{"id":18379,"date":"2019-12-06T11:12:40","date_gmt":"2019-12-06T05:42:40","guid":{"rendered":"https:\/\/www.cbselabs.com\/?p=18379"},"modified":"2021-09-18T15:15:47","modified_gmt":"2021-09-18T09:45:47","slug":"important-questions-for-class-12-biology-cbse-biodiversity","status":"publish","type":"post","link":"https:\/\/www.cbselabs.com\/important-questions-for-class-12-biology-cbse-biodiversity\/","title":{"rendered":"Important Questions for CBSE Class 12 Biology Biodiversity"},"content":{"rendered":"
1.Biodiversity<\/strong> can be defined as the occurrence of different types of genes, gene pools, species, habitats and ecosystem in a given region.<\/p>\n (i) The term biodiversity<\/strong> was given by a sociobiologist Edward Wilson<\/strong> to describe the combined diversity at all the levels of biological organisation.<\/p>\n (ii) There are more than 20,000 species of ants, 3,00,000 species of beetles, 28,000 species of fishes and nearly 20,000 species of orchids.<\/p>\n (iii) Biodiversity can be divided into following three levels:<\/p>\n (a)<\/strong> Genetic diversity<\/strong> is the diversity at the genetic level.<\/p>\n Example, Genetic variation in the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges might be in terms of the potency and concentration of the active chemical (reserpine) that the plant produces.<\/p>\n (b)<\/strong> Species diversity<\/strong> is diversity at the species level. For example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.<\/p>\n (c) Ecological diversity<\/strong> is the diversity at ecosystem level. For example, India with its deserts, rainforests, mangroves, coral reefs, wetlands, estuaries and alpine meadows has a greater ecosystem diversity.<\/p>\n 2. Global species diversity<\/strong> means total species present on the earth.<\/p>\n 3. Biodiversity in India<\/p>\n <\/p>\n 4. Patterns of biodiversity<\/strong> indicate that the biodiversity is not uniform throughout the world because it is affected by:<\/p>\n (i) Latitudinal gradients demonstrates the decrease in species diversity as we move away from the equator towards the poles.<\/p>\n For example,<\/p>\n (d) Reasons for Greater Biodiversity in Tropics<\/strong><\/p>\n (ii) Species-Area Relationships<\/strong><\/p>\n <\/p>\n NOTE On log scale the relationship becomes linear<\/p>\n logS = log C + Z logA where, S = Species richness, A=Area<\/p>\n C = Y-intercept, Z = Slope of the line (regression coefficient)<\/p>\n 5.\u00a0Importance of Species Diversity to the Ecosystem<\/strong><\/p>\n (i) According to ecologists, communities with more species tend to be more stable than those with less species.<\/p>\n (ii) Attributes of a stable community are<\/p>\n (iii) David Tilman\u2019s longterm experiments on ecosystem found that plots with more species showed less year-to-year variation in total biomass. He also showed that increased diversity contributed to higher productivity.<\/p>\n (iv) It is not clear how species richness contributes to the well-being of an ecosystem. But, it is enough to realise that rich biodiversity is not only essential for ecosystem health but imperative for the survival of the human race on this planet.<\/p>\n (v) Paul Ehrlich<\/strong> through his rivet popper hypothesis<\/strong> tried to explain the importance of biodiversity for the survival of species.<\/p>\n 6. Loss of biodiversity<\/strong> is caused by the over population, urbanisation and industrialisation.<\/p>\n (i) The colonisation of tropical Pacific Islands by humans have led to the extinction of more than 2,000 species of native birds.<\/p>\n (ii) The IUCN Red list (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.<\/p>\n (iii) Some latest examples of recent extinctions are dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller\u2019s sea cow (Russia) and three sub-species (Bali, Javan and Caspian) of tiger.<\/p>\n (iv) The last twenty years alone have witnessed the disappearance of 27 species.<\/p>\n (v) Presently, 12% of bird species, 23% of all mammal species, 32% of all amphibian species and 31% of all gymnosperm species in the world face the threat of extinction.<\/p>\n (vi) Careful analysis of records shows that amphibians appear to be more vulnerable to extinction.<\/p>\n (vii) The grim scenario of extinctions is the fact that more than 15,500 species world wide are facing the threat of extinction.