CBSE Class 11 Biology Biological Classification Notes

2. Biological Classification

POINTS TO REMEMBER :

SYSTEMS OF CLASSIFICATION :

• Earliest Classification was given by Aristotle. Divided plants into herbs, shrubs and trees. Animals into those with RBC’s and those who do not have it.

Two kingdom classification :

• Given by Carolous Linnaeus − Plant kingdom and Animal kingdom.

Five kingdom classification :

• By R. H. Whittaker. Monera, Protista, Fungi, Plantae and Animalia are the five kingdoms.

Kingdom Monera :

Bacteria :

• Have bacteria a sole member.

• Bacteria can have shapes like: Coccus (spherical), Bacillus (rod-shaped), Vibrio comma shaped) and sprillum (spiral shaped).

• Bacteria found almost everywhere and can be Photosynthetic autotrophs, Chemosynthetic autotrophs or Heterotrophs.

Archaebacteria :

• Differs from bacteria having different cell wall structure.

• They live in most harsh habitats

• Halophiles (salt-loving)

• Thermophiles (in hot springs)

• Acidophiles (high acidic condition)

• Methanogen (marshy area)

• Methanogen are also found in the gut of ruminant and produces biogas.

Eubacteria :

• Called true bacteria having a rigid cell wall, and if motile a flagellum.

• They also known as blue green algae or Cyanobacteria.

• Cyanobacteria are photosynthetic autotrophs.

• Unicellular, colonial or filamentous, marine and terrestrial algae.

• Colonies are surrounded by gelatinous sheath.

• Some of these can fix atmospheric nitrogen by specialized cells called heterocyst, e.g. Nostoc and Anabaena.

• Chemosynthetic autotrophs: Oxidize various inorganic substances like nitrates/nitrites, ammonia and use released energy for their ATP production.

• Heterotrophic bacteria:

Mycoplasma :

• Completely lack cell wall.

• Smallest living cells.

• Can survive without oxygen.

• Pathogenic in animals and plants.

Kingdom Protista :

• All are unicellular and eukaryotic.

• Mostly aquatic, can live in moist places.

• Forms a link between plants, animals and fungi.

• The cell contain nucleus and membrane bound organelles.

Chrysophytes :

• Includes diatoms and golden algae (desmids)

• Found in freshwater or marine water.

• Mostly planktonic ( passive swimmer)

• Photosynthetic.

• Cell walls overlap to fit together like a soap box.

• Cell wall contains silica hence indestructible.

• Their accumulation forms ‘Diatomaceous Earth’.

• Used in polishing, filtration of oils and syrups.

• Diatoms are the chief ‘producers’ in the oceans.

Dinoflagellates :

• Marine, photosynthetic.

• Cell wall has stiff cellulose plates.

• Appears yellow, green, brown, blue or red depending on the pigments.

• Have two flagella − one longitudinal and other transversely in a furrow between wall plates.

• Red Dinoflagellates (Gonyaulax) form red tides.

Euglenoids :

• Mostly fresh water form found in stagnant water.

• Instead of cell wall they have protein rich layer ‘pellicle’ which makes body flexible.

• They have two flagella one short and one long

• Photosynthetic in presence of sunlight but become heterotrophs if they do not get sunlight. e.g. Euglena 

Slime Moulds :
• Saprophytic Protists
• Form aggregates to form plasmodium grow on decaying twigs and leaves.
• Plasmodium forms fruiting bodies bearing spores at their tips.
• Spores have true walls which are extremely resistant and survive for many years.

Protozoans :
• All protozoans are heterotrophs and live as predators or parasites.
• Believed to be primitive relatives of animals.
• These are divided into four major groups on the basis of locomotery organelle they have.

Amoeboid protozoans :
• Move and Catch prey using pseudopodia, e.g., Amoeba.
• Many forms have silica shells on their surface.
• Some of them are parasitic e.g. Entamoeba.

Flagellated protozoans :
• Either free living or parasitic.
• They have flagella.
• Cause disease like sleeping sickness e.g., Trypanosome.

