CBSE Class 12 Syllabus 2027 Biology Reading Material

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CBSE Class 12
Syllabus 2027
Question Paper ·
Biology
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CBSE Class 12 Syllabus 2027 Question Paper Biology
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Class XII (2026-27)
Biology 044

Unit-Environmental Issues
Human population size has grown enormously over the last hundred years. This means
increases in demand for food, water, home, electricity, roads, automobiles and
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numerous other commodities. These demands are exerting tremendous pressure on
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our natural resources, and are also contributing to pollution of air, water and soil. The
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resources and pollution without halting the process of development. Pollution is
undesirable change in physical, chemical or biological characteristics of air, land, water
or soil. Agents that bring about such an undesirable change are called as pollutants. In
order to control environmental pollution, the Government of India has passed the
Environment (Protection) Act, 1986 to protect and improve the quality of our
environment (air, water and soil).

1. Air Pollution and its Control o m
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. needs. Air pollutants cause injury to all
We are dependent on air for our respiratory m
e yield of crops and cause premature death of
living organisms. They reduce growthaand
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ag affect the respiratory system of humans and of
plants. Air pollutants also deleteriously
animals. Harmful effects depend on the concentration of pollutants, duration of
exposure and the organism. Smokestacks of thermal power plants, smelters and other
industries release particulate and gaseous air pollutants together with harmless gases,
such as nitrogen, oxygen, etc. These pollutants must be separated/ filtered out before

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releasing the harmless gases into the atmosphere.

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Fig. 1 Electrostatic Precipitator

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There are several ways of removing particulate matter; the most widely used of which is
the electrostatic precipitator (Figure 1), which can remove over 99 per cent particulate
matter present in the exhaust from a thermal power plant. It has electrode wires that are
maintained at several thousand volts, which produce a corona that releases electrons.
These electrons attach to dust particles giving them a net negative charge. The
collecting plates are grounded and attract the charged dust particles. The velocity of air
between the plates must be low enough to allow the dust to fall. A scrubber (Figure 1)
can remove gases like sulphur dioxide. In a scrubber, the exhaust is passed through a
spray of water or lime. Recently we have realised the dangers of particulate matter that
are very very small and are not removed by these precipitators. According to Central
Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter
(PM 2.5) are responsible for causing the greatest harm to human health. These fine
particulates can be inhaled deep into the lungs and can cause breathing and respiratory
symptoms, irritation, inflammations and damage to the lungs and premature deaths.

Automobiles are a major cause for atmospheric pollution atleast in the metro cities. As
the number of vehicles increase on the streets, this problem is now shifting to the other
cities too. Proper maintenance of automobiles along with use of lead-free petrol or
diesel can reduce the pollutants they emit. Catalytic converters, having expensive
metals namely platinum-palladium and rhodium as the catalysts, are fitted into
automobiles for reducing emission of poisonous gases. As the exhaust passes through
the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and
water, and carbon monoxide and nitric oxide are changed to carbon dioxide and
nitrogen gas, respectively. Motor vehicles equipped with catalytic converter should use
unleaded petrol because lead in the petrol inactivates the catalyst. In India, the Air
(Prevention and Control of Pollution) Act came into force in 1981, but was amended in
1987 to include noise as an air pollutant. Noise is undesired high level of sound. We
have got used to associating loud sounds with pleasure and entertainment not realising
that noise causes psychological and physiological disorders in humans. The bigger the
city, the bigger the function, the greater the noise!! A brief exposure to extremely high
sound level, 150 dB or more generated
by take-off of a jet plane or rocket, may damage ear drums thus permanently impairing
hearing ability. Even chronic exposure to a relatively lower noise level of cities may
permanently damage hearing abilities of humans. Noise also causes sleeplessness,

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increased heart- beat, altered breathing pattern, thus considerably stressing humans.
Considering the many dangerous effects of noise pollution can you identify the
unnecessary sources of noise pollution around you which can be reduced immediately
without any financial loss to anybody? Reduction of noise in our industries can be
affected by use of sound absorbent materials or by muffling noise. Stringent following of
laws laid down in relation to noise like delimitation of horn-free zones around hospitals
and schools, permissible sound-levels of crackers and of loudspeakers, timings after
which loudspeakers cannot be played, etc., need to be enforced to protect ourselves
from noise pollution.

