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NCERT Solutions for Class 11 Biology Chapter 2 - Biological Classification

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Chapter number 2 "Biological Classification" of class 11 Biology subject throws light on the features of Kingdom Monera, Fungi, and Protista as given by the Whittaker System of Classification. The plant and animal kingdoms, which are technically known as Kingdoms Plantae and Animalia, respectively are introduced briefly in this chapter. Apart from the five Kingdoms mentioned above, Biological Classification also talks about the Kingdoms Viroids, Lichens, and Viruses. Following are the sub-topics that are a part of this chapter.

The minute differences in the morphological characteristics that originally led to animal and plant species classification were minute. The criteria based on which the five-kingdom classification was designed were cell structure, body organization, reproduction, mode of nutrition, and phylogenetic relationships. The entities classified in the five-kingdoms displays tremendous metabolic diversity.

  • Kingdom Monera

Kingdom Monera includes bacteria as well, even though bacterias are cosmopolitan in distribution.

  • Kingdom Protista

Organisms classified under Kingdom Protista are single-celled eukaryotes

  • Kingdom Fungi

The species included under Kingdom Fungi reveal substantial diversity in their structure and habitat.

  • Kingdom Plantae

Entities that consist of eukaryotic chlorophyll property come under the Kingdom Plantae.

  • Kingdom Animalia

All the multicellular, and heterotrophic eukaryotic entities, in which there is a dearth of a cell wall are a part of the Kingdom Animalia.

  • Viroids, Viruses, Lichens, and Prions

Viruses are infectious agents who either have a single-stranded RNA or double-stranded RNA surrounded with a protein coat. Whereas, viroids are also infectious agents, but short ones have a single-stranded RNA with no protein coat.


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


The classification systems keep on changing as new species are found and classified. Till now, the classification system has undergone several changes. The first-ever classification was given by Aristotle who divided plants into herbs, shrubs, and trees based on their habit and animals based on the presence or absence of red blood.

Later on, this classification system was rejected because it was misleading. Linnaeus then classified all organisms into two large kingdoms i.e. plants and animals. Since, this system could not distinguish between eukaryotes or prokaryotes, unicellular or multicellular organisms, it was also rejected. Further, three-kingdom and four-kingdom classification were proposed by Ernst Haeckel and Copeland respectively. These were soon replaced by the five-kingdom classification by R.H Whittaker. In this system, organisms were divided into five kingdoms on the basis of cell structure, body organization, mode of nutrition and reproduction, and phylogenetic relationships,namely monera, protista, fungi, plantae, and animalia. Even this classification system was not up to the mark, so corrections are being made in this. Thus, we can conclude that classification systems have undergone several changes over a period of time.

Q2. State two economically important uses of (a) heterotrophic bacteria (b) archaebacteria


 (a). Economically important uses of heterotrophic bacteria
1. Some heterotrophic bacteria are decomposers and they help in humus formation.
2. Heterotrophic bacteria like Rhizobium also aid in fixing nitrogen for plants.
3. Heterotrophic bacteria like Lactobacillus help in the formation of curd 

   (b). Economically important uses of archaebacteria
1. Archaebacteria such as Methanobacterium and some others are used in the production of gobar gas which is used as fuel as it contains methane.
2. Certain archaebacteria are used in bioleaching of minerals.

3. Archaebacteria such as Thermus aquaticus are used to obtain Taq polymerase enzyme which is used in recombinant DNA technology.

Q3. What is the nature of cell walls in diatoms?


The cell wall of diatoms is composed of two layers, thin overlapping shells which fit together in such a way that they look like a soap case. The cell wall is impregnated with silica in characteristic patterns. Diatom cell walls are almost indestructible and on accumulation, they form diatomaceous earth which is used for purification and filtration of petroleum and other crude products.

Q4. Find out what do the terms mean; algal bloom and red-tides; signify.


Algal bloom- An algal bloom is a term used for excessive growth of algae over a water body causing discoloration of the water body. This abnormal growth is due to availability of high amounts of mineral and nutrient content in water bodies spilled off from  fields and industries which contain chemicals utilized by algae for growth. Algal blooms result in the death of fishes and other aquatic organisms as it consumes the oxygen available for its own growth and metabolic processes.

