Set-III: Past Entrance Papers

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(d) Smut disease is caused by Ustilago species of basidiomycetes fungi. It is characterised by formation of black coloured chlamydospores or teleutospores called smut spore due to which the affected part becomes black.

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(c) The fungus that causes the disease ‘Ergot of Rye’ is Claviceps purpurea. It contains many poisonous alkaloids. The hallucinogenic drug LSD is extracted from this fungi.
– Rust of wheat is used by Puccinia graminis.
– Powdery mildew of pea is caused by Erysiphae.

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(b) Fungi are nutritionally saprophytes, which grow on dead and decaying matter. They secrete enzyme to the external medium where digestion takes place and digested food is absorbed by the body surface. They convert complex organic constituents of the dead body into simple soluble forms. That is why fungi are regarded as decomposers.

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(a) Viroids have free RNA without protein coat. Viroid, an infectious particle smaller than any of the known viruses, is an agent of certain plant diseases. The particle consists only of an extremely small circular RNA (ribonucleic acid) molecule, lacking the protein coat of a virus.
Dr. Theodor o. Diener, discovered viroids and also to distinguish it from a virus.

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(c) Infective constituent in viruses is either DNA or RNA, not protein. The simplest form consists of two basic components: nucleic acid (single- or double-stranded RNA or DNA) and a protein coat, the capsid, which functions as a shell to protect the viral genome from nucleases and which during infection attaches the virion to specific receptors exposed on the prospective host cell.

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(c) Prions are disease-causing agents having abnormally folded proteins. Prions induce other healthy proteins to fold incorrectly, leaving patches of useless debris and holes that tum brains to sponge, resulting in death. The disease has an incubation period in cattle of up to eight years.

Mad cow disease (or bovine spongiform encephal-opathy) is a transmissible, slowly progressive, degenerative, and fatal disease affecting the central nervous system of adult cattle. It’s related to a disease in humans called variant Creutzfeldt-Jakob disease (vCJD). Both disorders are universally fatal brain diseases caused by a prion.

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(c) Viroids in nature are sub-viral agents as infectious RNA particles, without protein coat.

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(d) Viroids, the smallest known pathogens, are naked, circular, single-stranded RNA molecules that do not encode protein but autonomously replicate when introduced into host plants. Viroids only infect plants; some cause economically important diseases in crop plants, while others appear to be benign.

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(b) TMV (Tobacco Mosaic Virus) is a rod-shaped virus. The rod has a core that contains helically coiled single-stranded RNA. There is a protective covering of protein called capsid around the infective part. Capsid consists of small subunits called capsomeres and has antigenic property.

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(a) All viruses are nucleoproteins (Nucleic acid $+$ Protein) in the structure. The nucleic acid (DNA and RNA) is the genetic material. In a particular virus either DNA or RNA is the genetic material. Both are never present in a virus. Single-stranded RNA or ss RNA – Tobacco mosaic virus (TMV)
Virus envelope is known as capsid. The capsid is composed of protein subunits called capsomere.

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(a) Plant viruses often contain parasites of their own, referred to as satellites. Satellite RNAs are dependent on their associated (helper) virus for both replication and encapsidation. Example-Tobacco Necrosis Virus (TNV). Viroids are infectious agents smaller than viruses. Bacteriophages are viruses that infect the bacteria. A prion is an infectious agent that is composed primarily of protein.

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(b) All the viruses are obligate parasite i.e. they remain inert outside the host cell. They have ability to syntheize nucleic acids and proteins by using host cellular machinery (ribosomes, tRNAs, aminoacids, energy). Three shapes are found in viruses helical (elongate body e.g. T.M.V), cuboidal (short broad body with rhombic rounded, polyhedral shape e.g. Poliomyelitis virus) and binal (with both cuboidal and helical parts \(e . g\). many bacteriophages like \(\mathrm{T}_{2}\) ). Antibiotics have no effect on them, antiviral drugs can only kill them.

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(a) Virus envelope is known as capsid. The capsid is composed of protein subunits called capsomere.

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(a) Mad cow disease is actually Bovine Spongiform Encephalopathy or BSE. In this disease cattles in Britain got spongy brain & ultimately gradual degradation of the nervous system. It is caused by some virus-like but nucleic acid devoid proteinaceous particles called prions (proteinaceous infectious particles).

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(a) Viruses can live only inside the host cell, using their machinery for its own metabolism.

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(d) Virus is a nucleoprotein entity which becomes active only inside a living cell utilizing the latter machinery for multiplication. Capsid is the protein covering the genetic material.