<\/p>\n Results of Loss of Biodiversity in a Region<\/strong><\/p>\n Causes of Biodiversity Losses<\/strong><\/p>\n These are mainly four as given below. They are also named as The Evil Quartet.<\/p>\n (i) Habitat Loss and Fragmentation<\/strong><\/p>\n (a) The main cause of extinction of species is the destruction of their habitat<\/p>\n (b) Examples,<\/p>\n (c) When large habitats are broken up into small fragments due to various human activities, mammals and birds requiring large territories and certain animals with migratory habits are badly affected, leading to their population decline.<\/p>\n (d) The degradation of many habitats by pollution also threatens the survival of many species, many have extincted in last 500 years.<\/p>\n (ii) Over-exploitation of natural resources by humans results in degradation and extinction of the resources. For example, Steller\u2019s sea cow, passenger pigeon and many marine fishes have extincted in last 500 years.<\/p>\n (iii) Alien (exotic) Species Invasions<\/strong><\/p>\n When alien (exotic) species are introduced unintentionally or deliberately, some become invasive and cause harmful impact resulting in extinction of the indigenous species. Examples,<\/p>\n (iv) Co-extinctions<\/strong> When a species become extinct, the plant and animal species associated with it in an obligatory manner, also become extinct. For example, if the host species becomes extinct, all those parasites exclusively found on it will also become extinct. In plant pollinator mutualism, extinction of one results in the extinction of the other.<\/p>\n 1.Identify A and B in the figure given below representing proportionate number of major vertebrate taxa.\u00a0[Delhi 2014]<\/strong> A represent mammals<\/p>\n B represents ambhibians\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 (1)<\/p>\n 2.Write the level of biodiversity\u00a0represented by a mangrove. Give another example falling in the same level.\u00a0\u00a0\u00a0 [Delhi 2014C]<\/strong><\/p>\n Ans<\/strong>.The mangroves represents biodiversity at ecological level. Other examples of ecological diversity are deserts, rainforests, coral reefs, etc.<\/p>\n 3.Name the type of biodiversity represented by the followings<\/strong><\/p>\n Ans.\u00a0(i)<\/strong> Genetic diversity<\/p>\n (ii)<\/strong> Genetic diversity<\/p>\n 4. Why is tropical environment able to support greater species diversity?\u00a0[Delhi 2011C]<\/strong><\/p>\n Ans.<\/strong> Tropical latitudes have remained\u00a0undisturbed for millions of years and had a long evolutionary time for species diversification. Thus, it supports greater species diversity.<\/p>\n 5. Eichhornia crassipes is an alien\u00a0hydrophyte introduced in India. Mention the problem posed by this plant.[All India 2010C]<\/strong><\/p>\n Ans<\/strong>. Water hyacinth (Eichhornia) introduced in\u00a0India is threatening the existing aquatic life in ponds and lakes, etc., as it clogs the stagnant water bodies very fast, thus, the native species are endangered.<\/p>\n 6.\u00a0The Amazon rainforest is referred to as the lungs of planet. Mention any one human activity which causes loss of biodiversity in this region.\u00a0[All India 2010C]<\/strong><\/p>\n Ans<\/strong>. Human activity causing loss of biodiversity are:<\/p>\n (i) Many plants are cut in Amazon rainforest<\/p>\n (ii) Forests are converted \u00a0 to grasslands for\u00a0raising beef cattle.<\/p>\n 7. Name the unlabelled areas A and B of the pie chart representing biodiversity of vertebrates showing the proportionate number of species of major taxa.\u00a0[Foreign 2009]<\/strong> Ans<\/strong>. \u00a0A- Fishes<\/p>\n B–<\/strong>\u00a0 Amphibians Ans.<\/strong> A- Insects<\/p>\n B–<\/strong>\u00a0Molluscs Ans.<\/strong> A- Fungi<\/p>\n B–<\/strong>\u00a0 Angiosperms Ans.<\/strong> Nile perch is the invasive fish introduced in Lake Victoria.<\/p>\n 11.List four causes of biodiversity loss.\u00a0[Delhi 2014C]<\/strong><\/p>\n Ans. \u00a0<\/strong>(i)<\/strong> Habitat loss and fragmentation (ii)<\/strong> Over-exploitation (iii)<\/strong> Alien species invasions<\/p>\n 12.What is meant by alien species invasion? Name one plant and one animal alien species that are a threat to our Indian native species. [All India 2013]<\/strong><\/p>\n Ans.<\/strong> Intentional or chance introduction of exotic species into new islands or countries by man is called alien species invasion.