Test: Environment - 3 - UPSC MCQ

• Due to salinity, plants are not able to draw as much water from the soil. When the soil salinity levels are high enough, the water in the roots is pulled back into the soil. The plants are not able to take in enough water to grow.

• The major source of salinity problems is usually irrigation water.

• Salt-affected soils can be corrected by:

  • Improving drainage: In soils with poor drainage, deep tillage can be used to break up the soil surface as well as claypans and hardpans, which are layers of clay or other hard soils that restrict the downward flow of water. Tilling helps the water move downward through the soil. Hence option 1 is correct.

  • Leaching: Leaching can be used to reduce the salts in soils. Adding enough low-salt water to the soil surface to dissolve the salts and move them below the root zone. The water must be relatively free of salts (1,500 – 2,000 ppm total salts), particularly sodium salts. A water test can determine the level of salts in your water. Hence option 2 is correct.

  • Reducing evaporation: Applying residue or mulch to the soil can help lower evaporation rates. As an increase in evaporation increases salinity. Hence option 3 is not correct.

  • Applying chemical treatments: Before leaching saline-sodic and sodic soils, treating them with chemicals, to reduce the exchangeable sodium content reduces salinity. Gypsum is the most commonly used to correct saline-sodic or sodic soils. Hence option 4 is correct.

• Earth is currently experiencing a biodiversity crisis. Recent estimates suggest that extinction threatens up to a million species of plants and animals, in large part because of human activities such as deforestation, hunting, and overfishing. Today, extinctions are occurring hundreds of times faster than they would naturally.

• The previous five mass extinction episodes are:

  • Ordovician-Silurian extinction: 444 million years ago

  • Late Devonian extinction: 383-359 million years ago

  • Permian-Triassic Extinction: 250 million years ago

  • Triassic-Jurassic Extinction: 210 million years ago

  • Cretaceous-tertiary Extinction: 65 Million Years Ago - The Cretaceous-Paleogene extinction event is the most recent mass extinction and the only one definitively connected to a major asteroid impact. Some 76 percent of all species on the planet, including all nonavian dinosaurs, went extinct during this period.

• Statement 1 is correct: During the long period (> 3 billion years) since the origin and diversification of life on earth, there were five episodes of mass extinction of species. The ‘Sixth Extinction’ presently in progress is different from the previous episodes in the rates; the current species extinction rates are estimated to be 100 to 1,000 times faster than in the pre-human times and our activities are responsible for the faster rates. Ecologists warn that if the present trends continue, nearly half of all the species on earth might be wiped out within the next 100 years.

• Statement 2 is correct: Some examples of recent extinctions include the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller’s Sea Cow (Russia) and three subspecies (Bali, Javan, Caspian) of the tiger. The last twenty years alone have witnessed the disappearance of 27 species.

• A sacred grove or sacred woods are any grove of trees that are of special religious importance to a particular culture. Sacred groves feature in various cultures throughout the world. In India, the introduction of Wild Life (Protection) Amendment Act, 2002, provides government protection to these lands.

• A strong concentration of these groves is found in Himachal Pradesh and Kerala. Other places where one can find sacred groves are Rajasthan, Bihar, Meghalaya and Maharashtra.

  • Himachal Pradesh: The state with the highest number of sacred groves, Himachal Pradesh is meticulous and extremely careful about these natural settings. Shipping is believed to be the largest deodar grove and contains trees that are thousands of years old.

  • Assam: Forest-dwelling tribes such as Bodo and Rabha inhabiting the plains and foothills of Western Assam have the tradition of maintaining sacred groves which are locally called “Than”.

  • Maharashtra: The groves in Maharashtra are called deorais or devrais and are concentrated in Pune, Ratnagiri, Raigad and Kolhapur. A rare variety of biodiversity prevails in these areas. The entire state contains approximately 250 groves.

  • Kerala: A state known for its stunning natural beauty, Kerala is home to 240 sacred groves known as kavus. These areas contain more than 3000 rare species of plants. Spread over more than 20 hectares, the largest grove is in Ernakulam.

  • Karnataka: Devara kadu is the sacred grove in Karnataka. The district of Kodagu has approximately 346 ‘devara kadu’s.

  • Bihar: Known as sarnas, the groves in Bihar are fairly small and only consist of 2 to 20 trees. Full of creepers, shrubs and grasses, these trees are generally collected in the Chotanagpur region.

