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State Board · Class 11 · Biology

Lesson 2: Systematics of Living Organisms

7 concepts · 56 practice questions with answers · Free to read

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Systematics and types of classification

Link to Std 9–10

The five-kingdom idea of Std 9–10 is studied here in detail: types of classification, categories, naming and the features of each kingdom.

From daily life

In a big shop goods sit in separate aisles, so we find things fast; classification does the same for organisms.

Simple definition

Systematics is the study of kinds and diversity of organisms and their comparative and evolutionary relationships (G. Simpson, 1961). Taxonomy is classification by rules; the term was introduced by A. P. de Candolle.

Cladogram of the three domainsCommon ancestorArchaeaextreme habitatsBacteriadifferent cell wallEukaryaeukaryotic cellProkaryoticWoese, 1990

In the figure : The figure shows three domains (Archaea, Bacteria, Eukarya) branching from one ancestor.

Rule 1 : Three kinds of classification — Artificial: few easily seen characters (habit, colour) – e.g. Linnaeus. Natural: objectively significant characters – e.g. Bentham and Hooker. Phylogenetic: common evolutionary descent – e.g. Engler and Prantl.

  • Easy : Grouping only by height and colour = artificial.
  • Medium : Bentham–Hooker belongs to which type? Natural.
  • Exam-type (CET) : ‘Based on common descent’ = phylogenetic, e.g. Engler–Prantl.

Rule 2 : Three domains (Carl Woese, 1990) — Archaea, Bacteria, Eukarya. A domain is larger than a kingdom. Archaea and Bacteria are prokaryotic; Eukarya is eukaryotic. All three have unique rRNA.

  • Easy : Archaea survive extreme heat, salt and acidity.
  • Medium : Archaea differ from Bacteria in cell wall structure.
  • Exam-type (CET) : Which is the larger unit, domain or kingdom? Domain.
Remember

Taxon = a group of any rank; category = the rank.

Common mistake and CET trap

Do not mix: Artificial = Linnaeus, Natural = Bentham–Hooker, Phylogenetic = Engler–Prantl. Trap: ‘domain is smaller than kingdom’ is wrong.

Shortcut

Memory clue : "A-N-P: Linnaeus, Bentham, Engler (artificial → natural → phylogenetic)".

Spot the difference

TypeBasisExample
ArtificialFew easy charactersLinnaeus
NaturalSignificant charactersBentham and Hooker
PhylogeneticCommon descentEngler and Prantl

Practice questions

Easy
  1. 1What is systematics?
  2. 2Who introduced the word taxonomy?
  3. 3Name the three domains.
Medium
  1. 4Who proposed three domains and when?
  2. 5Give an example and basis of artificial classification.
  3. 6Why are Archaea and Bacteria different though both prokaryotic?
Challenging
  1. 7Differentiate taxon and category.
  2. 8How is phylogenetic classification different from natural?
Show answers (try them yourself first)
  1. 1Study of kinds, diversity and evolutionary relationships of organisms.
  2. 2A. P. de Candolle.
  3. 3Archaea, Bacteria, Eukarya.
  4. 4Carl Woese, 1990.
  5. 5Linnaeus; few easily seen characters.
  6. 6Their cell-wall structure differs; Archaea live in extreme conditions.
  7. 7Category = rank; taxon = an actual group at that rank (e.g. Malvaceae).
  8. 8It is based on common evolutionary descent, not just significant characters.

Modern approaches in taxonomy

From daily life

A supermarket barcode instantly names a product; likewise an organism can be identified from its DNA ‘barcode’.

Simple definition

Chemotaxonomy classifies by chemical constituents. DNA barcoding identifies a species from its DNA sequence in a tiny tissue sample. Numerical taxonomy quantifies characters and classifies by algorithm.

Chemotaxonomy, DNA barcoding and numerical taxonomyChemotaxonomyDNA barcodingNumerical taxonomyChemical makeupCell wall:Archaea: no peptidoglycanBacteria: presentFungi: chitinPlants: celluloseDNA sequence from a tiny tissue1) barcodes ofknown species2) match theunknown sampleCharacters get numbersalgorithm (cluster analysis)Sokal and Sneath, 1963Uses: protecting endangered species, pest control, identifying vectors,identifying medicinal plants, authenticating natural health products

In the figure : Three modern methods and the two steps of DNA barcoding; uses below.

