NCERT Exemplar class 11 biology Solutions Biological Classification
NCRT TEXTBOOK QUESTIONS SOLVED
Multiple Choice Questions
1.Ail eukaryotic unicellular organisms belong to (a) Monera (b) Protista
(c) Fungi (d) Bacteria.
soln. (b): The Kingdom Protista (Gk. protistos = first of all) was proposed by Ernst Haeckel (1866). All single-celled eukaryotes are placed in Kingdom Protista. Phylogenetically, the Kingdom Protista acts as a connecting link between the prokaryotic kingdom – Monera on one hand and the complex multicellular kingdoms – Fungi, Plantae and Animalia
on the other hand. Protista are regarded as ancestors of all multicellular eukaryotic organisms.
2.The five kingdom classification was proposed by
(a) R.H. Whittaker (b) C. Linnaeus (c) A. Roxberg (d) Virchow.
soln.(a): In order to develop phylogenetic classification, R.H. Whittaker (1969) divided all the> organisms into five kingdoms on the basis of complexity of cell structure, body structure, mode of nutrition, ecological lifestyle and phylogenetic relationships.
Whittaker’s five kingdoms are Monera, Protista, Fungi, Plantae and Animalia.
3. Organisms living in salty areas are called as
(a) methanogens (b) halophiles
(c) heliophytes (d) thermoacidophiles.
soln. (b): Halophiles are a type of archaebacteria which occur in salt rich substrata (2.5-5.0 M) like salt pans, salt beds and salt marshes e.g., Halobacterium, Halococcus. Methanogens occur in marshy areas, thermoacidophiles grow in regions with very high temperature and heliophytes are the plants which grow well in presence of sunlight, (sun loving plants).
4.Naked cytoplasm, multinudeated and saprophytic are the characteristics of
(a) monera (b) protists
(c) fungi (d) slime moulds.
5.An association between roots of higher plants and fungi is called
(a) lichen (b) fern ,
(c) mycorrhiza (d) BGA.
soln. (c): An association between roots of higher plants and fungus is called mycorrhiza. It is a symbiotic association in which both the members are benefited. Depending upon the position of fungi, mycorrhiza are of two types – ectomycorrhiza (most of the fungus lies on the surface of root) and endomycorrhiza (most of the fungus resides inside the cortex of roots).
Fungus gets shelter and food from plant. It obtains its nourishment from cortical cells of roots Fungal hyphae are spread in the soil over a large area. They take part in absorption of water, dissolving essential minerals in organic debris and providing it to the plant allowing the plants to grow in areas deficient in inorganic minerals. Fungus secretes growth promoting substances and antimicrobial substances which protect roots from attack of pathogens. An example is association between fungus and roots of Pinus.
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.
soln. (d): Dikaryon is a stage/phase of a cell, in which, there are two nuclei. This condition arises, if fusion of cytoplasm (plasmogamy) is not immediately followed by fusion of nuclei (karyogamy). Karyogamy is delayed, it occurs just before meiosis. Dikaryon occurs in stage intervening between plasmogamy and karyogamy. Such cells are called dikaryotic cells and the phase is called dikaryophase.
7.Contagium vivum fluidum was proposed by
(a) D. J. Ivanowsky
(b) M. W. Beijerinck
(d) Robert Hooke.
soln. (b) : Martinus William Beijerinck (a Dutch microbiologist and botanist) gave a phrase, “Contagium vivum fluidum” (“contagious living fluid”), to describe a virus. He demonstrated that extract of infected plants of tobacco could cause infections in healthy plants.
8.Association between mycobiont and phycobiont are found in
(a) mycorrhiza (b) root
(c) lichens (d) BGA.
soln. (c): Lichens are symbiotic association between fungus (mycobiont) and alga (phycobiont). The mycobiont is usually an ascomycete and phycobiont is mostly blue green alga or green alga. Lichens can grow in extremely inhospitable conditions. In many ecosystems they are the pioneer species. The role of mycobiont is to provide body structure, anchorage to plant and absorption of minerals and water. Phycobiont provides food to fungus through photosynthesis.
9.Difference between virus and viroid is
(a) absence of protein coat in viroid but present in virus
(b) presence of low molecular weight RNA in virus but absent in viroid
(c) both (a) and (b)
(d) none of the above.
soln. (a): Viroids are smallest self replicating particles of low molecular weight. They are infectious RNA particles, lack protein coat
and cause disease only in plants. However, virus can have both DNA or RNA as genetic material and have protein coat.
