Environmental Issues: Class 12 Biology NCERT Chapter 16

Key Features of NCERT Material for Class 12 Biology Chapter 16 –  Environmental Issues

In the previous chapter 15, you studied what is biodiveristy and signifinace of conserving it. In this chapter of class 12 biology:Environmental Issues, you will understand what is an environmental issue and different issues in our environment like pollution, waste treatment, ozone depletion etc.

Quick revision notes

 With increment in human populace, requests for food, cover, water, power, streets, and autos are expanding quickly and applying pressure on environment and adjusting the natural soundness of biological system. All over the world, individuals are confronting an abundance of new and testing environmental issues each day. Some of them are-pollution, nursery impact, ozone consumption, deforestation and so on.

Pollution is bothersome change in physical, compound or organic properties of air, land, water or soil. The operators which cause unfortunate change are called contaminations.

What are Environmental Issues?

 Any human action carries alongside it, many symptoms. One part of it could realize advancement while the other side of the coin could be an unfavorable impact. These negative changes regularly lead to environmental issues that influence the natural parity of the environment.

 We can characterize environmental issues as the hurtful impacts of any human action on the environment. This incorporates both the natural and physical parts of the environment. Air pollution, water pollution, natural environment pollution, trash pollution, and so forth are a portion of the major environmental issues that are causing massive concern.

 To handle these environmental issues, ensuring the environment is essential. This aides in forestalling the unfavorable impacts as well as causes us to preserve the natural assets and natural environment for people in the future. Assurance of the environment isn’t just a social development but on the other hand is upheld by different laws that have been passed to guarantee that humans don’t abuse the assets any more.

Air Pollution and its Control

Air is fundamental for breath in every single living being. Contaminations decrease development and creation of yields just as unexpected passing of plants. The unsafe impact of pollution on all the living life forms relies on

  •  Convergence of contaminations.
  •  Length of presentation.
  •  Life forms included.

 Warm force plants, smelters and other enterprises discharge particulate and vaporous air toxins alongside innocuous gases, for example, nitrogen, oxygen and so on. These toxins ought to be sifted through before delivering the innocuous gases into the environment. There are numerous strategies for evacuating particulate issue; the most broadly utilized is the electrostatic precipitator.

 Electrostatic Precipitator-

can expel over 99% of particulate issue present in the fumes from warm force plant. scrubber for air pollution control

It has terminal wires that are kept up at a few thousand volts to create a crown that discharges electrons. These electrons join to clean particles giving them a net negative charge. The gathering plates are grounded and pull in the charged residue particles to that spotless air can go through electrostatic precipitator.

 A scrubber can evacuate gases like sulpher dioxide. The fumes is gone through shower of water or lime.

As indicated by CPCB (Central Pollution Control Board)particulate size less 2.5 micrometers or less in measurement (PM 2.5)cause most prominent mischief to human wellbeing.

The fine particles can be breathed in profound into the lungs and can cause breathing and respiratory side effects, disturbance, aggravations and harm to lungs and unexpected passing.

Cars are primary driver of barometrical pollution in metro urban communities. Appropriate upkeep of vehicles alongside utilization of without lead petroleum or diesel can decrease the toxins they radiate.

Exhaust systems contain platinum-palladium and rhodium as the impetus, are fitted into vehicles for lessening outflow of harmful gases. As the fumes goes through the exhaust system, unburnt hydrocarbons are changed over into carbon dioxide and waterand carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas . The vehicles fitted with exhaust system should utilize unleaded petroleum since lead in the petroleum inactivates the impetus.

 In Delhi, whole armada of open vehicle was changed over to packed natural gas (CNG) mode to diminish the quick expanding pollution level of metro. CNG is better than diesel since it is less expensive than petroleum and diesel, consume totally with leaving any buildup and can’t be debased like petroleum and diesel. In any case, the primary issue with exchanging over to CNG is the trouble of setting down pipelines to convey CNG through dissemination focuses/siphons and guaranteeing continuous flexibly.