1.1 Controlling Vehicular Air Pollution: A Case Study of Delhi
With its very large population of vehicular traffic, Delhi leads the country in its levels of
air-pollution – it has more cars than the states of Gujarat and West Bengal put together.
In the 1990s, Delhi ranked fourth among the 41 most polluted cities of the world. Air
pollution problems in Delhi became so serious that a public interest litigation (PIL) was
filed in the Supreme Court of India. After being censured very strongly by the Supreme
Court, under its directives, the government was asked to take, within a specified time
period, appropriate measures, including switching over the entire fleet of public
transport, i.e., buses, from diesel to compressed natural gas (CNG). All the buses of
Delhi were converted to run on CNG by the end of 2002. You may ask the question as
to why CNG is better than diesel. The answer is that CNG burns most efficiently, unlike
petrol or diesel, in the automobiles and very little of it is left unburnt. Moreover, CNG is
cheaper than petrol or diesel, cannot be siphoned off by thieves and adulterated like
petrol or diesel. The main problem with switching over to CNG is the difficulty of laying
down pipelines to deliver CNG through distribution points/ pumps and ensuring
uninterrupted supply. Simultaneously parallel steps taken in Delhi for reducing vehicular
pollution include phasing out of old vehicles, use of unleaded petrol, use of low-sulphur
petrol and diesel, use of catalytic converters in vehicles, application of stringent
pollution-level norms for vehicles, etc.
The Government of India through a new auto fuel policy has laid out a roadmap to cut
down vehicular pollution in Indian cities. More stringent norms for fuels means steadily
reducing the sulphur and aromatic content in petrol and diesel fuels. Euro III norms, for
example, stipulate that sulphur be controlled at 350 parts-per-million (ppm) in diesel and
150 ppm in petrol. Aromatic hydrocarbons are to be contained at 42 per cent of the
concerned fuel. The goal, according to the roadmap, is to reduce sulphur to 50 ppm in

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petrol and diesel and bring down the level to 35 per cent.
vehicle engines will also need to be upgraded. a
Mass Emission Standards (Bharat Stage II which is equivalent to Euro-II norms) are no
more applicable in any of the cities of India. Details of the latest Mass Emission
Standards in India are provided below (Table 1).
Table 1: Table Showing the Mass Emission Standards in India

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Type of Vehicles Norms Cities of Implementation

c. o Bharat Stage III s
Throughout the country since Octobere m
4 Wheelers
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Mumbai, Kolkata, Chennai, Bangalore,
4 Wheelers Bharat Stage IV
Surat, Kanpur, Agra, Lucknow and
Sholapur) since April, 2010
Throughout the country since October
3 Wheelers Bharat Stage III
2010
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Throughout the country since October
2 Wheelers Bharat Stage III
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2010

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agquality of Delhi has significantly improved. According
Thanks to the efforts made, the air
to an estimate, a substantial fall in CO2 and SO2 level has been found in Delhi between
1997 and 2005.

2. Water Pollution and its Control
Human beings have been abusing the water-bodies around the world by disposing into
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c. otaking cognizance of the fact that the water bodies are our lifelinesasemwell as that of all
them all kinds of waste. We tend to believe that water can wash away everything not
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ag rivers and drains? Due to such activities of human kind, the ponds, lakes, stream, rivers,
estuaries and oceans are becoming polluted in several parts of the world. Realising the
importance of maintaining the cleanliness of the water bodies, the Government of India
has passed the Water (Prevention and Control of Pollution) Act, 1974 to safeguard our
water resources.

