BIOLOGICAL CLASSIFICATION – Class XI Biology by TEACHING CARE online tuition and coaching classes

BIOLOGICAL CLASSIFICATION – Class XI Biology by TEACHING CARE online tuition and coaching classes

Biological Classification

  • Since the dawn of civilisation, there have been many attempts to classify living organisms. Different scientist defined and classified the organisms in different ways.

Two kingdom system of classification

  • Linnaeus (1707-1778) divided the living organisms into two kingdoms: Plantae and Animalia.
  • This system did not distinguish between the eukaryotes and prokaryotes, unicellular and multicellular organisms and photosynthetic (green algae) and non-photosynthetic (fungi) organisms.

Five Kingdom System of Classification

  • According to Robert H. Whittaker (1969), an American ecologist, non-chlorophyllous heterotrophic plants to be classified under kingdom Fungi. Five kingdoms in which the living world is divided are Monera, Protista, Fungi, Plantae/ Metaphyta (Plants) and Animalia/ Metazoa (Animals).
  • The classification is based mainly on following main criteria:

Complexity of cell structure: prokaryotic or eukaryotic

Complexity of cellular organization: unicellular to multicellular

Mode of nutrition: autotrophic or heterotrophic.

          Nature of wall: Cellulosic Peptidoglycan and chitin

Methods of reproduction: Sexual and Asexual

  • According to him all prokaryotic organism are grouped under kingdom Monera whereas all eukaryotic organism classified in four different kingdoms, i.e.; Protista, Animalia, Plantae and Fungi.

Kingdom Monera

  • This includes Prokaryotic organisms like, bacteria and cynobacteria.
  • There are different types of bacteria on the basis of shapes like, bacillus, vibrio, coccus etc. and on habits.
  • There two important types of bacteria (i) Archaebacteria (ii) Eubacteria

Archaebacteria are those bacteria which live in very harsh habitats viz; thermoacidophiles (hot streams), methanogens (marshy area) and halophiles (salt producing area).

Eubacteria are those bacteria which have rigid cell wall. These are cynobacteria (Nostoc, Anabaena), chemosynthetic bacteria, and heterotrophic bacteria (Rhizobium, Lactobacillus).

  • Some heterotrophic bacteria are very harmful. They cause various diseases like; typhoid, diphtheria, citrus canker, cholera, tetanus etc.


  • MLO (mycoplasma-like organisms) or PPLO (pleuropneumonia like organisms) was discovered by Nocard and Roux (1898) in pleural fluid of cattle having bovine pleuropneumonia.
  • They are the smallest (0.1 – 0.15 µm) and simplest free living Gram negative, monerans or procaryotes.
  • A cell wall is absent and survives without oxygen. Replicating disc is present at one of its ends.
  • Mycoplasma produces primary a typical pneumonia and mycoplasmal urethritis in humans, pleuropneumonia in animals, little leaf disease in Brinjal and witches broom in plants.
  • They change their body shape due to absence of cell wall that’s why they are known as “Joker of plant kingdom”.

Kingdom Protista

  • This kingdom includes all unicellular eukaryotic organisms. Some of them are autotrophic (protophyta) and some are heterotrophic (protozoa).
  • Photosynthetic protistans (protophyta) consists chrysophyta, dinoflagellates, euglenoids and slime moulds.


  • This includes diatoms and golden algae (desmids). They are found in fresh water as well as in marine.
  • They are microscopic and float passively in water currents (plankton).
  • Cell walls of diatoms in the form of two thin overlapping shells, like soap box.
  • The walls are embedded with silica and thus the walls are indestructible. Thus, diatoms have left behind large amount of cell wall deposits in their habitat;
  • This accumulation over billions of years is referred to as ‘diatomaceous earth’ which is used in polishing, filtration of oils and syrups.
  • Diatoms are the chief ‘producers’ in the oceans.


  • As name reflects, these are double flagellated photosynthetic organisms, mostly habitating in marine environment. They appear yellow, green, brown, blue or red depending on the main pigments present in their cells.
  • Some red dinoflagellates causes red tides in seas, like; Gonyaulax.