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(b) Enzymes are absent in viruses because they are unable to transmit their nucleic acid from one host cell to another.

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(c) Virus is an ultramicroscopic nucleoprotein entity which becomes active only inside a living cell. It resembles living beings due to the presence of genetic material and reproduction.

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(b) Viruses have either DNA or RNA as the genetic material. Viruses having RNA as the genetic material are known as retroviruses.

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(b) Influenza virus is a retrovirus wherein, the genetic material comprises of RNA.
There are three genera of influenza virus, identified by antigenic differences in their nucleoprotein and matrix protein:

Influenza virus A are the cause of all flu pandemics and are known to infect humans, other mammals, and birds (see also avian influenza).
– Influenza virus B is known to infect humans and seals.
– Influenza virus C is known to infect humans and pigs.

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(b) All viruses are nucleoprotein (Nucleic acid + Protein) in their structure. The nucleic acid (DNA and RNA) is genetic material. In a particular virus either DNA or RNA is genetic material. Both are never present in a virus. Hence viruses contain:
(i) Double stranded DNA(ds DNA) – Hepatitis B
(ii) Single stranded DNA (ss DNA) – coliphage
(iii) Double-stranded RNA (ds RNA) – Reo virus, wound Tumor virus
(iv) Single-stranded RNA(ss RNA) – Tobacco mosaic virus (TMV)

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(b) Lichen is a symbiosis between different organisms. It is composed of a fungal partner (mycobiont) and one or more photosynthetic partners (photobiont). The photosynthetic partner is generally green algae or cyanobacteria.
Lichens are well known as sensitive indicators of air pollution, particularly for sulphur dioxide. If air is very badly polluted with sulphur dioxide there may be no lichens present, just green algae may be found. If the air is clean, shrubby, hairy, and leafy lichens become abundant.

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(d) Lichens cannot grow in places where sulphur dioxide is present in the environment.

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(c) Saccharomyces cervisiae is a yeast used in making bread (Baker’s yeast) and commercial production of ethanol. Paramoecium & Plasmodium are of the animal kingdom while Pencillium is a fungi. Lichen is a composite organism formed from the symbiotic association of an algae and a fungus. Nostoc & Anabaena are examples of kingdom monera.

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(a) Lichens (coined by Theophrastus) are composite or dual organisms which are formed by a fungus partner or mycobiont (mostly ascomycetes) and an algal partner (mostly blue green algae). Fungus forms the body of lichen as well as its attaching and absorbing structures. Algae performs photosynthesis and provides food to the fungus.

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(d) Lichens are composite organisms formed by the symbiotic association between a fungus and alga. A saprophyte is an organism feeding on dead, decaying organic matter. An epiphyte is a plant growing over another plant. Parasites live inside their host.

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(b) The lichen fungus is typically a member of the Ascomycota, rarely a member of the Basidiomycota. The algal or cyanobacterial cells are photosynthetic, and as in higher plants, they reduce atmospheric carbon dioxide into organic carbon sugars to feed both symbionts. Both partners gain water and mineral nutrients mainly from the atmosphere through rain and dust. The fungal partner protects the alga by retaining water, serving as a larger surface area for capture of mineral nutrients, and, in some cases, provides minerals obtained from the substratum.

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(d) Lichens are composite organisms formed by the association between a fungus and a photosynthetic symbiont. The bulk of the lichen body is formed of fungus.

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(b) Lichens are composite organisms representing a symbiotic association between fungus and a algae. It can be crustose, foliose and fruticose types. They are the pioneer organisms in a new habitat. Lichens are used as indicator of air pollution. It does grow in the environment where the pollution level is high, \(\mathrm{SO}_{2}\) is a strong air pollutant and lichens are very sensitive to \(\mathrm{SO}_{2}\).

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(c) Lichens typically grow in harsh environments in nature. Most lichens, especially epiphytic fruticose species and those containing cyanobacteria, are sensitive to manufactured pollutants. Hence, they have been widely used as pollution indicator organisms.

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(b) Plasmogamy, the fusion of two protoplasts (the contents of the two cells), brings together two compatible haploid nuclei. At this point, two-parent cells are present in the same cell, but the nuclei have not yet fused. Incorrect statements can be corrected as Organisms that can fix atmospheric nitrogen in specialised cells are called heterocysts.
Karyogamy is nothing but the fusion of two nuclei means the production of diploid cell.
Organisms that depend on living plants are called heterotrophs.