Ciliated protozoans :
• These are aquatic, actively moving organisms due to presence of thousands of cilia. e.g., Paramecium.
• They have a cavity called gullet that opens to outside the cell.

Sporozoans :
• Lack any locomotery organelle.
• All members are parasitic.
• Have infective spore like stage in life cycle, e.g., Plasmodium which causes Malaria.

KINGDOM FUNGI :
• With the exception of yeasts which are unicellular all others are multicellular and filamentous.
• Consists of long slender thread like structure called hypha.
• Non chlorophyllous
• Network of hyphae called mycelium.
• Uninucleated or multinucleated (coenocytic)
• Cell wall made of complex polysaccharide called chitin.
• Grow in warm and humid places.
• Saprophytic, parasitic, symbiotic (Lichen)
• Reproduce asexually by spores conidia sporangiospores or zoospores.
• Sexual reproduction is by oospores, ascospores and basidiospores.
• Sexual cycle involves the following thee steps:
• Plasmogamy: fusion of protoplasms between two motile or non-motile gametes.
• Karyogamy: fusion of two nuclei
• Meiosis: zygote undergoes meiosis resulting haploid spores.

Phycomycetes :
• Found in aquatic habitat, on decaying wood in moist and damp places.
• Some of them are obligate parasite on plants.
• Mycelium is aseptate and coenocytic
• Asexual reproduction by zoospores (motile) or by aplanospores (nonmotile).
• Spores are produced endogenously in sporangium.
• Zygospore produced by fusion of gametes.
e.g., Rhizopus, Albugo.

Ascomycetes :
• Commonly known as ‘sac fungi’.
• Unicellular (yeasts) or multicellular (e.g. Penicillium)
• Saprophytic, decomposers, parasitic or coprophilous.
• Mycelium branched and septate.
• Asexual spores are called conidia produced exogenously on the conidiophores. Conidia on germination produce mycelium.
• Sexual spores are called ascospores produced endogenously in ascus produced inside fruiting body calledAscocarp.
e.g., Aspergillus, Neurospora.
(iii) Basidiomycetes
• Common known forms called mushrooms, bracket fungi or puffballs.
• Mycelium septate and branched.
• Asexual spores generally are not found.
• Vegetative reproduction by fragmentation.
• Sexual reproduction by fusion of vegetative or somatic cells of different strains to form basidium produced in basidiocarp.
• Basidium produces four basidiospores after meiosis.
e.g., Agaricus, Ustilago.

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. Viruses :
• They did not find a place in classification. Take over the machinery of host cell on entering it but as such they have inert crystalline structure. So, difficult to call them living or non-living.
• Pasteur gave the term ‘Virus’ i.e., poisonous fluid.
• D. J. Ivanowsky (1892) found out that certain microbes caused Tobacco Mosaic Disease in tobacco plant.

Important Questions for NCERT Class 11 Biology Biological Classification

Ques. Which pair of the following belongs to basidiomycetes?
(a) Puffballs and Claviceps
(b) Peziza and stink horns
(c) Morchella and mushrooms
(d) Birds nest fungi and puffballs 

Answer: D

Ques. Which of the following environmental conditions are essential for optimum growth of Mucor on a piece of bread ?
A. Temperature of about 25°C
B. Temperature of about 5°C
C. Relative humidity of about 5%
D. Relative humidity of about 95%
E. A shady place
F. A brightly illuminated place
Choose the answer from the following options.
(a) B, C and F only (b) A, C and E only
(c) A, D and E only (d) B, D and E only 

Answer: C

Ques. Which fungal disease spreads by seed and flowers?
(a) Loose smut of wheat
(b) Corn smut
(c) Covered smut of barley
(d) Soft rot of potato 

Answer: A

Ques. Which of the following secretes toxins during storage conditions of crop plants?
(a) Aspergillus          (b) Penicillium
(c) Fusarium            (d) Colletotrichum 

Answer: A

Ques. Black rust of wheat is caused by
(a) Puccinia             (b) Ustilago
(c) Albugo               (d) Phytophthora. 