Rule 1 : Chemotaxonomy — Cell-wall chemistry: Archaea lack peptidoglycan, bacteria have it; fungi = chitin; plants = cellulose.

  • Easy : Fungal cell wall is made of? Chitin.
  • Medium : Chemical reason to separate plants and fungi: cellulose versus chitin.
  • Exam-type (CET) : Which group has a wall without peptidoglycan? Archaea.

Rule 2 : DNA barcoding and numerical taxonomy — Step (a) collect barcode data of known species; (b) match the unknown sample's sequence with the library. Numerical taxonomy: R. Sokal and P. Sneath, 1963.

  • Easy : Two steps of barcoding? Collect data, then match.
  • Medium : Uses: endangered-species protection, pest control, vector identification, medicinal plant identification.
  • Exam-type (CET) : Cluster analysis is used in which method? Numerical taxonomy.

Rule 3 : Cladogram and phylogeny — Cladogram = branching diagram comparing organisms and their common ancestors. Phylogeny = evolutionary relationship; Woese's three-domain and Whittaker's five-kingdom systems are examples.

  • Easy : The three-domain diagram is a cladogram.
  • Medium : Besides morphology, phylogeny considers? Evolutionary relationships.
  • Exam-type (CET) : ‘A diagram of hypothetical relationship’ = cladogram.
Remember

DNA barcoding = DNA sequence from tiny tissue; numerical = algorithm.

Common mistake and CET trap

‘Linnaeus founded numerical taxonomy’ is wrong; Sokal and Sneath (1963). Trap: swapping chitin and cellulose.

Shortcut

Memory clue : "Barcode = Collect + Compare".

Spot the difference

MethodBasisExample / person
ChemotaxonomyChemical constituentsPeptidoglycan, chitin
DNA barcodingDNA sequenceSpecies identification
Numerical taxonomyNumerical characters + algorithmSokal and Sneath 1963

Practice questions

Easy
  1. 1What is chemotaxonomy?
  2. 2Fungal cell wall component?
  3. 3State two steps of DNA barcoding.
Medium
  1. 4Who proposed numerical taxonomy?
  2. 5Give two uses of DNA barcoding.
  3. 6What is a cladogram?
Challenging
  1. 7How would you separate plants and fungi chemically?
  2. 8Why is phylogeny better than classification based on morphology alone?
Show answers (try them yourself first)
  1. 1Classification based on chemical constituents.
  2. 2Chitin.
  3. 3Collect known data; match unknown sample.
  4. 4R. Sokal and P. Sneath (1963).
  5. 5Protecting endangered species; identifying medicinal plants.
  6. 6A branching pattern showing comparison and common ancestors.
  7. 7Cell wall: plants = cellulose; fungi = chitin.
  8. 8It also considers evolutionary relationships and metabolic similarities.

Taxonomic categories and hierarchy

From daily life

A postal address narrows country → state → district → city → street → house; taxonomic categories form a similar ladder.

Simple definition

Taxonomic hierarchy is the ranked ladder kingdom, division/phylum, class, order, family, genus, species. A taxon is a group of any rank (H. J. Lam, 1948).

Taxonomic hierarchy of China rose and cobraCategoryChina roseCobraKingdomPlantaeAnimaliaDivision / PhylumAngiospermaeChordataClassDicotyledonaeReptiliaOrderMalvalesSquamataFamilyMalvaceaeElapidaeGenusHibiscusNajaSpeciesrosa-sinensisnaja↑ common characters decrease as we go up

In the figure : The figure classifies China rose and cobra in seven obligatory categories.

Rule 1 : Categories and their order — Obligatory: kingdom, division/phylum, class, order, family, genus, species. Facultative: sub-order, sub-family, sub-class, series etc. Common characters decrease as we go up.

  • Easy : Smallest category: species.
  • Medium : Dog and cat are together in which rank? Order Carnivora (families differ: Canidae, Felidae).
  • Exam-type (CET) : Tiger, leopard, lion = one genus Panthera; brinjal and potato = genus Solanum.

Rule 2 : Defining the main categories — Species: organisms that interbreed naturally to give fertile offspring. Genus: closely resembling species that usually do not interbreed. Family: closely related genera (Hibiscus, Gossypium, Sida, Bombax → Malvaceae). Order: related families. Class: related orders. Division: related classes.