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(d) The size of various organisms/cells are Pleuropneumonia Like Organism (PPLO)-0.1 \(\mu \mathrm{m}\) Viruses-0.02-0.2 \(\mu \mathrm{m}\) Bacterial cell-1-2 \(\mu \mathrm{m}\) Eukaryotic cell-10-20 \(\mu \mathrm{m}\)

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(b) Cyanobacteria or blue-green algae are photosynthetic organisms that perform oxygenic photosynthesis. They have the ability of nitrogen fixation due to the presence of large pale cells called heterocyst in their filaments. Due to the presence of thick walls, heterocysts are impermeable to oxygen.

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(c) Green sulphur bacteria are anaerobic bacteria. They do not evolve oxygen during photosynthesis. Such type of photosynthesis is known as anoxygenic photosynthesis.

They do not use water as a source of reducing power. Instead, hydrogen is obtained from hydrogen sulphide.

Concept Enhancer Green sulphur bacteria, e.g. Chlorobium limicola, possesses bacteriophaeophytin as photosynthetic pigment. Cycas is a gymnosperm, Nostoc is a blue-green algae and Chara is a green algae. All of these produce oxygen during photosynthesis.

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(b) Methanogens are a group of obligate anaerobic ancient and primitive bacteria. They are involved in methanogenesis and produce methane gas in ruminant of cattles.

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(b) Methanogens belong to archaebacteria. It contains three major classes of primitive bacteria, i.e. methanogens, halophilic and thermoacidophilic. Methanogens are strict anaerobes, present in the gut of several ruminant animals (e.g. cows, etc.) and are responsible for production of methane gas from the dung of these animals.
Concept Enhancer Halophilic bacteria usually occur in salt-rich substrates like salt marshes, etc., and are aerobic chemoheterotrophs. Thermophilic bacteria have the dual ability to tolerate high temperature as well as high acidity. These are basically chemosynthetic.

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(a) Chromatophores are found in members of phototrophic bacteria. They contain bacteriochlorophyll pigments and carotenoids and take part in photosynthesis. In purple bacteria, such as Rhodospirillum rubrum, the light-harvesting proteins are intrinsic to the chromatophore membranes. However, in green sulphur bacteria, they are arranged in specialised antenna complexes called chlorosomes.

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(a) Archaebacteria are different from eubacteria in that eubacteria have cell membrane composed mainly of glycerol-ester lipids, while archaebacteria have membrane made
up of glycerol-ether lipid. Ether lipids are chemically more resistant then ester lipids. This stability helps archaebacteria to survive in high temperatures and in a very acidic or alkaline environment.

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(b) Cyanobacteria within the coralloid roots of Cycas are chemoheterotrophic and
specifically adapted to life in symbiosis. Only a few species of cyanobacteria
form associations with Cycas. Pinus is a gymnosperm. Equisetum belongs to
vascular plants and to the horse tail family. Psilotum belongs to division-Pteridophyta and is a fern-like plant.

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(d) Cyanobacteria contain chlorophyll but the chlorophyll is not located in chloroplasts, rather it is found in chromatophores which are infolding of the plasma membrane, where photosynthesis is carried out. Heterocysts are specialised nitrogen fixing cells formed by some filamentous cyanobacteria such as Nostoc. A basal body is an organelle formed from a centriole and a short cylindrical array of microtubules.

Pneumatophores are lateral roots that grow upward for varying distances and function as the site of oxygen intake for the submerged primary roots of mangrove plants.

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(d) Nostoc is a prokaryote. Prokaryotic cells lack membrane-bound organelles and well organised nucleus, i.e. nuclear envelope is absent. Penicillium, Agaricus, and Volvox are
eukaryotic.

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(a) The coralloid root of Cycas is symbiotically associated with nitrogen fixing blue-green algae, Anabaena cycadae and Nostoc punctiforme. These blue green-algae (cyanobacteria) are prokaryotic, photosynthetic, and autotrophic.

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(c) Maximum nutritional diversity is shown by the members of kingdom-Monera. Some of them are autotrophic (e.g. photosynthetic autotrophic or chemosynthetic autotrophic) while the vast majority are heterotrophs (e.g. saprotrophic or parasitic). Ecologically,
these may be producers or decomposers.