  • Rajasthan: These regions in Rajasthan take up various names- oraans of Jaisalmer, Jodhpur, Bikaner, kenkris of Ajmer, vanis of Mewar, shamlet dehs of Alwar. The largest area is covered by oraans that provide a different set of biodiversity in distinctive areas.

  • Meghalaya: Home to some of the richest groves in the country, Khasi hills in Meghalaya have one grove called law kyntangs in almost every village. Two of the largest ones are Mawphlang and Mausmai. The popular myth surrounding the forests dictate that anyone damaging the plants and trees of the grove will be killed by the forest spirit. This myth has kept people from destroying the area and thus, it is one of the best preserved natural areas.

Hence option (d) is the correct answer.

• The total amount or weight, or energy content, of (a portion of) organisms existing in a specific area at a particular time, is known as standing crop.

• Statement 1 is not correct: Each trophic level has a certain mass of living material at a particular time called as the standing crop. A standing crop is the total dried biomass of the living organisms present in a given environment. It is not limited to the food grains.

• Statement 2 is correct: The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area. The biomass of a species is expressed in terms of fresh or dry weight.

• Development of environmental statistics plays crucial role in sustainable development. To achieve 2030 Agenda for Sustainable Development, the ambit of environment statistics needs to cover all components of environment issues, from extent to quality, adaptation and mitigation measures to governance and regulation, so as to enable formulation of appropriate policies.

• The National Statistical Office (NSO) of the Ministry of Statistics and Programme Implementation has addressed this requirement in EnviStats-India report. The report highlights the data on various environmental factors as a means to raise awareness and help focus on the pivotality of environmental concerns.

Hence option (d) is the correct answer.

• The Protection of Children from Sexual Offenses Act, 2012 (POCSO) imposed restrictions on disclosing the identity of the victim of sexual offence. Hence, statement 1 is correct.

• Right to free and compulsory elementary education for all children in the 6-14 year age group are mentioned in the Article 21 of the Indian constitution. Hence, statement 2 is not correct. As per Section 155(2) CrPC, a police officer cannot investigate a non-cognizable offense without the order of a Magistrate.

• Pollens, which originate from plants

• Viruses, which are transmitted by people and animals

• Mould, bacteria, which are carried by people, animals, and soil and plant debris.

• Household pets, which are sources of saliva and animal dander (skin flakes).

• Droppings and body parts from cockroaches, rodents and other pests or insects.

• Viruses and bacteria.

• The protein in urine from rats and mice is a potent allergen. When it dries, it can become airborne.

• Animal dander and cat saliva, house dust, mites, parasites etc.

Hence option (d) is the correct answer.

• Statement 1 is correct and statement 2 is not correct: Organisms occupy a place in the natural surroundings or in a community according to their feeding relationship with other organisms. Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic level. Producers belong to the first trophic level, herbivores (primary consumer) to the second and carnivores (secondary consumer) to the third.

• The important point to note is that the amount of energy decreases at successive trophic levels. When an organism dies it is converted to detritus or dead biomass that serves as an energy source for decomposers. Organisms at each trophic level depend on those at the lower trophic level for their energy demands.

In a nutshell, forest fires cause following adverse impacts:

• Loss of valuable timber resources and depletion of carbon sinks. Hence option 1 is not correct and option 2 is correct.

• Degradation of water catchment areas resulting in loss of water.

• Loss of biodiversity and extinction of plants and animals.

• Loss of wildlife habitat and depletion of wildlife.

• Loss of natural regeneration and reduction in forest cover and production.

• Global warming resulting in rising temperature.

• Loss of carbon sink resource and an increase in the percentage of CO2 in the atmosphere.

• Change in the microclimate of the area making it unhealthy living conditions.

• Soil erosion affecting the productivity of soils and production.

• Ozone layer depletion. Hence option 3 is correct.

• Health problems leading to diseases.

• Indirect effects on agricultural production leading to loss of livelihood.

• The Zoological Survey of India (ZSI) was established on 1st July, 1916 to promote survey, exploration and research leading to the advancement in our knowledge of various aspects of exceptionally rich wildlife of the erstwhile ́British Indian Empire ́. Hence statement 1 is correct.

• The survey has its genesis in the establishment of the Zoological Section of the Indian Museum at Calcutta in 1875.

