Biological Classification Class 11 Biology Notes and Questions

Notes Class 11 Revision Notes

Please refer to Biological Classification Class 11 Biology notes and questions with solutions below. These revision notes and important examination questions have been prepared based on the latest Biology books for Class 11. You can go through the questions and solutions below which will help you to get better marks in your examinations.

Class 11 Biology Biological Classification Notes and Questions

Points to Remember

Systems of Classification :

  • Earliest classification was given by Aristotle. Divided plants into herbs, shrubs and trees.
    Animals into those with red blood and those who do not have it.
  • Two kingdom classification : Given by Carolous Linneaeus-Kingdom­ plantae and kingdom-Animalia.
  • Five kingdom classification : By R.H. Whittaker, Monera, Protista, Fungi, Plantae and Animalia are the five kingdoms.
  • The main criteria for classification of organisms into five kingdoms include cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships.

Kingdom Monera :

  • Has bacteria as sole members.
  • Bacteria can have shapes like : Coccus (spherical), Bacillus (rod-shaped), Vibrium (comma shaped) and spirillum (spiral shaped).
  • Bacteria found almost everywhere and can be Photosynthetic autotrophs, Chemosynthetic autotrophs or Heterotrophs.
Biological Classification Class 11 Biology
  • Halophiles (salt-loving)
  • Thermoacidophiles (in hot springs)
  • Methanogens (in marsh and in gut of ruminant animals. Produce methane gas.)
  • Photosynthetic autotrophs like Cyanobacteria (Blue-green algae BGA).Some like Anabaena and Nostoc have specialized cells called heterocysts for nitrogen fixation.
  • Algae bloom is rich growth of blue green algae over the surface of polluted water bodies.
  • Algae bloom releases neurotoxins, deplete oxygen and makes water unfit for use.
  • Chemosynthetic autotrophs : Oxidise various inorganic substances like nitrates/nitrites, ammonia and use released energy for their ATP proudction. They helps in nutrients recycling ofN, P, Fe and S.
  • Heterotophic bacteria : Decomposers help in making curd, production of antibiotic, N2 fixation, casuse disesaes like cholera, typhoid, tetanus and citrus canker.
    Mycoplasmas : Completely lack cell wall. Smallest living cells. Can survive without oxygen. Pathogenic in animals and plants.

(Comprises of all single celled eukaryotes)

Forms a link between plants, animals and fungi.

(i) Chrysophytes (Has diatoms and golden algae/desmids)
    Fresh water/marine, photosynthetic, microscopic plankton.

  • Chief producers in Ocean.
  • Cell walls have silica which makes it indestructible and cell walls overlap to fit together like a soap box.
  • Their accumulation forms ‘Diatomaceous Earth” (gritty soil)
  • Used in polishing, filtration of oils and syrups.

(ii) Dinoflagellates :

  • Marine, photosynthetic, cell wall has stiff cellulose plates.
  • Two flagella-one longitudinal and other transverse in a furrow between wall plates.
  • Example: Gonyaulax multiples rapdily, make sea appear red (red tides) and produce toxins to kill marine animals.

(iii) Euglenoids :

  • Found in stagnant fresh water.
    Have protein rich layer ‘pellicle’ which makes body flexible.
  • Photosynthetic in presence of sunlight but become heterotrophs if they do not get sunlight. (Mixotrophic nutrition)
  • Example: Euglena

(iv) Slime Moulds:

  • Saprophytic protists
  • Under suitable conditions form an aggregates called plasmodium, grows on decaying twigs and leaves.
  • During unfavourable conditions, plasmodium differentiates and forms fruiting bodies bearing spores at their tips.
  • Spores have true walls which are extremely resistant and survive for many years and dispersed by air currents.

(v) Protozoans : Are heterotrops and live as parasites. Have four major groups.

Amoeboid: Catch prey using pseudopodia, e.g., Amoeba. Entamoeba are parasite.

Flagellated : Have one or more lagella. Cause disease like Sleeping Sickness e.g., trypanosoma.

Ciliated : Have clilia to move food into gullet and help in locomotion. e.g., Paramoecium.

