Environment & Ecology Previous Year Questions (PYQ) with Answers

The correct answer is D, a - ii, b - i, c - iv, d - iii. Corbett National Park in Uttarakhand is India's oldest national park; it was set up in 1936 as Hailey National Park and in 1973 became the first reserve under Project Tiger. Sundarbans National Park in West Bengal lies in the Ganga–Brahmaputra delta, has the world's largest mangrove forest and is famous for its swimming Royal Bengal tigers; it is a UNESCO World Heritage Site. Bandhavgarh National Park in Umaria district of Madhya Pradesh has one of the highest densities of tigers in India, and the white tigers of Rewa were first found in this region. Sariska in Alwar district of Rajasthan lost all its tigers by 2005, and tigers were brought back from Ranthambore from 2008. Option A is wrong because it puts Corbett in Rajasthan and Sariska in Uttarakhand. Option B is wrong because it places Corbett in Madhya Pradesh and Bandhavgarh in Rajasthan. Option C is wrong because it puts Sundarbans in Madhya Pradesh and Sariska in West Bengal. Exam tip: Corbett Uttarakhand, Sundarbans West Bengal, Bandhavgarh MP, Sariska and Ranthambore Rajasthan.

The correct answer is D, Impala will die of starvation due to higher population. In this food chain grass is the producer, the impala is the herbivore and the hyena is the predator that keeps the impala population in check. If all hyenas are removed, impalas multiply quickly because nothing hunts them. The larger herd overgrazes the grassland until there is not enough food, and then many impalas starve and their numbers crash. This chain reaction, where removing a top predator upsets every level below it, is called a trophic cascade. It is also why predators such as tigers are protected: they keep an ecosystem in balance. A is wrong because without predators the impala population cannot stay stable; it first rises sharply. B is wrong because the impalas' good time lasts only until the grass runs out. C is wrong because the grassland is the first to suffer, from overgrazing. Exam tip: remove the predator, the prey multiplies, food runs out and the prey starves; only about 10 per cent of energy passes to the next level.

The correct answer is B, Endangered species. The Red Data Book is the source book that keeps a record of endangered animals, plants and fungi, so that governments and conservationists know which living species face the greatest risk of dying out. It is linked to the Red List prepared by the International Union for Conservation of Nature (IUCN), which was founded in 1948 and has its headquarters at Gland in Switzerland. Species at risk are placed in categories such as Critically Endangered, Endangered and Vulnerable, which together are called threatened species. Many countries, including India, also prepare their own Red Data Books for local species, and the Botanical Survey of India compiles one for Indian plants. Option A is wrong because the book is meant to help save living species; extinct species cannot be saved and are not its main record. Option C is wrong because common species are not at risk. Option D is wrong because invasive species, such as water hyacinth, are harmful newcomers and are tracked in separate lists. Exam tip: Red Data Book means endangered species; IUCN is at Gland, Switzerland, founded 1948.

The correct answer is B, Producers. Producers, the green plants and algae, are the most numerous living part of an ecosystem because every other organism depends on them for food. They make their own food by photosynthesis using sunlight, so they form the first trophic level of every food chain. Only about 10 per cent of the energy passes from one level to the next (Lindeman's ten per cent law), so each higher level can support fewer organisms. This gives the upright pyramid of numbers in a grassland: many grass plants, fewer grasshoppers, fewer frogs, and very few snakes and hawks. A is wrong because primary consumers, the herbivores, feed on producers and are fewer than them. C is wrong because secondary consumers, the small carnivores, are fewer still. D is wrong because tertiary consumers, the top carnivores such as the tiger or eagle, are the fewest of all. Exam tip: Producer → primary consumer → secondary consumer → tertiary consumer; about 90 per cent of energy is lost at each step; in a single-tree ecosystem the pyramid of numbers is inverted.

The correct answer is B, acid rain. Rain with a pH below 5.6 is called acid rain. Even clean rain is slightly acidic, with a pH of about 5.6, because carbon dioxide from the air dissolves in it to form weak carbonic acid; that is why 5.6, not 7, is the dividing line. Rain turns more acidic when sulphur dioxide and nitrogen oxides from coal-fired power plants, factories and vehicles mix with water vapour and form sulphuric and nitric acids. Acid rain corrodes marble and metal, kills fish in lakes and harms soil and forests. In India the best-known example is the damage to the Taj Mahal's white marble, often called 'marble cancer'. A is wrong because alkaline rain would have a pH above 7. C is wrong because 'mineral rain' is not a scientific term. D is wrong because hard water means water with dissolved calcium and magnesium salts; it is not a measure of how acidic rain is. Exam tip: rain pH below 5.6 = acid rain; culprits SO₂ and NOₓ; victim marble, as in the Taj Mahal.

