The VIDYANKER team has thoughtfully prepared the NCERT Solutions for Class 11 Biology Chapter 2, "Biological Classification" These solutions are designed to help you tackle the NCERT textbook questions with ease. We recommend going through the chapter's theory before diving into the solutions for a deeper understanding. Feel free to share these NCERT Solutions for Class 12 Biology with others—learning is always better when shared!
TEXT BOOK QUESTIONS SOLVED
1.Discuss how classification systems have undergone several changes over a period of time?
Ans. Biological classification refers to the systematic scientific process of listing the organisms into a series of groups and sub-groups according to their similarities and dissimilarities. Scientists have proposed several systems of classification which have undergone changes with time.
Earlier Aristotle proposed artificial system of classification, which divided animals and plants on basis of habitat. E.g., Aquatic (fish, whale), terrestrial (e.g., reptiles, cattle) and aerial (e.g., bat, birds). Then, natural system of classification was based on morphology^ anatomy, physiology, reproduction, ontogeny, cytochemistry, etc. After natural system, organisms were classified on basis of evolutionary relationships called phylogenetic system. It is based on cytotaxonomy, chemotaxonomy, numerical taxonomy and cladistic taxonomy.
2.State two economically important uses of:
(a) heterotrophic bacteria
(b) archaebacteria
Ans. (a) Heterotrophic bacteria: They include saprotrophic, symbiotic and parasitic bacteria. These are natural scavengers as they dispose of dead bodies, organic wastes, and release raw materials for reutilisation. They also contribute to sewage disposal, manure production etc. Symbiotic bacteria help in nitrogen fixation. Some bacteria arq employed in the production of a number of industrial products like lactic acid, curd, cheese, butter, vinegar etc. Serum, vaccines, vitamins, enzymes, and antibiotics are some preparations in which certain bacteria are used. e.g., Pseudomonas, Xanthomonas etc.
(b) Archaebacteria : Archaebacteria are employed in the production of gobar gas from dung and sewage and in ruminants, they cause fermentation of cellulose.
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3.What is the nature of cell-wall in diatoms?
Ans. The cell walls of the diatoms are impregnated with silica and thus cannot be destroyed. They form two thin overlapping shells which fit together as in a soap box. Thus, diatoms have left behind large amounts of cell wall deposits in their habitat.
Ans. The cell walls of the diatoms are impregnated with silica and thus cannot be destroyed. They form two thin overlapping shells which fit together as in a soap box. Thus, diatoms have left behind large amounts of cell wall deposits in their habitat.
4.Find out what do the terms ‘algal bloom’ and ‘red tides’ signify.
Ans. Algal bloom refers to an increase in the population of algae or bluegreen algae in water, which causes discoloration of the water body.
Ans. Algal bloom refers to an increase in the population of algae or bluegreen algae in water, which causes discoloration of the water body.
Red tides are caused by red dinoflagellates. They multiply fast and form large groups; as a result, the sea becomes red in colour. Poison from these can kill other marine species.
5.How are viroids different from viruses?
Ans. Viroids are the smallest known agent of infectious diseases that contain small single-stranded RNA molecule. They lack capsid and have no proteins associated with them. Viroids infect only plants. Whereas, viruses have genetic material surrounded by a protective coat of protein or lipoprotein. The genetic material of viruses are of 4 types – double-stranded DNA, double-stranded RNA, single-stranded DNA, single-stranded RNA. They infect both plants and animals.
6.Describe briefly the four major groups of protozoa.
Ans. Four major groups of Protozoa are:
- Amoeboid protozoans: These protazons live in fresh water, sea water or moist soil. They move and capture their prey by putting out pseudopodia (false feet) as in Amoeba. Marine forms have silica shells on their surface. Some of them such as Entamoeba are parasites.
- Flagellated protozoans: Members of this class are either free-living or parasitic. They have flagella. The parasitic forms cause diaseases such as sleeping sickness. Example: Trypanosoma.
- Ciliated protozoa or ciliates: These are aquatic individuals that form a large group of protozoa. Their typical features are the presence of numerous cilia on the entire body surface and the presence of two kinds of nuclei. All the cilia move in the same direction to push forward the water laden food inside a cavity called gullet. Example: Paramoecium, Vorticella, etc.