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
soln. (c): In fungi, sexual reproduction involves the formation and union of two gametes or their nuclei. Fusion of gametes involves union of cytoplasm called plasmogamy and fusion of nuclei, known as karyogamy. Plasmogamy is followed by karyogamy but in higher fungi karyogamy is delayed and it occurs before meiosis. Therefore, the correct sequence in sexual reproduction of fungal life cycle is plasmogamy, karyogamy and meiosis.
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
soln. (d): Virusisagroupofultramicroscopic, non-cellular, highly infectious agents that multiply only intracellularly inside living host cells without involving growth and division. Viruses are regarded as intermediate between non-living entities and living organisms. They are obligate parasites and are inert outside the host cell. They do not belong to any kingdom.
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
soln. (d): Phycomycetes is the group of fungi which is characterized by aseptate and coenocytic mycelium. They can live in a wide variety of habitat. They can be aquatic
or saprotrophic or parasitic or could be living in moist and damp places. Some examples of phycomycetes are Rhizopns (black bread mould), Mucor (dung mould), Albugo (parasitic fungi).
Very Short Answer Type Questions
1.What is the principle underlying the use of cyanobacteria in agricultural fields for crop improvement?
soln. Several cyanobacteria have the ability to fix atmospheric nitrogen. The filamentous forms possess special large pale cells or hetrocysts specialised to perform nitrogen fixation. Some of the fixed nitrogen comes out as excretion. After death of cyanobacteria the substratum becomes rich in nitrogen. Such nitrogen fixing cyanobacteria are now regularly inoculated in the rice fields. This saves consumption of nitrogen fertilisers, and. thus helps in crop improvement.
2.Suppose you accidentally find an old preserved permanent slide without a label. In your effort to identify it, you place the slide under microscope and observe the following features:-
(b) Well defined nucleus
(c) Biflagellate – one flagellum lying longitudi-nally and the other transversely.
What would you identify it as? Can you name the kingdom it belongs to?
soln. Slide is mounted with dinoflagellates, c.g. Ceratium, Gonyaulax. These are unicellular eukaryotes, they posses well defined nucleus. Dinoflagellates are biflagellates, have two different flagella; one longitudinal and other transverse. Dinoflagellates belong to Kingdom Protista.
3.How is the five-kingdom classification advan-tageous over the two kingdom classification?
soln. In two kingdom classification, Linnaeus divided all living organisms into two groups; plants and animals on the basis of presence and absence of cell wall, and ability or inability to photosynthesise. But some organisms were neither plants nor animals, like fungi, slime
moulds, viruses, lichens, and their position was not fixed. Whittaker proposed five kingdom
classification on the basis of cell structure, modes of nutrition, thallus organisation, reproduction, phylogenetic relationship. Five kingdoms were; Monera, Protista, Fungi, Plantae and Animalia. Kingdom Monera included mycoplasmas, bacteria etc., Protista included protozoans, slime moulds etc. still there was no fixed place for viruses.
4.Polluted water bodies have usually very high abundance of plants like Nostoc and Oscillatoria. Give reasons.
soln. Polluted water bodies are rich in organic matter. These nutrients result in the rapid growth of plants like Nostoc and Oscillatoria as they can tolerate adverse conditions like pollutants, due to presence of mucilage covering, resistant proteins. Thus cyanobacteria (c.g., Nostoc, Oscillatoria) produce algal blooms in polluted water bodies, imparting bad odour and colour.
5.Are chemosynthetic bacteria autotrophic or heterotrophic?
soln. Chemosynthetic bacteria are auto ¬trophic bacteria. They are able to manufacture their organic food from inorganic raw materials with the help of energy derived from exergonic chemical reactions involving oxidation of an inorganic substance present in the external medium. Thus, these bacteria are chemoautotrophic. The chemical energy obtained from oxidation reaction is trapped in ATP molecules. Examples are nitrifying bacteria, sulphur oxidising bacteria, and iron bacteria.
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?
soln. In biology, scientific names are used rather than common names because the same organisms may have different common/ local names in different regions of the same country or in different countries. But scientific names represent a particular organism in every part of the world. Pea is known as matar (Flindi), pattani (Tamil), vatana (Gujrati), kara (Kashmiri) in different regions of India. It can create confusion. But scientifically, pea is known as Pisum sativam all over the world.
