NEET Biology Class 12 Environmental Issues Notes

Environmental Issues

Pollution:  Pollution is any undesirable change in physical, chemical or biological characteristics of air, land, water or soil.

• The human population explosion increases the demand for food, water, homes, electricity, automobiles, etc.
• It leads to pollution.
• The Government of India has passed the Environment (Protection) Act, of 1986 to control environmental pollution and protect and improve the quality of our environment.

Air Pollution And Its Control

Causes of air pollution:

• Particulate & gaseous air pollutants from smokestacks of thermal power plants, smelters, etc.
• According central Pollution Control Board (CPCB), particulate size of less than 2.5µm in diameter (PM 2.5) causes the greatest harm to human health.
• Pollutants from automobiles.

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Harmful effects of air pollution:

• Particulates cause respiratory problems, irritation, inflammations and damage to lungs, and premature deaths.
• Reduction in growth and yield of crops and premature death of plants.

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Control of air pollution:

• Separate/filter out the particulate matter before releasing the harmless gases in the atmosphere. Use of lead-free petrol or diesel.
• Use of catalytic converters.
• Phasing out of old vehicles.
• Use of low-sulfur petrol and diesel.
• Application of pollution-level norms for vehicles, etc.
• Use of compressed natural gas (CNG). It is used in Delhi, in public transport (buses).

Advantages of CNG:

• It is better and cheaper than petrol and diesel. It burns almost completely.
• It cannot be siphoned off by thieves and adulterated.

NEET Biology Class 12 Environmental Issues Notes

Main problem of CNG: Difficulty in laying down pipelines to deliver CNG through distribution points/pumps.

Catalytic converter: It is the device that reduces the emission of poisonous gases. It has platinum-palladium and rhodium as catalysts. This converts

• Unburnt hydrocarbons → CO₂ + water
• Carbon monoxide → CO₂
• Nitric oxide → Nitrogen

Motor vehicles having catalytic converters should use unleaded petrol because lead in petrol inactivates the catalyst.

Biology Class 12 Notes For Neet

Electrostatic precipitator

• It is the device remove particulate matter.
• It can remove over 99% of particulate matter present in the exhaust from a thermal power plant.
• The electrons released from electrode wires (at several thousand volts) attach to dust particles giving a negative charge. The collecting plates attract charged dust particles
• The velocity of air between the plates must be low enough to allow the dust to fall.

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Environmental Issues NEET Notes

• A scrubber removes gases like SO₂. In this, the exhaust is passed through a spray of water or lime.
• Very small particulates are not removed by this precipitator.

Noise pollution

• Noise is an undesired high level of sound. In India, the Air
• (Prevention and Control of Pollution) Act (1981) was amended in 1987 to include noise as an air pollutant.

Sources of noise pollution:

Music instruments, loudspeakers, crackers, industries, etc.

Harmful effects of noise:

• Noise causes psychological and physiological disorders.
• A sound level above 150 dB (generated by the takeoff of a jet plane or rocket) may damage eardrums.
• Chronic exposure to relatively lower noise may damage the hearing abilities of humans.
• Sleeplessness, increased heartbeat and breathing, stress, etc.

Control of noise pollution:

Biology Class 12 Notes For Neet

• Use of sound absorbent materials in industries.
• Delimitation of horn-free zones around hospitals & schools.
• Permissible sound levels of crackers and loudspeakers.
• Delimit the timings of using loudspeakers.

Laws & policies in India control vehicular pollution:

• Autfuel policy: Cut down vehicular pollution in Indian cities.
• Euro III norms:
  • Control sulfur content at 350 ppm (parts per million) in diesel and 150 ppm in petrol.
  • The level of aromatic hydrocarbons is to be at 42% of the fuel.
  • In the future: Reduce sulfur to 5 ppm in petrol & diesel and bring down the level to 35%.
  • Upgrade vehicle engines.

