NCERT Exemplar: Biological Classification

Multiple Choice Questions

Q.1. All eukaryotic unicellular organisms belong to
(a) Monera
(b) Protista
(c) Fungi
(d) Bacteria
Ans. (b) Protista
Solution:
Monera is the kingdom of prokaryotes (organisms without a true nucleus and membrane-bound organelles). All eukaryotic unicellular organisms, which possess a true nucleus and membrane-bound organelles, are placed in the kingdom Protista. These include unicellular algae, protozoans and similar forms.

Protista

Q.2. The five-kingdom classification was proposed by
(a) R.H. Whittaker
(b) C. Linnaeus
(c) A. Roxberg
(d) Virchow
Ans. (a) R.H. Whittaker
Solution.
This phylogenetic classification was proposed by R.H. Whittaker (1969). He recognised important differences among organisms and created a separate kingdom Fungi. The five-kingdom classification of Whittaker is:

• Monera
• Protista
• Fungi
• Plantae
• Animalia

Whittaker used five criteria for this classification:

• Reproduction
• Cell structure
• Phylogenetic relationships (evolutionary history)
• Mode of nutrition
• Thallus organisation (level of organisation)

Q.3. Organisms living in salty areas are called:
(a) Methanogens 
(b) Halophiles
(c) Heliophytes 
(d) Thermoacidophiles
Ans. (b) Halophiles
Solution.

• Halophiles: Microorganisms, especially certain Archaea and bacteria, that live and thrive in environments with very high salt concentrations (e.g., salt lakes, salt pans).
• Thermoacidophiles: Microbes that tolerate high temperature and acidic conditions; many are found in hot springs or deep-sea hydrothermal vents. Example: Thermococcus.
• Methanogens: Anaerobic archaea found in marshy, swampy habitats, ruminant guts and sediments; they produce methane (CH4) as a metabolic product.
• Heliophytes: Sun-loving plants (term used for certain plants, not microbes).

Q.4. Naked cytoplasm, multi-nucleated and saprophytic are the characteristics of
(a) Monerans
(b) Protists
(c) Fungi
(d) Slime moulds
Ans. (d) Slime moulds
Solution.
Slime moulds are saprophytic protists that lack rigid cell walls during much of their life cycle; many show a multinucleate, naked cytoplasmic stage called the plasmodium. Their spores, however, have true walls and are dispersed by air currents.

Example:
(i) Acellular slime mould: Physarum
(ii) Cellular slime mould: Dictyostelium

Q.5. An association between roots of higher plants and fungi is called
(a) Lichen 
(b) Fern 
(c) Mycorrhiza 
(d) BGA
Ans. (c) Mycorrhiza
Solution.

• Mycorrhiza: A mutualistic association between fungi (mycobiont) and the roots of higher plants (often gymnosperms and angiosperms) in which fungi assist in water and mineral absorption while receiving carbohydrates from the plant.
• Lichens: Symbiotic association between algae (phycobiont) and fungi (mycobiont); commonly described as mutualistic and sometimes referred to as helotism.

Q.6. A Dikaryon is formed when
(a) Meiosis is arrested
(b) The two haploid cells do not fuse immediately
(c) Cytoplasm does not fuse
(d) None of the above
Ans. (b) The two haploid cells do not fuse immediately
Solution.
In many fungi, after plasmogamy (fusion of cytoplasm), the nuclei from the two haploid partners do not fuse immediately. This results in cells containing two distinct haploid nuclei (n + n) and the condition is called a dikaryon. The dikaryotic phase is characteristic of many Ascomycetes and Basidiomycetes; karyogamy (nuclear fusion) occurs later to form a diploid nucleus, which then undergoes meiosis.

Q.7. Contagium vivum fluidum was proposed by 
(a) D. J. Ivanowsky 
(b) M. W. Beijerinek
(c) Stanley 
(d) Robert Hooke
Ans. (b) M. W. Beijerinek
Solution.

• D.J. Ivanowsky (1892): Demonstrated that the sap of mosaic-infected tobacco remained infectious after passage through filters that retained bacteria; first evidence for a filterable infectious agent.
• M.W. Beijerinck (1898): Reproduced infection from filtered sap and described the infectious agent as a contagious living fluid, coining the term Contagium vivum fluidum (infectious living fluid); he proposed that it was a new form of infectious agent - a virus.
• W. M. Stanley (1935): Demonstrated that tobacco mosaic virus (TMV) could be crystallised; crystals were found to contain largely protein, helping to advance study of viral structure.