• The Zoological Survey of India and the Botanical Survey of India have surveyed more than 70% of the total geographical area of India for the assessment of total number of species of plants and animals. So far, about 81,000 species of animals and 49,000 species of plants, have been recorded by these two institutions, respectively.

• The objectives of ZSI are classified as follows:

  • Primary Objectives

  • Exploration, Survey, Inventorying and Monitoring of faunal diversity in various States,

  • Ecosystems and Protected areas of India.

  • Taxonomic studies of all faunal components collected.

  • Periodic review of the Status of Threatened and Endemic species.

  • Preparation of Red Data Book, Fauna of India and Fauna of States.

  • Bioecological studies on selected important communities/species.

  • Preparation of databases for the recorded species of the country.

  • Maintenance & Development of National Zoological Collections.

  • Training, Capacity Building and Human Resource Development.

  • Faunal Identification, Advisory services and Library Services.

  • Publication of results including Fauna of India and Fauna of States.

• Secondary Objectives:

  • Environmental Impact Studies.

  • Maintenance and Development of Museum at Headquarters and Regional Stations.

  • Development of ENVIS and CITES Centers.

  • Research Fellowship, Associateship and Emeritus Scientist Programmes.

  • Collaborative research programmes on Biodiversity with other Organizations.

  • GIS and Remote Sensing studies for animal diversity as well as for selected threatened species.

  • Chromosomal Mapping and DNA finger printing.

• The All India Tiger Estimation done quadrennially is steered by the National Tiger Conservation Authority with technical backstopping from the Wildlife Institute of India and implemented by State Forest Departments and partners. Hence statement 2 is not correct.

• Recently, the fourth cycle of the All India Tiger Estimation 2018, results of which were declared to the nation on Global Tiger Day last year by Prime Minister has entered the Guinness World Record for being the world’s largest camera trap wildlife survey.

• Recently, the Union Minister of Jal Shakti released the Dynamic Ground Water Resource Assessment Report for the entire country for the year 2022. Hence, statement 1 is not correct.

• As per the report, the total annual groundwater recharge is 437.60 billion Cubic Meters (BCM) and the annual groundwater extraction is 239.16 BCM. Assessment indicates an increase in groundwater recharge. Groundwater recharge is a hydrologic process in which water seeps from the earth's surface downward. Hence, statement 2 is correct.

• Statement 1 is correct and Statement 2 is not correct: A national park is an area which is strictly reserved for the betterment of the wildlife and where human activities like forestry, grazing or cultivation are not permitted. It is associated with the habitat of wild animal species like Rhino, Tiger etc. Some examples of national parks are Jim Corbett, Tadoba National Park etc.

• An area, whether within a sanctuary or not, can be notified by the state government to be constituted as a National Park, by reason of its ecological, faunal, floral, geomorphological, or zoological association or importance, needed to for the purpose of protecting & propagating or developing wildlife therein or its environment. No human activity is permitted inside the national park except for the ones permitted by the Chief Wildlife Warden of the state.

• A wildlife sanctuary is a protected area that is reserved for the conservation only of wildlife - animals and plant species. Human activities like harvesting or timber, collection of minor forest products and private ownership rights are allowed. Some examples are Periyar (Kerala), Ranipur (Uttar Pradesh) etc.

• A biosphere reserve is a special area of land or coastal environment in which multiple use of land is permitted by dividing it into certain zones. The natural or core zones. The natural or core zone consists of an undisturbed and legally protected ecosystem. The buffer zone surrounds the core area and is managed to accommodate a greater variety of resource use strategies.

• It takes into consideration the entire ecosystem. The purpose of the formation of the biosphere reserve is to conserve in situ all forms of life, along with its support system, in its totality, so that it could serve as a referral system for monitoring and evaluating changes in natural ecosystems.

• Statement 1 is correct: The United Nations Conference on Environment and Development (UNCED), also known as the Rio de Janeiro Earth Summit, the Rio Summit, the Rio Conference, and the Earth Summit (Portuguese: ECO92), was a major United Nations conference held in Rio de Janeiro from 3 to 14 June in 1992.

• Its aim was to put the concept of sustainable development at the forefront of our concerns and to seek common action to protect the planet from environmental degradation that even threatens to change the global climate.

• Statement 2 is correct: The three Rio Conventions—on Biodiversity, Climate Change and Desertification—derive directly from the 1992 Earth Summit. Each instrument represents a way of contributing to the sustainable development goals of Agenda 21. The three conventions are intrinsically linked, operating in the same ecosystems and addressing interdependent issues.