Sporozoans : Have infective spore like stage in life cycle, e.g., Plasmodium which causes malaria.

Kingdom Fungi

  1. Heterotrophic organisms
  2. Non chlorpohyllous hyphae
  3. Network of hyphae called mycelium
  4. Hyphae which have multinucleated cytoplasm are called coenocytic hyphae
  5. Cell wall of chitin and polysaccharides
  6. Cosmopolitan. Grow in warm and humid places.
  7. Saprophytic, parasitic, symbiotic (Lichen and Mycorrhiza) e.g., Puccinia,
    (wheat rust disease), Penicillium, Yeast (unicellular fungus).
  8. Reproduction can take place by vegetative means fragmentation, fission and budding. Asexual reproduction by spores-conidia, sporangiospores or zoospores. Sexual reproduction by Oospores, ascospores and basidiospores­ produced in fruiting bodies.
  9. Sexual cycle involves 3 steps :
    (i) Plasmogamy (fusion of Protoplasms.)
    (ii) Karyogamy (fusion of two nuclei.)
    (iii) Meiosis in zygote resulting in haploid spores.
  10. Dikaryophase is a condition of having dikaryon in an intervening dikaryotic stage (n + n e., two nuclei per cell) between plasmogamy and karyogamy in fungi like ascomycetes and basidiomycetes.

Classes of Fungi

(i) Phycomycetes :

  • grow on decaying wood or as obligate parasites on plants
  • Mycelium aseptate and coenocytic
  • Spores produced endogenously in sporangium.
  • Asexual reproduction by Zoospores or Aplanospores
  • Zygospores are formed by the fusion of gametes.
    e.g., Rhizopus, Albugo, Mucor

(ii) Ascomycetes :

  • also known as ‘sac fungi’
  • Are saprophytic, decomposers, parasitic or coprophilous (growing on dung).
  • Mycelium branched and septate
  • Asexual spores are called conidia produced exogenously on the conidiophores.
    Sexual sporesarecalled ascospores produced endogenously inascus,produced inside fruiting body called Ascocarp.
    e.g., Aspergillus, Neurospora, Saccharomyces (Unicellular fungi), Claviceps, morels, truffles

(iii) Basidiomycetes :

  • Mycelium septate and branched.
  • Generally asexual spores are not found.
  • Vegetative reproduction by fragmentation.
  • Sexual reproduction by fusion of vegetative or somatic cells to form basidium produced in basidiocarp.
  • Basidium produces four basidiospores exogenously after meiosis.

    e.g., Agaricus, Ustilago, Puccinia

(iv) Deuteromycetes :

  • Called as ‘Fungi Imperfecti’ as sexual form (perfect stage) is not known for them.
  • Once sexual form is discovered the member is moved to Ascomycetes or Basidiomycetes.
  • Mycelium is septate and branched.
  • Are saprophytic parasitic or decomposers.
    e.g., Alternaria, Colletotrichum, Trichoderma.


  • They did not find a place in biological classification.
  • Not truly living.
  • Non-cellular organisms which take over the machinery of host cell on entering it and become living but as such they have inert crystalline structure appear non-living. So, difficult to call them living or non-living.
  • Virus means venom or poisonous fluid. Pastuer gave the term ‘virus’.
  • D.J. Ivanowsky found out that certain microbes caused Tobacco Mosaic Disease in tobacco plant.
  • M.W. Beijerinek called fluid as ‘Contagium vivum fluidum’ as extracts of infected plants of tobacco could cause infection in healthy plants.
  • W.M. Stanely showed viruses could be crystallized to form crystals of protein which are inert outside their specific host.
  • Viruses are obligate parasites.

Structure ofVirus :

  • It is a nucleoprotein made up of protein coat called Capsid. Capsid is made up of capsomeres arranged in helical or polyhedral-geometric forms. Have either DNA or RNA as genetic material which may be single or double stranded.
  • Usually plant viruses have single stranded RNA; bacteriophages have double stranded DNA and animal viruses have single or double stranded RNA or double stranded DNA.

