The Air Prevention and Control of Pollution Act came into force in: (1) 1990 (2) 1981 (3) 1975 (4) 1985 (MCQ)

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Ans:- (B) 1981

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Mutations

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Charles Darwin (1859) in his book ' Origin of Species ' postulated that evolution or formation of newer species of organisms from the pre-existing ones occurs through accumulation of variations in the organisms. Without variations all the individuals of a species shall be alike. None of them would have better characteristics for being favoured in the struggle for existence and natural selection. A change in the environment could kill all of them. Variations increase the adaptability of the individuals and make them better fitted in the struggle for existence and hence natural selection. There are two sources of variations in the populations - recombinations and mutations . (i) Recombinations are also called continuous variations . They are not new traits but are formed by new combination of genes or traits already existing in the population. Recombinations are produced due to three reasons:  (a) Crossing over of nonsister chromatid segments during meiosis.  (b) Random segrega
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CLASSIFICATION Division : Bryophyta Class     : Hepaticopsida Order     : Marchantiales Family   : Marchantiaceae Genus   : Marchantia MORPHOLOGICAL FEATURES OF THE THALLUS- 1. The main plant body is gametophytic thallus. Gametophyte is small, well developed and  autotrophic. 2. The plant body is dorsiventral, the dorsal surfaces is dark green having a distinct midrib and  dichotomously branched. 3. The ventral or the lower surface bear numerous rhizoids and scales. 4. The rhizoids are unicellular and branched structures meant for anchorage and absorption. They  may be smooth walled or tuberculated (bearing peg-like projections). 5. The scales are purplish multicellular structures which protect the thallus from the dessication  by secreting the mucilage. 6. The dorsal surface also bears small gemma cups on the mid ribs. Inside the gemma cups many  erect stalked gemmae are present which helps in vegetative reproduction of Marchantia. 7. Sexual reproduction is oogamous. The male reproduc
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