આ MCQ મોડ્યુલ આના પર આધારિત છે: NCERT Exercises and Solutions: Biological Classification
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NCERT Exercises and Solutions: Biological Classification
🎓 Class 11
Biology
CBSE
Theory
Ch 2 – Biological Classification
⏱ ~8 min
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આ મૂલ્યાંકન આના પર આધારિત હશે: NCERT Exercises and Solutions: Biological Classification
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NCERT Exercises and Solutions: Biological Classification
2.6 Viruses, Viroids and Lichens — Beyond the Five Kingdoms
Whittaker's five kingdoms are a tidy framework, but a handful of biological objects defy them altogether. Viruses and viroids are not cellular — they do not fit any kingdom. Lichens are a partnership of two kingdoms living as one. Biology keeps its rebels here.
Viruses — Living or Non-living?
A virus is a molecular parasite that blurs the boundary of life. Outside a living host it behaves like a mineral — it can even be crystallised and stored on a shelf. Inside a host, however, it hijacks the cellular machinery and makes thousands of copies of itself.
Discovery Timeline
- Ivanowsky (1892) — showed that the agent of tobacco mosaic disease passed through filters that hold back bacteria; he called these "filterable agents".
- M.W. Beijerinck (1898) — demonstrated that the filtered extract could infect healthy tobacco plants; he named it contagium vivum fluidum — "contagious living fluid".
- W.M. Stanley (1935) — purified and crystallised the tobacco mosaic virus, proving that these agents are largely protein bound to nucleic acid.
Structure
Every virus consists of two parts:
- Nucleic acid — DNA or RNA, never both. This is the genome.
- Protein coat (capsid) — built from repeating subunits (capsomeres) that give the virus its geometric shape.
| Host | Genetic material | Typical example |
|---|---|---|
| Plants | Single-stranded RNA (ssRNA) | Tobacco mosaic virus (TMV) |
| Animals | ssRNA, dsRNA or dsDNA | Influenza, HIV, herpes |
| Bacteria (bacteriophages) | Double-stranded DNA (dsDNA) | T4 phage of E. coli |
Viral Diseases
In humans: mumps, smallpox, herpes, influenza, common cold, AIDS.
In plants: mosaic disease (tobacco, potato), leaf-rolling, leaf-curling, yellow vein disease, dwarfing.
Viroids — Even Simpler than Viruses
A viroid is a tiny, naked molecule of RNA — with no protein coat. Discovered by T.O. Diener (1971) as the agent of potato spindle tuber disease, viroids are the smallest known infectious agents. They are smaller than the genome of the smallest virus.
Prions — Infectious Proteins
A prion is a misfolded protein that coerces normal cellular proteins to misfold like itself. Prions contain no nucleic acid at all, yet they spread disease — bovine spongiform encephalopathy (mad cow disease) in cattle and Creutzfeldt-Jakob disease (CJD) in humans.
Lichens — A Partnership of Two Kingdoms
A lichen is a living contract between a fungus (the mycobiont) and an alga (the phycobiont). Neither partner could survive alone in the harsh habitats that lichens inhabit.
- The alga photosynthesises and provides organic food (sugars) to the fungus.
- The fungus gives the lichen its shape, shelters the algal cells from drying out, and absorbs minerals and water from the substrate.
Because lichens draw minerals directly from the atmosphere, they are extremely sensitive to polluted air — especially sulphur dioxide. Their absence is a dependable signal of contaminated air; their abundance, a clean one. Thus, lichens are natural pollution indicators and also pioneer colonisers of bare rock, preparing soil for mosses and ferns.
Chapter Summary
- Aristotle gave the first scientific classification; Linnaeus popularised the Two Kingdom scheme (Plantae, Animalia).
- R.H. Whittaker (1969) introduced the Five Kingdom scheme — Monera, Protista, Fungi, Plantae, Animalia — based on cell type, cell wall, body plan, nutrition and reproduction.
- Monera — all prokaryotes. Include archaebacteria (extreme habitats), eubacteria (cyanobacteria, chemosynthetic, heterotrophic) and the wall-less mycoplasmas.
- Protista — unicellular eukaryotes: chrysophytes (diatoms), dinoflagellates, euglenoids, slime moulds and protozoans.
- Fungi — heterotrophic eukaryotes with chitin walls. Classes: Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes.
- Plantae — multicellular autotrophic eukaryotes with cellulose walls; exhibit alternation of generations.
- Animalia — multicellular heterotrophic eukaryotes without cell walls; holozoic; sensory-neuromotor; mostly sexual reproduction.
- Viruses, viroids and prions are non-cellular agents outside all kingdoms. Lichens are alga-fungus partnerships and excellent pollution indicators.