7.A virus is considered as a living organism and an obligate parasite when inside a host cell. But virus is not classified along with bacteria or fungi. What are the characters of virus that are similar to non-living objects?
soln. Virus is an obligate parasite. It is inert outside the host cell. It does not grow, divide or reproduce like normal organisms. Viruses are intermediate between living and non-living entities. Characters of virus similar to non-living objects are – (i) Absence of protoplast, (ii) Ability to get crystallised, e.g., TMV, poliomyelitis virus, (iii) Inability to live independent of a living cell, (iv) High specific gravity which is found only in non-living objects, (v) Absence of respiration,
(vi)Absence of energy storing system,
(vii)Absence of growth and division, instead different parts are synthesised separately.
8.In the five kingdom system of Whittaker, how many kingdoms are eukaryotes?
soln. In five kingdom system of classification given by Whittaker, four kingdoms include eukaryotes; Protista, Fungi, Plantae and Animalia.
Short Answer Type Questions
1.Diatoms are also called as ‘pearls of ocean’, why? What is diatomaceous earth?
soln. The body of diatoms is covered by transparent siliceous shell. Their cell wall is glass like and made up of silica, known as frustules. Diatom frustules are highly ornamented, and so they are called ‘pearls of ocean’ or ‘jewels of sea’. As their siliceous frustules do not decay easily. So, they pile up at the bottom of water reservoirs and form big heaps called diatomaceous earth.
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 as’Fairy rings’. Can you explain this myth of fairy rings in biological terms?
soln. Fairy ring is a naturally occuring circular ring of mushrooms in a lawn, forest or woodland. A fairy ring starts when the propagule of a mushroom falls in a favourable spot and sends out a subterranean network of fine, tubular threads called hyphae. The hyphae grow out from the spore evenly in all directions, forming a circular mat of underground hyphal threads. The mushrooms that grow up from this circular underground mat form a similar pattern above ground. Gradually, the underground mycelium at the centre of the circle dies out. Its living outer edges, however, keep growing year by year, and hence the diameter of the ring gradually increases.
It continues to push outwards in an attempt to consume more nutrients. As it exhausts the nutrients on the inside of the circle, it will widen further and further as it looks for a new food source.
This process results in an ever-growing circle, that does not start to grow back inwards or cross over on itself because there’s no new food on the inside of the circle.
Multiple factors influence this circular growth pattern, including soil type and condition, amount of nutrients in the soil, obstructions underground, and dirt composition.
3. Neurospora – an ascomycetes fungus has been used as a biological tool to understand the mechanism of plant genetics much in the same way as Drosophila has been used to study animal genetics. What makes Neurospora so important as a genetic tool?
soln. Neurospora crassa is known as’Drosophila of Plant Kingd om’. Itisau sefulmodel organism as it can be easily cultured in laboratories due to simple life cycle and simple nutrient requirements. Neurospora crassa is the subject of intensive research leading to significant contributions. By using Neurospora mutants, Mary Mitchell reported the first example of gene conversion. Barbara McClintock, famous for her work in transposition, showed for the first time, that fungal chromosomes were
typically eukaryotic using it. Further, several aspects of metabolism and cytogenetics were first studied in it. The first sequencing of a mitochondrial nucleic acid came from this fungus and self-splicing of a mitochondrial
intron was demonstrated for the first time.Neurospora also made significant contributions to the study of the mechanisms underlying protein import into mitochondria. Moreover, mitochondrial plasmids were discovered and characterised. It has also been important in areas of biological research, including recombination, DNA repair, differentiation, morphogenesis and cell biology, and notably, DNA methylation and silencing, findings applicable not only to the fungi, but to other eukaryotes as well.
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?
soln. Cyanobacteria and heterotrophic bacteria have been clubbed together in Kingdom Monera because both are prokaryotes and have naked DNA, i.e., genetic material is not organised into nucleus, rather a coiled mass called nucleoid is present. They lack membrane bound organelles and have non-cellulosic cell wall.