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Water Pollution And Its Control

Domestic Sewage and Industrial Effluents:

• 0.1 % impurities make domestic sewage unfit for human use:
  • Suspended solids: Sand, silt, clay, etc.
  • Colloidal materials: Faecal matter, bacteria, cloth, paper fibers, etc.
  • Dissolved materials: Nutrients like nitrate, NH3, phosphate, Na, Ca, etc.
• Removal of dissolved materials, organic compounds, and toxic metal ions are most difficult.
• Domestic sewage contains biodegradable organic matter. It is a decomposed microorganism.
• The amount of biodegradable organic matter in sewage water is estimated by measuring Biochemical Oxygen Demand (BOD).
• During biodegradation, microbes consume O₂. It results in a sharp decline in dissolved O₂. This causes the death of aquatic organisms.
• The presence of more nutrients in water causes excess growth of planktonic algae (algal bloom). It imparts a distinct color to the water bodies and deteriorates the water quality resulting in the death of fish. Some bloom-forming algae are extremely toxic to human beings and animals.
• Water hyacinth (Eichhornia crassipes) is the most problematic aquatic weed (‘Terror of Bengal’). They grow abundantly in eutrophic water bodies.
• Sewage from homes and hospitals contains pathogens that cause dysentery, typhoid, jaundice, cholera, etc.
• Industrial wastewater contains toxic substances like DDT, heavy metals (mercury, cadmium, copper, lead, etc.), and organic compounds.

Biological magnification (Biomagnification)

• It is the accumulation of the toxicant (mercury, DDT, etc.) at successive trophic levels of a food chain.
• Organisms cannot metabolize or excrete the toxicant. So, it is passed on to the next trophic level.

NEET Biology Environmental Issues Important Notes

Biomagnification of DDT in an aquatic food chain:

DDT disturbs calcium metabolism in birds, which causes the thinning of eggshells and their premature breaking. It causes a decline in bird populations.

Eutrophication:

Biology Class 12 Notes For Neet

• It is the natural aging of a lake by nutrient enrichment.
• In a young lake, the water is cold and clear. With time, streams draining into the lake introduce nutrients (N2, P, etc.). It increases the lake’s fertility
• Thus plants & animals grow rapidly, and organic remains are deposited on the lake bottom. So, the lake grows shallower and warmer, with warm-water organisms.
• Marsh plants take root in the shallows and fill in the original lake basin. Eventually, the lake becomes land.
• Depending on climate, the size of the lake, and other factors, eutrophication may span thousands of years. However, pollutants like effluents from industries and homes accelerate eutrophication. This phenomenon is called
• Cultural or Accelerated Eutrophication.
• The prime contaminants are nitrates & phosphates. They overstimulate the growth of algae. It causes unsightlyscum and unpleasant odors and robs the water of dissolved oxygen. It leads to the death of other organisms.
• Heated (thermal) wastewater from electricity-generating units (For example, thermal power plants) eliminates organisms’ sensitive thigh temperature.
• It may enhance the growth of plants and fish in extremely cold areas but, only after causing damage to the indigenous flora and fauna.

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Integrated Waste Water Treatment

It includes artificial and natural processes. The townspeople of Arcata (northern coast of California) and biologists from the Humboldt State University created an integrated wastewater treatment process.

The cleaning occurs in 2 stages:

Sedimentation, filtering & chlorine treatments:

• After this, remaining pollutants like dissolved heavy metals were removed using an innovative approach.
• Biologists developed a series of six connected marshes over 60 hectares of marshland. Appropriate plants, algae, fungi, and bacteria were seeded in this area. They neutralize, absorb and assimilate pollutants.
• Thus, as the water flows through marshes, it gets purified naturally.

Environmental Issues Class 12 NEET Key Concepts and Summary

Friends of the Arcata Marsh (FOAM): FOAM is a citizens group for the upkeep and safeguarding of this project.

Ecological sanitation

• It is a sustainable system for handling human excreta, using dry composting toilets.
• This is a practical, hygienic, efficient, and cost-effective solution rather than wasted disposal.
• Human excreta can be recycled into a resource (as natural fertilizer). It reduces the need for chemical fertilizers.
• There are ‘EcoSan’ toilets in Kerala and Sri Lanka.

The government of India has passed the Water (Prevention and Control of Pollution) Act, of 1974 to safeguard water resources.

Wastes And Their Effects

Solid Wastes

Biology Class 12 Notes For Neet

• Solid wastes: Solid wastes refer to everything that goes out in the trash.
• Municipal solid wastes: Municipal solid wastes are wastes from homes, offices, stores, schools, hospitals, etc. that are collected and disposed by the municipality. All solid wastes cannot be completely burnt. Open dumps serve as the breeding ground for rats and flies.
• Sanitary landfills: Sanitary landfills are the substitute for open-burning dumps. In sanitary landfills, wastes are dumped in a depression or trench and covered with dirt.
• Limitations of Landfills:
  • The amount of garbage especially in metros has increased so much that these sites are getting filled too.
  • Seepage of chemicals, from the landfills pollutes the underground water resources.