  • Easy : Horse and ass are different species because their offspring (mule) is sterile.
  • Medium : Monkey and dog are in the same class Mammalia but different orders (Primates, Carnivora).
  • Exam-type (CET) : Division Angiospermae includes classes Dicotyledonae and Monocotyledonae.
Remember

From kingdom to species the groups get smaller; 7 obligatory ranks.

Common mistake and CET trap

Writing ‘species is the largest rank’ is wrong. Trap: ‘cat and dog in the same family’ is wrong (Felidae vs Canidae).

Shortcut

Memory clue : "King Philip Came Over For Good Soup (Kingdom, Phylum, Class, Order, Family, Genus, Species)".

Spot the difference

CategoryChina roseCobra
KingdomPlantaeAnimalia
OrderMalvalesSquamata
FamilyMalvaceaeElapidae
Genus / speciesHibiscus rosa-sinensisNaja naja

Practice questions

Easy
  1. 1What is a taxon?
  2. 2Smallest obligatory category?
  3. 3Who defined ‘taxon’?
Medium
  1. 4Name the genus of tiger, lion and leopard.
  2. 5Which ranks are common to dog and cat?
  3. 6Name two genera in family Malvaceae.
Challenging
  1. 7Why are horse and ass different species?
  2. 8How do common characters change going up and why?
Show answers (try them yourself first)
  1. 1A taxonomic group of any rank.
  2. 2Species.
  3. 3H. J. Lam (1948).
  4. 4Panthera.
  5. 5Kingdom, phylum, class, order (Carnivora); families differ.
  6. 6Hibiscus, Gossypium (or Sida, Bombax).
  7. 7Their offspring (mule) is not fertile.
  8. 8They decrease because groups become larger and more varied.

Nomenclature and the five-kingdom system

From daily life

A vegetable has a different name in each state, so traders use the scientific name; mango has over 50 Sanskrit names in Ayurveda.

Simple definition

Nomenclature is the scientific naming of organisms. In binomial nomenclature the name has two parts (genus + species); Carl Linnaeus introduced it in ‘Species Plantarum’ (1753).

Binomial nomenclature and five kingdomsHelianthus annuus L.Genus (capital)species (small)L. = LinnaeusFive kingdoms – Whittaker (1969)MoneraprokaryoticProtistaunicellular eukaryoteFungidecomposersPlantaeautotrophsAnimaliaheterotrophsArchaea and bacteria both go in Monera (prokaryotes); viruses/viroids lie outside the kingdoms

In the figure : Top: parts of Helianthus annuus L.; below: Whittaker's five kingdoms (1969).

Rule 1 : Rules of binomial nomenclature — Two Latin/Greek words; genus first (capital), species second (small); italics in print, underlined separately by hand; each word 3–13 letters; author's name after it (e.g. Mangifera indica L.).

  • Easy : Sunflower: Helianthus annuus – Helianthus = genus, annuus = species.
  • Medium : In Mangifera indica L., L. stands for Linnaeus.
  • Exam-type (CET) : The pre-2011 ICBN is now ICNAFP (Shenzhen Code): published 26 June 2018 after the 2017 Shenzhen congress.

Rule 2 : Five kingdoms (R. H. Whittaker, 1969) — Monera, Protista, Fungi, Plantae, Animalia. Linnaeus's two kingdoms could not hold bacteria, fungi or Euglena, so five kingdoms came; the system is phylogenetic.

  • Easy : Only prokaryotic kingdom among the five: Monera.
  • Medium : Euglena belongs to Protista (shows features of both).
  • Exam-type (CET) : Viruses and viroids are outside the five kingdoms.
Remember

Local names are many and limited; the scientific name is international and unique.

Common mistake and CET trap

Writing the species word in capital is wrong. Trap: ‘binomial system is Whittaker's’ – wrong; it is Linnaeus's, 1753.

Shortcut

Memory clue : "Genus = Grand (capital), species = small".

Spot the difference

PointCommon nameScientific name
FormVaries by regionBinomial, Latin
UseLocal communicationUniversal communication
ExampleMangoMangifera indica L.

