NCERT Solutions for Class 12 Science Biology Chapter 16 - Environmental Issues

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Non-biodegradable wastes are substances that are not decomposed naturally by the action by of microorganisms. It involves heavy metals such as arsenic, mercury, lead, polythene, DDT, synthetic fibres. Humans are the perimary source four producing non-biodegradable waste.

Hence, the correct answer is option c.

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According to the Central Pollution Control Board (CPCB), the particulate size of 2.5 micrometers our less indiameter are responsible four causing secure harm to human health and are inhaled deep into the lungs. These fine particles can cause breathing and respiratory disorders, irritations, inflammation and lungs damage as well as premature death.

Hence, the correct answer is option a.

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Styrofoam is a polystrene used four sound proofing of rooms such as in auditorium, movie halls, audio recording etc. It reduces and muffle the sound transfer through walls. This material also helps in absorption and reflection of sound waves as well as a also decreases the transmission of sound waves through barrier.

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CNG (Compressed Natural Gas) is a mixture of hydrocarbon. It consists of methane in gaseous form. It is non-toxic, colourless and non-carcinogenic gas.

Hence, the correct answer is option b.

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World's most problematic aquatic weed is $\frac{\mathrm{Eidahoernia}}{\mathrm{Ital}}$ $\frac{\mathrm{Cerassipes}}{\mathrm{Ital}}$ and is also called 'Terror of Bengal' They are introduced into the lakes of India four their beautiful flowers. But they caused havoc by their excessiue growth by  causing blocks in water bodies. They grow faster than the ability to remove them and cause imbalance in the water ecosystem.

Hence, the correct answer is option c.

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Biomagnification our biological magnification refers to the increase in the concentration of toxicants (DDT and mercury) at successive trophic levels. It ocurs because these toxic substances are accumulated by the organisms and cannot be metabolised or excreted then passed on to the next higher trophic level.

Hence, the correct answer is option d.

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The expanded form of DDT  is dischlorodiethy, trichloroethane. 

Hence, the correct answer is option b.

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Bones will take longer time for degradation as they are composed of collagen protein, in organic materials such as calcium, hydroxyaptite and organic compounds. Collagen protein is the most resistant protein for degradation and provides strength to bones. Inorganic ions such as calcium also provides strength bones.

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Dobson units (DU) is a term used far the measurement of the thickness of the ozone. in a coloumn of air from the ground to the top of the atmosphere.

Hence, the correct answer is option c.

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Burning of coal cause more indoor chemical pollution as a variety of air pollutants are released by burning such as CO₂, SO₂, NO₂ etc., Carbon monoxide is very dangerous and can interfere with the breathing process.

Hence, the correct answer is option a.

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The presence of large amount of nutrients in waters results in excessive growth of planktonic our free floating algal called algal bloom. It imparts different colours to the water bodies. This cause deterioration of the water quality and fish mortality.

Hence, the correct answer is option d.

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The loudness of a sound that a person can withstand without discomfort is about 80 dB.

Hence, the correct answer is option d.

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The major source of noise pollution would wide is caused due to transport system.
For example:- A extremely high sound level, 150 dB or movie generated by take off of a jet plane or rocket. This sound may damage ear drumbs and permanently impairing hearing ability.

Hence, the correct answer is option b.

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Catalytic converters house expensive metals such as platinum-palladium and rhodium. These metals are used as a catalyst and fitted into the automobiles for reducing the emission of poisnous gases. When the exhaust passes through the catalytic converted, the unburnt hydrocarbons are converted into carbon dioxide and water. Carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas.

Hence, the correct answer is option a.

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It is required to remove sulphur from petroleum products to reduce the emission of sulphur dioxide in exhaust fumes. Sulphur dioxide is harmful for the environment that led to cause acid rain results in damaging of buildings and plants. It also causes eye irritation and damage to respiratory system in humans.

Hence, the correct answer is option a.

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Suspended solids such as sand, slit, small stones etc., are heavy and submerged at the bottom of water. These are not easily dissolved with water and can be separated from water by sedimentation, filtration and soon.

Hence, the correct answer is option d.

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Hepatitis-B is an viral infection which is not caused due to the contamination of water. This disease is spread by sexual contact with an infected person, sharing of need us during blood transfusion, or from an infected mother to foetus.

Hence, the correct answer is option a.