5.At a stage of their cycle, ascomycetes fungi produce the fruiting bodies like apothecium, perithecium or deistothecium. How are these three types of fruiting bodies different from each other?
soln. Sexual spores of Ascomycetes called ascospores are endogenously produced in sac called ascus (pi. asci). Each ascus bears 4-8 ascospores, sometimes numerous. In higher Ascomycetes, asci are aggregated in definite fruiting bodies called ascocarps. The following three types of fruiting bodies are distinguished in Ascomycetes, the deistothecium, the perithecium, and the apothecium. The cleistdthecia are rounded and closed and have a peridium (outer envelope). There are no special openings, and the asci develop in the
fruiting body either randomly or in bundles. The spores, or ascospores, are released from the fruiting body after the decay or rupture of the peridium. Perithecia, which are pitcher shaped, oval, or spherical, have a narrow opening at the top. Apothecia are saucer-shaped or cup-shaped. Less frequently they resemble little cushions or caps on a stalk (for example, in morels). The asci are distributed on the upper side of the apothecia in the form of a hymenium.
6.What observable features in Trypanosoma would make you classify it under Kingdom Protista?
soln.Trypanosoma, a flagellated protozoon shows following characters of Kingdom Protista: it is an eukaryote, has well organised nucleus, possesses outer wall made of pellicle, exhibits parasitic nutrition, shows flagellar locomotion, shows asexual reproduction by binary fission and presence of membrane bound organelles.
7.Fungi are cosmopolitan, write the role of fungi in your daily life.
soln. Fungi are cosmopolitan in occurrence being present in air, water, soil, over and inside plants and animals. Fungi have both beneficial and harmful roles. For example, yeasts are used in brewing industry, baking industry as well as it causes various plant and animal diseases. Commercial antibiotic penicillin has been obtained from fungus Penicillium. Morels and mushrooms are group of edible fungi. However, Aspergillus another fungus contaminates food stuff like bread, jam, butter, syrups and also laboratory cultures.
Long Answer Type Questions
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.
soln. Algae and their spores exhibit enormous diversity and they vary greatly in their level of specialisation. Asexual reproduction by spores and their types are described below.
(i) Zoospores : Certain algae produce motile flagellated asexual spores called zoospores in sac called zoosporangium. Zoospore formation occurs during favourable conditions. During zoospore formation, flagella are withdrawn and organism comes to rest. The protoplasm undergoes repeated divisions and forms 8-16 daughter protoplasts. These daughter individuals called zoospore develop their individual cell wall and flagella, the parent cell wall is lost and new individuals attain independent existence. E.g., Chlamydomonas.
(ii)Aplanospores : These are non-motile asexual spores. They are formed by contraction of protoplasm and formation of new cellulose walls around it. These spores are formed under mildly unfavourable conditions. During favourable conditions, they germinate to form new filaments. E.g., Spirogyra.
(iii)Hypnospores : These are resting spores. These are thick walled aplanospores which develop in adverse conditions. Under favourable growth conditions, the spore can germinate to a new plant, e.g., Vaucheria.
(iv)Autospores : They are non-motile thin walled spores formed by parent cell division. These are similar to mother cell in the morphology and structure. E.g., Chlorella.
(v) Endospores : These are derived either from single cell or by fusion of several cells. After rupture of mother cell,under favourable conditions, endospores can spread, attach to substratum and germinate.
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 colours?
soln. The photosynthetic pigment present in the cdll of blue-green algae or cyanobacteria are chlorophyll-a, p-carotene, phycobillin, myxoxanthophyll, myxoxanthin, etc.
Photosynthetic pigment of red algae of Class Rodophyceae include chlorophyll-#, chlorophyll d, carotenes, xanthophylls and phycobilins. Phycobilins are water soluble and are of two types, i.e., . red-coloured phycoerythrin and blue-coloured phycocyanin.
Photosynthetic pigments of brown algae, (Class Phaeophyceae) include chlorophyll-#, c and carotenoids. The brown algae range in colour from olive green to various shades of brown depending upon the amount of the xanthophyll pigment, fucoxan thin present in them.
3.Make a list of algae and fungi that have commercial value as source of food, chemicals, medicines and fodder.
4.’Peat’ is an important source of domestic fuel
in several countries. How is ‘peat’ formed in
soln. Peat is formed by Sphagnum, (moss)
belonging to Division Bryophyta of Kingdom Plantae. Sphagnum often grows in acidic marshes where there is little decay. The older dead parts of moss and other marshy plants are slowly carbonised, compressed and fossilised over thousands of years to produce a dark spongy mass called peat. Peat is dried and compressed and cut to form blocks. The peat blocks are used as fuel. Peat is also a
source of good manure. It overcomes soil
alkalinity and increases its water retention as
well as aeration.
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.
soln. Biological classification is the scientific procedure of placing organisms into different groups and sub-groups on the basis of their similarities and dissimilarities.