The correct answer is C, It protects us from harmful radiation. The ozone layer shields us from the Sun's harmful ultraviolet rays, so when it thins, that protection is lost. It lies in the stratosphere, roughly 15 to 35 km above the Earth, and absorbs most of the UV-B and UV-C radiation. More UV reaching the ground means more skin cancer, cataracts and weaker immunity in people, and damage to crops and to plankton in the sea. The main culprits are chlorofluorocarbons (CFCs), once used in refrigerators, air conditioners and aerosol sprays; a single chlorine atom can destroy thousands of ozone molecules. The Montreal Protocol of 1987 phased these chemicals out. A is wrong because extra UV harms plants and lowers crop yields. B is wrong because ozone loss is about radiation, not the pollution of water. D is wrong because it does nothing to make soil more fertile. Exam tip: ozone layer = Earth's sunscreen in the stratosphere; CFCs damage it; Montreal Protocol 1987; World Ozone Day is 16 September.

The correct answer is D, Forest. A forest forms and runs on its own, without any human effort, so it is a natural ecosystem. Its plants make food by photosynthesis, animals feed on the plants or on one another, and fungi and bacteria break down dead matter and return nutrients to the soil, so the cycle keeps going by itself. Ponds, lakes, grasslands, deserts, rivers and oceans are other natural ecosystems. Ecosystems that people create and have to maintain are called artificial or man-made ecosystems. A is wrong because a crop field is sown, watered, weeded and harvested by farmers. B is wrong because an aquarium is a man-made tank that needs regular cleaning, feeding and aeration. C is wrong because a garden is planted and looked after by people, and left alone it would slowly change into something else. Exam tip: made by nature = natural (forest, pond, desert); made and kept by humans = artificial (crop field, aquarium, garden, park).

The correct answer is C, It is a community based rain water harvesting system. A johad is a small crescent-shaped earthen dam that villagers build together to catch and store rainwater. It is used mainly in Rajasthan and Haryana, where rain is scarce and falls in only a few months of the year. The water held behind the bund is used for cattle and farming, and much of it soaks into the ground, refilling wells and raising the water table. In Alwar district of Rajasthan, villagers working with the Tarun Bharat Sangh built many johads, and the Arvari river, which had dried up, began to flow again. A is wrong because a johad does not pump groundwater; it helps to recharge it. B is wrong because it collects rainwater running off the land, not water drawn from rivers. D is wrong because a johad is a storage structure, not a water filter. Exam tip: johad, Rajasthan and Haryana; kul, western Himalayas; bamboo drip irrigation, Meghalaya; zing, Ladakh.

The correct answer is B, 5th June. The United Nations General Assembly named 5 June as World Environment Day in 1972, and the day has been observed every year since 1974. The date recalls the opening day of the United Nations Conference on the Human Environment held at Stockholm from 5 to 16 June 1972, the first big world meeting on the environment. The same conference led to the creation of the United Nations Environment Programme, or UNEP, which leads the celebrations each year. Every year the day has a new theme and a host country; India hosted it in 2018 with the theme 'Beat Plastic Pollution'. A is wrong because May's main environment date is 22 May, the International Day for Biological Diversity. C is wrong because July has World Population Day on 11 July, not World Environment Day. D is wrong because 5 August is not linked with this day at all. Exam tip: 22 April, Earth Day; 22 May, Biodiversity Day; 5 June, World Environment Day; 16 September, World Ozone Day.

The correct answer is A, (d) and (e). Sulphur dioxide and nitric oxide are the gases behind acid rain. When coal, petrol and diesel are burnt in power plants, factories and vehicles, they release sulphur dioxide and oxides of nitrogen such as nitric oxide. These gases dissolve in the water droplets of clouds and form sulphuric acid and nitric acid, which then come down with the rain. Acid rain harms crops, soil, lakes and forests, and it eats into buildings and monuments. NCERT's Class 8 science book describes how acid rain corrodes the white marble of the Taj Mahal at Agra, a damage called marble cancer, with industries around Agra and the Mathura refinery among the sources. B is wrong because nitrogen and oxygen are the main, harmless gases of the air. C is wrong because oxygen and ozone do not form the acids that fall as acid rain. D is wrong because it pairs sulphur dioxide with ozone, which is not a cause of acid rain. Exam tip: acid rain, sulphur dioxide and nitrogen oxides; marble cancer, the Taj Mahal.