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The nuisance growth of aquatic plants and blooms-forming algae in natural waters is due to high concentration of phosphates and nitrates. They acts as an plant nutrients and overstimulate the growth of algae, results in unsightly scum and unpleasant odours and also decreases the dissolved oxygen in water and causes harm to aquatic life.

Hence, the correct answer is option d.

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The presence of large amounts of nutrients in the water results in the excessive growth of plank tonic (free-floating) algae called an algal bloom. All photosynthetic phytoplanktons have chlorophyll pigment and other algae also contains distinct pigments and impat different colours to the water.

Hence, the correct answer is option a.

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Bhopal gas tragedy occured due to the leakage of 45 tons of methyl isocynate gas from an insecticide plant on December 3, 1984.

Hence, the correct answer is option a.

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The catalytic converters in the automobiles convert the unburnt hydrocarbons into carbon dioxide and water and carbon monoxide and nitric oxides into carbon dioxide and nitrogen gas. Lead in the petrol inactivates the catalyst and cause the emission of unburnt hydrocarbons in the air that causes air pollution.

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The Air Act (Prevention and Control of Pollution) in India came into force in 1901 but this act was amended in the year 1987 to include noise as an air pollution.

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All the buses of Delhi are converted to run on CNG by the end of 2002.

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The over head water tanks receives water from various sources such as river, deep bore well and soon. They carry sand along with water and this sand water is the source of slit that get deposited in the water tanks.

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Pollutants produced due to activities of human such as release of effluents from the industries and homes radially accelerates the ageing process of lakes and this phenomenon is called cultural our accelerated eutrophication.

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The particulate matter causes secure harm to human health as these fine particles are in holed deep into the lungs and cause several breathing and respiratory issues such as irritation, inflammations our damage to the lungs as well as premature deaths.

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Polyblend is a fine powder of recycled modified plastic and raw material required to create this is any plastic film waste.

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The blend of polyblend and bitumen is used to lay roads. This enhanced the bitumen's water repellant properties and also helped to increase the road life by a factor of three.

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Plants such as babul, Lawsoni, Thevetia and colotropis acts as wind breaks in the agricultural field. The wind breaks helps to produce shelter from wind and protect soil from erosion.

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Fertizer industry can cause both air and water pollution as well as eutrophication.

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Algal bloom is the excessive growth of planktonic (free floating) algae due to the presence of large amounts of nutrients in water. This imparts a distinct colour to the water bodies.

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Biomagnification or biological magnification refers to the increases in concentration of the toxicant at successive trophic levels. It occurs due to the accumulation of toxicants by an organism and it cannot be metabolised our exereted and is then passed on to the next trophic level. Biomagnification is well known for DDT and mercury,.

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Domestic waste contains three types of impurities such as
(a) Suspended impurities
(b) Colloidal impurities
(c) Dissolved impurities

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Reforestation is the process of restoring of forest that was existed once but was removed in the past. This process occurs naturally in the deforested area.

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The best solution for the treatment electronic waste is recycling. Such can be recycled 95%-98% by weight.

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Yes, carpets and curtain or drapes that are placed on floor or wall surfaces can reduce noise level. Such objects are composed of fibres and they absorb sound waves as they acts as an good sound absorber and reduce noise level.

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Hybrid vehicle technology involves the use of technology to run the vehicles on dual mode such as petrol and CNG.
These vehicles helps to reduce the consumption of fuels such as petrol and diesel and thus reducing air pollution. 
For example:- Honda CR-Z

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Yes, it is true that when the dissolved oxygen level drops to zero, the water will become septic. Absence of oxygen in the water indicates that the water good for the life of aquatic plants and animals. They use water for respiratory. The sewage water when discharged into the water bodies, the micro organims present in the sewage water reduces the dissolved oxygen of water of feed on organic impurities.

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Carbon dioxide is an common green house gas and is produced by the burning of fossil fuels as wells as other organic materials. In crease in the level of carbon dioxide in the atmosphere results in global warming.

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Trees and shrubs grown near the boundary wall of the buildings helps in reducing noise level and acts as dust catchers.

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The conservation efforts biodiversity rich area gives better results. As the hills have better biodiversity than plains because of higher degree of involvement in plains.

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Slash and burn agriculture is also called 'hum cultification' in the north-eastern states of India. In this type of cultification, the farmers cut down the trees of the forest and burn the plant remains. The ash is used as a fertilizer and the land is used for farming or grazing of cattle. After cultification, the land is left for recovery from the effert cultification.

