Monday 24 October 2016

CBSE Class 11 - Biology - Chapter 2 - Biological Classification (Q and A)

CBSE Class 11 


Chapter 2 - Biological Classification

NCERT Chapter Solutions

CBSE Class 11 - Biology - Chapter 2 - Biological Classification (Q and A)

Q1: Discuss how classification systems have undergone several changes over a period of time?

Answer: The classification systems have undergone several changes with time.

The first attempt of classification was made by Aristotle. He classified plants as herbs, shrubs, and trees. Animals were classified on the basis of presence or absence of red blood cells. This system of classification failed to classify all the known organisms.

Linnaeus gave a two kingdom system of classification i.e. kingdom Plantae and kingdom Animalia. However, this system did not differentiate between unicellular and multicellular organisms and between eukaryotes and prokaryotes. Thus a large number of organisms could not be classified merely under the two kingdoms.

Later a five kingdom system of classification was proposed by R.H Whittaker in 1969. On the basis of characteristics, such as cell structure, mode of nutrition, presence of cell wall, etc., five kingdoms, Monera, Protista, Fungi, Plantae, and Animalia were formed.

Later Monera was divided further into Archaebacteria and  Eubacteria because Archaebacteria were different from bacteria in terms of different type of cell wall structure.

Q2: Who is known as Father of Taxonomy? Name the book he published on taxonomy. What's his the greatest contribution in naming species.

Answer: Linnaeus. In 1758 he published his famous book systema naturae. His greatest contribution to taxonomy was the use of binomial nomenclature for all species of animals and plants

Q3: State two economically important uses of:

(a) Heterotrophic bacteria
(b) Archaebacteria

(a) Uses of Heterotrophic bacteria

  • Commercial and Domestic Use: They (Lacto bacillus) help in the production of curd from milk.
  • Decomposers that help in the formation of humus.
  • Medicinal use: Many antibiotics are obtained from some species of bacteria.
  • Nitrogen Cycle: Many soil bacteria help in fixation of atmospheric nitrogen.

(b) Uses of Archaebacteria
  • Live in guts of  ruminant animals such as cows and buffaloes and they produce methane anaerobically (biogas) from the dung of these animals.
  • Methanogens are also involved in the formation of biogas and sewage treatment.

Q4: What is the nature of cell-walls in diatoms?

Answer: The cell wall of diatom is made of silica. It consists of two thin overlapping shells that fit into each other such as a soap box with lids. When the diatoms die, the silica in their cell walls gets deposited in the form of diatomaceous earth. This diatomaceous earth, being gritty, is used in polishing, filtration of oils and syrups.

Q5: Name the algae which is a source of iodine.

Answer: Brown algae called kelps, specially from species of Laminaria.

Q6: Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.


(a) Algal bloom refers to an increase in the population of algae or blue-green algae in water. Under warm conditions specially when sewage and inorganic waste added to water, there is sudden and explosive growth of these primary producer (blue-green algae). It leads to depetion of oxygen in water thus resulting in the death of fishes and other aquatic animals.

(b) Red tides are caused by red dinoflagellates (Gonyaulax). Due to their large population, the sea appears red in colour. Red alga release large amounts of toxins in water that can cause death of a large number of fishes.

Q7: How are viroids different from viruses?

Answer: Viroids are molecules of RNA without any protein coating. They are simpler than viruses, i.e. hundred nucleotides long and important infectious disease agents in plants (e.g. potato spindle tuber disease).

Q8: Who are believed to be primitive relatives of animals?

Answer: Protozoans

Q9: Describe briefly the four major groups of Protozoa.