  • They are unicellular mixotrophic organism. Mostly found in stagnant freshwater. They lack cell wall. Pellicle is the outermost covering.
  • They are photosynthetic in the presence of sunlight, when deprived of sunlight they behaves like heterotrophs by predating on other smaller organisms,
    g.; Euglena.

Slime moulds

  • Slime moulds are saprophytic protists. The body moves along decaying twigs and leaves engulfing organic material.
  • Under suitable conditions, they form an aggregation called plasmodium which may grow and spread over several feet.
  • During unfavorable conditions, the plasmodium differentiates and forms fruiting bodies bearing spores at their tips. The spores possess true walls. They are extremely resistant and survive for many years, even under adverse conditions.


  • All protozoans are heterotrophs and live as predators or parasites. There are four major groups of protozoans.
  • Amoeboid protozoans: These organisms live in fresh water, sea water or moist soil e.g. some of them are parasite e.g. Entamoeba
  • Flagellated protozoans: The members of this group are either free-living or parasitic. They have flagella. e.g. Trypanosoma
  • Ciliated protozoans: These are aquatic, actively moving organisms because of the presence of thousands of cilia. e.g. Paramoecium
  • Sporozoans : All are parasitic protozoans. e.g. Plasmodium (Malarial parasite)

Kingdom Fungi

  • The fungi constitute a unique kingdom of heterotrophic organisms. They show a great diversity in morphology and habitat.
  • They are multicellular eukaryotes except Yeast (unicellular). Fungi are filamentous having long, slender thread like – structure called hyphae. Network of hypha called as mycelia.
  • Cell wall of hypha made of chitin and polysaccherides.
  • Symbiotic association of fungus with algae called as Lichens, and with roots of higher plants called as
  • Reproduction in fungi are vegetative, asexual and sexual types.
  • There are different types of funguses like phycomycetes (Mucor and Rhizopus), ascomycetes or sac fungi (Penicillium, yeast, Neurospora, Aspergillus), basidiomycetes or club fungi (Agaricus and Puffballs) and Deuteromycetes or fungi imperfecti (Alternaria and Trichoderma)


  • They are found on decaying leaves and damp places and also as parasites.
  • Hyphal wall contains cellulose and other glycans in many members. In some cases chitin or fungus cellulose in also present.
  • The mycelium is aseptate coenocytic (multinucleate).
  • Asexual reproduction is through zoospores as well as aplanospores. Both the kinds of spores are produced in sporangia.
  • Zoospores are generally biflagellate.
  • The sexual reproduction takes place by fusion of similar (isogamy) and dissimilar (oogamy) gametes.
  • Gametes are usually non flagellate.
  • The common members are Albugo, Phytophthora, etc.

Ascomycetes (Sac Fungi)

  • They include pigmented moulds (brown, green, blue, pink), powdery mildews, yeasts, cup fungi, morels and buffles.
  • The mycelium consists of septate hyphae. Yeasts are an exception in that they are unicellular.
  • Cell wall contains chitin or fungus cellulose.
  • In majority of Ascomycetes, the common mode of asexual reproduction is through the formation of conidia, formed in chains exogenously.
  • Sexual reproduction is through auxospores, which are formed endogenously in a sac like structure called ascus (pl. asci).
  • The asci may occur freely or get aggregated into specific fructifications called ascocarps. Ascocarps are of many types: apothecium (cup like, e.g., Peziza), perithecium (flask shaped g., Neurospora) or cleistothecium (closed e.g., Penicillium). The fructifications of some Ascomycetes are edible, e.g., morels, buffles, etc.
  • Yeast, Penicillium, Aspergillus and Claviceps are common examples.

Basidiomycetes (Club Fungi)

  • They are the most advanced and most commonly seen fungi as their fructifications are often large and conspicuous, g., mushrooms, toadstools, puff balls, bracket fungi, etc.
  • Basidiomycetes are among the best decomposers of wood. They are able to decompose both cellulose and lignin.
  • Motile structures or cells are absent.
  • Sexual reproduction actually causes plasmogamy or fusion of protoplasts without fusion of their nuclei. Karyogamy is delayed for long. The intervening phase is called dikaryophase. It produces a new mycelium called secondary mycelium.
  • Secondary mycelium is long lived. It consists of profusely branched septate hyphae in which the septa possess dolipore or central pore with barrel shaped outgrowths.
  • Dikaryophase or secondary mycelium may multiply by different types of spores, chlamydospores, ascidiospores, uredospores, teleutospores, etc.