• Agenda 21 is a non-binding action plan of the United Nations with regard to sustainable development. Since 2015, Sustainable Development Goals are included in the newer Agenda 2030.

• Bio-fertilizers are specific types of living organisms like symbiotic bacteria, Cyanobacteria (also called blue-green algae), seaweeds etc. that can bring about nutrient enrichment of soil in many different ways.

• Anabaena azollae, Anabaena cycadae, Azolla pinnata and Nostoc are different plants that enhance the productivity of soil when added to it.

• Bacteria like Rhizobium fix nitrogen for plants and Nostoc, Azolla, and Cyanobacteria that are great nitrogen fixers, are used as biofertilizers in crop fields, most frequently.

Hence all the options are correct.

• In bacteria, fungi and lower plants, various kinds of thick-walled spores are formed which help them to survive unfavourable conditions – these germinate on availability of suitable environment. In higher plants, seeds and some other vegetative reproductive structures serve as means to tide over periods of stress besides helping in dispersal – they germinate to form new plants under favourable moisture and temperature conditions. They do so by reducing their metabolic activity and going into a state of ‘dormancy’ under favourable conditions.

• In animals, the organism, if unable to migrate, might avoid the stress by escaping in time. The familiar case of bears going into hibernation during winter is an example of escape in time. Some snails and fish go into aestivation to avoid summer–related problems-heat and dessication. Under unfavourable conditions many zooplankton species in lakes and ponds are known to enter diapause, a stage of suspended development.

Hence both the options are correct.

• Statement 1 is not correct: Thermoregulation is energetically expensive for many organisms. This is particularly true for small animals like shrews and humming birds. Heat loss or heat gain is a function of surface area. Since small animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; then they have to expend much energy to generate body heat through metabolism. This is the main reason why very small animals are rarely found in polar regions.

• Statement 2 is correct: Some organisms are able to maintain homeostasis by physiological (sometimes behavioural also) means which ensures constant body temperature, constant osmotic concentration, etc. All birds and mammals, and a very few lower vertebrate and invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation). Evolutionary biologists believe that the ‘success’ of mammals is largely due to their ability to maintain constant body temperature and thrive whether they live in Antarctica or in the Sahara desert.

• The National Disaster Management Authority (NDMA) is headed by the Prime Minister of India. Hence, statement 1 is not correct.

• It is the apex body for Disaster Management in India. Setting up of NDMA and the creation of an enabling environment for institutional mechanisms at the State and District levels is mandated by the Disaster Management Act, 2005. Hence, statement 2 is correct. It lays down policies on disaster management.

• Use of unleaded gasoline: It could reduce the emission of CO and HC and significantly decrease the quantity of vehicle exhaust particulate matter by 60%. Hence option 1 is not correct.

• Use of low-sulphur petrol and diesel: Low sulphur fuel is essentially cleaner for the environment and better for engines. It means fewer particulates (fine sooty emissions), which have been linked to asthma and cancer, and fewer sulphur oxides, which cause acid rain. Hence option 2 is correct.

• Use of catalytic converters in Vehicles: As exhaust emission passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, while carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas. Unleaded petrol is the best fuel for automobiles fitted with catalytic converters to reduce air pollution. Hence option 3 is not correct.

• Use of methanol blended petrol: Methanol is a promising fuel as it is clean, cheaper than fossil fuels and a good substitute for heavy fuels. A study, in which methanol (M-15) was blended with petrol and used in the existing BS-IV standard cars, found that the carbon dioxide emission had reduced substantially. Hence option 4 is correct.

• There are many non-governmental organizations that oppose cruelty to animals. People for the Ethical Treatment of animals (PETA) & People for Animals (PFA) are two such organizations.

• These organizations work for the welfare of animals. Animal lovers across the world are of the opinion that animals too have rights to live and develop peacefully like human beings.

• In India Legal protection is offered to animals through the Prevention of Cruelty to Animals (PCA) Act- 1960 which was enacted in December 1960 with the objective of preventing infliction of unnecessary pain and suffering to animals.

• In exercise of powers conferred by this Act, the central Government made the Prevention of Cruelty to Animals (Establishment and Regulation of Societies for Prevention of Cruelty to Animals) Rules, 2001.

