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                                                                            Table of Contents 
           1.    Solved Environment Prelims Questions 2011-20 .............................................................................................................................. 18 
              1.1.     2011-2012 ...................................................................................................................................................................................... 18 
              1.2.     2013 ................................................................................................................................................................................................ 22 
              1.3.     2014 ................................................................................................................................................................................................ 25 
              1.4.     2015 ................................................................................................................................................................................................ 29 
              1.5.     2016 ................................................................................................................................................................................................ 32 
              1.6.     2017 ................................................................................................................................................................................................ 35 
              1.7.     2018 ................................................................................................................................................................................................ 37 
              1.8.     2019 ................................................................................................................................................................................................ 39 
              1.9.     2020 ................................................................................................................................................................................................ 42 
           2.    Environment, Habitat and Ecosystem ................................................................................................................................................. 44 
              2.1.     Environment .................................................................................................................................................................................. 44 
              2.2.     Habitat ............................................................................................................................................................................................ 44 
                     2.2.1.   Difference Between Habitat and Environment ................................................................................................................................. 44 
              2.3.     Ecosystem ...................................................................................................................................................................................... 44 
                     2.3.1.   Classification of Ecosystems .............................................................................................................................................................. 44 
                     2.3.2.   Difference Between Ecology, Environment, Habitat & Ecosystem ................................................................................................... 44 
              2.4.     Components of an Ecosystem ..................................................................................................................................................... 45 
                     2.4.1.   Abiotic Components .......................................................................................................................................................................... 45 
                     2.4.2.   Effect of Abiotic Components on Terrestrial Primary Producers (Plants) ......................................................................................... 46 
                     2.4.3.   Biotic Components ............................................................................................................................................................................ 47 
           3.    Ecology – Principles and Organizations .............................................................................................................................................. 48 
              3.1.     Levels of Organizations in Ecology............................................................................................................................................. 48 
                     3.1.1.   Individual and Species ....................................................................................................................................................................... 48 
                     3.1.2.   Population ......................................................................................................................................................................................... 48 
                     3.1.3.   Community ........................................................................................................................................................................................ 48 
                     3.1.4.   Ecosystem ......................................................................................................................................................................................... 49 
                     3.1.5.   Biome ................................................................................................................................................................................................ 49 
                     3.1.6.   Biosphere .......................................................................................................................................................................................... 50 
              3.2.     Principles of Ecology .................................................................................................................................................................... 50 
                     3.2.1.   Adaptation......................................................................................................................................................................................... 50 
                     3.2.2.   Variation ............................................................................................................................................................................................ 51 
                     3.2.3.   Speciation .......................................................................................................................................................................................... 51 
                     3.2.4.   Mutation ........................................................................................................................................................................................... 52 
                     3.2.5.   Natural Selection ............................................................................................................................................................................... 52 
                     3.2.6.   Evolution ........................................................................................................................................................................................... 52 
                     3.2.7.   Extinction .......................................................................................................................................................................................... 52 
           4.    Functions of an Ecosystem.................................................................................................................................................................... 54 
              4.1.     Ecological Succession ................................................................................................................................................................... 54 
                     4.1.1.   Stages in Ecological Succession ......................................................................................................................................................... 54 
                     4.1.2.   Primary Succession ............................................................................................................................................................................ 54 
                     4.1.3.   Secondary Succession ....................................................................................................................................................................... 54 