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2.1 Domestic Sewage and Industrial Effluents
As we work with water in our homes in the cities and towns, we wash everything into
drains. Have you ever wondered
where the sewage that comes out of
our houses go? What happens in
villages? Is the sewage treated
before being transported to the
nearest river and mixed with it? A
mere 0.1 per cent impurities make
domestic sewage unfit for human use
(Figure 2). You have read about sewage treatment plants in Chapter 10. Solids are
relatively easy to remove, what is most difficult to remove are dissolved salts such as
nitrates, phosphates, and other nutrients, and toxic metal ions and organic compounds.
Domestic sewage primarily contains biodegradable organic matter, which readily
decomposes – thanks to bacteria and other micro-organisms, which can multiply using
these organic substances as substrates and hence utilise some of the components of
sewage. It is possible to estimate the amount of biodegradable organic matter in
sewage water by measuring Biochemical Oxygen Demand (BOD). Can you explain
how? In the chapter on microorganisms you have read about the relation between BOD,
microorganisms and the amount of biodegradable matter.

Figure 3 shows some of the changes
that one may notice following
discharge of sewage into a river.
Micro-organisms involved in
biodegradation of organic matter in the
receiving water body consume a lot of
oxygen, and as a result there is a
sharp decline in dissolved oxygen
downstream from the point of sewage
discharge. This causes mortality of fish
and other aquatic creatures.
Presence of large amounts of nutrients
in waters also causes excessive growth of planktonic (free-floating) algae, called an

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algal bloom (Figure 4) which imparts a distinct colour to the water bodies. Algal blooms
cause deterioration of the water quality and fish mortality. Some bloom-forming algae
are extremely toxic to human beings and animals.
You may have seen the beautiful
mauve-colored flowers found on
very appealingly-shaped floating
plants in water bodies. These
plants which were introduced into
India for their lovely flowers have
caused havoc by their excessive
growth by causing blocks in our
waterways. They grow faster than
our ability to remove them. These
are plants of water hyacinth
(Eichhornia crassipes), the world’s most problematic aquatic weed, also called ‘Terror of
Bengal’. They grow abundantly in eutrophic water bodies, and lead to an imbalance in
the ecosystem dynamics of the water body.
Sewage from our homes as well as from hospitals are likely to contain many
undesirable pathogenic microorganisms, and its disposal into a water without proper
treatment may cause outbreak of serious diseases, such as, dysentery, typhoid,
jaundice, cholera, etc.
Unlike domestic sewage, waste water from industries like petroleum, paper
manufacturing, metal extraction and processing, chemical manufacturing, etc., often
contain toxic substances, notably, heavy metals (defined as elements with density > 5
g/cm3 such as mercury, cadmium, copper, lead, etc.) and a variety of organic
compounds. A few toxic substances, often present in industrial waste waters, can
undergo biological magnification (Biomagnification) in the aquatic food chain.
Biomagnification refers to increase in concentration of the toxicant at successive trophic
levels. This happens because a toxic substance accumulated by an organism
cannot be metabolised or excreted, and is thus passed on to the next higher trophic
level. This phenomenon is well known for mercury and DDT. Figure 5 shows
biomagnification of DDT in an aquatic food chain. In this manner, the concentration of
DDT is increased at successive trophic levels; say if it starts at 0.003 ppb (ppb = parts
per billion) in water, it can ultimately reach 25 ppm (ppm = parts per million) in fish-

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eating birds, through biomagnification. High concentrations
a and their premature breaking,
metabolism in birds, which causes thinning of eggshell
eventually causing decline in bird populations.
Eutrophication is the natural aging of a lake by nutrient enrichment of its water. In a
young lake the water is cold and clear, supporting little
life. With time, streams draining into the lake introduce
nutrients such as nitrogen and phosphorus, which
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encourage the growth of aquatic organisms. As the
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organic debris pile up, the lake grows shallower and
warmer, with warm-water organisms supplanting
those that thrive in a cold environment. Marsh plants
take root in the shallows and begin to fill in the original
lake basin. Eventually, the lake gives way to large