Amoeba (image credits: wikimedia)

Amoeboid protozoans:

  • live in fresh water, sea water or moist soil
  • lack flagella and have pseudopodia (false feet) for capturing prey or for locomotion e.g. amoeba
  • Marine forms have silica shells on their surface.
  • Mostly heterotrophs some are parasites like Entamoeba

Flagellated protozoans:

  • free-living or parasitic
  • have flagella e.g. Euglena
  • autotrophic or heterotrophic
  • The parasitic forms cause diseases such as sleeping sickness. Example: Trypanosoma.
 Watch Euglena Flaggelum movement in the following video:

Ciliated protozoans:

  • aquatic
  • cilia present which help in locomotion
  • have a cavity (gullet) that opens to the outside of the cell surface. e.g. paramecium


  • have an infectious spore-like stage in their life cycle
  • protozoan parasite Plasmodium causes malaria
  • Leishmania, another parasitic protozoan causes Kala-azar

Q10: Plants are autotrophic. Can you think of some plants that are partially heterotrophic?

Answer: Plants contain green pigment called chrolophyll which carries out photosynthesis to prepare food. There plants are autotrophic. However there are a few plants which are partly heterotrophic e.g. insectivorous plants.

They have various means of capturing insects so as to supplement their diet with required nutrients derived from insects. Examples of insectivorus plants are pitcher plant (Nepenthes), Venus fly trap, bladderwort, and sundew plant.

Q11: What do the terms phycobiont and mycobiont signify?

Answer: In the symbiotic life like in lichens, the algal component of the lichens is reffered as phycobiont (prepares food by photosynthesis). While the fungal component is called mycobiont (absorbs water and nutrient from soil and provides raw material).

Q12: Give a comparative account of the classes of Kingdom Fungi under the following:

   (i) Mode of nutrition
   (ii) Mode of reproduction


Phycomycetes: Ascomycetes Basidiomycetes Deuteromycetes
Mode of nutrition obligate parasites on plants or are found on decaying matter such as wood. sporophytic, decomposers, parasitic or coprophilous (growing on dung). decomposers in soil or on logs and tree stumps.
OR parasites in plants causing diseases such as rusts and smuts.
Mode of reproduction Asexual reproduction (motile zoospores or non-motile aplanospores) Asexual reproduction. Sexual reproduction takes place through ascospores Asexual reproduction
Asexual reproduction(spores call aconidia)

Q13: What are the characteristic features of Euglenoids?

① unicellular protists (commonly found in fresh)

② elastic body covering made up of protein (pellicle)

③ bear two flagella on the anterior end of the body. It helps in propulsion in water

④ Cytostome and Reservoir - the cell mouth leading into a tubular cytopharynx which opens into a vesicle called reservoir.

⑤ a prominent red pigment spot (stigma). It is sensitive to light.

⑥ Reproduction - is by binary fission.

⑦ Mostly photosynthetic (chlorophy present). In dark they behave similar to heterotrophs by capturing other small aquatic organisms.

⑧ contain Contractile Vacuole - for osmoregulation.

Q14: Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.


  1. Viruses are extremely small and can be seen only under electron microscope.
  2. Their size ranges from 10 nm to 300 nm in diameter.
  3. Virus has a simple structure consisting of a core and a cover. The core particle is the genetic material, either DNA or RNA. The cover is a protein coat called capsid.
  4. A virus cannot reproduce by itself. For its reproduction it needs to enter the cell of some organism.
  5. Most of the viruses, infecting plants, have single stranded RNA as genetic material. On the other hand, the viruses infecting animals have single or double stranded RNA or double stranded DNA.
  6. Bacteriophages or viruses infecting bacteria mostly have double stranded DNA
  7. A.I.D.S, small pox, mumps, and influenza are some common examples of viral diseases.

Q15: Organise a discussion in your class on the topic- Are viruses living or non-living?

1. Though viruses possess nucleic acids as genetic material like the living organisms but they cannot make copies of DNA for reproduction on their own. Presence of nucleic acid (DNA or RNA) suggests that viruses are alive.

2. They can also respond to their environment (inside the host cell) in a limited manner

3. They can make copies of themselves to reproduce only inside a living cell. They are non-cellular and can be crystallized. Thus, they are considered non-living.

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