                     4.1.4.   Autogenic and Allogenic Succession ................................................................................................................................................. 56 
                     4.1.5.   Succession in Plants........................................................................................................................................................................... 56 
                     4.1.6.   Succession in Water .......................................................................................................................................................................... 56 
              4.2.     Homeostasis in Ecosystem ........................................................................................................................................................... 56 
                     4.2.1.   Homeostasis ...................................................................................................................................................................................... 57 
           5.    Energy Flow Through an Ecosystem – Trophic Levels ....................................................................................................................... 58 
              5.1.     Food Chain ..................................................................................................................................................................................... 58 
                     5.1.1.   Grazing food chain ............................................................................................................................................................................ 58 
                     5.1.2.   Detritus food chain ............................................................................................................................................................................ 58 
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              5.2.     Food Web ....................................................................................................................................................................................... 59 
                     5.2.1.   Types of Biotic Interactions in a Food Web ....................................................................................................................................... 60 
              5.3.     Ecological Pyramids ...................................................................................................................................................................... 62 
                     5.3.1.   Pyramid of Numbers ......................................................................................................................................................................... 62 
                     5.3.2.   Pyramid of Biomass ........................................................................................................................................................................... 63 
                     5.3.3.   Pyramid of Energy ............................................................................................................................................................................. 63 
                     5.3.4.   Limitations of Ecological Pyramids .................................................................................................................................................... 64 
                     5.3.5.   Biomagnification – Pollutants and Trophic Level .............................................................................................................................. 64 
           6.    Biogeo Chemical Cycling or Nutrient Cycling .................................................................................................................................... 66 
              6.1.     Types of Nutrient Cycles .............................................................................................................................................................. 66 
              6.2.     Carbon Cycle (Gaseous Cycle) ..................................................................................................................................................... 66 
                     6.2.1.   Steps in Carbon Cycle ........................................................................................................................................................................ 66 
              6.3.     Nitrogen Cycle (Gaseous Cycle) .................................................................................................................................................. 67 
                     6.3.1.   Nitrogen Fixing – N  to NH  ............................................................................................................................................................... 67 
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                     6.3.2.   Nitrification – Ammonia to Nitrates .................................................................................................................................................. 69 
                     6.3.3.   Ammonification – Urea, Uric Acid to Ammonia ................................................................................................................................ 69 
                     6.3.4.   Denitrification – Nitrate to Nitrogen ................................................................................................................................................. 69 
              6.4.     Methane (CH ) Cycle (Compound Gaseous Cycle) ................................................................................................................... 70 
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                     6.4.1.   Natural Sources of Methane Emissions ............................................................................................................................................. 71 
                     6.4.2.   Human Sources of Methane Emissions ............................................................................................................................................. 71 
                     6.4.3.   Methane Sink .................................................................................................................................................................................... 72 
              6.5.     Phosphorus Cycle (Sedimentary cycle) ...................................................................................................................................... 73 
              6.6.     Sulphur Cycle (Sedimentary cycle) ............................................................................................................................................. 73 
                     6.6.1.   Steps in Sulphur Cycle ....................................................................................................................................................................... 73 
           7.    Natural Ecosystems ................................................................................................................................................................................ 75 
              7.1.     Terrestrial Ecosystems or Biomes ............................................................................................................................................... 75 
                     7.1.2.   Tundra Biome .................................................................................................................................................................................... 75 
                     7.1.3.   Taiga or Boreal Biome ....................................................................................................................................................................... 76 
                     7.1.4.   Temperate Deciduous Biome (North-Western Europe – British Type Climate) ................................................................................ 76 
                     7.1.5.   Temperate Rainforest Biome ............................................................................................................................................................ 76 
                     7.1.6.   Sub-Tropical Deciduous Biome in Eastern China, South-eastern USA ............................................................................................... 76 
                     7.1.7.   Steppe or Temperate Grassland Biome............................................................................................................................................. 76 
                     7.1.8.   Temperate Deciduous Biome (Mediterranean Climate) ................................................................................................................... 76 
                     7.1.9.   Tropical Deciduous Biome (Monsoon Climate) ................................................................................................................................. 76 
                     7.1.10.  Savanna or Tropical Wet and Dry Biome ........................................................................................................................................... 76 