Solid wastes are of 3 types:

1. Bio-degradable: They undergo a natural breakdown.
2. Non-biodegradable: For example plastic packets, polybags, polystyrene etc.
   • Eco-friendly packaging can be used instead of plastics.
   • For example, Carrying cloth, natural fiber carry-bags, etc.
3. Recyclable: For example, Plastics, e-waste, etc.

Hospital wastes contain disinfectants, harmful chemicals, and pathogenic microorganisms. They are incinerated.

E-waste (electronic wastes):

• All irreparable electronic goods are known as e-waste.
• They are buried in landfills or incinerated.
• Recycling is the only eco-friendly solution for the treatment of e-waste. However, during recycling, the workers are exposed to toxic substances present in e-waste.
• Over half of the e-waste in the developed world is exported to developing countries (China, India, Pakistan, etc.), where many metals (Cu, Fe, Si, Ni, and Au) are recovered during the recycling process.

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Polyblend: A Remedy for Plastic Waste

• Ahmed Khan (A plastic sack manufacturer in Bangalore) developed Polyblend. It is a fine powder of recycled modified plastic.
• Polyblend is mixed with the bitumen and is used to lay roads.
• A Blend of Polyblend and bitumen enhances the bitumen’s water-repellant properties and helps increase road life.

Agro-Chemicals And Their Effects

• Inorganic fertilizers, pesticides, herbicides, fungicides, etc. are toxic to target organisms that are important components of the soil ecosystem. These are biomagnified in the terrestrial ecosystems.
• Chemical fertilizers cause eutrophication.

Integrated Organic Farming

Biology Class 12 Notes For Neet

• It is a cyclical, zero-waste procedure, where waste products from one process are cycled in as nutrients for other processes. This allows the maximum utilization of resources and increases the efficiency of production.
• Ramesh Chandra Dagar (a farmer in Sonipat, Haryana) included bee-keeping, dairy management, water harvesting, composting and agriculture in Integrated Organic

Farming. Its advantages are given below:

• They support each other and allow an economical and sustainable venture.
• Need for chemical fertilizers, as dung is used as manure.
• Crop waste is used to create compost (natural fertilizer) or generate natural gas (provides energy for the farm).
• Dagar has created the Haryana Kisan Welfare Club, with a membership of 5000 farmers spread information on the practice of integrated organic farming.

Class 12 Biology Notes For Neet

Radioactive Wastes

• The use of nuclear energy has two very serious problems:
  • Accidental leakage.For example, the Three Mile Island incident &
  • Chornobyl incident.
  • Safe disposal of radioactive wastes.
• Nuclear radiation causes mutations. It is lethal at high doses. At lower doses, it causes disorders such as cancer.
• It is recommended to store nuclear wastes in shielded containers buried within rocks, about 500 m deep below the earth’s surface. But, the public opposes this method.

Greenhouse Effect And Global Warming

Green House Effect:

• The greenhouse is a small glass house used for growing plants during winter. The glass panel lets the light in but does not allow heat to escape. Thus the greenhouse warms up.
• The greenhouse effect is a natural phenomenon that causes the heating of the Earth’s surface and atmosphere. It maintains the present average temperature (15).
• Without the greenhouse effect, the average temperature at
• Earth’s surface would have been at –18°C.
• Clouds & gases reflect 1/4th of the incoming solar radiation and absorb some of it. But half of it falls on Earth’s surface heating it, while a small amount is reflected.
• Earth’s surface re-emits heat as infrared radiation. But a part of it is absorbed by atmospheric gases (CO₂, CH₄, etc.) and so cannot escape into space. These gases (greenhouse gases) radiate heat energy.
• It comes to Earth’s surface, heating it again. It causes the greenhouse effect.
• Overheating of the Earth due to increased levels of greenhouse gases is called global warming.
• During the past century, the temperature of Earth has increased by 0.6C, most of it during the last 3 decades.
• Contribution of greenhouse gases to total global warming:
• CO₂ (60%), CH₄(20%), CFCs (14%) and N₂O (6%).

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Impacts of global warming:

• Climatic changes (for example, El Nineffect).
• Melting of polar ice caps, Himalayan snow caps, etc.
• Future impact: Rise in sea level submerging coastal areas.

Control of global warming:

• Reduce the use of fossil fuels.
• Improve the efficiency of energy usage.
• Reduce deforestation and plant trees.
• Slowing down the growth of the human population.