- Sporozoans: These are endoparasites causing diseases and some other pathogens. These organisms are unicellular and their body covered with a pellicle. They have neither cilia nor flagella. They include the malaria causing parasite Plasmodium.
7.Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Ans. Some insectivorous plants like Drosera, Nepenthes, Utricularia are partially heterotrophic plant. These plants possess low levels of nitrogenous compounds but are otherwise autotrophic. They trap various insects to obtain nitrogenous compounds from them. Rest, the food i.e., carbohydrate is manufactured by themselves.
8.What do the terms phycobiont and mycobiont signify?
Ans. Lichens are good examples of symbiotic life of algae and fungi. The part constituted by algae is called Phycobiont and the part constituted by fungi is called Mycobiont. Fungi provide minerals and support to the alage, whereas algae provide nutrition to the fungi.
9.Organise a discussion in your class on the topic – ‘Are viruses living or non-living’?
Ans. Viruses are midway between a non-living entity and a living organism. It is very hard to decide whether it belongs to the category of a living or that of a non-living entity. Some characters of viruses are inclined towards their non-living nature whereas many other characters are inclined towards 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?
Ans. Characteristic Features of Euglenoids:
→ Fresh water organisms that seen in stationary or standing water.
→ They do not possess a cell wall; however, they have a layer around their body, known as pellicle, composed of proteins that gives flexibility to their bodies.
→ These organisms are autotrophs when in the presence of sunlight, whereas they are heterotrophs in the absence of sunlight.
→ The eye spot is very small and light sensitive.
11.Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.
Ans. Viruses are small infectious agents that can infect all forms of life. A virus consists of genetic material surrounded by a protein coat. The genetic material may be present in the form of DNA or RNA. Most of the viruses, infecting plants, have single stranded RNA as genetic material. On the other hand, the viruses infecting animals have single or double stranded RNA or double stranded DNA.
Bacteriophages or viruses infecting bacteria mostly have double stranded DNA. Their protein coat called capsid is made up of capsomere subunits. These capsomeres are arranged in helical or polyhedral geometric forms. A.I.D.S, small pox, mumps, and influenza are some common examples of viral diseases.
12.Give a comparative account of the classes of Kingdom Fungi under the following:
(i) mode of nutrition (ii) mode of reproduction
Ans. (A) Phycomycetes: This group of fungi includes members such as Rhizopus, Albugo, etc.
(i) Mode of nutrition
They are obligate parasites on plants or are found on decaying matter such as wood.
(ii) Mode of reproduction
Asexual reproduction takes place through motile zoospores or non-motile aplanospores that are produced endogenously in sporangium.
Sexual reproduction may be of isogamous, anisogamous, or oogamous type. It results in the formation of thick-walled zygospore.
(B) Ascomycetes: This group of fungi includes members such as Penicillium, Aspergillus, Claviceps, and Neurospora.
(i) Mode of nutrition
They are sporophytic, decomposers, parasitic or coprophilous (growing on dung).
(ii) Mode of reproduction
Asexual reproduction occurs through asexual spores produced exogenously, such as conidia produced on conidiophores.
Sexual reproduction takes place through ascospores produced endogenously in saclike asci and arranged inside ascocarps.
(C) Basidiomycetes: This group of fungi includes members such as Ustilago, Agaricus and Puccinia.
(i) Mode of nutrition
They grow as decomposers in soil or on logs and tree stumps. They also occur as parasites in plants causing diseases such as rusts and smuts.
(ii) Mode of reproduction
Asexual reproduction takes place commonly through fragmentation. Asexual spores are absent.
Sex organs are absent but sexual reproduction takes place through plasmogamy. It involves fusion of two different strains of hyphae. The resulting dikaryon gives rise to a basidium. Four basidiospores are produced inside a basidium.
(D) Deuteromycetes: This group of fungi includes members such as Alternaria, Trichoderma, and Colletotrichum.
(i) Mode of nutrition
Some members are saprophytes while others are parasites. However, a large number act as decomposers of leaf litter.
(ii) Mode of reproduction
Asexual reproduction is the only way of reproduction in deuteromycetes. It occurs through asexual spores called conidia.
Sexual reproduction is absent in deuteromycetes.