Q.8. Association between mycobiont and phycobiont are found in
(a) Mycorrhiza 
(b) Root 
(c) Lichens 
(d) BGA
Ans. (c) Lichens
Solution.
Lichens are composite organisms formed by the symbiotic association of a fungal partner (mycobiont) and a photosynthetic partner, an alga or cyanobacterium (phycobiont). The association is usually mutualistic: the phycobiont provides carbohydrates by photosynthesis and the mycobiont offers protection and absorption of minerals and water.

Q.9. The Difference between Virus and Viroid is
(a) Absence of protein coat in viroid but present in the virus.
(b) Presence of low molecular weight RNA in the virus but absent in viroid.
(c) Both (a) and (b)
(d) None of the above.
Ans. (a) Absence of protein coat in viroid but present in the virus.
Solution.
Viroids are infectious agents composed only of a short, circular, single-stranded RNA without any protein coat. Viruses, by contrast, consist of nucleic acid (DNA or RNA) enclosed within a protein coat (capsid); many viruses also have an outer envelope. Viroids cause diseases in plants (e.g., potato spindle tuber disease, chrysanthemum stunt) and are smaller than viruses.

Q.10. With respect to the fungal sexual cycle, choose the correct sequence of events.
(a) Karyogamy, Plasmogamy and meiosis
(b) Meiosis, Plasmogamy and Karyogamy
(c) Plasmogamy, Karyogamy and Meiosis
(d) Meiosis, Karyogamy and Plasmogamy
Ans. (c) Plasmogamy, Karyogamy and Meiosis
Solution.
The sexual cycle in fungi involves three main steps:

• Plasmogamy: Fusion of the cytoplasm of two compatible haploid cells (gametes or gametangia) without immediate fusion of nuclei.
• Karyogamy: Fusion of the two haploid nuclei to form a diploid nucleus (2n).
• Meiosis: Reduction division in the diploid nucleus producing haploid spores (restoring the haploid phase).

Q.11. Viruses are non-cellular organisms but replicate themselves once they infect the host cell. To which of the following kingdoms do viruses belong?
(a) Monera 
(b) Protista 
(c) Fungi 
(d) None of these
Ans. (d) None of these
Solution.

• Viruses are not placed in the five-kingdom classification because they are acellular and lack cellular organisation.
• They are neither prokaryotes nor eukaryotes and cannot carry out metabolic processes or replicate independently outside host cells.
• Viruses are inert outside their specific host cells and require host cellular machinery to replicate; therefore they are not assigned to any kingdom of cellular life.

Q.12. Members of Phycomycetes are found in
(i) Aquatic habitats
(ii) On decaying wood
(iii) Moist and damp places
(iv) As obligate parasites on plants 
Choose from the following options:
(a) None of the above
(b) (i) and (iv)
(c) (ii) and (iii)
(d) All of the above
Ans. (d) All of the above
Solution.
Members of Phycomycetes (a group of lower fungi) occur in a wide range of habitats including aquatic environments, on decaying wood, in moist and damp places and some are obligate parasites on plants.

Very Short Answer Type Questions

Q.1. What is the principle underlying the use of cyanobacteria in agricultural fields for crop improvement?

Ans.

• Cyanobacteria (blue-green algae; BGA) are autotrophic microorganisms capable of photosynthesis.
• Some cyanobacteria (e.g., Nostoc and Anabaena) possess specialised cells called heterocysts where atmospheric nitrogen (N₂) is fixed to ammonia, making nitrogen available to plants.
• In paddy fields and other agricultural systems, these cyanobacteria act as biofertilisers, enriching soil nitrogen and increasing soil organic matter and fertility.

Q.2. Suppose you accidentally find an old preserved permanent slide without a label. In your effort to identify it, you place the slide under the microscope and observe the following features:
(a) Unicellular
(b) Well-defined nucleus
(c) Biflagellate-one flagellum lying longitudinally and the other transversely.
What would you identify it as? Can you name the kingdom it belongs to?

Ans.

