NCERT Solutions Class 11 Biology Chapter 2

NCERT Solutions for Class 11 Biology Chapter 2 

Class 11 Biology Chapter 2, titled “Biological Classification,” sheds light on the characteristics of the Kingdom Monera, Fungi, and Protista as defined by the Whittaker System of Classification. This chapter describes the plant and animal kingdoms, which are technically known as Kingdoms Plantae and Animalia, respectively. Apart from the five Kingdoms mentioned above, the Kingdoms of Viroids, Lichens, and Viruses are also discussed in Biological Classification. 

There are practise questions at the end to help students gauge their understanding of the topics explained in the chapter. Students looking for answers to the questions can refer to NCERT Solutions for Class 11 Biology Chapter 2 by Extramarks.

NCERT Solutions for Class 11 Biology Chapter 2 – Biological Classification 

The NCERT Solutions for Class 11 Biology Chapter 2 by Extramarks is created with the sole purpose of assisting students in solving NCERT textbook questions accurately. Students can access the solutions by clicking here:

NCERT Solutions for Class 11 Biology Chapter 2 – Biological Classification 


NCERT Solutions for Class 11 Biology Chapter 2 – Biological Classification 

The process of scientists grouping living organisms is referred to as biological classification. In Chapter 2, students will learn about the different kingdom classifications proposed by biologists Linnaeus and R. H. Whittaker. Linnaeus divided organisms into two kingdoms: Animalia for animals and Plantae for plants, while R. H. Whittaker divided them into five kingdoms. 

In the NCERT Biology Class 11 Chapter 2, each kingdom is thoroughly discussed, allowing you to prepare more quickly and effectively. Diagrams are also included to help you visualise the organisms. Let’s go over the topics covered in this chapter of Class 11 Biology. 

What is Biological Classification? 

Biological classification is a method by which scientists classify all organisms into hierarchical groups and subgroups based on their characteristics and environment. 

Aristotle was the first scientist to use scientific classification to classify organisms. He divided the plants into trees, shrubs, and herbs based on their morphological characteristics. 

The living organisms were divided into five kingdoms by RH Whittaker: Monera, Protista, Fungi, Plantae, and Animalia. He classified the organisms based on the characteristics listed below: 

  • Cell type
  • Cell Wall
  • Nuclear membrane
  • Body 
  • Mode of nutrition

Classification of Five Kingdoms

The five kingdoms are classified as follows: Monera, Protista, Fungi, Plantae, and Animalia. The thallus organisation, cell structure, diet, phylogenetic relationship, and reproduction, all played a role in the classification. 

Monera Kingdom: 

Prokaryotic microorganisms such as bacteria belonging to the Monera Kingdom.

  • They do not contain well-defined nuclei. 
  • Organelles bound to the cell membrane aren’t present. 
  • They live as free-living or parasitic organisms in extreme environments, such as springs, snow, and deep oceans. 


They are classified into the following categories based on their shape: 

  • Coccus (cocci) – Spherical 
  • Bacillus (bacilli) – Rod-shaped 
  • Vibrium (vibrio) – Comma-shaped 
  • Spirillum (spirilla) – Spiral-shaped 


Here are the different modes of nutrition for bacteria:

  • Autotrophic 
  • Chemotrophic 
  • Saprophytic 
  • Heterotrophic 

Protista Kingdom: 

Unicellular eukaryotes are included in the Protista Kingdom. 


  • They have a well-defined nucleus and organelles that are membrane-bound. 
  • They reproduce through both sexual and asexual modes. 
  • They are photosynthetic and live in marine water. 
  • They have a yellow, green, brown, and red appearance due to the presence of various pigments. 


Protista is divided into five groups based on their habitat. 

  • Chrysophytes 
  • Dinoflagellates 
  • Euglenoid 
  • Slime mould 
  • Protozoans 


Diatoms and golden algae, known as desmids, are chrysophytes. As in a soapbox, the diatom’s cell wall is embedded with silica and forms two thin overlapping sheaths. Diatoms are used in oil and syrup filtration and polishing.