Diseases caused in humans :

Mumps, Small pox, herpes, influenza and AIDS etc. In plants, symptoms can be mosaic formation, leaf rolling and curling, yellowing and vein clearing, dwarfing and stunted growth.


  • Infectious agent, free RNA (lack protein coat)
  • RNA has low molecular weight.
  • Causes potato spindle tuber disease.
  • Discovered by TO. Diener.


  • Symbiotic association between algal component (Phycobiont) and fungal component (mycobiont). Algae provides food. Fungi provides shelter and absorb nutrients and water for alga.
  • Good pollution indicators as they do not grow in polluted areas.


o First scientific approach to classify the organisms
o Used simple morphological characters
o Classify the plant into herb, shrub & tree.
o Classified animals on the basis of presence / absence of Red blood

o This system did not clear the position of unicellular/multicellular,prokaryotic/eukaryotic organisms.

o Five kingdom classification in 1969
o Basis of 5 Kingdom → Five Criteria
• Cell structure,
• Thallus organisation,
• Mode of nutrition,
• Reproduction and
• Phylogenetic relationships.

o The five kingdoms are :
• Monera
• Protista
• Fungi
• Plantae
• Animalia.

o Prokaryotic,
o Cellular body organisation,
o Non- cellulosic cell wall
o Mode of nutrition is autotrophic and heterotrophic. # Highest diversity
o Cell wall is made up of polysaccharides and amino acids. # Peptidoglycan
o Members of the Kingdom Monera à Bacteria
o Most abundant micro-organisms
o Bacteria are grouped under four categories based on their shape:
• Coccus → Spherical.
• Bacillus → Rod shape.
• Vibrio → Comma shape.
• Spirillum → Spiral.
o Bacteria as a group show the most extensive metabolic diversity

o They live in some of the most harsh habitats.
• Halophiles à Salty area.
•Thermoacidophilesà Hot springs.
• Methanogens à Marshy area
o Methanogens are present in the gut of several ruminant animals such as cows and buffaloes and they are responsible for the production of methane (biogas) from the dung of these animals.
o Archaebacteria differ from other bacteria
• In having a different cell wall structure à This feature is responsible for their survival in extreme conditions.

o True bacteria.
o Characterised by the presence of a rigid cell wall
o If motile, have a flagellum

o Blue green algae
o Have Chlorophyll – a (similar to higher plants) and are autotrophic.
o Present in fresh water/ marine water as well as on land (terrestrial).
o The colonies are generally surrounded by gelatinous sheath.
o They often form blooms in polluted water bodies.

8. Chemosynthetic autotrophic bacteria oxidise various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production.

9. Cyanobacteria can fix atmospheric nitrogen in specialised cells called HETEROCYST, e.g., Nostoc and Anabaena

10. Bacteria play a great role in recycling nutrients

11. Heterotrophic bacteria are the most abundant in nature.

12. Majority of heterotrophic bacteria are important decomposers.

13. Heterotrophic bacteria play significant role in human life.

14. They are helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots.

15. Cholera, typhoid, tetanus, citrus canker are well known diseases caused by different heterotrophic bacteria.

16. Bacteria reproduce mainly through (fission in favourable condition), by spores (during unfavourable condition).

o They completely lack a cell wall.
o They are the smallest living cells known and can survive without oxygen.
o Many mycoplasmas are pathogenic in animals and plants.

o Unicellular eukaryotes.
o Cell wall present or absent.
o Cellular body organization.
o Autotrophic or Heterotrophic.
o Kingdom Protista includes all unicelled eukaryotes
o Members of Protista are primarily aquatic.
o Forms a link with the others dealing with plants, animals and fungi.

19. Important Protista

20. CHRYSOPHYTE( chief producer of ocean)
o Includes diatoms and golden algae (desmids).
o Cell walls à two thin overlapping shells, which fit together as in a soap box.
o The walls are embedded with silica so the wall is indestructible.
o Diatomaceous earth is the cell wall of diatoms which is gritty in nature and used in polishing, filtration of oil and syrup.

o Mostly marine and photosynthetic.
o Most of them have two flagella
o The cell wall has stiff cellulose plates on the outer surface.
o Sometime Red dinoflagellates (Example: Gonyaulax) undergo such rapid multiplication that they make the sea appear red (red tides). Toxins released by such large numbers may even kill other marine animals such as fish.
o Yellow, Brown, Green, Blue or Red according to the pigments in cells.