• The described features match dinoflagellates, unicellular eukaryotic protists that commonly have two flagella: one longitudinal and one transverse, often lying in grooves or furrows between thecal plates.
• Presence of a well-defined nucleus indicates a eukaryote; unicellular eukaryotes such as dinoflagellates belong to the kingdom Protista.

Q.3. How is the five-kingdom classification advantageous over the two-kingdom classification?
Ans. 

Two-kingdom classification divided life only into Plantae and Animalia. It failed to reflect important fundamental differences among organisms. Major limitations were:

• It did not distinguish between prokaryotes and eukaryotes. Prokaryotic bacteria and cyanobacteria were inappropriately grouped with other eukaryotes.
• It did not separate unicellular and multicellular organisms properly; unicellular algae and multicellular algae were both placed under plants despite large differences.
• It failed to separate autotrophic photosynthetic organisms from heterotrophic non-photosynthetic organisms (for example, Fungi were grouped with plants earlier despite differences in nutrition and physiology).

Advantages of the Five-Kingdom Classification:

• It placed Fungi in a separate kingdom recognising their heterotrophic saprophytic mode of nutrition and absorptive lifestyle.
• It created Protista to accommodate unicellular eukaryotic organisms (e.g., Chlamydomonas, Amoeba, Paramecium) thereby making plant and animal kingdoms more homogeneous.
• It separated prokaryotes into Monera, distinguishing them from eukaryotic kingdoms on the basis of cellular organisation and presence/absence of membrane-bound organelles.

Q.4. Polluted water bodies have usually a very high abundance of plants like Nostoc and Oscillatoria. Give reasons.

Ans.

• Polluted water bodies (ponds, ditches, lakes) often contain high levels of nutrients such as nitrates and phosphates from sewage and agricultural runoff.
• Such nutrient enrichment stimulates rapid growth of phytoplankton and cyanobacteria, leading to algal blooms-dense populations that can colour the water.
• Many bloom-forming cyanobacteria (e.g., Nostoc, Oscillatoria) can tolerate and proliferate in eutrophic conditions; some species produce toxins harmful to humans and animals, and blooms can cause oxygen depletion and fish mortality.

Algal Bloom

Q.5. Are chemosynthetic bacteria-autotrophic or heterotrophic?
Ans. Chemosynthetic bacteria oxidise inorganic compounds (e.g., ammonia, nitrite, sulphur compounds) to obtain energy which they use to fix CO2 into organic matter. Therefore chemosynthetic bacteria are autotrophic.

Q.6. The common name of pea is simpler than its botanical (scientific) name Pisum sativum. Why then is the simpler common name not used instead of the complex scientific/botanical name in biology?

Ans.

Common (vernacular) names vary regionally and linguistically. The same common name may refer to different species in different places, and one species can have many common names. To avoid confusion and to have a single standard name recognised internationally, the binomial nomenclature (scientific name) is used: Pisum sativum refers to the garden pea consistently worldwide.

Q.7. A virus is considered as a living organism and an obligate parasite when inside a host cell. But the virus is not classified along with bacteria or fungi. What are the characters of the virus that are similar to non-living objects?

Ans.

• Outside host cells, viruses are inert particles (often crystalline) and show no metabolism, growth or independent reproduction.
• Viruses lack cellular organisation and the metabolic machinery required for self-replication; they can replicate only inside living host cells using host enzymes and organelles.
• Because of these non-living characteristics outside a host, viruses are not classified with cellular life forms such as bacteria or fungi.

Q.8. In the five-kingdom system of Whittaker, how many kingdoms are eukaryotes?
Ans.
In Whittaker's five-kingdom system, four kingdoms-Protista, Fungi, Plantae and Animalia-are composed of eukaryotic organisms (cells with nucleus and membrane-bound organelles).

Short Answer Type Questions

Q.1. Diatoms are also called as 'pearls of ocean', why? What is diatomaceous earth?
Ans.

Diatoms possess distinctive silica-impregnated cell walls (frustules) with intricate sculpturing and ornamentation that are often lustrous; for this reason they are called the 'pearls of the ocean'. Over geological time, the silica walls of diatoms accumulate in sediments to form diatomaceous earth (also called kieselguhr), a gritty, porous deposit used commercially as a polishing agent, filter medium (e.g., filtration of oils, syrups), and in some industrial applications. Diatoms are major primary producers in aquatic ecosystems.