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(a) Thermophiles live in very hot places, with temperature ranging from \(60^{\circ}-80^{\circ} \mathrm{C}\). Many thermophiles(some eubacteria and archaebacteria) are autotrophs and have metabolisms based on sulphur.
Some thermophilic archaebacteria form the basis of food webs around deep-sea thermal vents, where they must withstand extreme temperature and pressures. Archaebacteria can grow in highly acidic \((\mathrm{pH}=0.7)\) and very basic \((\mathrm{pH}=11)\) environments.

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(d) Anabaena is a free-living nitrogen-fixing cyanobacterium that can form symbiotic association with water fern Azolla.

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(b) Bacterial chromosomes are circular DNA molecules.

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(b) The organisms obtaining energy by chemical reactions independent of light are called chemotrophs. The reductants obtained from the environment may be inorganic (in the case of chemoautotrophs) or organic (in the case of chemoheterotrophs).
Photoautotrophs organisms that make their own food by photosynthesis, using light energy. Saprozoic organisms obtain food from dead and decaying matter.

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(a) Plasmid is an extrachromosomal material capable of replicating independently from the main chromosome. Plasmids usually possess antibiotic resistance genes.

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(c)

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(b) The cytoplasmic membrane of bacteria is invaginated at certain places into the cytoplasm in the form of tubules, which are called mesosomes; on their surface are found enzymes associated with respiration. Mesosome works as mitochondia in the bacterial cell.

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(b) Nucleoid or chromatin body or genophore in bacteria occupies 10-20%
molecule in which all the genes are linked. It is over a thousand times longer than the cell itself and is, therefore, highly folded. It lacks histone proteins.

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(d) Plasmids are small, self-replicating, extrachromosomal, non-essential genetic elements in bacteria. Each plasmid has a ring of circular, supercoiled, double-stranded DNA. They carry genes for replication and for one or more cellular non-essential functions. These are also called minichromosomes or dispensable autonomous elements.

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(a) Diatoms are single-celled plant like protists that produce intricately structured cell walls made of nano(-) silica \(\left(\mathrm{SiO}_{2}\right)\). Thus, the walls are indestructible. Hence, only option \((a)\) is wrong and the rest of the options are correct.

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(b) Fresh water protozoans live in hypotonic environment so, for regulation of excess of water which comes in the protoplasm through the process of endosmosis, contractile vacuoles have developed. When these protozoans are placed in marine water, i.e. hypertonic water, the contractile vacuoles become disappear because the process of endosmosis does not occur, and thus, water does not come in the protoplasm.

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(c) Euglena is a connecting link between animals and plants. Euglena contains chlorophyll, yet it resembles animals, because it feeds like animals in the absence of sunlight. It resembles the ancestral form from which the plants and animals evolved.

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(a) Unicellular organisms such as Amoeba, Paramecium have some organelles called contractile vacuole for excretion. These are freshwater animals, i.e. they live in a hypotonic solutions. Therefore, water flows from outside to inside of the body of the organism.
The contractile vacuoles in these organisms collect this excess water and gradually increase in size. When the vacuoles reach a critical size they contract, squeezing out their contents through the process of simple diffusion.

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(a) Sporozoans are endoparasites. They lack locomotory organelles like cilia, flagella, pseudopodia, etc., e.g. Plasmodium. Pseudopodia are found in amoeboid protozoans, e.g., Amoeba, Entamoeba, etc. Therefore, statement (a) is wrong while the rest of the statements are correct.

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(d) In primary succession on rocks, lichens secrete acids to dissolve rock, and help in weathering and soil formation. So, lichens are pioneer species to colonise the bare rock.

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(b) In fungi, the cell wall contains chitin or cellulose along with other polysaccharides, proteins, and lipids. Only in some fungi, e.g. Phytophthora or other oomycetes a purely cellulosic cell wall is present. Hence, only option (b) is wrong, and the rest of the options are correct. Concept Enhancer Chitin is chemically \(\mathrm{N}\)-acetyl glucosamine. The exoskeleton of insects also contains this chemical.

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(a) Fungi represent the highest number of species in the world. Around 100000
species of fungi have been formally described by taxonomists but the global
biodiversity of kingdom-Fungi is not fully understood.

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(c) Ustilago has haplontic life cycle. In their sexual phase, only zygospore is diploid structure. All others are haploid, such a sexual cycle is termed as haploid or haplontic.

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(d) Some common fungal inhabitants of soil help to combat diseases caused by soil-borne plant pathogens. These include Trichoderma harzianum which are found in damp soils. They have an inhibitory effect on the growth of the mycelium of Pythium. They serve to suppress fungi causing damping-off disease of the seedlings and thereby influence favourably the growth of crops.