• Accordingly, Societies for Prevention of Cruelty to Animals (SPCAs) have been organized on state and district level across the country. The Animal Welfare Board of India, at Chennai, conducts and co-ordinates various activities pertaining to rescue, rehabilitation, care and welfare of animals. We should take care of animals and encourage others to do the same.

• The Prevention of Cruelty to Animals (PCA) Act- 1960 contains following Rules:

  • Performing Animals Rules – 1973 and Performing Animals (registration) Rules-1972.

  • Transport of Animals Rules-1978 and 2001.

  • Prevention of Cruelty (slaughter house) Rules-2000.

  • Prevention of Cruelty to Animals (establishment and regulation of society for prevention of cruelty to animals) Rules-2001.

  • Breeding of and Experiments on Animals (control and supervision) Rules-1998 as amended in February 2001.

Hence the correct option is (a)

• Carbon Credit: A carbon credit (also known as carbon offset) is a credit for greenhouse emissions reduced or removed from the atmosphere by an emission reduction project, which can be used by governments, industry, or private individuals to compensate for the emissions they generate elsewhere. Hence, statement 1 is correct.

• Those that cannot easily reduce emissions can still operate, at a higher financial cost. Carbon credits are based on the "cap-and-trade" model that was used to reduce sulfur pollution in the 1990s. Hence, statement 2 is correct.

• One carbon credit is equal to one metric ton of carbon dioxide, or in some markets, carbon dioxide equivalent gases (CO2-eq). Hence, statement 3 is correct.

• For aquatic organisms the quality (chemical composition, pH) of water becomes important. The salt concentration (measured as salinity in parts per thousand), is less than 5 in inland waters, 30-35 in the sea and > 100 in some hypersaline lagoons.

• Some organisms are tolerant of a wide range of salinities (euryhaline) but others are restricted to a narrow range (stenohaline). Many freshwater animals cannot live for long in seawater and vice versa because of the osmotic problems, they would face.

• Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly which can live in freshwater, brackish water, or saltwater. The green crab is an example of a euryhaline invertebrate that can live in salt and brackish water. Hence option (a) is the correct answer.

• Stenohaline describes an organism, usually fish, that cannot tolerate a wide fluctuation in the salinity of the water.

Habitat destruction could be caused as a result of:

• Clearing of forest areas for settlement or agricultural expansion, commercial lodgings, large hydel schemes, fire, human and livestock pressure, etc.

• Pollution (both air and water) stresses ecosystem, mismanagement of industrial and agriculture wastes threaten both terrestrial and aquatic ecosystem.

• Over exploitation, mainly for commercial purposes like meat, fur, hides, body organs, medicine, etc. o Accidental or deliberate introduction of exotic species which can threaten native flora and fauna directly by predation or by competition and also indirectly by altering the natural habitat or introducing diseases.

• Fragmentation of forests into subdivisions destroys habitat for wildlife, including rare species such as the Florida black bear and the red-cockade woodpecker. Some wild animals like bears, bobcats and foxes are unable to adapt to changes in the forest.

• Critical natural habitat and its associated biodiversity are diminished in wars around the world. Similarly, actions such as deforestation, habitat destruction and degraded human waste disposal-all associated with war and its aftermath can affect other key ecosystem services such as erosion control, water quality and food production.

• Destruction of habitats is caused on account of land being taken by new roads. This prevents free movement of animals or birds from their habitats either in search of food or for the purpose of migration from one place to another.

• Wounding and killing of animals hit by motor vehicles and trains, or victims from drowning when falling into steep-sided canals.

• Fish are also affected. Salmon, for instance, are frequently indirectly affected by roads. Impervious edges to roads, such as concrete, increase the flow of water from the road into streams, leading to a build-up of sediment, increased water temperature and pollution. Water running off from roads is the biggest hazard, as salmon are very sensitive to these irregular "flash flows".

• Disturbance to animals arising from noise, light, movement and human activity. For example, to breed successfully, songbirds require a noiseless atmosphere.

Hence correct answer is option (a).

• They are both liquid and solid aerosols that remain suspended in the atmosphere. Hence statement 1 is correct.

• The effect of particulate pollutants largely depends on the particle size. Air-borne particles such as dust, fumes, mist etc., are dangerous for human health. Hence statement 2 is not correct.

• Particulate pollutants bigger than 5 microns are likely to lodge in the nasal passage, whereas particles of about 10 microns enter into lungs easily.

• These are present in vehicle emissions, smoke particles from fires, dust particles and ash from industries.