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Joint forest management (JFM) was started by go Government of India in 1980. It has introduced the concept of local communities for protection and management of forests. In return for their services to the forests, these local communities get benefit from various forest products such as fruits, gum, rubber, medicine and soon. In this way the forests can be conserved in a sustainable manner.

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The cornea of the human eyes absorbs UV-B radiation and high dose of UV-B causes in flammation of cornea called snow-blindness long-term exposure may permanently damages the cornea.

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High DDT concentration disturb the calcium metabolism in birds that causes thining of eggshells and their premature breaking causes decline in the population of birds.

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(i) True, both the methods are non-polluting and environment friendly.
(ii) The two applications of solar energy are:-
(a) Solar light
(b) Solar hot water system
(iii) Photovoltaic cell is a form of photoelectric cell that converts the light energy into electrical energy by photovoltaic cell.

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Electronic wastes (e-wastes) are irreparable computers and other electronic goods. They are burried in the land fiels or incinerated. These wastes contains several metals like copper, iron, nickel, gold, silver and plastic.
Examples of e-wastes:- Computers, printers, scanners, webcam, mobile phones, etc.
The only way for disposal of e-waste is recycling. But their recycling pollute the water, soil and the air.

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Organic framing or integrated organic farming is an cyclical, zero-waste procedure. In which the waste products from one process are cycled and used as a nutrient for other processes.
This procedure was started by Ramesh chandra Dagar, a farmer in sonipat, Haryana.
Advantages:-
1. Organic farming allows the maximum utilization of resources and also increases the efficiency of production.
2. The chemical fertilizers are replaced by cattle excreta (cow dung), which is used as a manure.
3. This process involves bee-keeping, dairy management, water haruesting, compositing and agriculture in a chain. This method support each other and also allow an exteremely economical and sustainable venture.
4. The crop waste is used for the formation of compost, that can be used as a natural fertiliser or can be used for the generation of natural gas to fulfil the energy needs.

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(i) Irrigation without proper drainage of water results in water logging in the soil.
(ii) This draws salt to the soil surface and then the salt is deposited as thin crust on the surface of land or it starts collecting at the roots of the        plants.
(iii) The increased salt content severly harm the plant growth and extremely damaging to agriculture.

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The multipurpose trees are type of trees that can be grown to provide more than one benefits.
For example:-
Neem $\frac{\left(\mathrm{Azadirachtaindica}\right)}{\mathrm{Ital}}$:- This plant is used as an insect repellant, antibiotic, fire woods or windbreaks.
Coconut $\frac{\left(\mathrm{Cocus} \mathrm{nucifera}\right)}{\mathrm{Ital}}$:- This plant is used for food, purification of water, roof that ching, firewoods, rope making, fertilizer (cocopit) and shade.

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Characteristics of modern and files:-
(i) It involves covering and compaction of wastes in order to prevent the waste from being blow by wind.
(ii) For gas extration and power generation, 1 and fill gas extraction systems are installed.
(iii) Developed methods that contain leachate such as plastic liners or lining clay.
Reasons for the use of modern 1 and fills:-
(i) Modern 1 and fills stimulates the prevention of waste by recovery and reclycing.
(ii) Landfill creates suitable cost for waste disposal that constantly prevent the unnecessary waste trans portaion.
(iii) This method of land filling, also reduce the negative effect on the environment caused due to 1 and filling of waste.

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Electrostatic precipitator is a device used for the removal of suspended dust particles from a gas or exhaust by the application of high voltage electrostatic charge.
This device can remove over 99% particulate matter present in the exhaust from a thermal power plant. It contains electrode wires that are maintained at thousand volts. This produces a corona that releases electrons. Electron relased are attach to the dust particles that give them a net negative charge. The collecting plates are then grounded and attract the charged dust particles. The velocity of the air is maintained to be low enough in order to allow the dust particles to fall. A scrubber helps in the removal of gases such as sulphar dioxide and in this, the exhaust is passed through a spray of water or time.

Answer:

(i) Biomagnification is the ecological term used to describe the accumulation of DDT and mercury at different trophic level.
(ii) Higher DDT concentration in birds disturbs their, calcium metabolism that causes thinning of egg shell and premature breaking. It results        in the decline in the population of birds.
(iii) Yes, accumulation of DDT causes eutrophication. It is the natural ageing of a lake by nutrient enrichment in the water.
(iv) Yes, it affects the BOD, as increases in biochemical oxygen Demand results in a decrease in dissolved oxygen in the water body.
(iv) Minamata disease is caused due to eating fish that accumulate mercury.