The correct answer is A, Fig. Each fig species is pollinated only by its own tiny fig wasp, and the two have evolved together over millions of years. A fig 'fruit' is really a closed bulb, the syconium, with hundreds of small flowers inside. A female wasp squeezes in through a tiny opening, pollinates the flowers and lays her eggs in some of them. The young wasps grow inside, mate, and the new females fly out carrying pollen to another fig. Without the wasp the fig cannot set seed, and without the fig the wasp cannot breed; this is obligate mutualism. Figs such as the banyan and peepal are keystone species, because their fruit feeds many birds and mammals through the year. Option B is wrong because mahua flowers are pollinated mainly by bats and some birds. Option C is wrong because sandalwood, a root hemiparasite, is visited by many kinds of insects, not one. Option D is wrong because silk cotton (semal) is pollinated mainly by birds. Exam tip: fig and fig wasp are the classic example of co-evolution and obligate mutualism.

The correct answer is B, 1973. Project Tiger was launched on 1 April 1973 by the Government of India under Prime Minister Indira Gandhi, from Jim Corbett National Park in Uttarakhand, to save the Bengal tiger and its habitat. It began with nine tiger reserves, including Corbett, Kanha, Bandipur, Ranthambore, Sundarbans and Manas, and the network has since grown to more than fifty. Each reserve has a core area free of human activity and a buffer zone around it. Since 2005 the project is run by the National Tiger Conservation Authority, a statutory body under the Wildlife (Protection) Act, and the tiger census is done every four years. A, 1985, is not linked to the tiger programme. C, 1972, is the year of the Wildlife (Protection) Act, the law that came a year before the project and is often confused with it. D, 1970, is when India banned tiger hunting. Exam tip: 1970 hunting ban, 1972 Wildlife Act, 1973 Project Tiger, 1992 Project Elephant.

The correct answer is D, Bihar. The Rajgir Zoo Safari stands at Rajgir in Nalanda district of Bihar, in the hills around the old Magadhan capital of Rajgriha. It was opened to visitors in 2022 and is laid out as a safari: people move through the enclosures in vehicles while tigers, lions, leopards, bears and herbivores range in open spaces. A glass bridge and a nature safari were built beside it, and the whole site sits within the wooded country of the Pant Wildlife Sanctuary. Option A is wrong because Tamil Nadu's best-known zoo is the Arignar Anna Zoological Park at Vandalur near Chennai. Option B is wrong because Madhya Pradesh has the Van Vihar National Park at Bhopal. Option C is wrong because Gujarat's Sakkarbaug Zoo at Junagadh is the one known for breeding Asiatic lions. Exam tip: remember Rajgir in Bihar for the zoo safari and the glass bridge, and Rajgriha as the first capital of Magadha.

The correct answer is C, Jim Corbett National Park. It is India's first national park, set up in 1936 as Hailey National Park, in the Nainital area of present-day Uttarakhand. It was later called Ramganga National Park and was renamed in the 1950s in honour of Jim Corbett, the famous hunter who turned into a naturalist and wrote 'Man-Eaters of Kumaon'. Project Tiger was launched here in 1973, and the park lies along the Ramganga river in the foothills of the Himalayas. Option A is wrong because Gir in Gujarat, the last home of the Asiatic lion, became a national park only in 1975. Option B is wrong because Kaziranga in Assam, famous for the one-horned rhinoceros, became a national park in 1974. Option D is wrong because Rajaji National Park in Uttarakhand was formed in 1983 by joining three sanctuaries. Exam tip: the first national park went from Hailey (1936) to Ramganga to Jim Corbett, and Project Tiger began here in 1973.

The correct answer is D, Turbidity of water. NTU stands for Nephelometric Turbidity Unit. A nephelometer shines a beam of light through a water sample and measures how much of it is scattered sideways by suspended particles such as clay, silt, algae and microbes; the more the scattering, the more turbid, or cloudy, the water is. Turbidity is a key test for drinking water because the particles can shield germs from chlorine and other disinfectants, so water supply agencies try to keep it very low before the water reaches homes. High turbidity in a river or lake also cuts off sunlight for aquatic plants. Option A is wrong because water pressure is measured in units such as the pascal or the bar. Option B is wrong because temperature is measured in degrees Celsius or in kelvin. Option C is wrong because acidity is shown on the pH scale, where 7 is neutral and values below 7 are acidic. Exam tip: NTU = turbidity (cloudiness); pH = acidity; BOD = organic pollution, in milligrams per litre.

