Important Notes For NEET Biology - Environmental Issues

Find below the important notes for the chapter, Environmental Issues, as per NEET Biology syllabus. This is helpful for aspirants of NEET and other exams during last-minute revision. Important notes for NEET Biology- Environmental Issues covers all the important topics and concepts useful for the exam. Check BYJU’S for the full set of important notes and study material for NEET Biology and solve the NEET Biology MCQs to check your understanding of the subject.

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Environmental Issues

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Environmental Issues – Important Points, Summary, Revision, Highlights

Environmental Issues

Environmental pollution is a serious issue that the world is facing today. Any undesirable change in the environment is harmful to all living organisms. The Environment Protection Act was passed in 1986 to improve and maintain the quality of the environment. It is important to protect our natural resources and environment for sustainable development.

Air Pollution and Control

All living organisms need air to breathe and any undesirable change in the quality of air leads to various diseases, allergies and reduces the growth of plants.

Air pollution is caused due to natural and man-made sources. The excessive quantities of gases and particulate matter lead to air pollution.

Air Pollutants: Air pollutants are of two types; primary and secondary.

Primary pollutants are introduced directly into the atmosphere, e.g. carbon dioxide, carbon monoxide, sulphur oxides, methane, CFCs, ammonia, particulate matter, etc. They are released in the atmosphere by burning fossil fuels, industries, motor vehicles, volcanic eruptions, nuclear radiations, etc.

Secondary pollutants are formed by the reacting primary pollutants and are not emitted directly, e.g. PAN (peroxyacetyl nitrate) formed by nitrogen oxides and volatile organic compounds such as methane, ozone in the troposphere, photochemical smog (a mixture of smoke, sulfur dioxide and secondary pollutants).

Smoke coming out of various industries, thermal power plants have to be treated to remove particulate matter and gaseous pollutants before releasing harmless gases (nitrogen, oxygen, etc.) into the atmosphere.

An electrostatic precipitator is used to remove particulate matter. Dust particles get negatively charged by attaching to the electrons produced by electrodes and get collected. Sulphur dioxide is removed by a scrubber.

Particulate matter of the size >2.5 µm is harmful and causes various respiratory complications.

Catalytic converters: As automobiles are one of the major causes of air pollution in cities, catalytic converters are being used in the vehicle to reduce the emission of harmful gases.

They contain Pt, Pd and Rh as catalysts, that convert unburnt hydrocarbons to water and CO2 and nitric oxide (NO) and carbon monoxide (CO) to nitrogen gas and carbon dioxide. The unleaded petrol must be used in these vehicles as the lead interferes in the catalytic process.

CNG (Compressed Natural Gas): CNG (methane) is more efficient in burning and produces less harmful gases, so the use of CNG is preferred over diesel and petrol.

Noise is also an air pollutant and the same was added in the amendment of Air Prevention and Control of Pollution Act (1981) in 1987. A very loud sound (150 dB) such as produced by the rocket or jet plane can cause permanent damage to eardrums even on exposure for a short duration.

Global warming and Greenhouse effect: The Greenhouse effect is a natural phenomenon responsible for trapping the heat in the Earth’s atmosphere. Had it not been for the greenhouse effect, the average temperature of the Earth’s surface would have been -18℃ rather than 15℃.

The main greenhouse gases are carbon dioxide and methane.

The increase in greenhouse gases has resulted in an increase in the average temperature and global warming. In the past century, Earth’s average temperature has increased by 0.6℃. This has led to El Nino effect, melting of polar ice caps and Himalayan glaciers. If this continues, it will result in a substantial rise in the sea level and submerging of coastal areas.

Global warming can be reduced by taking various measures such as reforestation, efficient use of energy, cutting down the usage of fossil fuel, etc.

Ozone Hole: The Ozone layer of the stratosphere absorbs and shields us from the harmful ultraviolet rays of the Sun. The thickness of the ozone layer is measured in Dobson Units (DU).

Ozone hole refers to the depletion of the ozone layer in the stratosphere. The main causative agents are CFCs (chlorofluorocarbons or freons) used as aerosol and refrigerants.

The UV rays present in the stratosphere act on CFCs to release chlorine free-radicals. These free radicals catalyse the degradation of ozone to form molecular oxygen. As Cl only acts as a catalyst and not consumed, they continuously damage the ozone layer.

UV-B causes a mutation in DNA and it is the reason for various cancers. UV-B also causes inflammation in the eye (snow-blindness) and damages the cornea.

Montreal Protocol (1987) was signed to control the depletion of the ozone layer.

Water Pollution and Control

With the intent to protect water resources, the Water Prevention and Control of Pollution Act (1974) was passed.

Industrial effluents and domestic sewage are polluting our rivers. Not all the wastewater is being treated by sewage treatment.

Even 0.1 percent impurities in domestic sewage are harmful to humans present. These impurities include solid (sand, clay, etc.), colloidal (excreta, paper and cloth fibres, bacteria) and dissolved impurities (ammonia, nitrate, sodium, phosphate, calcium, etc.). It is most difficult to remove dissolved salts, organic compounds and toxic metal ions.

BOD (biological oxygen demand) measures an amount of biodegradable matter present in the sample. Sewage treatment plants (STPs) are used to treat wastewater before releasing it into water resources.

Where sewage is discharged, there is a sharp decline in the oxygen content due to its usage by microorganisms for biodegradation of organic matter.