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masses of floating plants (bog), finally converting into

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land. Depending on climate, size of the lake and other
factors, the natural aging of a lake
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thousands of years. However, pollutants from man’s
activities like effluents from the industries and homes
can radically accelerate the aging process. This phenomenon has been called Cultural
or Accelerated Eutrophication. During the past century, lakes in many parts of the earth
have been severely eutrophied by sewage and agricultural and industrial wastes. The

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prime contaminants are nitrates and phosphates, which act as plant nutrients. They

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can literally choke to death.
Heated (thermal) wastewaters flowing out of electricity-generating units, e.g., thermal
power plants, constitute another important category of pollutants. Thermal wastewater
eliminates or reduces the number of organisms sensitive to high temperature, and may

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enhance the growth of plants and fish in extremely cold areas but, only after causing
damage to the indigenous flora and fauna.

2.2 A Case Study of Integrated Waste Water Treatment
Wastewater including sewage can be treated in an integrated manner, by utilising a mix
of artificial and natural processes. An example of such an initiative is the town of Arcata,
situated along the northern coast of California. Collaborating with biologists from the
Humboldt
State University, the townspeople created an integrated waste water treatment process
within a natural system. The cleaning occurs in two stages – (a) the conventional
sedimentation, filtering and chlorine treatments are given. After this stage, lots of
dangerous pollutants like dissolved heavy metals still remain. To combat this, an
innovative approach was taken and (b) the biologists developed a series of six
connected marshes over 60 hectares of marshland. Appropriate plants, algae, fungi and
bacteria were seeded into this area, which neutralise, absorb and assimilate the
pollutants. Hence, as the water flows through the marshes, it gets purified naturally.
The marshes also constitute a sanctuary, with a high level of biodiversity in the form of
fishes, animals and birds that now reside there. A citizens group called Friends of the
Arcata Marsh (FOAM) are responsible for the upkeep and safeguarding of this
wonderful project.
All this time, we have assumed that removal of wastes requires water, i.e., the creation
of sewage. But what if water is not necessary to dispose off human waste, like excreta?
Can you imagine the amount of water that one can save if one didn’t have to flush the
toilet? Well, this is already a reality. Ecological sanitation is a sustainable system for
handling human excreta, using dry composting toilets. This is a practical, hygienic,
efficient and cost-effective solution to human waste disposal. The key point to note here
is that with this composting method, human excreta can be recycled into a resource (as
natural fertiliser), which reduces the need for chemical fertilisers. There are working
‘EcoSan’ toilets in many areas of Kerala and Sri Lanka.

3. Solid Wastes
Solid wastes refer to everything that goes out in trash. Municipal solid wastes are
wastes from homes, offices, stores, schools, hospitals, etc., that are collected and
disposed by the municipality. The municipal solid wastes generally comprise paper,