International initiatives are also being taken to reduce the emission of greenhouse gases.

Class 12 Biology Notes For Neet

Ozone Depletion In The Stratosphere

• ‘Bad’ ozone is formed in the troposphere (lower atmosphere).
• It harms plants and animals.
• ‘Good’ ozone is found in the stratosphere. It acts as a shield absorbing ultraviolet radiation from the sun.
• UV rays are highly injurious since they cause mutation.
• The thickness of the ozone (O₃) in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU).
• In the stratosphere, UV rays act on molecular oxygen (O₂) causing the production of ozone. UV rays cause the degradation of ozone to  O₂ These processes are balanced.
• However, this balance is disrupted due to zone degradation by chlorofluorocarbons (CFCs used as refrigerants).
• CFCs move upward and reach the stratosphere. UV rays act on them releasing Cl atoms. In the presence of Cl (catalyst), ozone degrades to O₂ This causes ozone depletion. It has formed The ozone hole over the Antarctic region.
• UV radiation of wavelengths shorter than UV-B are almost completely absorbed by Earth’s atmosphere. But, UVB causes DNA mutation.
• It causes aging of the skin, damage to skin cells, and skin cancers. A high dose of UV-B causes inflammation of the cornea (snow-blindness), cataracts, etc. It permanently damages the cornea.
• The Montreal Protocol: An international treaty (Canada, 1987) to control the emission of ozone-depleting substances.

Degradation By Improper Resource Utilisation & Maintenance

Soil erosion and desertification:

• Human activities like over-cultivation, deforestation, grazing, and poor irrigation practices, lead to soil erosion. It results in arid patches of land and desertification.
• Increased urbanization also creates desertification.

Water logging and soil salinity:

• These are the problems as a part of the Green Revolution.
• Irrigation without proper drainage of water leads to water logging in the soil.
• It draws salt to the surface of the soil. The salt is deposited on the land surface or collected at the plant roots. This damages the agriculture.

NEET Biology Class 12 Chapter Environmental Issues Detailed Notes

Deforestation

• It is the conversion of forested areas to non-forested ones.
• Almost 40% of forests have been lost in the tropics, compared to only 1% in the temperate region.
• National Forest Policy (1988) of India has recommended 33% forest cover for the plains and 67% for the hills. But we have only 19.4% of forest cover (it was about 30% at the beginning of the 20th century).

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Reasons for deforestation:

• Conversion of forest to agricultural land.
• For timber, firewood, cattle ranching, etc.
• Slash and burn agriculture (Jhum cultivation) in the north-eastern states of India. In this, the farmers cut down the forest trees and burn the plant remains. The ash is used as a fertilizer and the land is used for farming or grazing.
• After cultivation, the area is left for several years to allow its recovery. In earlier days, enough time was given for recovery. Overpopulation and repeated cultivation decreased the recovery phase, resulting in deforestation

Consequences Of deforestation 

• Atmospheric CO₂ is enhanced because trees that could hold a lot of carbon in their biomass are lost.
• Loss of biodiversity due to habitat destruction.
• Disturbs hydrologic cycle.
• Soil erosion and Desertification.

Class 12 Biology Notes For Neet

Reforestation: The process of restoring a forest that once existed in the past. It may occur naturally in a deforested area. We can speed it up by planting trees.

People’s Participation in Conservation of Forests

1. Bishnoi movement:

• In 1731, the king of Jodhpur in Rajasthan asked to arrange wood for constructing a new palace. The minister and workers went to a forest near a village, inhabited by
• Bishnois. The Bishnois thwarted them from cutting down the trees. A Bishnoi woman Amrita Devi hugged a tree. The king’s men cut down the tree along with Amrita Devi. Her three daughters and hundreds of ofBishnois also lost their lives saving trees.
• The government of India has instituted the Amrita Devi
• Bishnoi Wildlife Protection Award for individuals or communities from rural areas for extraordinary courage and dedication in protecting wildlife.

NEET Study Material for Environmental Issues Chapter

2. ChipkMovement of Garhwal Himalayas:

• In 1974, local women participated in protecting trees from the axe of contractors by hugging them.
• The government of India in the 1980s introduced the concept of
• Joint Forest Management (JFM) works closely with the local communities for protecting and managing forests. In return for their services, the communities get the benefit of forest products (fruits, gum, rubber, medicine, etc.).