# Biological Classification (NEET Biology Class 11): Five Kingdoms, Monera to Animalia

Source: https://tracknation.in/story/biological-classification-neet-biology-class-11-five-kingdoms-monera-to-animalia (TrackNation — free UPSC notes with PYQs)

> NEET Class 11 Biological Classification, mined from NCERT: the history from Aristotle to Whittaker's five kingdoms, then Monera, Protista, Fungi, Plantae and Animalia in full — with every NEET-favourite example (Nostoc, diatoms, Gonyaulax, Rhizopus, Penicillium, Plasmodium) plus viruses, viroids, prions and lichens. Ends with MCQs, PYQs and an Active Recall prompt.

## 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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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*

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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

**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.