Key Terms
Monera
Protista
Fungi
Plantae
Animalia
Archaebacteria
Eubacteria
Cyanobacteria
Mycoplasma
Protozoa
Diatom
Dinoflagellate
Euglenoid
Slime Mould
Mycelium
Hyphae
Phycomycetes
Ascomycetes
Basidiomycetes
Deuteromycetes
Virus
Viroid
Prion
Lichen
Phycobiont
Mycobiont
Red tide
Algal bloom
NCERT Exercises — Chapter 2
1. Discuss how classification systems have undergone several changes over a period of time.
Classification has evolved in step with our ability to see into the microscopic world. Aristotle made the first scientific attempt (~350 BCE) using simple morphology — herbs/shrubs/trees and red-blooded/bloodless animals. Linnaeus (18th century) formalised a Two Kingdom scheme (Plantae, Animalia) that served until the microscope showed it was inadequate — it failed to separate prokaryotes from eukaryotes, photosynthetic from non-photosynthetic, and unicellular from multicellular organisms. In 1969 R.H. Whittaker proposed the Five Kingdom system based on cell type, cell wall, body plan, nutrition, reproduction and phylogeny — the scheme used today.
2. State two economically important uses of: (a) heterotrophic bacteria (b) archaebacteria.
(a) Heterotrophic bacteria — (i) produce curd from milk (Lactobacillus) and aid in cheese/yoghurt making; (ii) fix atmospheric nitrogen in legume root nodules (Rhizobium), increasing soil fertility and crop yield.
(b) Archaebacteria — (i) methanogens in the gut of cattle produce methane, which is harnessed as biogas (gobar gas); (ii) thermoacidophiles and halophiles yield heat- and salt-tolerant enzymes used in industrial processes and biotechnology.
(b) Archaebacteria — (i) methanogens in the gut of cattle produce methane, which is harnessed as biogas (gobar gas); (ii) thermoacidophiles and halophiles yield heat- and salt-tolerant enzymes used in industrial processes and biotechnology.
3. What is the nature of cell-walls in diatoms?
Diatom cell walls are made of two overlapping halves that fit together like a soap-dish. They are embedded with silica, making them indestructible. After the cells die, these glassy shells pile up on the sea floor as diatomaceous earth, used in polishing, filtration and as a mild abrasive.
4. Find out what do the terms 'algal bloom' and 'red-tides' signify.
Algal bloom: an explosive multiplication of algae (often cyanobacteria) in water bodies enriched with nutrients, producing a thick green scum that depletes oxygen and suffocates fish.
Red tide: a sudden bloom of red-pigmented dinoflagellates (e.g., Gonyaulax) in the sea. The water turns rusty-red and the toxins released poison fish and, through shellfish, humans.
Red tide: a sudden bloom of red-pigmented dinoflagellates (e.g., Gonyaulax) in the sea. The water turns rusty-red and the toxins released poison fish and, through shellfish, humans.
5. How are viroids different from viruses?
A virus has two parts: a nucleic acid (DNA or RNA) core wrapped in a protein coat (capsid). A viroid is simply a short circular strand of RNA alone — no protein coat. Viroids are therefore smaller and structurally simpler than viruses. Discovered by T.O. Diener (1971) as the cause of potato spindle tuber disease.
6. Describe briefly the four major groups of Protozoa.
(i) Amoeboid protozoans — move and feed by pseudopodia; freshwater, marine or soil; Amoeba is free-living, Entamoeba causes dysentery.
(ii) Flagellated protozoans — propel by flagella; Trypanosoma causes sleeping sickness.
(iii) Ciliated protozoans — covered with cilia; swim rapidly in water; Paramecium.
(iv) Sporozoans — parasitic protozoans with an infectious spore-like stage; Plasmodium causes malaria.
(ii) Flagellated protozoans — propel by flagella; Trypanosoma causes sleeping sickness.
(iii) Ciliated protozoans — covered with cilia; swim rapidly in water; Paramecium.
(iv) Sporozoans — parasitic protozoans with an infectious spore-like stage; Plasmodium causes malaria.
7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Yes. Insectivorous plants such as Venus flytrap (Dionaea), pitcher plant (Nepenthes) and Bladderwort (Utricularia) trap and digest insects to obtain nitrogen from nutrient-poor soil. Parasitic plants such as Cuscuta (dodder) and Loranthus tap directly into the host's vascular tissue. All of these still photosynthesise to some extent — hence "partially heterotrophic".
8. What do the terms phycobiont and mycobiont signify?
They are the two partners of a lichen. The phycobiont is the algal partner (often a green alga or cyanobacterium) that performs photosynthesis. The mycobiont is the fungal partner that provides the physical structure, absorbs minerals and water, and protects the alga. Together they form a self-sufficient dual organism.