                     7.1.11.  Tropical Rainforest Biome ................................................................................................................................................................. 77 
                     7.1.12.  Desert Biome ..................................................................................................................................................................................... 79 
              7.2.     Aquatic Ecosystems ...................................................................................................................................................................... 80 
                     7.2.1.   Aquatic Organisms ............................................................................................................................................................................ 80 
                     7.2.2.   Factors Limiting the Productivity of Aquatic Habitats ....................................................................................................................... 80 
              7.3.     Ecosystem Services & Goods ....................................................................................................................................................... 81 
                     7.3.1.   Quantifying the Economic Value of Natural Ecosystems (Ecosystem valuation) .............................................................................. 81 
                     7.3.2.   The Economics of Ecosystems and Biodiversity (TEEB) ..................................................................................................................... 81 
                     7.3.3.   Payment for Ecosystem Services (PES) .............................................................................................................................................. 82 
                     7.3.4.   Ecosystem Services by Seagrass ........................................................................................................................................................ 83 
                     7.3.5.   Ecosystem Services by Seaweed ....................................................................................................................................................... 84 
           8.    Wetland Ecosystem ................................................................................................................................................................................ 86 
              8.1.     Differences Between Wetlands and Lakes ................................................................................................................................. 86 
              8.2.     Estuarine Wetland Ecosystem ..................................................................................................................................................... 86 
                     8.2.1.   Importance of Estuaries .................................................................................................................................................................... 87 
                     8.2.2.   Differences between Lagoon and Estuary ......................................................................................................................................... 87 
                     8.2.3.   Estuarine Vegetation ......................................................................................................................................................................... 88 
                     8.2.4.   Indian Estuarine Ecosystem............................................................................................................................................................... 88 
                     8.2.5.   Issues of Indian Estuarine Ecosystem ................................................................................................................................................ 88 
              8.3.     Mangroves ..................................................................................................................................................................................... 88 
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                      8.3.1.    Adaptive Mechanism of Mangroves.................................................................................................................................................. 88 
                      8.3.2.    Mangroves in India ............................................................................................................................................................................ 90 
                      8.3.3.    Global Status of Mangrove Cover...................................................................................................................................................... 91 
                      8.3.4.    Importance of mangroves ................................................................................................................................................................. 91 
                      8.3.5.    Threats to Mangroves and Associated Consequences ...................................................................................................................... 92 
               8.4.      Importance of Wetlands .............................................................................................................................................................. 93 
               8.5.      Reasons for the Depletion of Wetlands ..................................................................................................................................... 95 
                      8.5.1.    Mitigation of Wetland Destruction ................................................................................................................................................... 95 
               8.6.      Measures to Protect Wetlands .................................................................................................................................................... 95 
                      8.6.1.    Wetlands International ..................................................................................................................................................................... 95 
                      8.6.2.    National Plan for Conservation of Aquatic Eco-systems (NPCA) ....................................................................................................... 95 
                      8.6.3.    Wetlands (Conservation and Management) Rules 2010 ................................................................................................................... 96 
                      8.6.4.    Wetlands (Conservation & Management) Rules 2017 ...................................................................................................................... 96 
                      8.6.5.    Ramsar Convention on Wetlands ...................................................................................................................................................... 97 
                      8.6.6.    Ramsar Site........................................................................................................................................................................................ 98 
                      8.6.7.    Ramsar Sites of India ....................................................................................................................................................................... 100 
                      8.6.8.    Largest and Smallest and Oldest Ramsar Sites of India ................................................................................................................... 104 
            9.    Evolution of the Biosphere ................................................................................................................................................................. 106 
               9.1.      Hadean Eon .................................................................................................................................................................................. 106 
               9.2.      Archean Eon ................................................................................................................................................................................. 108 
               9.3.      Proterozoic Eon ........................................................................................................................................................................... 108 
                      9.3.1.    Events that Can Cause Global Cooling ............................................................................................................................................. 108 
               9.4.      Phanerozoic Eon .......................................................................................................................................................................... 108 
                      9.4.2.    Paleozoic Era ................................................................................................................................................................................... 109 