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food wastes, plastics, glass, metals, rubber, leather, textile, etc. Burning reduces the
volume of the wastes, although it is generally not burnt to completion and open dumps
often serve as the breeding ground for rats and flies. Sanitary landfills were adopted as
the substitute for open-burning dumps. In a sanitary landfill, wastes are dumped in a
depression or trench after compaction, and covered with dirt everyday. If you live in a
town or city, do you know where the nearest landfill site is? Landfills are also not really
much of a solution since the amount of garbage generation specially in the metros has
increased so much that these sites are getting filled too. Also there is danger of
seepage of chemicals, etc., from these landfills polluting the underground water
resources.
A solution to all this can only be in human beings becoming more sensitive to these
environment issues. All waste that we generate can be categorised into three types –
(a) bio-degradable,
(b) recyclable and
(c) the non-biodegradable.
It is important that all garbage generated is sorted. What can be reused or recycled
should be separated out; our kabadiwallahs and rag-pickers do a great job of separation
of materials for recycling. The biodegradable materials can be put into deep pits in the
ground and be left for natural breakdown. That leaves only the nonbiodegradable to be
disposed of. The need to reduce our garbage generation should be a prime goal,
instead, we are increasing the use of non-biodegradable products. Just pick any
readymade packet of any ‘good quality’ eatable, say a biscuit packet, and study the
packaging – do you see the number of protective layers used? Note that atleast one
layer is of plastic. We have started packaging even our daily use products like milk and
water in polybags!! In cities, fruits and vegetables can be bought packed in beautiful
polystyrene and plastic packaging – we pay so much and what do we do? Contribute
heavily to environmental pollution. State Governments across the country are trying to
push for reduction in use of plastics and use of eco-friendly packaging. We can do our
bit by carrying cloth or other natural fibre carry-bags when we go shopping and by
refusing polythene bags.
Hospitals generate hazardous wastes that contain disinfectants and other harmful
chemicals, and also pathogenic micro-organisms. Such wastes also require careful
treatment and disposal. The use of incinerators is crucial to disposal of hospital waste.

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Irreparable computers and other electronic goods are known
a Over half of the e-wastes
wastes). E-wastes are buried in landfills or incinerated.
generated in the developed world are exported to developing countries, mainly to China,
India and Pakistan, where metals like copper, iron, silicon, nickel and gold are
recovered during recycling process. Unlike developed countries, which have specifically
built facilities for recycling of e-wastes, recycling in developing countries often involves
manual participation thus exposing workers to toxic substances present in e-wastes.
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Recycling is the only solution for the treatment of e-waste, provided it is carried out in an
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3.1 Case
A plastic sack manufacturer in Bangalore has managed to find the ideal solution to the
ever-increasing problem of accumulating plastic waste. Ahmed Khan, aged 57 years
old, has been producing plastic sacks for 20 years. About 8 years ago, he realised that
plastic waste was a real problem. Polyblend, a fine powder of recycled modified plastic,
was developed then by his company. This mixture is mixed with the bitumen that is
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used to lay roads. In collaboration with R.V.College of Engineering and the Bangalore

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City Corporation, Ahmed Khan proved that blends of Polyblend and bitumen, when
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used to lay roads, enhanced the bitumen’s
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increase road life by a factor of a
three. The raw material for creating Polyblend is any
plastic film waste. So, against the price of Rs. 0.40 per kg that rag pickers had been
getting for plastic waste, Khan now offers Rs.6. Using Khan’s technique, by the year
2002, more than 40 kms of road in Bangalore has already been laid. At this rate, Khan
will soon be running short of plastic waste in Bangalore, to produce Polyblend. Thanks
to innovations like Polyblend, we might still avoid being smothered by plastic waste.
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being increasingly used. These incidentally, are also toxic to non-target organisms, that
are important components of the soil ecosystem. Do you think these can be
biomagnified in the terrestrial ecosystems? We know what the addition of increasing
amounts of chemical fertilisers can do to aquatic ecosystems vis-à-vis eutrophication.
The current problems in agriculture are, therefore, extremely grave.
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4.1 Case Study of Organic Farming
Integrated organic farming is a cyclical, zero-waste procedure, where waste products
from one process are cycled in as nutrients for other processes. This allows the
maximum utilisation of resource and increases the efficiency of production. Ramesh
Chandra Dagar, a farmer in Sonipat, Haryana, is doing just this. He includes bee-
keeping, dairy management, water harvesting, composting and agriculture in a chain of
processes, which support each other and allow an extremely economical and
sustainable venture. There is no need to use chemical fertilisers for crops, as cattle
excreta (dung) are used as manure. Crop waste is used to create compost, which can
be used as a natural fertiliser or can be used to generate natural gas for satisfying the
energy needs of the farm. Enthusiastic about spreading information and help on the
practice of integrated organic farming, Dagar has created the Haryana Kisan Welfare
Club, with a current membership of 5000 farmers.