• Particulates in the atmosphere may be viable or non-viable.

• Viable pollutants are the organic substances or minute living organisms which are spreaded in the atmosphere and cause harmful effects for ex: bacteria, fungus, viruses and other organic particulates, while the non viable pollutants are the inorganic materials or non living particles like fog, mist, dust, fumes etc.

• Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert condition in an oxygen-deficient environment.

• It involves a change in chemical composition. The word is coined from the Greek-derived elements pyro “fire” and lysis “separating”.

• It is most commonly used in the treatment of organic materials. It is one of the processes involved in charring wood.

• It is considered as the first step in the processes of gasification or combustion.

• The process is used heavily in the chemical industry, for example, to produce ethylene, many forms of carbon, and other chemicals from petroleum, coal, and even wood, to produce coke from coal.

• Aspirational applications of pyrolysis would convert biomass into syngas and biochar, waste plastics back into usable oil, or waste into safely disposable substances.

Hence option (d) is the correct answer.

Additional information:

• Fermentation: It is the chemical breakdown of a substance by bacteria, yeasts, or other microorganisms, typically involving effervescence and the giving off of the heat.

• Bio-methanation: It is a process by which organic material is microbiologically converted under anaerobic conditions to biogas.

• Incineration: It is a way to treat waste through controlled burning. Waste is shredded and heated to over 1025 degree Celsius in a furnace.

• Earthquake waves are basically of two types — body waves and surface waves. Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. Hence, the name body waves. There are two types of body waves. They are called P and S-waves. P-waves move faster and are the first to arrive at the surface. These are also called ‘primary waves. The P-waves are similar to sound waves. They travel through gaseous, liquid and solid materials. Hence, statement 1 is not correct.

• S-waves arrive at the surface with some time lag. These are called secondary waves. An important fact about S-waves is that they can travel only through solid materials. Hence, statement 2 is not correct.

• Habitat loss and fragmentation: This is the most important cause driving animals and plants to extinction. This habitat loss mainly happens due to tropical rain forests. For eg. The Amazon rain forest (it is so huge that it is called the ‘lungs of the planet’) harbouring probably millions of species is being cut and cleared for cultivating soya beans or for conversion to grasslands for raising beef cattle. Besides total loss, the degradation of many habitats by pollution also threatens the survival of many species. 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 population declines.

• Over-exploitation: Humans have always depended on nature for food and shelter, but when ‘need’ turns to ‘greed’, it leads to over-exploitation of natural resources. Many species extinctions in the last 500 years (Steller’s sea cow, passenger pigeon) were due to overexploitation by humans.

• Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive, and cause decline or extinction of indigenous species. The Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake; introduction of the African catfish Clarias gariepinus for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.

• Co-extinctions: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate. Another example is the case of a coevolved plant-pollinator mutualism where extinction of one invariably leads to the extinction of the other.

Hence, all are correct options.

• Radiation Pollution or Radioactive pollution can be defined as the release of radioactive substances or high-energy particles into our natural resources as a result of human activity, either by accident or by design. It is the uncontrolled distribution of radioactive material in a given environment.

• Radioactive substances emit rays like alpha (α) rays, gamma (γ) rays and beta (β)rays. These rays are emitted from unstable radioactive substances so as to become stable. In this way, these are gradually reduced in their value.

• The time taken by a radioactive substance to get reduced up to the half of its initial value is called a half-life period.

• The unit applied to express the decay of a radioactive substance is called as Becquerel.

• Radiation pollution may be caused by both –

  • Natural radiations

  • Man-made radiations

• Cosmic radiations, ultraviolet radiations etc. are examples of Natural Radiations.

• The application of explosive devices, testing of bombs, leakage from nuclear reactors, mining of radioactive material, use of nuclear weapons etc. are man-made sources of radiation pollution.

Hence option (d) is the correct answer.

• Biological Oxygen Demand is defined as the amount of dissolved oxygen required by aerobic microorganisms to breakdown the organic materials in a sample of water at a specific temperature & timeframe. Hence statement 1 is correct.

• The amount of BOD in the water is a measure of the amount of organic material in the water, in terms of how much oxygen will be required to break it down biologically.

• Biological oxygen demand can be used as an indicator of the level of environmental pollution.

• Clean Water would have a BOD value of less than 5 ppm whereas highly polluted water could have a BOD value of 17 ppm or more. Hence statement 2 is not correct.