Dinoflagellates are photosynthesis and marine microorganisms. They assist marine plants in photosynthesis. Gonyaulax, a red dinoflagellate, is one type of dinoflagellate that reproduces rapidly and forms red tides. 


It’s a type of freshwater organism that lives in still water. Euglenoid acts as autotroph (uses chloroplasts to produce sugar through photosynthesis) in the presence of sunlight and as heterotroph (does not use chloroplasts to produce sugar through photosynthesis) when there is no sunlight. 

Slime Moulds 

Slime moulds are saprophytes, meaning they rely on dead and decayed organic matter to survive. They form plasmodium, which is a type of aggregation. They produce highly resistant spores in unfavourable conditions. 


Heterotrophs are protozoans. They are either predators or parasites. 

Classification of Protozoans 

Amoeboid Protozoans can be found in both fresh and saltwater. They have irregular bodies that change shape frequently. 

Flagellated Protozoans are parasitic microorganisms that live on their own. Trypanosoma is an example. 

Ciliated Protozoans are active-moving aquatic organisms. For example paramecium 

Sporozoans include spore-forming infectious agents, such as Plasmodium, the malaria-causing parasite. 

Fungi Kingdom: 

Heterotrophic organisms are included in the fungi kingdom, and they rely on Extracellular digestion. 


  • They can be found in the air, water, soil, or even animals. 
  • Fungi are filamentous and produce hyphate, which are long, slender, thread-like structures. 
  • Chitin makes up the cell wall. 
  • They can be parasitic or saprophytic. 
  • They have a symbiotic relationship with lichens, which are algae, and mycorrhiza, which are the roots of higher plants. 
  • Fungi reproduce asexually through vegetative means such as fragmentation, fission, budding, or the formation of conidia/sporangia spores/ zoospores. 
  • Oospores, ascopores, and basidiospores are used in sexual reproduction. 

Note: A phycobiont is an algal component of a lichen, while a mycobiont is a fungal component. Algae provide food for fungi, and fungi provide algae with shelter.

Fungi Classification: 

Fungi are classified into different classes based on their mycelium mode of spore formation and fruiting bodies. 

  • Phycomycetes are plant parasites. The mycelium is coenocytic and septate. 
  • Mushrooms, bracket fungi, and puffballs are all basidiomycetes. Their mycelium is septate and branched. 
  • Ascomycetes, or sac fungi, are multicellular fungi like Penicillium. Their mycelium is septate and branched. 
  • Deuteromycetes are known as imperfect fungi because they lack sexual reproduction. Mycelium is branched and septate. 

Plantae Kingdom: 

Chlorophyll-containing, eukaryotic autotrophic organisms are a part of the Plantae kingdom.


  • As in the case of insectivorous plants like Cuscuta, they can be partially autotrophic and partially heterotrophic. 
  • They have a nucleus, chloroplast, and cellulosic cell walls that are all distinct. 

Note that plants are autotrophs, meaning they prepare their own food through photosynthesis. 

They are heterotrophic in part because their food requirements are met in part by other organisms. 

Animalia Kingdom: 

The kingdom Animalia is made up of heterotrophic eukaryotic, multicellular organisms. 


  • Their cells are devoid of cell walls. 
  • Food is consumed in a holozoic mode of nutrition. 
  • Food is stored in the form of glycogen or fat. 
  • They have specialised sensory and neuromotor systems and are capable of locomotion. 
  • They have distinct patterns of growth. 
  • They reproduce through sexual means. 


Viruses are acellular structures, and that’s why they do not fit into Whittaker’s five kingdom classification system. They are made up of nucleic acid (DNA or RNA) that is encased in a protein coat. Only a host cell can grow and multiply these viruses. Viruses exist outside of the host cell as crystals. They infect the host and cause significant damage. Cold, flu, polio, and AIDS are examples of common viruses. 