 Auto Fuel Policy :

The Government of India has spread out a guide to chop down the vehicular air pollution in numerous urban areas of India. The objective of this arrangement is to decrease Sulfur to 50 ppm in petroleum and diesel and diminish levels of sweet-smelling hydrocarbons to 35% of the fuel. The Bharat Stage II will be relevant to all vehicles in all urban areas April, 1, 2005. The urban communities (like Delhi, Mumbai, Chennai, Kolkata and so forth.) should meet Euro III outflow standards from April 1, 2005 and Euro IV Emission standards from April 1, 2010

 In India, the Air (Prevention and Control of Pollution) Act came into power in 1981 and was corrected in 1987 to incorporate clamor as an air pollutant.Noise is undesired elevated level of sound. High solid level more prominent than 150 dB or more created by departure or a fly plane or rocket may harm ear drums in this way for all time impairing hearing capacity.

 Commotion likewise causes restlessness, expanded heart pulsating, modified breathing example, in this manner impressively focusing on humans.Decrease of commotion in ventures can be influenced by utilization of sound spongy materials or by stifling clamor. 

Water Pollution and Control

Water bodies are life saver of human creatures just as other creatures. Because of removal of a wide range of waste and other anthropogenic activities the lakes, lakes, stream, waterway, estuaries and seas are getting contaminated in a few pieces of world. The Government of India has passed the Water (Prevention and Control of Pollution) Act, 1974 to ensure the water assets.

water pollution and control

Household Sewage and Industrial Effluents-

The sewage that comes out from house and office makes the residential sewage. A minor 0.1% degradations make residential sewage mismatched for human use. Solid wastes are commonly easy to empty anyway separated salts as nitrates, phosphates and various supplements and unsafe metal particles and natural blends present in residential wastes are moderately difficult to remove.

Residential sewage mostly contains biodegradable natural issue, which can be easily rotted by microorganisms like organisms and developments. They use natural wastes as supplements.

 Organic Oxygen Demand (BOD)

The microorganisms that deteriorate natural wastes in water bodies use a lot of oxygen that result into sharp lessening in separated oxygen downstream from the reason for sewage discharge. This causes mortality of fish and other maritime creatures.

sewage treatmentBody suggest the proportion of oxygen that would be eaten up if all the natural issue is one liter of water were oxidized by tiny life forms. The BOD test measures the pace of take-up of oxygen by little scope life structures in a case of water. In an indirect manner BOD is an extent of the natural issue present in the water. The more unmistakable the BOD of waste water, more is its debasing potential. 

Algal Bloom

DDT grouppings The closeness of enormous proportion of natural enhancements in water causes over the top advancement of planktonic or free floating green development called algal Bloom. In light of this shade of water bodies get changed. This may cause crumbling of the water quality and fish mortality.

 Water hyacinth (Eichhornia crassipes) is the world’s most risky maritime weed. They are brought into India for their incredible blooms that have caused ruin by their over the top advancement by causing impedes in our water bodies. This weed is usually known as ‘Terrorof Bengal’.

Biomagnification of Biological MagnificationHurtful materials present in mechanical wastes and water from farmhouse containing pesticides and weedicides enters the developed lifestyle of maritime animals. The extension in the assembly of toxins at every dynamic trophic level is called natural intensification. The most generally perceived toxic substance that gets gathered at dynamic trophic levels joins DDT and Mercury. High groupings of DDT upset calcium absorption in fowls, which causes lessening of eggshell and their troublesome breaking, at long last causing decline in feathered animal masses. 


It is the natural maturing of a lake by organic enhancement of its water. Because of expansion of supplements, for example, nitrogen and phosphorus that support the development of sea-going life form the collection of natural stays in course of time prompts will lowing of lake. Throughout the hundreds of years the residue and natural flotsam and jetsam accumulates at the base of lake and energize the development of swamp plants in the shallow and start to fill in the first lake bowl. Inevitably enormous masses of drifting plants develops lastly changing over into land.

 The toxins from man’s exercises, for example, effluents from the businesses and homes drastically quicken the maturing of lake. This marvel is called Cultural or Accelerated Eutrophication. Fundamental contaminants incorporate nitrates, phosphates that go about as plant nutrients.They increment the development of green growth, causing unattractive filth and terrible scents, and draining the disintegrated oxygen of water which is significant for other amphibian life.