Deuteromycetes (Fungi Imperfecti)

  • Deuteromycetes is an artificial class of fungi that has been created to include all those fungi in which sexual stage is not known or they have not been classified and placed anywhere else as yet.
  • The mycelium is usually septate. Coenocytic forms are not known.
  • Asexual reproduciton often occurs by conidia along with some other types of spores. In some cases even asexual spores are absent.
  • It is believed that most members of Deuteromycetes are actually Ascomycetes members in which sexual reproduction is either absent or yet to be discovered.


Kingdom Plantae

  • Kingdom Plantae includes all eukaryotic chlorophyll-containing organisms commonly called plants. The plant cells have prominent chloroplasts that have green pigment chlorophyll and cell wall mainly made of cellulose. Chlorophyll traps solar energy to converts light energy into chemical energy.
  • A few members are partially heterotrophic such as the insectivorous plants or parasites. Bladderwort and Venus fly trap are examples of insectivorous plants and Cuscuta is a parasite.
  • Plantae includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms.
  • Life cycle of plants has two distinct phases – the diploid sporophytic and the haploid gametophytic – that alternate with each other. The lengths of the haploid and diploid phases, and whether these phases are free–living or dependent on others, vary among different groups in plants. This phenomenon is called alternation of generation.

Kingdom Animalia

  • In five kingdom classification of Whittaker there is no mention of some acellular organisms like viruses and viriods and lichens.


  • Viruses are ultramicroscopic, non-cellular, infectious, non-cytoplasmic most primitive, filterable, obligate parasites.
  • Smaller than bacteria and can pass through bacteria proof filters.
  • Devoid of most of the biosynthetic enzymes.
  • No growth outside host, no division.
  • Uses metabolic energy of host.
  • Contain only one type of nuclei acid either DNA or RNA.
  • Viruses are host specific because they infect only a single species and definite cells of the host.
  • Transmissible from diseased to healthy organisms.
  • Effective in very small doses. Most of them are highly resistant to germicides and extreme physical conditions.
  • Genetic element remain enclosed inside a protein coat known as capsid.
  • Simplest known form of life.
  • Viruses are intermediate between living and non-living.



  • It is discovered by T.O. Diener in 1971.
  • They lack protein coat hence they named as viroid.
  • They are smaller than viruses.
  • They cause potato spindle tuber disease.
  • They have a free RNA.
  • The molecular weight of RNA is low in viriods.


  • They are in symbiotic association between algae and fungi.
  • They algae is known as phycobiont that helps in synthesise food.
  • The fungi is known as mycobiont which absorbs water and nutrients from soil.


  • Proteinaceous infections particle sub viral entity devoid of their own genetic material.
  • Discovered by Alper et al (1966).
  • Stanley B. Prusiner : Studied isolated and identified the causal agent of Scrapie, Kuru and mad cow disease in 1982 and was awarded nobel prize for prions in 1997.




  1. Who gave the concept of two kingdom classification?
  2. Write one significant character of kingdom Monera.
  3. What is the role of heterocyst?
  4. Which protistan forms diatomaceous earth?
  5. Which one is known as club fungi?
  6. Deuteriomycetes is known as Fungi imperfecti. Why?




  1. Write the two characters of Archaebacteria with example.
  2. What are the different types of protozoans?
  3. Define following terms: (a) Plasmogamy (b) Karyogamy (c) Symbionts
  4. Draw a labeled diagram of Bacteriophage virus.
  5. Which types of bacteria helps in recycling of phosphorus , nitrogen, iron and sulphur?