They are the tiniest infectious structures known, containing only nucleic acid and no protein shell. 


Algae and fungi are known to form symbiotic relationships. The two algae are autotrophic, meaning they synthesise their own food. The mushroom pair provides both safety and shelter. 

Q.1 Discuss how classification systems have undergone several changes over a period of time?


The biological classification system has undergone tremendous change guided by scientific understanding and a need to define and categorize each organism precisely on the basis of its morphological, anatomical and genetic attributes. The steps given below show how the present system of classification has evolved into its form.

  • The earliest methods of classification were based out of the need to use plants or animals and didn’t have any scientific basis.
  • Aristotle defined a classification method whereby he used the morphological characters to classify plants and animals.
  • Linnaeus defined a two-kingdom system of plants and animals. this included all plants and animals irrespective of their varied forms and features.
  • R.H.whittaker (1969) proposed a five-kingdom classification system. This mode of classification system includes cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationship. In this classification system, a clear differentiation between photosynthetic and non-photosynthetic organisms was made.

Q.2 State two economically important uses of:

(a) heterotrophic bacteria

(b) archaebacteria


The two economic uses of heterotrophic bacteria are:

  • Many heterotrophic bacteria help in decomposing dead and decaying organisms. This leads to the production of humus which increases soil fertility.
  • Heterotrophic bacteria are also used in the production of antibiotics. Many known antibiotics are produced by Streptomyces, which are filamentous soil bacteria.

The two economic uses of archaebacteria are:

  • Methanogens are archaebacteria that produce methane gas as a metabolic bi-product. These bacteria are naturally found in the dung of cows and buffaloes. Some examples of methanogens are Methanococcus jannaschii and Methanobacterium thermoautotrophicum. Methanogens are used for commercial production of methane gas.
  • Methanogens are also useful for the treatment of sewage in villages and municipal sewage treatment plants. Under anaerobic conditions soluble carbon compounds of wastes and wastewater are degraded stepwise to methane and other gases.

Q.3 What is the nature of cell-walls in diatoms?


In diatoms, the cell walls form two thin overlapping shells, which fit together closely. The walls cannot be destroyed as they are embedded with silica. The cell walls show a wide diversity in form but are usually almost bilaterally symmetrical, hence the group name – diatom.

Q.4 Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.


Algal bloom: The algal bloom is a phenomenon occurs when contaminants like nitrates and phosphates from untreated sewage are released into water bodies. the presence of an excessive amount of nutrients such as nitrates and phosphates overstimulate the growth of algae. This overstimulation of algal growth (algal bloom) reduces the dissolved oxygen content of the water, which in turn causes other life forms to perish. Algal bloom affects water quality and causes fish and other aquatic life mortality. Some algae can be toxic to humans too.

Algal blooms are often green but they could also be other colours like red or green depending upon the predominant species of algae causing the bloom.

Red Tides: Red or brown coloured algal blooms are called red tides. Red tides are caused by red dinoflagellates (example Gonyaulax) which accumulate due to rapid multiplication making the sea appear red. Toxins released by such large numbers of algae may kill other marine animals such as fish.

Q.5 How are viroids different from viruses?


The difference between viroids and viruses are as follows:

Viroid Virus
Genome size 246 to 467 nucleotide long 2 kb or more in size
RNA/ DNA Highly complimentary, circular single-stranded RNA Known to be RNA, DNA double-stranded or single-stranded
Protein Coat Absent Present
Host Plant pathogen Both plant and animals
Discovery Potato spindle tuber viroid by Theodor Otto Diener in 1971 Tobacco mosaic virus by Martinus Beijerinck in 1898
Number known Around 30 Around 5000 described in detail but millions more known to exist.

Q.6 Describe briefly the four major groups of Protozoa.