5. Radioactive Wastes
Initially, nuclear energy was hailed as a non-polluting way for generating electricity.
Later on, it was realised that the use of nuclear energy has two very serious inherent
problems. The first is accidental leakage, as occurred in the Three Mile Island and
Chernobyl incidents and the second is safe disposal of radioactive wastes.
Radiation, that is given off by nuclear waste is extremely damaging to organisms,
because it causes mutations at a very high rate. At high doses, nuclear radiation is
lethal but at lower doses, it creates various disorders, the most frequent of all being
cancer. Therefore, nuclear waste is an
extremely potent pollutant and has to be dealt with utmost caution.
It has been recommended that storage of nuclear waste, after sufficient pre-treatment,
should be done in suitably shielded containers buried within the rocks, about 500 m
deep below the earth’s surface. However, this method of disposal is meeting stiff
opposition from the public. Why do you think this method of disposal is not agreeable to
many people?

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6. Greenhouse Effect and Global Warming
The term ‘Greenhouse effect’ has been derived
from a phenomenon that occurs in a
greenhouse. Have you ever seen a
greenhouse? It looks like a small glass house
and is used for growing plants especially during
winter. In a greenhouse the glass panel lets the
light in, but does not allow heat to escape.
Therefore, the greenhouse warms up, very
much like inside a car that has been parked in
the sun for a few hours.
The greenhouse effect is a naturally occurring
phenomenon that is responsible for heating of
Earth’s surface and atmosphere. You would be
surprised to know that without greenhouse
effect the average temperature at surface of
Earth would have been a chilly –18oC rather
than the present average of 15oC. In order to
understand the greenhouse effect, it is
necessary to know the fate of the energy of
sunlight that reaches the outermost
atmosphere (Figure 6). Clouds and gases
reflect about one-fourth of the incoming solar radiation, and absorb some of it but
almost half of incoming solar radiation falls on Earth’s surface heating it, while a small
proportion is reflected back. Earth’s surface re-emits heat in the form of infrared
radiation but part of this does not escape into space as atmospheric gases (e.g., carbon
dioxide, methane, etc.) absorb a major fraction of it. The molecules of these gases
radiate heat energy, and a major part of which again comes to Earth’s surface, thus
heating it up once again. This cycle is repeated many a times. The above-mentioned
gases – carbon dioxide and methane – are commonly known as greenhouse gases
(Figure 7) because they are responsible for the greenhouse effect.
Increase in the level of greenhouse gases has led to considerable heating of Earth
leading to global warming. During the past century, the temperature of Earth has
increased by 0.6 oC, most of it during the last three decades. Scientists believe that this

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rise in temperature is leading to deleterious changes in the
odd climatic changes (e.g. El Nino effect), thus leadingato increased melting of polar ice
caps as well as of other places like the Himalayan snow caps. Over many years, this
will result in a rise in sea level that can submerge many coastal areas. The total
spectrum of changes that global warming can bring about is a subject that is still under
active research.
How can we control global warming? The measures include cutting down use of fossil
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fuel, improving efficiency of energy usage, reducing deforestation, planting trees and
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slowing down the .growth of human population. International initiatives are also beingse
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taken to reduce the emission of greenhouse gases into the atmosphere.

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7. Ozone Depletion in the Stratosphere
You have earlier studied in the Chemistry textbook of
Class XI about ‘bad’ ozone, formed in the lower
atmosphere (troposphere) that harms plants and
animals. There is ‘good’ ozone also; this ozone is
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found in the upper part of the atmosphere called the
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stratosphere, and it acts as a shield absorbing
ultraviolet radiation from the sun. UVla
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injurious to living organisms since DNA and proteins
of living organisms preferentially absorb UV rays,
and its high energy breaks the chemical bonds within
these molecules. The thickness of the ozone in a
column of air from the ground to the top of the

