Chapter 2 – Biological Classification Questions and Answers: NCERT Solutions for Class 11 Biology

Class 11 Biology NCERT book solutions for Chapter 2 - Biological Classification Questions and Answers.

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

Aristotle was the first to introduce the scientific classification. He used simple morphological characters to classify plants into trees, shrubs, and herbs. He divided the animals into two groups, one with red blood and one without.
Linnaeus introduced a two-kingdom classification, which includes Plantae and Animalia, respectively, of plants and animals. But this classification does not classify eukaryotes and prokaryotes, single-celled and multicellular organisms, photosynthetic (green algae) and non-photosynthetic (fungal) organisms. Therefore, the system was found to be less significant as it did not include more features.
Thus, the classification of living organisms has undergone several changes. R.H. Whittaker introduced five-kingdom classification, including Monera, Protista, Fungi, Plantae and Animalia. Some of the characteristics included in this classification – the structure of cells, body organization, mode of nutrition, mode of reproduction, and phylogenetic relationship to classify organisms. Subsequently, a three-domain system was proposed, which divided Kingdom Monera into two domains, leaving the remaining eukaryotic kingdoms in the third domain, thereby classifying the six kingdom.

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

a) Heterotrophic bacteria are used in the production of vitamins, antibiotics, cheese and curd.
They help fix nitrogen and are used in the formation of humus.
b) Archaebacteria are used in Biogas production.
They are used in the bioleaching of mines.

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

In diatoms, cell walls are embedded with silica imparting characteristic patterns onto the walls and are indestructible. These diatoms leave large amounts of cell wall deposits in their habitat to accumulate to form the diatomaceous earth.

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

Algal blooms are found in contaminated water. They are an overgrowth of algae, especially blue-green algae (cyanobacteria). Their growth leads to water pollution. They inhale carbon dioxide and exhale oxygen.
Rapid multiplication of red-pigmented dinoflagellates, such asGonaulax, gives the sea a red color, a phenomenon known as red tides. These algae produce toxins that kill fish and other aquatic organisms.

5. How are viroids different from viruses?

(i) Viroids are small infectious agents with single-stranded RNA without a protein coat, but viruses have single-stranded or double-stranded RNA bound with protein-coat.
(ii) Viroids are very small in size compared to viruses.
(iii) Viroids infect only plants, while viruses infect plants, animals, and microorganisms.

6. Describe briefly the four major groups of Protozoa.

Four major groups of Protozoa are as follows
Amoeboid protozoans:Found in aquatic environment; they move and catch their prey using pseudopodia.
Flagellated protozoans:These protozoans are free-living or parasitic. Their locomotory structure is flagella.
Ciliated protozoans:They live in aquatic environments and the presence of cilia makes them actively moving.
Sporozoans:They contain a wide variety of organisms, producing infectious spores throughout their life cycle. Their spore-like phase helps them move from one host to another.

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

Insectivores and carnivores plants are partially heterotrophic, these organisms are green and autotrophic, but they prey and digest small components for their nitrogen supply.

8. What do the terms phycobiont and mycobiont signify?

Lichens are a symbiotic association of fungi and algae. Phycobiont is part of algae and part of mycobiont fungi. Mycobiont provides structural cover that protects the algae from unfavorable conditions. Similarly, phycobionts prepare food by the process of photosynthesis, which is used by both organisms.

9. Give a comparative account of the classes of Kingdom Fungi under the following:
(i) mode of nutrition (ii) mode of reproduction


Mode of nutrition
Saprophytic or parasitic
Decomposers, Saprophytic or parasitic or coprophilous
Decomposers, Saprophytic or parasitic
Mode of reproduction
Asexual reproduction by zoospore (motile) Aplanospore (non-motile)
Sexual reproduction – zygote can be similar or dissimilar in morphology
Through asexual spores called conidia and sexual spores are known as ascospores
By vegetation reproduction through budding.
Fusion of two somatic cells for the formation of basidiospores is Plasmogamy
Through asexual spores called conidia.

10. What are the characteristic features of Euglenoids?

The typical features of Eugenoids are:
(i) Absence of cell wall.
(ii) Their body is flexible because there is a protein-rich layer called pellicle.
(iii) Two flagellas of different length are found.
(iv) They are autotrophic in the presence of sunlight and heterotrophic in the absence of sunlight.

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

Viruses are infectious agents that crystallize in structure when found outside the host cell. The genetic material is either DNA or RNA (never both) and they are located within the protein core. If the virus that infects plants has single-stranded RNA, then the viruses that infect animals are single or double-stranded DNA or RNA. Capsid is their protein coat, which in turn is made up of small subunits called capsomers, which protect nucleic acid.
Common viral diseases are –Influenza, AIDS, Herpes and Rabies.

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

Non-living Characters
(i) No cellular structure
(ii) They can be stored in bottles like crystals
(iii) There will be no energy storage or energy liberation systems
(iv) They cannot grow or multiply outside the host
Living characters
(i) They are host-specific
(ii) The presence of genetic material
(iii) The ability to multiply
(iv) They have antigenic properties
(v) They are obligate parasites
(vi) Mutations occur
List of subtopics covered in Chapter 2 – Biological Classification:
Kingdom Monera
Kingdom Protista
Kingdom Fungi
Kingdom Plantae
Viruses, Viroids, Prions And Lichens