Excessive nutrients stimulate the growth of algae resulting in HAB (Harmful Algal Bloom). They reduce the amount of oxygen and also release toxins, which are harmful to aquatic organisms and even to birds and humans, who eat them.

Water hyacinth is the most problematic weed as it grows rapidly. It is known as “Terror of Bengal”.

Polluted water has many pathogenic microbes causing various diseases such as typhoid, dysentery, cholera, jaundice, etc.

Biomagnification: Industrial waste also contains heavy metals such as mercury, copper, cadmium, lead, etc. Toxic substances of industrial waste may get into the aquatic food chain. Its effect gets magnified as we go higher at each trophic level. This happens due to the accumulation of toxic substances.

Example of biomagnification: DDT concentration increases at successive trophic levels. From 0.003 ppb of DDT in water to as high as 25 ppm in birds that eat fish. This causes premature thinning and breaking of eggshell due to disruption in calcium metabolism.

Eutrophication: It refers to the ageing of a lake naturally over a period of thousand years. The lake grows shallower and warmer as the organic matter piles up and eventually converts into a land.

Industrial effluents accelerate the process of eutrophication. Nitrates and phosphates are the main contaminants, which stimulate the growth of algae. This declines the oxygen content of water. Toxins present in the pollutants kill the aquatic organisms and decomposition of dead fish population further depletes the dissolved oxygen level. Many lakes have been choked to death by this process.

In Arcata (California), a natural system is created to treat wastewater. After the first stage of conventional filtration, sedimentation and chlorine treatment, the effluent is passed to a series of 6 naturally developed and connected marshes to absorb, neutralise and assimilate dangerous pollutants.

EcoSan Toilets: An efficient and hygienic solution for disposal of human excreta is dry composting toilets. The human waste can be recycled and used as a natural fertiliser. There are many EcoSan toilets developed in Kerala and Sri Lanka.

Solid Wastes

The municipal solid wastes are kept at open dumping places and burnt. Often it is not burnt completely resulting in rats, pigs and flies breeding there. Sanitary landfills are used in place of open dumps, but they are also getting filled. Moreover, there are chances of chemical seepage and pollution of underground water so landfills are not a permanent solution for the disposal of solid wastes.

The only solution is the sensitivity towards environmental issues and awareness of hazardous effects.

Sorting of wastes into biodegradable, recyclable and non-biodegradable helps in disposal of the wastes accordingly.

Incinerators are used to dispose of hospital waste. Electronic wastes (e-waste) are either buried in landfills or incinerated. The e-waste from developed countries is transported to developing countries to recover metals like copper, gold, nickel, etc. Manual recycling exposes workers to toxic substances.

Polyblend: In Bangalore, Ahmed Khan developed polyblend from recycled plastic, which is used with bitumen to lay roads. It enhances the water-repelling property of bitumen and triples the road life.


Chemical fertilisers and pesticides are used to increase the yield of the crop by many folds. They are toxic to not only insects and pests but also to other harmless species, which are an essential part of the soil ecosystem. Moreover, they are drained to water resources leading to eutrophication.

The solution is to use biofertilizers and shift to organic farming practices.

Integrated organic farming: It is zero waste procedure, where waste from one process is utilized as a nutrient in the other processes.

In Sonipat, a farmer, Ramesh Chandra Dagar (created Haryana Kisan Welfare Club) has applied the above process and it has proven out to be a sustainable, economical and environment-friendly venture. Dairy management, composting, agriculture, water harvesting and bee-keeping, all are included in a chain of processes. Cattle excreta is used as manure. Compost is created from crop waste, which is used to generate biogas or natural fertilizer.

Radioactive wastes

Radiation is lethal for organisms. Even a lower dose for a longer duration can cause various disorders including mutation and cancer. Although nuclear energy is beneficial and a non-polluting way to get energy but an accidental leakage can lead to grave problems, e.g. Chernobyl and Three Mile Island incidents.

Moreover, it is important to cautiously dispose of radioactive wastes. The storage of radioactive wastes should be done in proper containers after the pre-treatment. They must be buried deep (500 m) under the earth’s surface.

Degradation of Natural Resources (Improper utilisation and maintenance)

Soil erosion and desertification: Removal of fertile topsoil due to various human activities and poor irrigation practices. The large patches of barren land create a desert over time.

Waterlogging and soil salinity: Waterlogging brings salt to the surface and it gets deposited. This damages the growth of crops as it starts collecting at the root level.

Deforestation: Plains should have 33 percent forest cover and hills 67 percent, as recommended by the National Forest Policy (1988). The forest cover of India shrunk to 21.54 percent from 30 percent in the 20th century.

Urbanisation and converting forest to agricultural land to fulfil the need of ever-increasing population is the main reason for deforestation.

Jhum cultivation (slash and burn agriculture) present in the north-eastern states has also led to deforestation.

Deforestation leads to soil erosion, loss of biodiversity, disturbed hydrologic cycles and desertification.

Reforestation can restore and reverse the process. There have been many attempts to protect forests:

  • Amrita Devi Bishnoi and many of the villagers died saving trees in Jodhpur, Rajasthan (1731)
  • Chipko movement to protect trees in Garhwal Himalayas (1974)
  • Joint Forest Management (JFM, 1980) has been developed to increase the participation of local communities to protect and manage forests

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