The four major groups of protozoans are as follows:

Amoeboid protozoans:

  • Found in fresh water, sea water or moist soil
  • Move and capture the prey by using pseudopodia (false feet) as in Amoeba
  • Marine forms have silica shells on their surface
  • Some are parasites e.g. Entamoeba

Flagellated protozoans:

  • Free-living or parasitic
  • Movement by flagella
  • The parasitic forms cause diseases such as sleeping sickness. Example: Trypanosoma

Ciliated protozoans:

  • Aquatic and very motile
  • Presence of hair-like organelles called cilia on the pellicle (cell body). Cilia are shorter than flagella and occur in large numbers. Cilia are used for movement and food gathering.
  • Presence of a cavity (gullet) that opens to the outside of the cell surface.
  • Rows of cilia move in a synchronised manner for locomotion and also to steer food into the gullet. Example: Paramecium


  • Parasitic protozoans
  • They lack organelles for locomotion like cilia or flagella
  • All sporozoans lack contractile vacuole
  • They have complex life cycles a part of which is spent in host organisms
  • Some sporozoans pass from host to host via an infectious spore stage
  • Example: Plasmodium (malarial parasite) which causes malaria

Q.7 Plants are autotrophic. Can you think of some plants that are partially heterotrophic?


Plants are mostly autotrophic which means that they possess the pigment chlorophyll. With the help of chlorophyll, they manufacture their own food by performing photosynthesis. However, a few members of the plant kingdom are partially heterotrophic, for example, the insectivorous plants or parasites. These plants typically grow in nitrogen and mineral deficient soils and compensate for their nutritional requirement by their partial heterotrophic nature. These insectivorous plants have evolved mechanisms to trap insects from which they derive minerals and nutrition. Bladderwort and Venus flytrap are examples of insectivorous plants.

The other partially heterotrophic plant is Cuscuta that lives like a parasite on many trees and absorbs nutrition from the host plant.

Q.8 What do the terms phycobiont and mycobiont signify?


The phycobiont and mycobiont are the algal and fungal partners, respectively, which are in a symbiotic relationship with each other in nature. These are known as lichens and this is a mutually beneficial partnership. The algal partner, phycobiont (also called photobiont) is autotrophic and provides food to the fungi. The fungal or mycobiont partner provides shelter, nutrients and water to the algal partner.

Q.9 Give a comparative account of the classes of Kingdom Fungi under the following:

(i) Mode of nutrition

(ii) Mode of reproduction


(i) Mode of nutrition

(ii) Mode of reproduction

Q.10 What are the characteristic features of Euglenoids?


Characteristic features of Euglenoids are:

  • Euglenoids are a group of flagellates commonly found in stagnant pools of freshwater and ditches or damp soil.
  • Instead of a cell wall, they have a protein-rich layer called pellicle which makes their body flexible. The pellicle is composed of proteinaceous strips underneath the cell membrane giving them a distinctive striation.
  • They have one or two flagella that they use for swimming. Those have two flagella, one is short and another is long. Both the flagella are used for locomotion.
  • They are photosynthetic in the presence of sunlight, however, when deprived of sunlight they behave like heterotrophs by predating on other smaller organisms.
  • Euglena reproduces by fission. It splits lengthwise into two.
  • The euglenoids have chlorophyll a and chlorophyll b and they store their photosynthetic product in an unusual form called paramylon starch.

Q.11 Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.


A complete virus particle is known as virion. It consists of nucleic acid, either DNA or RNA, surrounded by a coat of protein called capsid. These are formed from identical protein subunits called capsomeres. Proteins associated with nucleic acid are known as nucleoproteins, and the association of viral capsid proteins with viral nucleic acid is called a nucleocapsid. Viruses are classified into four types based on their structure:

Polyhedral / icosahedral Viruses: These are non-enveloped viruses in which the capsomeres are arranged in geometric shape around the genetic material which is either double or single-stranded DNA or RNA. The icosahedron shape has 20 equilateral triangle faces and 12 corners. Example: polio causing virus

Helical viruses: These viruses are non-enveloped with capsomeres arranged as a helix around the nucleic acid giving rise to elongated rods or flexible filaments. Example: tobacco mosaic virus

Complex viruses: The complex viruses have complex combinations of structures that may or may not be completely consistent between viruses of the same species. Example tailed bacteriophage, poxviruses.