Practice questions

Easy
  1. 1Who introduced binomial nomenclature and in which book?
  2. 2Which word is the genus in Helianthus annuus?
  3. 3Who proposed the five-kingdom system?
Medium
  1. 4How is a scientific name written in print?
  2. 5How many letters should each word have?
  3. 6Why was the two-kingdom system inadequate?
Challenging
  1. 7What is ICBN called now?
  2. 8Why are scientific names better than common names?
Show answers (try them yourself first)
  1. 1Linnaeus; ‘Species Plantarum’ (1753).
  2. 2Helianthus.
  3. 3R. H. Whittaker (1969).
  4. 4In italics.
  5. 53 to 13.
  6. 6Organisms like bacteria, fungi, Euglena showing characters of both kingdoms did not fit.
  7. 7ICNAFP (Shenzhen Code).
  8. 8They are the same everywhere, allowing international communication.

Kingdom Monera

From daily life

Curd-making germs and stomach-upsetting germs belong to the same kingdom; tiny size, big jobs.

Simple definition

Monera are unicellular prokaryotes with no definite nucleus; DNA is a circular nucleoid, small circular DNA = plasmid; wall of peptidoglycan.

Bacterial shapes and archaebacteria / eubacteriaCoccussphericalBacillusrod-shapedVibriocomma-shapedSpirillumspiralArchaebacteriaextremophiles: halophiles, thermophilesEubacteria (true bacteria)peptidoglycan wall

In the figure : Four shapes: coccus (round), bacillus (rod), vibrio (comma), spirillum (spiral); two groups below.

Rule 1 : Features of Monera — No membrane-bound organelles (mitochondria, chloroplast, ER); ribosomes 70S and smaller; reproduction by binary fission/budding, rarely conjugation; a few photo/chemo-autotrophs, most heterotrophs.

  • Easy : Bacillus is rod-shaped; coccus is round.
  • Medium : Plasmid = small extra-chromosomal DNA.
  • Exam-type (CET) : Ribosome size in bacteria? 70S (smaller than eukaryotic).

Rule 2 : Archaebacteria and Eubacteria — Archaebacteria: extremophiles – halophiles (salty), thermophiles (hot), methanogens (gut of cows, biogas); no peptidoglycan. Eubacteria: peptidoglycan wall; autotrophs (Chlorobium, Chromatium) or heterotrophs.

  • Easy : Biogas bacteria: methanogens.
  • Medium : Lactobacillus curdles milk; Azotobacter fixes nitrogen; Streptomyces makes antibiotics.
  • Exam-type (CET) : In cyanobacteria (Nostoc) the heterocyst fixes nitrogen.
Remember

Mycoplasma = smallest living forms; no cell wall.

Common mistake and CET trap

‘Monera have a nucleus’ is wrong. Trap: Mycoplasma has a wall – wrong; hence it resists common antibiotics.

Shortcut

Memory clue : "Coccus = Circle, Bacillus = Bar, Vibrio = comma ‘V’, Spirillum = Spring".

Spot the difference

PointArchaebacteriaEubacteria
Cell wallNo peptidoglycanPeptidoglycan present
HabitatExtreme (extremophiles)Common habitats
ExampleMethanogens, halophilesLactobacillus, Chlorobium

Practice questions

Easy
  1. 1Name the four shapes of bacteria.
  2. 2What is a nucleoid?
  3. 3What is a plasmid?
Medium
  1. 4Who are extremophiles?
  2. 5Differentiate halophiles and thermophiles.
  3. 6Give two useful and two harmful roles of bacteria.
Challenging
  1. 7Why is Mycoplasma resistant to common antibiotics?
  2. 8What does a heterocyst do?
Show answers (try them yourself first)
  1. 1Coccus, bacillus, vibrio, spirillum.
  2. 2The circular DNA region without a membrane.
  3. 3Small extra-chromosomal circular DNA.
  4. 4Archaebacteria that live in extreme conditions.
  5. 5Halophiles tolerate high salinity; thermophiles tolerate high temperature.
  6. 6Useful: curdling, nitrogen fixation; harmful: typhoid, cholera, tuberculosis, tetanus.
  7. 7It lacks a cell wall.
  8. 8Nitrogen fixation.

Kingdoms Protista and Fungi, lichens

From daily life

Yeast that raises bread, mould on damp roti and mushrooms after rain are fungi; the tiny pond-water organisms are Protista.

Simple definition

Protista are unicellular eukaryotes linking plants, fungi and animals. Fungi are eukaryotic heterotrophs with extracellular digestion, body of hyphae, chitin wall. A lichen is an alga and a fungus living together.

