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NCERT Class 11 Biology Chapter 2 Biological Classification and Virus
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Biological Classification and Virus
Chapter: 2
BIOLOGY
TEXTUAL QUESTIONS ANSWERS
Q.1. Discuss how classification systems have undergone several changes over a period of time?
Ans. The classification systems have undergone several changes with time. The first attempt of classification was made by Aristotle. He classified plants and animals. Thereafter, Linnaeus gave a two kingdom system of classification. It consists of kingdom Plantae and kingdom Animalia. This was followed by five kingdom system of classification proposed by R.H Whittaker in 1969: Kingdoms Monera, Protista, Fungi, Plantae, and Animalia.
Q.2. State two economically important uses of:
(a) Heterotrophic bacteria.
Ans. Heterotrophic bacteria:
(i) Pseudomonas biodegrades petroleum spillage.
(ii) Preparation of yogurt, curd and cheese-Streptococcus lactis converts lactose into lactic acid which converts milk to yogurt, curd and cheese.
(b) Archaebacteria.
Ans. Archaebacteria Methanogens are used in production of gobar gas from dung and sewage. They are involved in the formation of biogas and sewage treatment.
Q.3. What is the nature of cell-walls in diatoms?
Ans. The body of diatoms is covered by silica shell called frustule.
Q.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 blue-green algae in water resulting in discoloration of the water body. This increases the biological oxygen demand (BOD), resulting in the death of fishes and other aquatic animals.
Red-tides – Toxic proliferation of dino-flagellates; Gonyaulax and Gymnodinium make the sea water look red.
Q.5. How are viroids different from viruses?
Ans. Viroids are smallest self replicating particles discovered by Diener. Viroids are infectious RNA particles devoid of protein coat whereas viruses have capsid and genetic material as RNA or DNA.
Q.6. Describe briefly the four major groups of Protozoa.
Ans. On the basis of locomotory organelles, the protozoans are divided into four groups:
Flagellated Protozoans, Amoeboid Protozoans, Sporozoans and Ciliated Protozoans.
Q.7. Plants are autotrophic. Can you think of some plants that are par tially heterotrophic?
Ans. Plants have autotrophic mode of nutrition as they contain chlorophyll pigment.
Insectivorous plants are partially heterotrophic. They capture insects to get nitrogen from insects example: pitcher plant (Nepenthes), Drosera, Utricularia.
Q.8. What do the terms phycobiont and mycobiont signify?
Ans. Phycobiont is the algal component of the lichens and mycobiont is the fungal component. Algae prepare food for fun- gi and fungus provides shelter to algae and absorbs water and nutrients from the soil. This is symbiotic relationship.
Q.9. Give a comparative account of the classes of Kingdom Fungi under the following:
(i) Mode of nutrition.
(ii) Mode of reproduction.
Ans. (A) Phycomycetes include Rhizopus, Albugo etc.
(i) Mode of nutrition: They are Parasites or Saprotrophs.
(ii) Mode of reproduction: Asexual reproduction takes place through motile zoospores or non-motile aplanospores 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: includes Penicillium, Aspergillus, Claviceps, and Neuro-spora.
(i) Mode of nutrition: They are Parasites or Saprotrophs.
(ii) Mode of reproduction: Asexual reproduction occurs through asexual spores produced exogenously conidia produced on conidiophores.
Sexual reproduction takes place through ascospores produced endog-enously in sac-like asci and arranged inside ascocarps.
(C) Basidiomycetes: includes Ustilago, Agaricus and Puccinia.
(i) Mode of nutrition: They are Parasites or Saprotrophs.
(ii) Mode of reproduction: Asexual reproduction takes place com-monly through fragmentation. Asexual spores are absent.
Sexual reproduction takes place through plasmogamy and gives rise to a basidium. Four basidiospores are produced inside a basidium.
(D) Deuteromycetes: includes Alternaria, Trichoderma, and Colletotrichum.
(i) Mode of nutrition: They are sapro-phytes or parasites.
(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.
Q.10. What are the characteristic fea-tures of Euglenoids?
Ans. Euglenoids-
(i) They are without cellulose cell wall.
(ii) Majority are fresh water organisms.
(iii) Body is covered by thin flexible pro- tein covering called pellicle.
(iv) Pellicle has stripes called myonemes and is made of fibrous elastic protein.
(v) Metaboly – Creeping movements by expansion and contraction of their body.
(vi) Mode of nutrition is mixotrophic (Hol-ophytic + Saprobic/Holozoic).
(vii) They have two flagella (one long and another short). Flagella bear hairs called tinsels. Each flagella arises from a basal granule called blepha-roplast.
(viii) Chromatophores have chlorophyll a and b.
(ix) Euglenoids multiply by longitudinal binary fission in favorable conditions. Palmella stage is seen during unfavorable conditions.
Example – Euglena.
Q.11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.
Ans. Virus has two parts – nucleotide (genome) and capsid.
Nucleotide – is viral chromosome made of single molecule of nucleic acid either DNA or RNA.
Capsid – is proteinaceous covering around the virus made of sub units called capsomers.
Envelope – is loose membranous covering in some viruses. It consists of proteins (from virus), lipids and carbohydrates (from host). It is made of sub units called peplomers e.g. HIV, Herpes virus.
A.I.D.S, small pox, mumps, and influ-enza are examples of viral diseases.
Q.12. Organise a discussion in your class on the topic- Are viruses living or nonliving?
Ans. Viruses are microscopic organisms that have characteristics of both living and nonliving.
A virus consists of a strand of DNA or RNA covered by a protein coat. This presence of nucleic acid (DNA or RNA) suggests that viruses are alive.
It is inert outside the host cell. It can be crystalized and stored indefinitely. Virus does not grow. It uses the host cell for its multiplication. It lacks mo-tility and irritability. These indicate that viruses are non-living.