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atmosphere is measured in terms of Dobson units
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production and degradation of ozone in the stratosphere. Of late, the balance has been
disrupted due to enhancement of ozone degradation by chlorofluorocarbons (CFCs).
CFCs find wide use as refrigerants. CFCs discharged in the lower part of atmosphere
move upward and reach stratosphere. In stratosphere, UV rays act on them releasing Cl
atoms. Cl degrades ozone releasing molecular oxygen, with these atoms acting merely
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as catalysts; Cl atoms are not consumed in the reaction. Hence, whatever CFCs are
added to the stratosphere, they have permanent and continuing affects on Ozone
levels. Although ozone depletion is occurring widely in the stratosphere, the depletion is
particularly marked over the Antarctic region. This has resulted in formation of a large
area of thinned ozone layer, commonly called as the ozone hole (Figure 8).
UV radiation of wavelengths shorter than UV-B, are almost completely absorbed by
Earth’s atmosphere, given that the ozone layer is intact. But, UV-B damages DNA and
mutation may occur. It causes aging of skin, damage to skin cells and various types of
skin cancers. In human eye, cornea absorbs UV-B radiation, and a high dose of UV-B
causes inflammation of cornea, called snow-blindness, cataract, etc. Such exposure
may permanently damage the cornea.
Recognising the deleterious affects of ozone depletion, an international treaty, known as
the Montreal Protocol, was signed at Montreal (Canada) in 1987 (effective in 1989) to
control the emission of ozone depleting substances. Subsequently many more efforts
have been made and
protocols have laid down definite roadmaps, separately for developed and developing
countries, for reducing the emission of CFCs and other ozone depleting chemicals.

8. Degradation by Improper Resource Utilisation and Maintenance
The degradation of natural resources can occur, not just by the action of pollutants but
also by improper resource utilisation practices. Soil erosion and desertification: The
development of the fertile top-soil takes centuries. But, it can be removed very easily
due to human activities like over-cultivation, unrestricted grazing, deforestation and poor
irrigation practices, resulting in arid patches of land. When large barren patches extend
and meet over time, a desert is created. Internationally, it has been recognised that
desertification is a major problem nowadays, particularly due to increased urbanisation.
Waterlogging and soil salinity: Irrigation without proper drainage of water leads to
waterlogging in the soil. Besides affecting the crops, waterlogging draws salt to the
surface of the soil. The salt then is deposited as a thin crust on the land surface or starts
collecting at the roots of the plants. This increased salt content is inimical to the growth
of crops and is extremely damaging to agriculture. Waterlogging and soil salinity are
some of the problems that have come in the wake of the Green Revolution.

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9. Deforestation
Deforestation is the conversion of forested areas to non-forested ones. According to an
estimate, almost 40 per cent forests have been lost in the tropics, compared to only 1
per cent in the temperate region. The present scenario of deforestation is particularly
grim in India. At the beginning of the twentieth century, forests covered about 30 per
cent of the land of India. By the end of the century, it shrunk to 19.4 per cent, whereas
the National Forest Policy (1988) of India has recommended 33 per cent forest cover for
the plains and 67 per cent for the hills.
How does deforestation occur? A number of human activities contribute to it. One of the
major reasons is the conversion of forest to agricultural land so as to feed the growing
human population. Trees are axed for timber, firewood, cattle ranching and for several
other purposes.
Slash and burn agriculture, commonly called as Jhum cultivation in the north-eastern
states of India, has also contributed to deforestation. In slash and burn agriculture, the
farmers cut down the trees of the forest and burn the plant remains. The ash is used as
a fertiliser and the land is then used for farming or cattle grazing. After cultivation, the
area is left for several years so as to allow its recovery. The farmers then move on to
other areas and repeat this process. In earlier days, when Jhum cultivation was in
prevalence, enough time-gap was given such that the land recovered from the effect of
cultivation. With increasing population, and repeated cultivation, this recovery phase is
done away with, resulting in deforestation.
What are the consequences of deforestation? One of the major effects is enhanced
carbon dioxide concentration in the atmosphere because trees that could hold a lot of
carbon in their biomass are lost with deforestation. Deforestation also causes loss of
biodiversity due to habitat destruction, disturbs hydrologic cycle, causes soil erosion,
and may lead to desertification in extreme cases.
Reforestation is the process of restoring a forest that once existed but was removed at
some point of time in the past. Reforestation may occur naturally in a deforested area.
However, we can speed it up by planting trees with due consideration to biodiversity
that earlier existed in that area.