Diatoms

Q.2. There is a myth that immediately after heavy rains in forest, mushrooms appear in large number and make a very large ring or circle, which may be several metres in diameter. These are called 'Fairy rings'. Can you explain this myth of fairy rings in biological terms?
Ans.

• After heavy rains, moisture and nutrients in the soil stimulate growth of subterranean fungal mycelium.
• The fungal mycelium (for example of Agaricus species) grows radially outward from a central point. The fruiting bodies (basidiocarps, i.e., mushrooms) appear at the margins of the expanding mycelial colony, producing a ring of mushrooms on the soil surface.
• This circular pattern of fruiting bodies is called a fairy ring.

Fairy Rings

Q.3. Neurospora-an ascomycetes fungus has been used as a biological tool to understand the mechanism of genetics much in the same way as Drosophila has been used to study animal genetics. What makes Neurospora so important as a genetic tool?
Ans.

• Neurospora crassa is easy to culture and has a predominantly haploid life cycle; mutations show immediate phenotypic effects (no masking by a second allele), making genetic analysis straightforward.
• Beadle and Tatum used Neurospora to show that genes are linked to specific biochemical functions, formulating the one gene-one enzyme (later refined to one gene-one polypeptide) hypothesis.

Q.4. Cyanobacteria and heterotrophic bacteria have been clubbed together in Eubacteria of kingdom Monera as per the "Five Kingdom Classification" even though the two are vastly different from each other. Is this grouping of the two types of taxa in the same kingdom justified? If so, why?
Ans.

• Yes. Despite differences in nutrition (cyanobacteria are photosynthetic while many bacteria are heterotrophic), both groups are prokaryotes and share fundamental cellular and molecular features: absence of a nuclear envelope, lack of membrane-bound organelles, naked circular DNA, and 70S ribosomes.
• These shared structural and biochemical characteristics justify placing cyanobacteria and heterotrophic bacteria together in Kingdom Monera (Eubacteria).

Q.5. At a stage of their cycle, ascomycetes fungi produce the fruiting bodies like apothecium, perithecium or cleistothecium. How are these three types of fruiting bodies different from each other?
Ans.

• Apothecium: A wide, open, saucer-shaped or cup-shaped fruiting body; often fleshy and sessile. It exposes asci (spore-bearing sacs) directly to the environment.
• Cleistothecium: A completely closed, globose fruiting body with no specialised opening; asci are enclosed and released only when the structure ruptures or decays.
• Perithecium: A flask-shaped fruiting body that opens to the outside via a pore or ostiole (an apical opening), allowing ascospores to be discharged through the pore.

Perithecium

Q.6. What would observable features in Trypanosoma make you classify it under Kingdom Protista?

Ans.
Trypanosoma is a unicellular eukaryote with a well-defined nucleus (nuclear envelope), membrane-bound organelles, 80S ribosomes, and a flagellum with the typical 9+2 microtubular arrangement. These features identify it as a protist; Trypanosoma belongs to the kingdom Protista.

Q.7. Fungi are cosmopolitan. Write the role of fungi in your daily life.

Ans.

• Food and beverages: Baker's yeast (Saccharomyces cerevisiae) is used to leaven bread; yeasts are used in fermentation to produce alcoholic beverages (wine, beer, whisky).
• Food products: Certain cheeses (e.g., Roquefort) are ripened using fungi; edible mushrooms (e.g., Agaricus), morels (Morchella) and truffles are culinary delicacies.
• Medicines and biotechnology: Many important drugs are derived from fungi or their metabolites (see below).

Antibiotics and useful fungal metabolites:

• Cyclosporin A is produced by Trichoderma polysporum (and related fungi) and is used as an immunosuppressive drug to prevent organ transplant rejection.
• Statins (cholesterol-lowering agents) have been produced by fungi such as Monascus purpureus and from fungal derivatives.
• Fungi also serve as sources of enzymes, organic acids and other industrial products.
• Some fungi are pathogenic causing plant, animal and human diseases; understanding them is critical for health and agriculture.

Long Answer Type Questions

Q.1. Algae are known to reproduce asexually by variety of spores under different environmental conditions. Name these spores and the conditions under which they are produced.
Ans.