Answer: A

Ques. Columella is a specialized structure found in the sporangium of
(a) Spirogyra         (b) Ulothrix
(c) Rhizopus          (d) none of these. 

Answer: C

Ques. Puccinia forms uredia and
(a) telia on wheat leaves
(b) aecia on barberry leaves
(c) pycnia on barberry leaves
(d) aecia on wheat leaves.

Answer: A

Ques. Mycorrhiza is correctly described as
(a) parasitic association between roots and some fungi
(b) symbiotic relationship between fungi and roots of some higher plants
(c) symbiosis of algae and fungi
(d) relation of ants with the stem of some trees.

Answer: B

Ques. The black rust of wheat is a fungal disease caused by
(a) Albugo candida
(b) Puccinia graminis tritici
(c) Melampsora lini
(d) Claviceps purpurea. 

Answer: B

Ques. Select the wrong statement.
(a) Cell wall is present in members of fungi and plantae.
(b) Mushrooms belong to basidiomycetes.
(c) Pseudopodia are locomotory and feeding structures in sporozoans.
(d) Mitochondria are the powerhouse of the cell in all kingdoms except monera.

Answer: C

Ques. Cell wall is absent in
(a) Mycoplasma     (b) Nostoc
(c) Aspergillus       (d) Funaria. 

Answer: A

Ques. True nucleus is absent in
(a) Vaucheria      (b) Volvox
(c) Anabaena      (d) Mucor.

Answer: C

Ques. Nuclear membrane is absent in
(a) Penicillium       (b) Agaricus
(c) Volvox             (d) Nostoc. 

Answer: D

Ques. Absorptive heterotrophic nutrition is exhibited by
(a) algae            (b) fungi
(c) bryophytes    (d) pteridophytes. 

Answer: B

Ques. Pick up the wrong statement.
(a) Some fungi are edible.
(b) Nuclear membrane is present in Monera.
(c) Cell wall is absent in Animalia.
(d) Protists have photosynthetic and heterotrophic modes of nutrition.

Answer: B

Ques. Which one of the following living organisms completely lacks a cell wall?
(a) Cyanobacteria          (b) Sea-fan (Gorgonia)
(c) Saccharomyces        (d) Blue-green algae

Answer: B

Ques. Which of the following is correct about viroids?
(a) They have RNA with protein coat.
(b) They have free RNA without protein coat.
(c) They have DNA with protein coat.
(d) They have free DNA without protein coat.

Answer: B

Ques. Mad cow disease in cattle is caused by an organism which has
(a) inert crystalline structure
(b) abnormally folded protein
(c) free RNA without protein coat
(d) free DNA without protein coat.

Answer: B

Ques. Which of the following statements is incorrect?
(a) Prions consist of abnormally folded proteins.
(b) Viroids lack a protein coat.
(c) Viruses are obligate parasites.
(d) Infective constituent in viruses is the protein coat. 

Answer: D

Ques. Viroids differ from viruses in having
(a) DNA molecules without protein coat
(b) RNA molecules with protein coat
(c) RNA molecules without protein coat
(d) DNA molecules with protein coat. 

Answer: C

Ques. Which of the following statements is wrong for viroids?
(a) They cause infections.
(b) Their RNA is of high molecular weight.
(c) They lack a protein coat.
(d) They are smaller than viruses. 

Answer: B

Ques. Select the wrong statement.
(a) The term ‘contagium vivum fluidum’ was coined by M. W. Beijerinck.
(b) Mosaic disease in tobacco and AIDS in human being are caused by viruses.
(c) The viroids were discovered by D.J. Ivanowsky.
(d) W.M. Stanley showed that viruses could be crystallised.

Answer: C

Ques. Which of the following shows coiled RNA strand and capsomeres?
(a) Polio virus           (b) Tobacco mosaic virus
(c) Measles virus      (d) Retrovirus

Answer: B

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