Classification of Protista and fungi, and lichenProtistaFungiPlant-like: diatoms, dinoflagellatesEuglenoids: 2 flagella, pellicleAnimal-like: Amoeba, ParameciumFungus-like: slime mouldsPhycomycetes : Mucor, RhizopusAscomycetes : Aspergillus, YeastBasidiomycetes : Agaricus, PucciniaDeuteromycetes : AlternariaLichen = alga (phycobiont) + fungus (mycobiont); pollution indicator

In the figure : Left: four kinds of Protista; right: four classes of fungi; below: lichen.

Rule 1 : Types of Protista — Plant-like: diatoms (silica shell; diatomaceous earth for polishing/filtration), dinoflagellates (Gonyaulax = red tide). Euglenoids: two flagella, pellicle; autotroph in light, heterotroph in dark. Animal-like: Amoeba (pseudopodia), Trypanosoma (flagella), Paramecium (cilia), Plasmodium (sporozoan, malaria). Fungus-like: Myxomycetes.

  • Easy : Amoeba moves by pseudopodia; Paramecium by cilia.
  • Medium : Red tide is caused by Gonyaulax (a dinoflagellate).
  • Exam-type (CET) : Plasmodium causes malaria; Entamoeba amoebic dysentery; Trypanosoma sleeping sickness.

Rule 2 : Classes of fungi and lichens — Phycomycetes (Mucor, Rhizopus, Albugo), Ascomycetes (Aspergillus, Penicillium, Neurospora, yeast), Basidiomycetes (Agaricus, Puccinia, Ustilago), Deuteromycetes (Alternaria; asexual only). In lichen the phycobiont gives food, the mycobiont gives shelter and water; lichens indicate pollution.

  • Easy : Mushroom = Basidiomycetes (Agaricus).
  • Medium : Coenocytic hyphae = aseptate multinucleate (Phycomycetes).
  • Exam-type (CET) : ‘Imperfect fungi’ are Deuteromycetes (no sexual stage known).
Remember

Penicillium = antibiotic; yeast = bakery; Puccinia = plant pathogen.

Common mistake and CET trap

Do not confuse Plasmodium (parasite) and plasmodium (slime-mould cell mass). Trap: calling Ascomycetes ‘club fungi’ is wrong (sac fungi; club = Basidiomycetes).

Shortcut

Memory clue : "P-A-B-D: Phyco (algal), Asco (sac), Basidio (club), Deutero (imperfect)".

Spot the difference

ClassCommon nameExample
PhycomycetesAlgal fungiMucor, Rhizopus
AscomycetesSac fungiAspergillus, yeast
BasidiomycetesClub fungiAgaricus, Puccinia
DeuteromycetesImperfect fungiAlternaria

Practice questions

Easy
  1. 1What type of cells do Protista have?
  2. 2What is diatomaceous earth?
  3. 3What causes red tide?
Medium
  1. 4What is the fungal cell wall made of?
  2. 5How does Euglena nourish itself in two ways?
  3. 6Give two differences between Phycomycetes and Ascomycetes.
Challenging
  1. 7Why are lichens pollution indicators?
  2. 8Define mycobiont and phycobiont.
Show answers (try them yourself first)
  1. 1Unicellular eukaryotic.
  2. 2Deposits of diatom silica shells; used for polishing and filtration.
  3. 3Gonyaulax (a dinoflagellate).
  4. 4Chitin.
  5. 5Photosynthesis in light (autotroph); heterotroph in absence of light.
  6. 6Phycomycetes: aseptate coenocytic hyphae; Ascomycetes: septate hyphae, sac fungi.
  7. 7They do not grow in polluted places, so their presence shows clean air.
  8. 8Mycobiont = fungal partner; phycobiont = algal partner (cyanobacteria/green algae).

Kingdoms Plantae and Animalia, acellular organisms

From daily life

Leaves make food in sunlight, a cow eats grass, and a cold virus has no cell of its own yet multiplies inside ours – three different worlds.

Simple definition

Plantae: multicellular, chlorophyll, cellulose wall, alternation of generations. Animalia: multicellular heterotrophs, holozoic nutrition, no cell wall or chlorophyll. Acellular organisms: viruses and viroids, outside the five kingdoms.