  1. Classify the different types of bacteria on the basis of their structure.
  2. Write short notes on Eubacteria.
  3. Explain the structure of Mycoplasma and also deduce its pathogenic effect on both plant and animals.
  4. How many types of fungi? Explain them with at least three characters each of them.
  5. Write a short note on

(a)      Virus                              (b)      Viroids

(c)      Prions                             (d)      Lichens                 (e)      Plasmodium




Pick (Ö) the correct option :

  1. Blue green algae belong to the kingdom

(1)   Protista                             (2)      Fungi

(3)   Monera                              (4)      Plantae

  1. Ecologically, multicellular decomposers are

(1)   Fungi                                (2)      Saprotrophic plants

(3)   Saprotrophic animals         (4)      Monerans

  1. According to Whittaker, one of the following is the most primitive evolutionary group

(1)   Plantae                              (2)      Fungi

(3)   Protista                             (4)      Monera

  1. Who discovered bacteria?

(1)   Leeuwenhoek                     (2)      Lederberg

(3)   Brown and Zinder              (4)      None of these

  1. Gram stain represents

(1)   A technique for staining bacteria, developed by Christian Gram

(2)   A stain got from Gram

(3)   A cytochemical technique for differentiation of mitochondria

(4)   A trade name

  1. Some bacteria have a capsule at outside of cell wall. It is made of

(1)   Protein                              (2)      Cellulose

(3)   Fat                                    (4)      Mucopolysaccharide

  1. Bacteria having a tuft of flagella at both ends are called

(1)   Peritrichous                       (2)      Lophotrichous

(3)   Amphitrichous                   (4)      Atrichous

  1. The bacterial genome is called

(1)   Incipient nucleus               (2)      Genophore

(3)   Nucleoid                            (4)      All of these

  1. In prokaryotes the ribosomes are

(1)   50 S                                  (2)      80 S

(3)   70 S                                  (4)      30 S

  1. Pasteurization is performed at

(1)   100°C for 15 minutes         (2)      82°C for 30 minutes

(3)   72°C for 20 minutes           (4)      62° for 30 minutes

  1. Milk is spoiled/fermented by

(1)   Rhizobium                          (2)      Lactobacillus

(3)   Azotobacter                        (4)      Clostridium

  1. Crown gall is due to

(1)   Agrobacterium                    (2)      Clostridium

(3)   Mycobacterium                   (4)      Erwinia

  1. Biogas is produced by

(1)   Eubacteria                        (2)      Archaebacteria

(3)   Mycoplasma                       (4)      Cyanobacteria

  1. An obligate anaerobe is

(1)   Ulothrix                              (2)      Spirogyra

(3)   Methane bacteria               (4)      Chlamydomonas

  1. In protists the locomotory organelles are

(1)   Flagella

(2)   Flagella, cilia and pseudopodia

(3)   Flagella and cilia

(4)   Flagella, cilia, pseudopodia and wrigglers

  1. A special fungus has following characters:

(a) They reproduce only through asexual spore known as conidia

(b) The mycelium is septate and branched

(c) They commonly known as fungi imperfecti

Above all characters are applicable for one the following is:

(1)   Ascomycetes                      (2) Basidiomycetes

(3)   Deuteromycetes                 (4) Phycomycetes

  1. Organism lacking protein coat but having genetic material is:

(1)   Prion                                 (2) Virion

(3)   Viroid                                (4) Viruses

  1. Match column I with Column II

Column I                         Column II

  • Mycoplasma (i) Colon
  • Chrysophytes (ii) Plasmodium
  • Slime moulds (iii) Witches broom
  • Entamoeba           (iv) Golden algae






  1. Discuss how classification systems have undergone several changes over a period of time?
  2. State two economically important uses of:

          (a) heterotrophic bacteria

          (b) archaebacteria

  1. What is the nature of cell-walls in diatoms?
  2. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.
  3. How are viroids different from viruses?



  1. Describe briefly the four major groups of Protozoa.
  2. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
  3. What do the terms phycobiont and mycobiont signify?
  4. Give a comparative account of the classes of Kingdom Fungi under the following:

(i) mode of nutrition

(ii) mode of reproduction

  1. What are the characteristic features of Euglenoids?




  1. Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.
  2. Organise a discussion in your class on the topic – Are viruses living or nonliving?
  3. What is alternation of generation?
  4. Write the characters of Dinoflagellates and Slime moulds.
  5. Explain the role of Chemosynthetic and Heterotrophic bacteria with expamle.