\u00a0For example,\u00a0Nile perch introduced into Lake Victoria in East Africa caused loss of more than 200 species of cichlid fish. Plant alien species-Lantana camara<\/strong> and animal alien species – Clarius gariepinus<\/strong> are a threat to our Indian native species.<\/p>\n 13. Justify with the help of an example where a deliberate attempt by humans has led to the extinction of a particular species.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 [Delhi 2011]<\/strong><\/p>\n Ans.<\/strong> Over-exploitation of natural resources or over hunting of animals has led to extinction of particular species,<\/p>\n e.g. Steller’s sea cow and passenger pigeon.<\/p>\n 14. The given graph shows species-area relationship. Write the equation of the Curve A and Explain. [All India 2011]<\/strong> Ans.<\/strong> The equation for the curve A is<\/p>\n S\u00a0– CAZ<\/sup><\/p>\n where, S-Species richness,<\/p>\n A- Area C-Y-interecept,<\/p>\n Z- Slope of line<\/p>\n (regression coefficient)<\/p>\n (i) Alexander Von Humboldt observed that within a region, species richness increased with increasing explored area, but only up to a limit.<\/p>\n (ii) The relation between species richness and area for a wide variety of taxa like angiosperms, birds, fishes, etc., turns out to be a rectangular hyperbola.<\/p>\n 15.With the help of an example, explain how alien species invasion causes biodiversity loss?\u00a0<\/strong>[Delhi 2011]<\/strong><\/p>\n or<\/strong><\/p>\n Alien species are a threat to native species. Justify taking examples of an animal and a plant alien species.\u00a0[All India 2010]<\/strong><\/p>\n or<\/strong><\/p>\n Sometimes alien species affect the indigenous organisms leading to their extinction. Substantiate this statement with the help of any two examples.\u00a0[Delhi 2010 C]<\/strong><\/p>\n Ans.<\/strong> Alien species become invasive, compete with the native species and cause extinction of indigenous species.<\/p>\n (i)<\/strong> Introduction of Nile perch into Lake Victoria lead to extinction of more than 200 species of cichlid fish in that lake.<\/p>\n (ii)<\/strong> Carrot grass (Parthenium and Lantana) introduced in our country have become invasive and cause environmental damage. They pose a threat to the native species of plants in our forests.<\/p>\n 16.Giving two reasons explain why\u00a0there is more species biodiversity in tropical latitudes than in temperate ones.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 [All India 2010]<\/strong><\/p>\n Ans.<\/strong> Biodiversity is more in tropical latitudes than in temperate ones. The reasons are:<\/p>\n (i) Speciation is a function of time. The\u00a0temperate regions were subjected to frequent glaciation in the past, while the tropics have remained undisturbed and so had longer time to evolve more species diversity.<\/p>\n (ii) More solar radiation is available in tropical region. This leads directly to more productivity and indirectly to greater species diversity.<\/p>\n (iii) The environment of tropics is less seasonal and relatively more constant and predictable, which encourages niche specialisation and species diversity.<\/p>\n 17.In the biosphere, immense\u00a0biological diversity exists at all levels of biological organisation. Explain any two levels of\u00a0biodiversity.\u00a0\u00a0\u00a0\u00a0 [All India 2010]<\/strong><\/p>\n Ans.<\/strong> Levels of biodiversity in biosphere<\/p>\n (i)<\/strong> Genetic diversity It refers to the\u00a0diversity of genes within a species.<\/p>\n For example, there are more than 50,000 genetically different strains of rice in India.<\/p>\n (ii)<\/strong> Species diversity It refers to the number of different species within a given region. For example, Western Ghats have a greater amphibian species diversity than Eastern Ghats.<\/p>\n 18.List the features that make a stable biological community.\u00a0[All India 2010]<\/strong><\/p>\n Ans.<\/strong> Features of stable biological community<\/p>\n (i)<\/strong> It should not show much variation in productivity from year-to-year.<\/p>\n (ii)<\/strong> It should be resistant or resilient to occasional disturbances both natural and man-made.<\/p>\n (iii)<\/strong> It must be resistant to invasions of alien species.