Structure of a bacteriophage; viroid and prionDNAHead: DNACollarSheathBasal plateTail fibresBacteriophageVirus: protein coat (capsid)+ DNA or RNA (never both)Inactive outside host cell;inside, takes charge of host machineryViroid: only RNA, no coat(Diener 1971; potato disease)Prion: abnormally folded protein(mad cow disease)

In the figure : Parts of a bacteriophage; on the right, viroid and prion.

Rule 1 : Kingdoms Plantae and Animalia — Plantae: mostly autotrophs; some insectivorous (Venus fly trap, pitcher plant) and parasitic (Cuscuta). Two groups: Cryptogamae and Phanerogamae. Animalia: multicellular, mostly motile, determinate growth.

  • Easy : Cuscuta = a parasitic plant.
  • Medium : Plants vs fungi: wall cellulose vs chitin; nutrition autotrophic vs heterotrophic.
  • Exam-type (CET) : ‘Extracellular digestion’ belongs to which kingdom? Fungi.

Rule 2 : Viruses and viroids — Virus: protein coat (capsid, capsomeres) + DNA or RNA (never both); inactive outside a host, takes over host machinery inside – an ‘infectious nucleoprotein’. Viroid: only RNA, no coat (Diener, 1971). Prion: abnormally folded protein.

  • Easy : Virus infecting bacteria: bacteriophage (usually double-stranded DNA).
  • Medium : Pasteur named ‘virus’; Beijerinck called it ‘contagium vivum fluidum’; Stanley crystallised it.
  • Exam-type (CET) : An infectious agent with only RNA and no coat: viroid (potato spindle tuber).
Remember

A virus has DNA or RNA, never both; a viroid has no protein coat.

Common mistake and CET trap

‘Viruses are living cells’ is wrong; they are acellular. Trap: ‘TMV has DNA’ is wrong (TMV is an RNA virus).

Shortcut

Memory clue : "Virus = Coat + Core; Viroid = Core only".

Spot the difference

PointVirusViroid
Protein coatPresent (capsid)Absent
Genetic materialDNA or RNAOnly RNA (small)
ExampleTMV, bacteriophagePotato spindle tuber

Practice questions

Easy
  1. 1Name the two major groups of Plantae.
  2. 2Name a parasitic plant.
  3. 3What type of nutrition do animals have?
Medium
  1. 4What is a capsid?
  2. 5What is a bacteriophage?
  3. 6Give two differences between virus and viroid.
Challenging
  1. 7Why are viruses called infectious nucleoproteins?
  2. 8What is a prion and one disease?
Show answers (try them yourself first)
  1. 1Cryptogamae and Phanerogamae.
  2. 2Cuscuta.
  3. 3Heterotrophic, holozoic.
  4. 4The protein coat of a virus, made of capsomeres.
  5. 5A virus that infects bacteria.
  6. 6A virus has a protein coat, a viroid does not; a viroid is only RNA and smaller than a virus.
  7. 7They are made of protein + nucleic acid and are infectious in a host cell.
  8. 8An infectious abnormally folded protein; mad cow disease.

Quick revision of the whole lesson

ConceptKey fact
TypesArtificial (Linnaeus), natural (Bentham–Hooker), phylogenetic (Engler–Prantl)
Three domainsArchaea, Bacteria, Eukarya – Woese 1990
Modern methodsChemotaxonomy; DNA barcoding; numerical (Sokal–Sneath 1963)
HierarchyKingdom → Division → Class → Order → Family → Genus → Species
NamingBinomial; Linnaeus 1753; ICNAFP 2018
Five kingdomsWhittaker 1969: Monera, Protista, Fungi, Plantae, Animalia
MoneraShapes: coccus, bacillus, vibrio, spirillum
FungiPhyco-, Asco-, Basidio-, Deuteromycetes; chitin
Virus / viroidVirus = coat + DNA/RNA; viroid = RNA only (Diener 1971)

🎯 Most important points for the exam

  • Three kinds of classification and their founders.
  • Three domains and five kingdoms (years and scientists).
  • Rules of binomial naming (genus capital, species small, italics).
  • The seven steps of the hierarchy.
  • Archaebacteria vs eubacteria; bacterial shapes.
  • Four classes of fungi; lichen = alga + fungus.
  • Virus, viroid and prion differences.
Study mantra

Understand the concept → draw the figure → memorise the key points → solve questions yourself.