Enveloped viruses: These viruses are helical and icosahedrons shapes but have an outer envelope that surrounds the virus capsomeres. The envelope is a lipid bilayer containing glycoproteins embedded in the lipid. Example: Herpes virus.

Genetic Material of Viruses:

  • It can be RNA or DNA but not both at the same time in a virus.
  • Viruses infecting plants have single-stranded RNA.
  • Viruses infecting animals have either single or double-stranded RNA or double-stranded DNA.
  • Bacteriophages usually have double-stranded DNA.

Four viral diseases: Rabies, Influenza, Herpes, HIV

Q.12 Organise a discussion in your class on the topic – Are viruses living or non-living?


The debate whether viruses are living or non-living is an old one and till today, a consensus has not been reached.

Characteristics that classify viruses as living:

  • They have complex molecule assemblies that include nucleic acids, proteins, carbohydrates, lipids and genetic material.
  • They also make copies of themselves to reproduce.
  • They are sensitive to external factors such as temperature, chemicals and radiations.

Characteristics that classify viruses as non-living:

  • They cannot replicate on their own – they need a host cell to provide them with the machinery to replicate.
  • They can remain in the dormant state forever till they find the right host to multiply.
  • They have only one type of nucleic acid, i.e., either DNA or RNA. All the living things possess both the types of nucleic acid.

Though it is challenging to categorise viruses, it can be said with enough confidence that viruses are some form of life. Nature is so diverse that the classification system that humans have made for their ease of use may not fit that diversity.

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FAQs (Frequently Asked Questions)

1. Is Biology of Class 11 a simple subject?

Class 11 Biology isn’t a difficult subject as such. It does, however, necessitate a significant amount of reading, as well as time and effort on the part of the students. Biology also requires a lot of memorisation. However, keep in mind that memorisation without conceptual understanding is merely a collection of facts that won’t help you much in exams. Biology is a high-scoring subject if you plan ahead of time and work hard from the start of the academic year. 

2. What are the advantages of using the particular NCERT Solutions for Class 11 Biology Chapter 2?

The following are some of the advantages of using the NCERT Solutions Class 11 Biology Chapter 2: 

  1. Solutions are accurate and have been prepared as per the latest guidelines of CBSE
  2. Written in simple language, making it easier for students to understand the concept.
  3. Prepared by subject-matter experts.

3. What is the best way to take notes for "Biological Classification"?

NCERT Biology Class 11 Chapter 2 contains a wealth of useful information, keywords, and characteristics. It’s also a fairly lengthy chapter. As a result, do keep these points in mind when making notes for it: 

  • Only include the most important details. 
  • Create a list of bullet points. 
  • While referring to NCERT Solutions, keep notes that are crisp, clear, and concise. 
  • Wherever possible, use diagrams. 

4. How does the classification of the Five Kingdoms differ from the classification of the Two Kingdoms?

Cell structure (complex eukaryotic or simple prokaryote), body structure (unicellular or multicellular), nutrition (autotrophic or heterotrophic), and lifestyle are all factors in the classification of five kingdoms. As a result, it is more practical than the classification of two kingdoms. 

5. Is the NCERT textbook sufficient for passing exams?

NCERT books are essential for a thorough understanding of all of your fundamentals. The various problems are well-structured, and have varying levels of difficulty. These books provide easy-to-understand explanations of complex topics. The exercises in the NCERT books will give you a good idea of how the paper will be laid out.