The correct answer is B, Cadmium pollution. Itai-itai disease is long-term cadmium poisoning, first noticed around 1912 in the Toyama region of Japan, where mines upstream released cadmium into the Jinzu river and it built up in the rice and water used by villagers. Cadmium damages the kidneys and makes bones soft and brittle, so patients suffered repeated fractures and severe pain in the spine and joints; the name means it hurts, it hurts in Japanese. It became one of the four big pollution diseases of Japan. Option A is wrong because mercury pollution causes Minamata disease, also from Japan, which spread through eating fish from a bay polluted with methylmercury. Option C is wrong because arsenic in groundwater causes arsenicosis, with skin lesions and cancers, as seen in West Bengal and Bangladesh. Option D is wrong because too much nitrate in drinking water causes blue baby syndrome, or methaemoglobinaemia, in infants. Exam tip: cadmium–itai-itai, mercury–Minamata, nitrate–blue baby, fluoride–fluorosis.

The correct answer is A, b d a c. Nokrek Biosphere Reserve is in the Garo Hills of Meghalaya; Manas is in Assam along the Bhutan border; Similipal is in Mayurbhanj district of Odisha; and Seshachalam lies in the Eastern Ghats of Andhra Pradesh. Nokrek is valued as a gene pool of wild citrus, Manas is also a tiger reserve and a World Heritage Site, Similipal is known for its tigers and waterfalls, and the Seshachalam hills are home to the red sanders tree. India began creating biosphere reserves under UNESCO’s Man and the Biosphere (MAB) programme, and the Nilgiri Biosphere Reserve, set up in 1986, was the first. Option B is wrong because it places Manas in Odisha and Similipal in Assam. Option C is wrong because it puts Similipal in Andhra Pradesh and Seshachalam in Odisha. Option D is wrong because it swaps the states of Nokrek and Manas. Exam tip: Nokrek–Meghalaya, Manas–Assam, Similipal–Odisha, Seshachalam–Andhra Pradesh, and Nilgiri (1986) the first.

The correct answer is A, 1 and 4. Valmiki National Park and Bhimbandh Wildlife Sanctuary are both in Bihar, while the other two are in other States. Valmiki National Park, with its tiger reserve, lies in West Champaran district in the far north-west of Bihar, along the Nepal border, where it adjoins Nepal's Chitwan National Park. It takes its name from the sage Valmiki, whose ashram is believed to have stood in this forest. Bhimbandh Wildlife Sanctuary lies in Munger district in south Bihar and is known for its hot springs. Option B is wrong because both Dudhwa and Gajner are outside Bihar. Option C is wrong because Gajner Wildlife Sanctuary is near Bikaner in the Thar desert of Rajasthan. Option D is wrong because Dudhwa National Park is in Lakhimpur Kheri district of Uttar Pradesh, famous for its swamp deer. Exam tip: Valmiki is in West Champaran in north Bihar, Bhimbandh in Munger in south Bihar; Dudhwa is Uttar Pradesh and Gajner is Rajasthan.

The correct answer is D, More than one of the above. Carbon dioxide, water vapour and CFCs are all greenhouse gases, because each of them traps the heat that the Earth gives off and warms the lower atmosphere. Water vapour is the most plentiful greenhouse gas in the air, while carbon dioxide from burning coal, oil and gas is the main one that human activity keeps adding. CFCs, once used in refrigerators and aerosol sprays, do double damage: they trap heat and they also destroy the ozone layer, which is why the Montreal Protocol of 1987 phased them out. Methane and nitrous oxide are other important greenhouse gases. Option A is incomplete because carbon dioxide is only one of the gases listed that trap heat. Option B is incomplete because water vapour also traps heat but is not the only such gas here. Option C is incomplete because CFCs are greenhouse gases too, but so are the other two. Exam tip: the main greenhouse gases are water vapour, carbon dioxide, methane, nitrous oxide and CFCs.

The correct answer is D, Statement-I is incorrect but Statement-II is correct. Rainforest soil is actually poor in nutrients, even though the forest above it is the richest on land. Heat and heavy rain make dead leaves decompose within weeks, and the released nutrients are taken up almost at once by the dense roots and fungi of the trees. So most nutrients are stored in the living biomass, not in the soil, and only a thin layer of humus lies on the surface. Constant rain also washes minerals down through leaching, leaving red, acidic, laterite-type soils rich mainly in iron and aluminium oxides. This is why cleared rainforest land loses its fertility after a few harvests. Statement-II is right because fast decomposition is exactly what this hot, wet climate causes. Options A and B are wrong because Statement-I is false. Option C is wrong because it reverses which statement is true. Exam tip: in a rainforest the nutrients sit in the trees, not the soil; cool forests keep more in the soil because decay is slow.