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8.What do the terms phycobiont and mycobiont signify?, Soln. A lichen is structurally organised, entity consisting of the permanent association, of a fungus and an alga. The fungal component of a lichen is called mycobiont and the algal, component is called phycobiont. Both mycobiont and phycobiont are associated, in symbiotic union in which the fungus is predominant and alga is subordinate partner. – ; Fungus, provides the structural covering that protects alga from unfavourable conditions,, i.e., drought, heat, etc. It also traps moisture from the atmosphere and anchors the, lichen to a rock, tree bark, leaves and other similar supports. The alga prepares organic food by, the process of photosynthesis from carbon dioxide. If the algal component is cyanobacteria (bluegreen alga), they fix atmospheric nitrogen in addition to preparation of food., 9.Organise a discussion in your class on the topic – ‘Are viruses living or non-living’?, Soln. Viruses are regarded as intermediate between non-living entities and living, organisms. It is very difficult to ascertain whether they are living or non-living. Some . characters of, viruses suggest their non-living nature whereas many other characters suggest their living nature., They resemble non-living objects in –, (i) Lacking protoplast., (ii)Ability to get crystallised., (iii)Inability to live independent of 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 synthesized separately., Viruses resemble living beings in –, (i)Being formed of organic macromolecules which occur only in living beings., (ii)Presence of genetic material., (iii)Ability to multiply or reproduce although only inside living cell., (iv)Occurrence of mutations., (v) Occurrence of enzyme transcriptase in most viruses., (vi)Some viruses like Pox virus contains vitamins like riboflavin and biotin., (vii)Infectivity and host specificity., (viii)Viruses are ‘killed’ by autoclaving and ultraviolet rays., (ix)They breed true to their type. Even variations are inheritable., (x) They take over biosynthetic machinery of the host cell and produce chemicals required for their, multiplication., (xi)Viruses are responsible for a number of infectious’ diseases like common cold, epidemic, influenza, chicken pox., 10.What are the characteristic features of Euglenoids?, Soln. The euglenoid flagellates are the most interesting organisms having a mixture of animal and, plant characteristics. The characteristic features are:, (i) They are unicellular flagellates., (ii)These protists lack a definite cellulose cell wall. Instead the cells are covered by, a thin membrane known as pellicle. The pellicle is composed of protein, lipid and carbohydrates., (iii)One or two flagella which help these protists in active swimming are present. If two flagella are, present, then one is long and other is short. They are tinsel – shaped i.e., with two longitudinal, rows of fine hairs. Each flagellum has its own basal granule. The two flagella join with each other, at a swelling, called paraflagellar body and finally only one long flagellum emerges out through the, cytostome., (iv)Cell at the anterior end possesses an eccentric mouth or cytostome which leads into a flaskshaped cavity viz. gullet or cytopharynx. Gullet opens into a large basal reservoir., (v) At one end of the reservoir, the cytoplasm contains an orange red stigma (eye spot). The eye

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spot is a curved plate with orange-red granules and contains red pigment astaxanthin. Both, paraflagellar body and eye spot act as photoreceptors., (vi)Just below the reservoir is found a contractile vacuole having many feeding canals. The, contractile vacuole takes part in osmoregulation. It expands and pumps its fluid contents in the, reservoir., (vii)The mode of nutrition in euglenoids is holophytic or photoautotrophic. Some euglenoids show, mixotrophic nutrition (both holophytic as well as saprobic mode)., (viii)Cytoplasm is differentiated into ectoplasm and endoplasm. Nucleus is large and occurs, roughly in middle. The envelope and nucleolus persist during cell division., (ix)Each chloroplast is composed of a granular matrix traversed by 10-45 dense bands and is, covered by 3-membraned envelope. They contain the photo¬synthetic pigments-chlorophyll – n, b., They store carbohydrates as paramylon bodies, scattered throughout the cytoplasm., (x) Asexual reproduction occurs by longitudinal binary fission. The flagellum is duplicated before, cell division., (xi)Under unfavourable condition the euglenoids form cysts to perennate the dry period., (xii)Sexual reproduction is not observed., 11.Give a brief account of viruses with respect to their structure and nature of genetic, material. Also name four common viral diseases., Soln. Virus (L. poisonous fluid) is a group of ultramicroscopic, non-cellular, highly infectious, agents that multiply only intracellularly- inside the living host cells without involving growth and, division. Outside the host cells, they are inert particles. They are nucleoproteins having one or, more nucleic acid molecule, either DNA or RNA, encased in a protective coat of protein or, lipoprotein. A virus consist of two parts – nucleoid (genome) and capsid. An envelope and few, enzymes are present in some cases,, (i) Nucleoid : The nucleic acid present in the virus is called nucleoid and it represents viral, chromosome. It is made up of a single molecule of nucleic acid. It may be linear, or circular and nucleic acid can be DNA or RNA. It is the infective part of virus which utilizes the, metabolic machinery of the host cell for synthesis and assembly of viral components., (ii)Capsid : It is a protein covering around genetic material. Capsid have protein subunits called, capsomeres. Capsid protects nucleoid from damage from physical and chemical agents. ,, (iii)Envelope : It is the outer loose covering present in certain viruses like animal viruses (e.g., HIV), but rarely present in plant and bacterial viruses and made of protein of viral origin and, lipid and, carbohydrate of host. Outgrowths called spikes may be present. Envelope proteins have subunits, called peplomers. A virus without envelope is naked virus., (iv)Enzymes : Rarely, lysozymes are found in bacteriophages. Reverse transcriptase enzyme, (catalyses RNA to DNA synthesis) is found in some RNA viruses like HIV. Some common viral, diseases are – influenza, polio, measles, chickenpox, hepatitis, AIDS, bird flu, SARS (Severe, Acute Respiratory Syndrome) etc., 12.Give a comparative account of the classes of Kingdom Fungi under the following:, (i) mode of nutrition (ii) mode of reproduction, Soln.