Asexual reproduction in algae occurs through different types of spores adapted to environmental conditions. The common types are:

• Zoospores: Motile, flagellated spores produced under favourable conditions; they swim and germinate to form new thalli.
• Aplanospores: Thin-walled, non-motile spores formed under less favourable conditions but not extreme; they germinate when conditions improve.
• Hypnospores (or cysts): Thick-walled, non-motile resistant spores formed under unfavourable or harsh conditions to survive until conditions become suitable.
• Akinetes: Resting spores in some cyanobacteria and algae where the entire cell becomes thick-walled and stores reserves to survive unfavourable periods.
• Palmella stage: Under drought conditions some unicellular algae form a gelatinously enclosed stage (palmella) where protoplasts are protected until moisture returns.

Q.2. Apart from chlorophyll, algae have several other pigments in their chloroplast. What pigments are found in blue-green, red and brown algae that are responsible for their characteristic colors?
Ans.

Algae contain accessory pigments in addition to chlorophyll that determine their characteristic colours and allow absorption of different wavelengths of light:

• Blue-green algae (cyanobacteria): Contain phycobiliproteins such as phycocyanin and phycoerythrin, along with chlorophyll a; phycobilins give blue and red hues.
• Brown algae (Phaeophyceae): Contain chlorophyll a and c, carotenoids and xanthophylls; the predominant xanthophyll fucoxanthin gives brown or olive colours.
• Red algae (Rhodophyceae): Possess chlorophyll a and accessory pigment phycoerythrin, which imparts red colour; some also have chlorophyll d.

Q.3. Make a list of algae and fungi that have commercial value as source of food, chemicals, medicines and fodder.
Ans.

(a) Economic Importance of Algae

• Many marine algae are consumed as food: Porphyra (nori), Laminaria, Sargassum and others are edible seaweeds.
• Unicellular algae such as Chlorella and Spirulina are rich in proteins and nutrients and are used as food supplements (even considered for space food).
• Certain red and brown algae produce phycocolloids: Algin (from brown algae) and carrageenan (from red algae) are used as thickening, stabilising and gelling agents; agar (from Gelidium and Gracilaria) is widely used in microbiological media and in food such as jellies and ice creams.
• Other commercial products: bromine can be obtained from some red algae (e.g., Polysiphonia); Macrocystis is a source of potash; Laminaria and Fucus are sources of iodine.

(b) Economic Importance of Fungi

• Edible fungi: mushrooms (e.g., Agaricus), morels (Morchella) and truffles are consumed as food.
• Fermentation: yeasts (Saccharomyces cerevisiae) are used in baking and alcoholic fermentation (beer, wine, spirits).
• Pharmaceuticals and industrial products:
  • Cyclosporin A from Trichoderma species is used as an immunosuppressant in organ transplantation.
  • Statins and other clinically important compounds have fungal origins or are produced by fungal fermentation.
• Fungi are sources of enzymes, organic acids and other metabolites used in industry and biotechnology.

Q.4. 'Peat' is an important source of domestic fuel in several countries. How is 'peat' formed in nature?
Ans.

• Peat is formed from partially decomposed plant material (commonly mosses like Sphagnum) under waterlogged, acidic and anaerobic conditions where complete decomposition is prevented.
• The accumulation of such partially decayed vegetation over long periods forms peat bogs. Peat is soft, retains water and can be dried and used as a domestic fuel in regions where other fuels are scarce.
• Sphagnum species also serve as packing material due to their high water-holding capacity.

Q.5. Biological classification is a dynamic and ever-evolving phenomenon which keeps changing with our understanding of life forms. Justify the statement taking any two examples.
Ans.

• Example 1: The formation of Kingdom Protista in the five-kingdom system grouped together diverse unicellular eukaryotes (such as Chlamydomonas, Chlorella, Amoeba, Paramecium) that were earlier scattered between Plantae and Animalia because the earlier two-kingdom system could not reflect differences in cellular organisation and life cycles.
• Example 2: Recognition of Fungi as a separate kingdom highlighted major differences in nutrition and physiology (absorptive heterotrophy, chitinous cell walls) from plants; fungi were earlier treated as plants but later separated when their unique features and evolutionary relationships became clear.
• As new data (especially molecular and phylogenetic information) accumulates, classification systems are revised-thus biological classification remains dynamic and continually refined.