Red tides- Red tide is the red coloration of seawater due to the presence of dinoflagellate Gonyaulax. This dinoflagellate produces toxins that lead to the death of fish.

Q5. How are viroids different from viruses?


Viroids are different from viruses in the following aspects :

  1. Viroids are smaller in size than viruses.
  2. Viruses are made up of protein encapsulating the genetic material whereas viroids are free RNA particles.
  3. Viroids cause diseases in plants whereas viruses infect both plants and animals.

Q6. Describe briefly the four major groups of Protozoa.


All protozoans are single-celled, cell-wall-lacking, heterotrophic organisms that live as predators or parasites. Protozoans are considered to be primitive relatives of animals. Protozoa are divided into four groups based on their organ of motility.

  1. Amoeboid protozoa- This type of protozoa is found in freshwater, seawater, or moist soil. They can move and capture their prey with the help of pseudopodia. The pseudopodia are the extensions of the cell membrane. Example: Amoeba.
  2. Flagellated protozoa- These protozoa can be parasitic or free-living. They use their flagella for movement. Example Trypanosoma causing sleeping sickness.
  3. Ciliated protozoa- These protozoa possess many cilia on their bodies for movement. Ciliated protozoa are characterized by the presence of two nuclei i.e. macronuclei and micronuclei. Example: Paramoecium
  4. Sporozoa- These protozoa include organisms that have an infectious spore-like stage in their life cycle. Sporozoans do not possess cilia or flagella. They are mostly endoparasites. E.g. Plasmodium.

Q7. Plants are autotrophic. Can you think of some partially heterotrophic plant?


  • Plants are autotrophic organisms as they prepare their food materials by converting light energy into chemical energy. However, some plants can adapt to the heterotrophic mode of nutrition for some specific requirements.
  •  For example, the Pitcher plant ( Nepenthes ) is green and autotrophic but it grows in nitrogen-deficient soil. So, in order to fulfill its nitrogen needs, it preys upon insects. The leaf of Nepenthes is modified into a pitcher-like structure. In this structure, insects get trapped and are digested by strong digestive enzymes present in it.
  •  Since the plant is performing photosynthesis and it is carnivorous only for obtaining nitrogen, it is said to be partially heterotrophic.

Q8. What do the terms phycobiont and mycobiont signify?


  • Phycobiont and mycobiont are parts of a lichen. 
  • A lichen refers to a symbiotic association of algae and fungi. In this association, fungi derive nutrition from algae as it performs photosynthesis due to which inorganic molecules are converted to organic food in presence of light while the fungi provide shelter to algae. 
  • The term phycobiont signifies the algal component of a lichen whereas mycobiont signifies the fungal component of lichen.

Q9. Give a comparative account of the classes of Kingdom Fungi under the following: 

  1. mode of nutrition

  ii. mode of reproduction


A comparative account of the classes of Kingdom Fungi is as follows:











Mode of


These are


These are


These have







can be


parasites or


nutrition. They




parasitic and




i.e. grow on



or parasitic.




decaying matter.


(growing on dung)


decomposers also.


Mode of








Mode of




reproduction takes 

place through 


while spores are 


reproduction is


takes place

takes place




through the





formation of


occurs via

through the





formation of


(motile) or











takes place





by ascospore


has not been





identified in


takes place


this group.









Q10. What are the characteristic features of Euglenoids?


Characteristic features of Euglenoids:

  1. Euglenoid is a group of unicellular protists with mixotrophic nutrition (both autotrophic and heterotrophic).
  2. Euglenoids lack a cell wall. Their bodies are covered by a proteinaceous membrane called the pellicle.
  3. Euglenoids contain chlorophyll pigment, so they are photoautotrophic. However, in the absence of light, they behave like heterotrophs. Thus, they have mixotrophic nutrition.
  4. Euglenoids possess two flagella at the anterior surface.
  5. Euglenoids have both plant-like and animal-like characters. For example, the presence of chlorophyll is a plant character while the absence of a cell wall is an animal character.


Q11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also, name four common viral diseases.