                      9.4.3.    Mesozoic Era ................................................................................................................................................................................... 110 
                      9.4.4.    Cenozoic Era .................................................................................................................................................................................... 112 
                      9.4.5.    Anthropocene epoch ....................................................................................................................................................................... 113 
            10.   Biodiversity and Loss of Biodiversity ................................................................................................................................................ 114 
               10.1.     Definitions ................................................................................................................................................................................... 114 
                      10.1.1.  Biodiversity ...................................................................................................................................................................................... 114 
                      10.1.2.  Genetic diversity ............................................................................................................................................................................. 114 
                      10.1.3.  Species diversity .............................................................................................................................................................................. 116 
                      10.1.4.  Ecological diversity .......................................................................................................................................................................... 116 
                      10.1.5.  Endemism ........................................................................................................................................................................................ 117 
                      10.1.6.  Bioprospecting & Biopiracy ............................................................................................................................................................. 117 
                      10.1.7.  Types of Species .............................................................................................................................................................................. 117 
               10.2.     Importance of a Healthy Biodiversity ...................................................................................................................................... 117 
               10.3.     Causes for the Loss of Biodiversity ........................................................................................................................................... 118 
                      Global Assessment Report on Biodiversity and Ecosystem Services 2019 .................................................................................................... 118 
                      10.3.2.  Habitat Loss and Fragmentation ..................................................................................................................................................... 118 
                      10.3.3.  Alien Species Invasions .................................................................................................................................................................... 119 
                      10.3.4.  Over-exploitation ............................................................................................................................................................................ 121 
                      10.3.5.  Species Extinction ............................................................................................................................................................................ 122 
                      10.3.6.  Genetically Modified Organisms (GMO/Transgenic Organism) ...................................................................................................... 122 
                      10.3.7.  Trade in Wildlife .............................................................................................................................................................................. 123 
                      10.3.8.  Pollution and Climate Change ......................................................................................................................................................... 123 
               10.4.     Consequences of Loss of Biodiversity ...................................................................................................................................... 123 
                      10.4.1.  Affects Livelihood ............................................................................................................................................................................ 123 
                      10.4.2.  Human-Animal Conflict ................................................................................................................................................................... 123 
                      10.4.3.  Increased Zoonoses due to Habitat Loss ......................................................................................................................................... 125 
                      10.4.4.  Adverse Changes to Biotic Interactions ........................................................................................................................................... 125 
            11.   Biodiversity Conservation ................................................................................................................................................................... 126 
               11.1.     In situ conservation .................................................................................................................................................................... 126 
                      11.1.1.  Reserved & Protected Forests ......................................................................................................................................................... 126 
                      11.1.2.  Wildlife Sanctuaries or Wildlife Refuges ......................................................................................................................................... 126 
                      11.1.3.  Biosphere Reserve ........................................................................................................................................................................... 126 
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                   11.1.4.  National Park ................................................................................................................................................................................... 127 
                   11.1.5.  Eco-Sensitive Zones (ESZs) or Ecologically Fragile Areas (EFAs) ...................................................................................................... 127 
                   11.1.6.  Conservation Reserves .................................................................................................................................................................... 128 
                   11.1.7.  Community Reserves ....................................................................................................................................................................... 128 
                   11.1.8.  Sacred Groves.................................................................................................................................................................................. 128 
             11.2.    Ex Situ Conservation ................................................................................................................................................................... 128 
                   11.2.1.  Botanical Garden ............................................................................................................................................................................. 128 
                   11.2.2.  Zoo .................................................................................................................................................................................................. 128 
             11.3.    National Efforts and Initiatives for Biodiversity Conservation ............................................................................................ 129 
                   11.3.1.  Wildlife Mitigation Measures – Eco-Bridges or Eco-Ducts .............................................................................................................. 129 
                   11.3.2.  Quarantine Centres to Check Invasive Species................................................................................................................................ 129 