9. Give a comparative account of the classes of Kingdom Fungi under the following: (i) mode of nutrition (ii) mode of reproduction.
| Class | Nutrition | Asexual | Sexual |
|---|---|---|---|
| Phycomycetes | Saprophytic / parasitic (mostly aquatic, on dung/damp wood) | Zoospores or aplanospores (in sporangia) | Zygospore formation |
| Ascomycetes | Mostly saprophytic; some parasitic or coprophilous | Conidia on conidiophores | Ascospores in asci (ascocarp) |
| Basidiomycetes | Saprophytic (wood decomposers), parasitic (rusts, smuts) | Rare; mostly by fragmentation | Basidiospores on basidia (basidiocarp) |
| Deuteromycetes | Saprophytic or parasitic; many are decomposers | Conidia (the only known spores) | Sexual stage not known |
10. What are the characteristic features of Euglenoids?
Euglenoids are mostly freshwater protists. They lack a rigid cell wall; instead the cell is covered by a flexible, protein-rich pellicle. Two flagella of unequal length emerge from the anterior end — one long, one short. A red photoreceptive spot ("eyespot") helps orient the cell to light. In sunlight euglenoids are photosynthetic (carrying chloroplasts); in darkness they feed heterotrophically on small organisms and particles. Euglena is the classic example.
11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.
A virus is a non-cellular, obligate parasite consisting of a nucleic-acid core wrapped in a protein coat (capsid) built from subunits called capsomeres. The genetic material is either DNA or RNA — never both. Plant viruses usually carry single-stranded RNA (ssRNA); animal viruses can carry ssRNA, dsRNA or dsDNA; bacteriophages typically carry dsDNA.
Four common viral diseases in humans: mumps, smallpox, influenza, AIDS. (Others: common cold, herpes, polio, chickenpox.)
Four common viral diseases in humans: mumps, smallpox, influenza, AIDS. (Others: common cold, herpes, polio, chickenpox.)
12. Organise a discussion in your class on the topic "Are viruses living or non-living?"
A balanced view:
Arguments for living: Viruses contain genetic material (DNA/RNA); they reproduce and make faithful copies of themselves; they undergo mutation and evolve (witness new strains of influenza); they can infect and cause disease.
Arguments for non-living: They are not cellular; they show no metabolism of their own — all metabolic activity occurs only inside a host; outside the host they can even be crystallised like a mineral and stored indefinitely.
Conclusion: Viruses occupy a grey zone — they are best described as "obligate intracellular parasites on the edge of life".
Arguments for living: Viruses contain genetic material (DNA/RNA); they reproduce and make faithful copies of themselves; they undergo mutation and evolve (witness new strains of influenza); they can infect and cause disease.
Arguments for non-living: They are not cellular; they show no metabolism of their own — all metabolic activity occurs only inside a host; outside the host they can even be crystallised like a mineral and stored indefinitely.
Conclusion: Viruses occupy a grey zone — they are best described as "obligate intracellular parasites on the edge of life".
13. List the four basic shapes of bacteria with one example of each. L1 Remember
Coccus (spherical) — Streptococcus; Bacillus (rod) — Bacillus subtilis; Vibrio (comma) — Vibrio cholerae; Spirillum (spiral) — Spirillum volutans.
14. Why are lichens regarded as good pollution indicators? L3 Apply
Lichens absorb all their minerals directly from the atmosphere, without the filtering effect of soil. Pollutants such as SO₂ dissolve in the cells and quickly kill the alga, killing the lichen. A healthy lichen flora therefore means clean air, while absence of lichens on tree trunks in a city signals air contamination.
15. Differentiate between septate and coenocytic mycelium with examples. L2 Understand
Septate mycelium has cross-walls (septa) dividing each hypha into separate cells; found in Ascomycetes, Basidiomycetes, Deuteromycetes (Penicillium, Agaricus). Coenocytic mycelium lacks cross-walls — the hypha is a continuous multinucleate tube; found in Phycomycetes (Rhizopus, Mucor).
Competency-Based Questions
A botany researcher collects lichens from three sites: a forest 50 km outside Delhi, a roadside tree inside Delhi, and a tree next to a coal-burning power plant. She finds abundant lichens on the forest tree, very few on the roadside tree and none near the power plant.
Q1. Explain the observation in terms of air quality. L3 Apply
Lichens absorb minerals and water from the atmosphere and are extremely sensitive to SO₂ and other pollutants. The forest has clean air (abundant lichens); the roadside has moderate vehicle pollution (few lichens); the power plant area is heavily polluted with SO₂ (no lichens).
Q2. Which partner inside the lichen is being killed first by SO₂? L4 Analyse
The algal partner (phycobiont) is typically affected first. SO₂ damages chlorophyll and blocks photosynthesis; once the alga dies, the fungal partner starves and the whole lichen collapses.