 Coordinated Waste Water Treatment

 Wastewater including sewage can be treated in a coordinated manner, by consolidating fake and natural procedures. A case of such an activity is the town of Arcata, arranged along the northern shore of California .The local individuals in collabaration with Humboldt State University made an incorporated waste water treatment process inside a natural framework. The cleaning happens in two phases –

(a) the regular sedimentation, sifting and chlorine medicines are given.

(b) To battle with contaminations like broke down overwhelming metals , the researcher built up a progression of six associated swamps more than 60 hectares of marshland where plants, green growth, parasites and microscopic organisms were seeded which kill, ingest and acclimatize the toxins.

As the water courses through the bogs, it gets purged naturally. The bogs additionally establish an asylum, which is profoundly different as fishes, creatures and fowls that currently dwell there.

A residents bunch called Friends of the Arcata Marsh (FOAM) are answerable for the wellbeing of this venture.

Environmental sterilization is an economical framework for overseeing human excreta, utilizing dry fertilizing the soil latrines. This is a pragmatic, sterile, productive and practical answer for human garbage removal. The significant part is that with this treating the soil strategy, human excreta can be reused into natural compost. There are working ‘EcoSan’ latrines in numerous territories of Kerala and Sri Lanka

 Strong Wastes

Civil strong wastes will be wastes from home, workplaces, stores, schools, emergency clinics and so forth that are gathered and arranged by the region. It comprises of paper, food wastes, plastics, glass, metals, elastic, cowhide, material etc.Burning lessens the volume of the wastes yet the waste commonly not consumed to irts culmination and open dumps regularly fill in as the favorable place for rodents and flies. Sterile landfills were utilized an alternative for open consuming dumps where wastes are dumped in a downturn or channel after compaction and secured with soil each day. There is a peril of drainage of synthetic concoctions from these landfills dirtying the underground water assets.

Metropolitan wastes :

Bio-degradable wastes, Recyclable wastes, Non-biodegradable waste

  • The biodegradable materials can be placed into profound pits in the ground and be left for natural breakdown
  • Kabadiwallahs and cloth pickers work admirably of division of materials for reusing of various types of wastes.
  • Polyblend – Polyblend is the most ideal approach to battle with ever-expanding issue of aggregating plastic waste .It is a fine powder of reused adjusted plastic which is blended in with the bitumen .Polyblend and bitumen, when used to lay streets, upgraded the bitumen’s water repellant properties, and assisted with expanding street life by a factor of three.
  •  Medical clinics create perilous wastes that contain disinfectants and other synthetics and alos pathogenic small scale living beings. Such wastes need cautious treatment and removal. Incinators are utilized for removal of clinic wastes.

Electronic wastes-

Unrepairable PCs and other electronic merchandise are known as electronic wastes (e-wastes). E-wastes are covered in landfills or burned. Over portion of the e-wastes created in the created world are sent out to creating nations, predominantly to China, India and Pakistan, where metals like copper, iron, silicon, nickel and gold are recuperated during reusing process. Reusing is the main answer for the treatment of e-wastes gave it is done in an environment-accommodating way

Agro-synthetic concoctions and other impacts

Utilization of inorganic manures and pesticides has been expanded many crease because of green upset for upgrading crop creation. The pesticides and bug sprays are harmful to non-target creatures that are significant segments of the dirt biological system. They are biomagnified in the earthbound biological system and furthermore causes eutrophication in amphibian environments .

Natural Farming

Coordinated natural cultivating is a cyclic, zero-squander strategy in which squander items from one procedure are cycled in as supplements for other procedures to permit the most extreme use of asset and increment the proficiency of creation. It incorporates honey bee keeping, dairy the board, water gathering, treating the soil and horticulture in a chain of procedures which bolster one another and permit an amazingly prudent and supportable endeavor. No concoction manure is utilized in this procedure.