                   11.3.3.  Preservation of the Western Ghats and the Eastern Ghats ............................................................................................................ 129 
                   11.3.4.  Historic Citizen Movements to Conserve Biodiversity .................................................................................................................... 130 
             11.4.    International Efforts and Initiatives for Biodiversity Conservation ..................................................................................... 131 
                   11.4.1.  UN Convention on Biological Diversity (CBD) .................................................................................................................................. 131 
                   11.4.2.  World Heritage Sites ....................................................................................................................................................................... 133 
                   11.4.3.  Man and Biosphere Programme (MAB programme) ...................................................................................................................... 133 
                   11.4.4.  Decade on Ecosystem Restoration .................................................................................................................................................. 133 
                   11.4.5.  Global Partnership on Forest and Landscape Restoration (GPFLR) ................................................................................................. 134 
                   11.4.6.  United Nations Strategic Plan for Forests 2017–2030 .................................................................................................................... 134 
                   11.4.7.  Biodiversity Finance Initiative (BIOFIN) ........................................................................................................................................... 134 
             11.5.    Biodiversity Hot Spots ............................................................................................................................................................... 134 
                   11.5.1.  Biodiversity Hotspots in India .......................................................................................................................................................... 135 
                   11.5.2.  Hope Spots ...................................................................................................................................................................................... 135 
          12.   Wildlife Conservation – Part I............................................................................................................................................................. 136 
             12.1.    Regulating Trade in Wildlife ..................................................................................................................................................... 136 
                   12.1.1.  Convention on International Trade in Endangered Species of Wild Fauna & Flora (CITES) ............................................................ 136 
                                  th
                   12.1.2.  The 18  Conference of the Parties to CITES (CoP18) ...................................................................................................................... 137 
                   12.1.3.  Monitoring the Illegal Killing of Elephants (MIKE) ........................................................................................................................... 137 
                   12.1.4.  The Wildlife Trade Monitoring Network (TRAFFIC) ......................................................................................................................... 138 
                   12.1.5.  Coalition Against Wildlife Trafficking (CAWT) ................................................................................................................................. 138 
                   12.1.6.  Policies and Laws Concerning CITES in India ................................................................................................................................... 138 
             12.2.    Convention on Migratory Species (CMS) ................................................................................................................................ 139 
                   12.2.1.  Classification of Species Under CMS ............................................................................................................................................... 139 
                   12.2.2.  CMS COP13 ..................................................................................................................................................................................... 139 
                   12.2.3.  Central Asian Mammals Initiative ................................................................................................................................................... 140 
             12.3.    International Union for Conservation of Nature (IUCN) ....................................................................................................... 140 
                   12.3.1.  IUCN Red List or Red Data List or Red Book .................................................................................................................................... 140 
                   12.3.2.  BirdLife International ...................................................................................................................................................................... 141 
             12.4.    Tiger Conservation ..................................................................................................................................................................... 142 
                   12.4.1.  Threats Faced by Tiger Population .................................................................................................................................................. 142 
                   12.4.2.  Measures Taken by the Government for Tiger Conservation ......................................................................................................... 142 
                   12.4.3.  Project Tiger (PT) ............................................................................................................................................................................. 143 
                   12.4.4.  Core and Buffer Zones in Tiger Reserves ......................................................................................................................................... 143 
                   12.4.5.  Tiger Task Force............................................................................................................................................................................... 143 
                   12.4.6.  National Tiger Conservation Authority (NTCA)................................................................................................................................ 144 
                   12.4.7.  Tiger corridors in the country .......................................................................................................................................................... 144 
                   12.4.8.  Tiger Census .................................................................................................................................................................................... 145 
                   12.4.9.  2018 Tiger Census Report ............................................................................................................................................................... 146 
                   12.4.10. International Efforts Towards Tiger and Snow Leopard Conservation ............................................................................................ 147 
             12.5.    Conservation of Snow Leopard ................................................................................................................................................. 149 
                   12.5.1.  Project Snow Leopard ..................................................................................................................................................................... 149 
          13.   Wildlife Conservation – Part II ........................................................................................................................................................... 150 
             13.1.    Elephant Conservation ............................................................................................................................................................... 150 
                   13.1.1.  Difference between African Elephant and Asian Elephant.............................................................................................................. 150 
                   13.1.2.  Difference between African Forest Elephant and African Savanna Elephant ................................................................................. 150 
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