22. EUGLENOIDS (e.g. Euglena)
o Not have cell wall, but have a protein rich layer called pellicle
o Pellicle makes their body flexible.
o They have two flagella, a short and a long one.
o Photosynthetic in presence of sunlight but in absence they are heterotrophic.
o Considered link between animal and plant kingdom # Myxotrophic Nutrition
o Photosynthetic pigments are similar to higher plants.

o Saprophytic protists
o Act as decomposer.
o Under suitable conditions, they form an aggregation called plasmodium
o Plasmodium may grow and spread over several feet.
o During unfavourable conditions, the plasmodium differentiates

•  forms fruiting bodies bearing spores at their tips.
o The spores possess true walls.
o They are extremely resistant.
o The spores are dispersed by air currents.

o All protozoans are heterotrophs
o Live as predators or parasites.
o Primitive relatives of animals.

o Ameboid protozoans
• have pseudopodia to capture the food
• marine protozoans has silica in their wall.
•e.g. Entamoeba is a parasite.

o Flagellated protozoans
• either free living or parasite.
• Parasitic forms cause disease.
• Sleeping sickness is caused by Trypanosoma.

o Ciliated protozoan
• Actively moving organisms
• Presence of thousands of cilia.
• They have a cavity (gullet) that opens to the outside of the cell surface.
• The water laden with food to be steered into the gullet through ciliary movement.
• Example: Paramecium.

o Sporozoans:
•Infectious spore-like stage in their life cycle.
•Example-Malaria parasite PLASMODIUM

o Eukaryotic
o Chitinous cell wall (chitin and polysaccharides)
o Multicellular with loose tissue
o All heterotrophic(saprophyte/parasite).
o Prefer to grow in warm and humid places.
o Fungi are filamentous.
o Their bodies consist of long, slender thread-like structures called hyphae.
o The network of hyphae is known as mycelium.
o Multinucleated mycelium à coenocytic mycelium.
o Symbiotic association of algae with fungi is called lichen.
o Fungi also show symbiotic association with higher plants is called mycorrhiza.
o Reproduction in fungi can take place

• Vegetative means – fragmentation, fission and budding
• Asexual reproduction is by spore called conidia or sporangiospores or zoospores.
• Sexual reproduction is by oospores, ascospores and basidiospores.

o Fruiting body is the structure which produce spores.
o The sexual cycle involves the following three steps:
• Plasmogamy- fusion of protoplasm of gametes.
• Karyogamy-fusion of nuclei of gametes.
• Zygotic meiosis resulting in formation of haploid spores.
o On the basis of morphology of the mycelium, mode of spore formation and fruiting bodies fungi are divided in following classes.
• Phycomycetes.
• Ascomycetes.
• Basidiomycetes.
• Deuteromycetes.

o The mycelium is aseptate and coenocytic.
o Asexual reproduction takes place by zoospores (motile) or by aplanospores (nonmotile) produce endogenously i.e. inside sporangium.
o Sexual reproduction is isogamous/anisogamous/oogamous type.
o Examples; The bread mould : Rhizopus, Mucor, Albugo (causative agent of white rust of mustard / Crucifer).

o They are mostly multicellular.
o Yeast (saccharomyces) is unicellular.
o saprophytic, decomposers, parasitic or coprophilous (growing on dung)
o Mycelium is branched and septate.
o The asexual spores à Conidia

• born exogenously on conidiophore
• on germination produce mycelium.

o Sexual spores are called ascospores

• produced endogenously in sac like asci/ascus.
• Ascocarp is fruiting body where asci are arranged.
• Dikaryotic phase is found.
• After plasmogamy of gametes, dikaryotic mycelium is formed.
• After some time karyogamy occur in this dikaryotic mycelium.