9.1 Case Study of People’s Participation in Conservation of Forests
People’s participation has a long history in India. In 1731, the king of Jodhpur in
Rajasthan asked one of his ministers to arrange wood for constructing a new palace.

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m
m .co

m .co s em
se The minister and workers went to a forest near a village,la
a g inhabited by Bishnois, to cut
down trees. The Bishnoi community is known for its peaceful co-existence with nature.
The effort to cut down trees by the kings was thwarted by the Bishnois. A Bishnoi
woman Amrita Devi showed exemplary courage by hugging a tree and daring king’s
men to cut her first before cutting the tree. The tree mattered much more to her than her
own life. Sadly, the king’s men did not heed to her pleas, and cut down the tree along
with Amrita Devi. Her three daughters and hundreds of other Bishnois followed her, and
m
o m
thus lost their lives saving trees. Nowhere in history do we find a commitment of this
c m .co
. beings sacrificed their lives for the cause of the environment.se
em of India has recently instituted the Amrita Devi Bishnoi Wildlife a
magnitude when human

as g l
l
The Government
g ashown
a
Protection Award for individuals or communities from rural areas that have
extraordinary courage and dedication in protecting wildlife.
You may have heard of the Chipko Movement of Garhwal Himalayas. In 1974, local
women showed enormous bravery in protecting trees from the axe of contractors by
hugging them. People all over the world have acclaimed the Chipko movement.
Realising the significance of participation by local communities, the Government of India

o m
c
. and managing forests. In return for their
in 1980s has introduced the concept of Joint Forest Management (JFM) so as to work

m
e benefit of various forest products (e.g., fruits,
closely with the local communities for protecting
s
services to the forest, the communitiesaget
l
gum, rubber, medicine, etc.), andagthus the forest can be conserved in a sustainable
manner.

Summary
Major issues relating to environmental pollution and depletion of valuable natural
resources vary in dimension from local, regional to global levels. Air pollution primarily
m
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c. oautomobiles. They are harmful to humans, animals and plants, and
results from burning of fossil fuel, e.g., coal and petroleum, in industries and in
mtherefore must be .co
s e
s em removed to keep our air clean. Domestic sewage, the most common
g l a source of
la a
ag pollution of water bodies, reduces dissolved oxygen but increases biochemical oxygen
demand of receiving water. Domestic sewage is rich in nutrients, especially, nitrogen
and phosphorus, which cause eutrophication and nuisance algal blooms. Industrial
waste waters are often rich in toxic chemicals, especially heavy metals and organic
compounds. Industrial waste waters harm living organisms. Municipal solid wastes also
create problems and must be disposed off in landfills. Disposal of hazardous wastes like
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defunct ships, radioactive wastes and e-wastes requires additional efforts. Soil pollution
primarily results from agricultural chemicals (e.g., pesticides) and leachates from solid
wastes deposited over it.
Two major environmental issues of global nature are increasing greenhouse effect,
which is warming Earth, and depletion of ozone in the stratosphere. Enhanced
greenhouse effect is mainly due to increased emission of carbon dioxide, methane,
nitrous oxide and CFCs., and also due to deforestation. It may drastically change rainfall
pattern, global temperature, besides deleteriously affecting living organisms. Ozone in
the stratosphere, which protects us from harmful effects of ultraviolet radiation, is
depleting fast due to emission of CFCs thus increasing the risks of skin cancer,
mutation and other disorders.

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