Q3. Viroids are best described as: L1 Remember
(b) Naked RNA molecules without a protein coat — discovered by T.O. Diener (1971) as the cause of potato spindle tuber disease.
Q4. Why are prions sometimes described as "the most unusual pathogens known"? L5 Evaluate
Prions contain no nucleic acid at all — they are just misfolded proteins. Yet they multiply (by converting normal proteins into misfolded copies) and cause fatal diseases like BSE ("mad cow") and Creutzfeldt-Jakob disease. Every other pathogen — bacteria, virus, viroid — carries at least some nucleic acid. Prions therefore overturn the idea that DNA/RNA is essential for infection.
Q5. A plant virus infects a tobacco plant and a bacteriophage infects E. coli. Compare their genetic material and structure. L4 Analyse
The plant virus (e.g., TMV) carries single-stranded RNA and has a simple rod-shaped capsid of repeating protein subunits. The bacteriophage (T4) carries double-stranded DNA packed inside an icosahedral head, with a contractile tail, base plate and tail fibres that attach to and inject DNA into the bacterial cell — a far more elaborate architecture suited to penetrating a thick bacterial wall.
Assertion–Reason Questions
Options: (A) Both A and R are true; R explains A. (B) Both true; R does not explain A. (C) A true, R false. (D) A false, R true.
Assertion (A): Lichens are good pollution indicators.
Reason (R): Lichens absorb minerals only from soil and therefore resist airborne pollutants.
(C) — A is true but R is false. Lichens absorb minerals directly from the atmosphere, making them sensitive to airborne pollutants such as SO₂, which is why they indicate pollution.
Assertion (A): Viruses can be crystallised.
Reason (R): Outside a host cell, viruses behave like inert chemicals.
(A) — Both true; R correctly explains A. W.M. Stanley (1935) crystallised TMV on this basis.
Assertion (A): Viroids are smaller than viruses.
Reason (R): Viroids have only a free RNA molecule without any protein coat.
(A) — Both true; R correctly explains A.
Frequently Asked Questions - NCERT Exercises and Solutions: Biological Classification
What are the most-asked NCERT exercise questions in Chapter 2 Biological Classification?
NCERT Class 11 Biology Chapter 2 Biological Classification exercises cover definitions, classification, structure-function relationships, labelled diagrams, and application-based questions. The MyAiSchool exercise set provides full step-by-step solutions for every NCERT question, aligned with the CBSE board exam pattern. Students should master scientific terminology, diagram labelling, and concept comparison tables to score full marks.
How should students approach labelled diagram questions in Biological Classification?
For labelled diagram questions in NCERT Class 11 Biology Chapter 2 Biological Classification: (1) draw a clean, large, proportional diagram with sharp pencil lines, (2) label each part with horizontal lines on the right or left side, (3) use scientific terminology (Latin/Greek names where applicable), (4) write a 1-2 line description below if asked. The MyAiSchool solutions provide editable reference diagrams aligned with NCERT textbook figures.
What types of CBSE board questions come from Chapter 2?
CBSE Class 11 Biology board questions from Chapter 2 (Biological Classification) typically include: (1) 1-mark MCQs on definitions and classification, (2) 2-mark short-answers on structure-function or comparisons, (3) 3-mark labelled-diagram questions, (4) 5-mark long-answer essays combining diagram + description + significance. The MyAiSchool exercise set tags each question by mark weight and Bloom level (L1-L6).
How do I compare two biological concepts in 5-mark questions?
For 5-mark comparison questions in NCERT Class 11 Biology Chapter 2: (1) use a two-column table with feature headings down the left side, (2) compare on at least 5-6 features (structure, function, location, examples, significance), (3) include one labelled diagram if relevant, (4) end with one line on biological significance. The MyAiSchool solutions follow this CBSE-aligned tabular format consistently for full marks.
What are common mistakes in Chapter 2 exercises?
Common mistakes in NCERT Class 11 Biology Chapter 2 (Biological Classification) include: (1) confusing similar scientific names or terminology, (2) skipping diagram labels or drawing too small, (3) missing examples in classification questions, (4) writing essay-style answers when a table is expected, (5) forgetting to mention biological significance. The MyAiSchool solutions highlight these traps so students avoid losing marks unnecessarily.
How does the MyAiSchool solution differ from other NCERT solution sets?
MyAiSchool Class 11 Biology Chapter 2 Biological Classification solutions use NEP 2024-aligned pedagogy with Bloom Taxonomy tagged questions (L1 Remember to L6 Create), step-by-step working with biological reasoning, fully labelled SVG diagrams, comparison tables, interactive simulations, and Competency-Based Questions (CBQs) for board exam practice. Each solution is verified against NCERT textbook and CBSE marking schemes.
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