Radioactive Wastes

Atomic vitality has two intense issues 

The radiation delivered from atomic wastes is amazingly harming to natural life forms as it makes changes happen at extremely high rate. It has been suggested that capacity of atomic wastes after adequate pre-treatment ought to be done in reasonably protected compartments and covered inside the stone about 500m far beneath the earth surface.

Green House Effect and Global Warming

greenhouse gases effectThe nursery impact is a naturally happening wonder that is liable for warming of Earth’s surface and environment because of increment in convergence of carbon dioxide and methane gas. Mists and gases reflect around one-fourth of the approaching sun oriented radiation and assimilate some of it however practically 50% of approaching sunlight based radiation falls on Earth’s surface warming it, while a little extent is reflected back. The outside of earth re-discharges heat as infrared radiation yet some portion of this doesn’t reflected back because of ozone depleting substances that prompts warming of earth air. An unnatural weather change is caused because of nursery impact.

Researchers accept that this ascent in temperature is prompting hurtful changes in the environment and bringing about odd climatic changes (for example El Nino impact) , consequently prompting expanded liquefying of polar ice tops.

An unnatural weather change can be constrained by

  • Chopping down utilization of petroleum product
  • Improving effectiveness of vitality utilization 
  • Decreasing deforestation 
  • Planting tree
  • Hindering the development of human populace.

Ozone Depletion in the Stratosphere

Ozone found in the upper piece of the air called stratosphere goes about as a shield engrossing bright radiation structure the sun. UV beams are exceptionally damaging to living beings.

The thickness of the ozone-layer in a segment of air starting from the earliest stage the head of the air is estimated in tems of Dobson units (DU). Ozone layer retains the destructive UV-beams. It causes maturing of skin, harm to skin cells and different kinds of skin tumors. In human eye, cornea assimilates UV-B radiation, and a high portion of UV-B causes irritation of cornea, called snow-visual deficiency waterfall, and so on. Such presentation may forever harm the cornea.

Chlorofluro Carbons drain the ozone layer. The piece of environment with lesser grouping of ozone is called ozone gap.

Steps prompting ozone consumption :

  • UV-beams split CFCs and delivery nuclear chlorine (Cl)
  • UV-beams likewise split ozone into oxygen. 
  • Chlorine iotas trap oxygen molecules and ozone isn’t framed again from oxygen. This prompts consumption of ozone in the stratosphere.


 It is the transformation of forested regions to non-forested ones because of human exercises like slice and consume agribusiness likewise called Jhum development where ranchers chop down trees and consume the plant remains. Debris is utilized as a compost and the land is then utilized for cultivating or cows nibbling ;utilization of manures and cutting of trees for ventures and private use. Fundamental outcome of deforestation incorporates

  • Upgraded carbon dioxide focus
  • Loss of biodiversity
  • Upset hydrologic cycles 
  • Soil disintegration 
  • Desertification and so forth.

Reforestation: Process of reestablishing a backwoods that was expelled sooner or later of time previously.

The Government of India has as of late began the Amrita Devi Bishnoi Wildlife Protection Award for people or networks from provincial regions that have indicated exceptional fearlessness and commitment in ensuring natural life.

Chipko Movement – In 1974, neighborhood ladies of Garhwal Himalayas indicated gigantic fortitude in shielding trees from the hatchet of temporary workers by embracing them. Individuals everywhere throughout the world have valued the Chipko development.

Understanding the significance of cooperation by neighborhood networks, the Government of India in 1980s has presented the idea of Joint Forest Management (JFM) in order to work intimately with the nearby networks for securing and overseeing backwoods.

(Environmental Issues: Class 12)


Q: Is deforestation an environmental issue? Why?

Ans. Indeed, Deforestation is an environmental issue. Backwoods have a significant task to carry out in the nature of an environment. Natural woods go about as biodiversity holds. They are likewise carbon sinks, helping in keeping out carbon from the climate and seas. Carbon dioxide and other gases, thusly, cause an Earth-wide temperature boost and atmosphere changes. Also, accordingly wrecking woods have a negative issue on the environment.

(Environmental Issues: Class 12)

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