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Biological Classification – Class 11 Biology notes, important questions and MCQs

NCERT Class 11 Biology, chapter 2. Notes, key terms, important questions with answers and MCQs.

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Chapter overview

Whittaker's five-kingdom system classifies organisms as Monera, Protista, Fungi, Plantae and Animalia based on cell type, organisation, nutrition and more. Viruses, viroids and lichens are special cases.

Five kingdoms

  • Monera: prokaryotes (bacteria, cyanobacteria, archaebacteria); cell wall present.
  • Protista: unicellular eukaryotes (diatoms, dinoflagellates, Euglena, slime moulds, protozoans like Plasmodium).
  • Fungi: heterotrophic, chitin cell wall; Phycomycetes, Ascomycetes, Basidiomycetes, Deuteromycetes.

Acellular forms

  • Viruses: nucleoprotein, obligate parasites; TMV (RNA), bacteriophage (DNA).
  • Viroids: free RNA without protein coat (potato spindle tuber disease); prions: infectious proteins (mad cow disease).
  • Lichens: symbiosis of alga (phycobiont) and fungus (mycobiont); indicators of clean air.

Key terms

Five-kingdom classification
Whittaker's system (1969) with Monera, Protista, Fungi, Plantae, Animalia
Viroid
infectious free RNA lacking a protein coat
Saprophyte
an organism that feeds on dead and decaying organic matter, like many fungi

Important questions with answers

Why are diatoms called the "chief producers" of the oceans?2 marks

They are microscopic, photosynthetic and extremely abundant in oceans, so they make a large share of the food (and oxygen) in marine food chains.

Give the criteria used by Whittaker for the five-kingdom classification.3 marks

Cell structure (prokaryotic or eukaryotic), body organisation (unicellular or multicellular), mode of nutrition (autotrophic or heterotrophic), reproduction and phylogenetic relationships.

Describe the structure of a virus and of a bacteriophage, list three diseases caused by viruses, and explain why viruses are called "living–non-living".5 marks

A virus has nucleic acid (DNA or RNA, never both) enclosed in a protein coat (capsid) made of capsomeres; plant viruses usually have single-stranded RNA, and bacteriophages usually have double-stranded DNA with a head and tail. Diseases: common cold, AIDS, mumps, polio, smallpox, herpes, influenza (also tobacco mosaic in plants). Outside a host cell, viruses are inert and can be crystallised like chemicals (non-living). Inside a host, they use the host machinery to make copies of themselves and can mutate (living), so they lie on the border.

Quick revision

  • Fungal cell wall = chitin.
  • Lichens indicate clean air.
  • Viruses are not placed in the five kingdoms.

Exam tips

  • Archaebacteria live in extreme habitats (halophiles, thermoacidophiles, methanogens).
  • For fungi, remember one example per class: Phycomycetes – Rhizopus, Albugo; Ascomycetes – yeast, Penicillium; Basidiomycetes – Agaricus, rusts and smuts; Deuteromycetes – Alternaria, Trichoderma.

Practice MCQs

  1. Five-kingdom classification was proposed by

    1. Whittaker
    2. Linnaeus
    3. Darwin
    4. Haeckel
    Show answer

    Answer: (a) Whittaker. R.H. Whittaker, 1969.

  2. Bacteria belong to kingdom

    1. Monera
    2. Protista
    3. Fungi
    4. Plantae
    Show answer

    Answer: (a) Monera. Prokaryotes.

  3. Cell wall of fungi is made of

    1. cellulose
    2. chitin
    3. peptidoglycan
    4. pectin
    Show answer

    Answer: (b) chitin. Chitin.

  4. Lichen is an association of

    1. bacterium and fungus
    2. alga and fungus
    3. alga and bacterium
    4. virus and fungus
    Show answer

    Answer: (b) alga and fungus. Mutualism.

  5. Red tides in the sea are caused by

    1. dinoflagellates (e.g. Gonyaulax)
    2. diatoms
    3. cyanobacteria
    4. euglenoids
    Show answer

    Answer: (a) dinoflagellates (e.g. Gonyaulax). Toxic blooms.

  6. Viroids differ from viruses in lacking

    1. RNA
    2. nucleic acid
    3. DNA
    4. protein coat
    Show answer

    Answer: (d) protein coat. Free RNA.

  7. Methanogens belong to

    1. eubacteria
    2. fungi
    3. cyanobacteria
    4. archaebacteria
    Show answer

    Answer: (d) archaebacteria. Produce methane.

  8. Euglena is called a connecting link because it

    1. is photosynthetic in light but heterotrophic in darkness
    2. is a fungus
    3. has a cell wall of chitin
    4. lives only in soil
    Show answer

    Answer: (a) is photosynthetic in light but heterotrophic in darkness. Plant-like and animal-like features.

All chapters of Class 11 Biology

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.