over billions of years these walls have piled into large deposits of diatomaceous earth.
Q16. Which kingdom contains organisms that are prokaryotic, some of which are chemosynthetic autotrophs?
(a) Fungi
(b) Plantae
(c) Protista
(d) Monera
Show answer
Answer: (d) — Monera holds all prokaryotes — bacteria and cyanobacteria. Chemosynthetic autotrophic bacteria oxidise inorganic substances such as nitrates, nitrites and ammonia to obtain energy, playing a key role in nutrient cycling.
Q17. Lichens represent a symbiotic association between:
(a) A bacterium and an alga
(b) An alga (phycobiont) and a fungus (mycobiont)
(c) Two different fungi
(d) A fungus and the roots of a higher plant
Show answer
Answer: (b) — In a lichen the algal partner prepares food by photosynthesis while the fungal partner provides shelter and absorbs mineral nutrients and water. Lichens are excellent pollution indicators because they will not grow in polluted air.
Q18. Mycorrhiza is an association between a fungus and:
(a) An alga
(b) The roots of higher plants
(c) A cyanobacterium
(d) An insect
Show answer
Answer: (b) — In mycorrhiza the fungus absorbs mineral ions and water from the soil and passes them to the plant root, while the plant supplies the fungus with sugars and nitrogenous compounds.
Q19. The sexual spore of Basidiomycetes is the:
(a) Basidiospore, borne externally on a basidium
(b) Ascospore, borne inside an ascus
(c) Conidium
(d) Zoospore
Show answer
Answer: (a) — Basidiospores are produced EXTERNALLY on a club-shaped basidium — contrast Ascomycetes, whose ascospores are produced INSIDE a sac-like ascus. Inside versus outside is exactly the distinction NEET tests.
Q20. Which of the following is NOT a criterion used by Whittaker for his five-kingdom classification?
(a) Phylogenetic relationships
(b) Mode of locomotion
(c) Cell structure
(d) Mode of nutrition
Show answer
Answer: (b) — Whittaker's criteria were cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships. Mode of locomotion was not among them.
NEET Previous Year Questions (PYQs)
Real NEET-pattern recall questions with explanations in our own words.
Q21. Methanogens belong to: (NEET PYQ)
(a) Archaebacteria
(b) Eubacteria
(c) Slime moulds
(d) Dinoflagellates
Show answer
Answer: (a) — Methanogens are archaebacteria of marshy/anaerobic habitats; they live in ruminant guts and produce methane (biogas).
Q22. Which of the following is the chief producer in the oceans? (NEET PYQ)
(a) Diatoms
(b) Cyanobacteria
(c) Euglenoids
(d) Dinoflagellates
Show answer
Answer: (a) — Diatoms (chrysophytes) are the chief 'producers' in the oceans owing to their abundance and photosynthesis.
Q23. The smallest living cells, completely lacking a cell wall, are: (NEET PYQ)
(a) Mycoplasma
(b) Archaebacteria
(c) Diatoms
(d) Cyanobacteria
Show answer
Answer: (a) — Mycoplasma (PPLO) lack a cell wall, are the smallest known living cells, and can survive without oxygen.
Q24. Heterocysts, the site of nitrogen fixation, are found in: (NEET PYQ)
(a) Rhizopus
(b) Paramoecium
(c) Nostoc
(d) Euglena
Show answer
Answer: (c) — Cyanobacteria such as Nostoc and Anabaena fix atmospheric nitrogen in specialised cells called heterocysts.
Q25. The cell wall of diatoms is mainly composed of: (NEET PYQ)
(a) Peptidoglycan
(b) Chitin
(c) Cellulose
(d) Silica
Show answer
Answer: (d) — Diatom walls are embedded with indestructible silica in two soap-box-like overlapping shells; their deposits form diatomaceous earth.
Q26. Red tides are caused by the rapid multiplication of: (NEET PYQ)
(a) Dinoflagellates
(b) Euglenoids
(c) Slime moulds
(d) Diatoms
Show answer
Answer: (a) — Red dinoflagellates such as Gonyaulax multiply so fast that the sea appears red; their toxins can kill marine animals.
Q27. Sleeping sickness in humans is caused by: (NEET PYQ)
(a) Paramoecium
(b) Entamoeba
(c) Trypanosoma
(d) Plasmodium
Show answer
Answer: (c) — Trypanosoma is a flagellated protozoan that causes sleeping sickness; Plasmodium (a sporozoan) causes malaria.
Q28. Penicillium, a source of antibiotics, belongs to the class: (NEET PYQ)
(a) Phycomycetes
(b) Deuteromycetes
(c) Ascomycetes
(d) Basidiomycetes
Show answer
Answer: (c) — Penicillium is an ascomycete (sac-fungus); ascomycetes produce sexual ascospores inside sac-like asci.
Q29. The 'imperfect fungi', in which only the asexual phase is known, are the: (NEET PYQ)
(a) Phycomycetes
(b) Ascomycetes
(c) Deuteromycetes
(d) Basidiomycetes
Show answer
Answer: (c) — Deuteromycetes reproduce only by asexual conidia; once a sexual stage is discovered they are moved to Asco- or Basidiomycetes.
Q30. Viroids differ from viruses in: (NEET PYQ)
(a) Being larger than bacteria
(b) Lacking a protein coat
(c) Possessing a cell wall
(d) Having only DNA
Show answer
Answer: (b) — Diener (1971) found viroids to be free, low-molecular-weight RNA that lacks the protein coat present in viruses.
Q31. The genetic material of a bacteriophage is usually: (NEET PYQ)
(a) Single-stranded DNA
(b) Double-stranded RNA
(c) Single-stranded RNA
(d) Double-stranded DNA
Show answer
Answer: (d) — Bacteriophages (viruses infecting bacteria) are usually double-stranded DNA viruses. A virus carries either RNA or DNA, never both.
Q32. Lichens are widely used as: (NEET PYQ)
(a) Sources of biogas
(b) Producers of antibiotics
(c) Nitrogen fixers
(d) Pollution indicators
Show answer
Answer: (d) — Lichens (a symbiosis of an algal phycobiont and a fungal mycobiont) do not grow in polluted areas, so they are excellent pollution indicators.
Active Recall Prompt
Write everything you can recall, naming each group first. Cover: the five-kingdom history (Aristotle, Linnaeus, Whittaker); Monera (bacterial shapes, archaebacteria, cyanobacteria, mycoplasma); Protista (diatoms, dinoflagellates, euglenoids, protozoans); Fungi (the four classes with examples); and Viruses, Viroids, Prions, Lichens. Begin each fact with its organism/group and end it with a full stop.