<\/p>\n 19.Write any two hypothesis put forth by ecologists explaining the existence of greater biodiversity in tropical regions than in temperate regions. [Foreign 2010]<\/strong><\/p>\n Ans<\/strong>. Hypothesis put forth by ecologists explaining the existence of greater biodiversity in tropical regions, than in temperates are:<\/p>\n (i) Speciation is a function of time, the temperate regions were subjected to frequent glaciation in the past, while the tropics have remained undisturbed and hence, had longer time to evolve more species diversity.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 (1)<\/p>\n (ii) The tropical environments are less seasonal and relatively more constant\u00a0and predictable than temperate regions, niche specialisation has been promoted\/favoured by such constant environments and hence, there is greater species diversity.<\/p>\n 20.Name the sociobiologist who popularised the term biodiversity. Identify the levels of biodiversity in India represented by<\/strong><\/p>\n Ans. \u00a0<\/strong>Edward Wilson, a sociobiologist popularised the term biodiversity. (1\/2)<\/p>\n (i) Species diversity<\/strong> Western Ghats have a\u00a0greater amphibian species diversity than the Eastern Ghats.<\/p>\n (ii)<\/strong> Genetic diversity<\/strong> India has more than 50,000 genetically different strains of rice.<\/p>\n (iii) Ecological diversity <\/strong>Presence of deserts, mangroves and coral reefs in India in greater than in Scandinavian country like\u00a0Norway.<\/p>\n 21.Observe the global biodiversity distribution of major plant taxa in the diagram and answer the questions that follow.<\/strong> Ans. (i) Ferns and allies.<\/p>\n (ii) They grow in humid and shady places\u00a0and need water for fertilisation. Due to the high temperature and dry condition, few of them survived.<\/p>\n (iii) Fungi has saprotrophic mode of nutrition,\u00a0they depend only on organic matter for their survival and hence, survive in any environment.<\/p>\n (iv) Angiosperms are most advanced and\u00a0algae are most primitive.<\/p>\n 22. The following graph shows the species-area relationship. Answer the following questions as directed.<\/strong> (ii) Write the situations as discovered by the ecologists when the value of Z (slope of the line) lies between<\/strong><\/p>\n What does Z stand for?<\/strong><\/p>\n (iii) When would the slope of the line ‘b’ become steeper? [All India 2014]\u00a0<\/strong><\/p>\n Ans. \u00a0(i)\u00a0<\/strong>Alexander Von Humboldt studied the\u00a0relationship shown in above graph. He observed that the species richness in an area increased with an increase in exploring area, up to a certain limit only.<\/p>\n (ii)<\/strong> (a)<\/strong> Ecologists have observed that when the value of Z lies between 0.1 – 0.2 when the species are considered for a small or average area.<\/p>\n (b)<\/strong> When the value of Z lies between\u00a00.6-1.2, the area considered is very large. Z represents the slope of the line, i.e. regression coefficient.<\/p>\n (iii)<\/strong> The slope of the line ‘b’ will become steeper when very large areas such as continents are considered for species area relationship.<\/p>\n 23. Explain giving three reasons, why\u00a0tropics show greatest levels of species diversity? [All India 2014]<\/strong><\/p>\n\n
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Previous Years Examination Questions<\/span>\u00a0<\/strong><\/h3>\n
1 Mark Questions\u00a0<\/strong><\/span><\/h3>\n
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\nAns. \u00a0<\/strong>In the above mentioned figure, among the major vertebrate taxa<\/p>\n\n
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\n8.Name the unlabelled areas A and B of the pie chart representing the global biodiversity of invertebrates showing their proportionate number of species of major taxa.\u00a0[Delhi 2009]<\/strong>
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\n9.Name the unlabelled areas A and B of the pie chart representing the biodiversity of plants showing their proportionate number of species of major taxa. [All India 2009]<\/strong>
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\n10.About 200 species of cichlid fish became extinct when a particular fish was introduced in Lake Victoria of Africa. Name the invasive fish.\u00a0[Foreign 2008]\u00a0<\/strong><\/p>\n2 Marks Questions\u00a0<\/strong><\/span><\/h3>\n
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3 Marks Questions\u00a0<\/strong><\/span><\/h3>\n
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\n(i) Name the naturalist who studied the kind of relationship shown in the graph. Write the observations made by him.<\/strong><\/p>\n\n