Notes of Ch 2 Biological Classification | Class 11th Biology

Study Material and Notes of Ch 2 Biological Classification Class 11th Biology

Topics in the Chapter

  • Systems of Classification
  • Kingdom Monera
  • Kingdom Protista
  • Kingdom Fungi
  • Classes of Fungi
  • Viruses
  • Structure of Virus
  • Diseases caused in humans
  • Viroids
  • Lichens

System of Classification

• Earliest classification was given by Aristotle. He 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. They are:
(i) Kingdom plantae
(ii) Kingdom Animalia

Five kingdom classification: Given by R.H. Whittaker. They are:
(i) Monera
(ii) Protista
(iii) Fungi
(iv) Plantae
(v) Animalia

• The main criteria for classiÆcation of organisms into Æve 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, Chemosyn thetic autotrophs or Heterotrophs.

• Bacteria are divides in two parts:
(i) Archaebacteria
(ii) Eubacteria

• 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 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 of N, 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 aniamls and plants.

Kingdom Protista

• It 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.

→ Cell walls have silica which makes it indestructible and cell walls overlap to fit together like a soap box.

→ Their accumulation forms 'Diagomaceous 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 trnasverse 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 ëpellicleí 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 fruting bodies bearing spores at their tips.

• Spores have true walls which are exrtremely resistant and survive for many years and dispersed by air currents.
(v) Protozoans: Are heterotrops and live as predators or parasites. Have four major groups.

• Amoeboid: Catch prey using pseudopodia. Example: Amoeba. Entamoeba are parasite.

• Flagellated : Have one or more flagella. 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

• Heterotrophic organisms

• Non chlorpohyllous hyphae

• Network of hyphae called mycelium

• Hyphae which have multinucleate cytoplasm are called coenocytic hyphae

• Cell wall of chitin and polysaccharides

• Cosmopolitan. Grow in warm and humid places.

• Saprophytic, parasitic, symbiotic (Lichen and Mycorrhiza) e.g., Puccinia, (wheat rust disesae), Penicillium, Yeast is a unicellular fungus.

• Reprouction 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.

• Sexual cycle involves 3 steps:
(i) Plasmogamy (fusion of Protoplasms.)
(ii) Karyagamy (fusion of two nuclei.)
(iii) Meiosis in zygote resulting in haploid spores.

• Dikaryophase is a condition of having dikaryon in an intervening dikaryotic stage (n + n i.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 repdouction by Zoospores or Aplanospores

→ Zygospores are formed by the fusion of gametes. Example: 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 spores are called ascospores produced endogenously in ascus, produced inside fruiting body called Ascocarp.

→ Example: Aspergillus, Neurospora, Sacharomyces (Unicellular fungi), Claviceps, morels, trufles.

(iii) Basidiomycetes:

→ Mycelium septate and branched.

→ Generally asexual sprors 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.
Example: 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 t o Ascomycetes or Basidiomycetes.

→ Mycelium is septate and branched.

→ They are saprophytic parasitic or decomposers.

→ Example: Alternaria, Colletotrichum, Trichoderma.


→ They did not find a place in 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 of 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 crystatls of protein which are inert outside their specific host.

→ Viruses are obligate parasites.

Structure of Virus:

→ 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 T.O. 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.

NCERT Solutions of Class 12 Biological Classification

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