  • Viruses are acellular, nucleoprotein entities that can utilize the synthetic machinery of a living cell of another organism for its multiplication. It infects a variety of plants, animals, and microbes.
  • Structure of viruses- A virus consists of two parts i.e. a nucleoid and capsid. An envelope is present in some cases. A few enzymes are also found.
  1. Nucleoid- It represents the viral chromosome or genetic material of chromosomes. Nucleoid is made of a single molecule of nucleic acid that can be linear or circular. It is the infection-causing part of the virus. The genetic material of the virus can be either DNA or RNA. The DNA containing viruses are called deoxy-viruses while RNA containing viruses are called riboviruses. The nucleic acid can be double-stranded DNA, double-stranded RNA, Single-stranded DNA, or single-stranded RNA.
  2. Capsid- It refers to the proteinaceous covering around the virus which protects the nucleoid from physical and chemical damage. The capsid contains several subunits called capsomeres.
  3. Envelope- A loose membranous covering found in some animal viruses. It is rarely seen in plants and bacterial viruses. Based on the presence or absence of an envelope, viruses can be enveloped or naked. The envelope consists of viral proteins, lipids, carbohydrates, etc. It possesses subunits called telomeres. The surface of the envelope may have outgrowths called spikes.
  4. Enzymes- Viruses contain enzymes such as lysozyme, RNA polymerase, RNA transcriptase, reverse transcriptase, etc.
  • Some common viral diseases are common cold, AIDS, swine flu, hepatitis.

Q12. Organize a discussion in your class on the topic; Are viruses living or nonliving?


Viruses are considered to be intermediates between living and non-living entities. They resemble living beings in the following aspects:

  Viruses are made up of organic macromolecules which is a characteristic of only living    beings.

  1. Viruses possess genetic material.
  2. In the presence of a suitable host, viruses reproduce or multiply.
  3. Viruses show the presence of enzymes like transcriptase, vitamins like riboflavin, etc.
  4. Viruses can show mutations, antigenic properties, infectivity, host specificity, etc.

Thus, based on these features, viruses must be categorized as living. However, viruses also resemble non-living characters in the following aspects:

  1. Viruses lack protoplast.
  2. Viruses are unable to live independently as living cells.
  3. Viruses do not show respiration, energy-storing system, growth, division, etc.
  4. Viruses can be crystallized.

Thus, based on these features viruses can be classified as non-living. The status of the virus as living or non-living is controversial.


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Also See    
NCERT Solutions for Class 11 Biology Chapter 1 - The Living World NCERT Solutions for Class 11 Biology Chapter 3 - Plant Kingdom NCERT Solutions for Class 11 Biology Chapter 4 - Animal Kingdom
NCERT Solutions for Class 11 Biology Chapter 5 - Morphology of Flowering Plants NCERT Solutions for Class 11 Biology Chapter 6 - Anatomy of Flowering Plants NCERT Solutions for Class 11 Biology Chapter 7 - Structural Organization in Animals
NCERT Solutions for Class 11 Biology Chapter 8 - Cells: The Unit of Life NCERT Solutions for Class 11 Biology Chapter 9 - Biomolecules NCERT Solutions for Class 11 Biology Chapter 10 - Cell Cycle and Division
NCERT Solutions for Class 11 Biology Chapter 11 - Transport in Plants NCERT Solutions for Class 11 Biology Chapter 12 - Mineral Nutrition NCERT Solutions for Class 11 Biology Chapter 13 - Photosynthesis in Higher Plants
NCERT Solutions for Class 11 Biology Chapter 14 - Respiration in Plants NCERT Solutions for Class 11 Biology Chapter 15 - Plant Growth and Development NCERT Solutions for Class 11 Biology Chapter 16 - Digestion and Absorption
NCERT Solutions for Class 11 Biology Chapter 17 - Breathing and Exchange of Gases NCERT Solutions for Class 11 Biology Chapter 18 - Body Fluids and Circulation NCERT Solutions for Class 11 Biology Chapter 19 - Excretory Products and their Elimination
NCERT Solutions for Class 11 Biology Chapter 20 - Locomotion and Movement NCERT Solutions for Class 11 Biology Chapter 21 - Neural Control and Coordination NCERT Solutions for Class 11 Biology Chapter 22 - Chemical Coordination and Integration

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