o Examples;

• Neurospora (used in genetics and biochemistry),
• Penicillium(antibiotic)
• Claviceps (ergot fungus),
• Aspergillus,
• Yeast (used in bread and beer industry)
• morels ,truffles (edible fungi)

o The mycelium is branched and septate.
o Vegetative reproduction by fragmentation
o Asexual spores are generally not found.
o The sex organs are absent
o Plasmogamy takes place between two vegetative or somatic cell of different strain/genotype & dikaryotic mycelium is formed which give rise BASIDIUM where KARYOGAMY & MEOSIS take place.

o Basidium are arranged in basidiocarp (fruiting body).
o Basidium produce exogenous basidiospores.
o Basidiospores are haploid.
o Some common members are
•  Agaricas (mushroom),
•  Ustilago (smut) and
•  Puccinia (rust)
•  bracket fungi or puffballs.

o Imperfect stage i.e. sexual reproduction is absent/not known right now.
o The mycelium is septate and branched.
o They reproduce asexually by conidia.
o Members are saprophytes or parasites
o Large number of them are decomposers of litter
o Help in mineral cycling.
o Some examples are Alternaria, Colletotrichum and Trichoderma.

o All eukaryotic
o chlorophyll-containing organisms
o Cell wall mainly made of cellulose.
o Body organisation is tissue/organ type.
o Autotrophic but some plants are partial heterotroph.

•  Insectivorus plant like venus fly trap & bladder-wort are example of partial heterotroph.
•  Cuscuta is example of parasite.

o Life cycle of plants has two distinct phases → the diploid sporophytic and the haploid gametophytic – that alternate with each other. this is called ALTERNATION OF GENERATION.
o Plantae includes
•  Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms

o Heterotrophic eukaryotic organisms.
o Multicellular
o Lack cell walls.
o Store food reserves as glycogen or fat.
o Their mode of nutrition is holozoic – by ingestion of food.
o They follow a definite growth pattern
•  Grow into adults that have a definite shape and size.
o Higher forms show elaborate sensory and neuromotor mechanism.
o Most of them are capable of locomotion.
o The sexual reproduction is by copulation of male and female
o Embryological development

32. There is no place of virus, viriods and lichens in WHITTAKER FIVE KINGDOM CLASSIFICATION.

o Non-cellular organisms (?)
o Characterised by having an inert crystalline structure outside the living cell.
o When virus attack a host cell it controls the host cells machinery, replicate here and kill the host cell.
o The term virus that means venom or poisonous fluid was given by Pasteur.
o D.J. Ivanowsky (1892) recognised certain microbes as causal organism of the mosaic disease of tobacco. #Filtrate property of virus
o M.W. Beijerinek (1898) → Contagium vivum fluidum (infectious living fluid).
o W.M. Stanley (1935) showed that viruses could be crystallised (Protein crystals)
o They are inert outside their specific host cell.
o Viruses are obligate parasites
o Genetic material either DNA or RNA.
o Generally plant virus has ss RNA as genetic material.
o Generally animal virus has ds DNA as genetic material.
o Bacteriophage generally has ds DNA.
o Chemically virus is a nucleoprotein.
o The protein coat called capsid made of small subunits called capsomeres, protects the nucleic acid.
o These capsomeres are arranged in helical or polyhedral geometric forms.
o Viruses cause diseases like mumps, small pox, herpes and influenza and AIDS.
o In plants, the symptoms of virus can be mosaic formation, leaf rolling and curling, yellowing and vein clearing, dwarfing and stunted growth.

o Discovered by DIENER in 1971
o It is a free RNA ,no protein coat
o Smaller than virus.
o Viroid has low molecular weight.

35. LICHEN :
o Symbiotic association between Algae & Fungi

•  PHYCOBIONT(algae)
•  MYCOBIONT(fungi)

o Phycobiont make food for mycobiont also in return mycobiont provides shelter and water mineral to algae.
o Lichen is very close relationship # Mutualism
o They are good indicator of pollution (not found in polluted area).

Biological Classification Class 11 Biology

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