CBSE Class 12 Biology Revision Notes Chapter 16

Class 12 Biology Chapter 16 Notes

Class 12 Biology, Chapter 16, explains Environmental Issues. There is a high demand for food, clothing, housing, gasoline, automobiles, etc. due to the growing human population. The pressure that all of these demands are putting on the land, the water, the air, and other natural resources causes pollution, environmental degradation, biodiversity loss, and other environmental problems.

Because it completely explains and covers all of the concepts, the collection of Chapter 16 Biology Class 12 Notes meets  the current CBSE requirements. Students can utilise the Class 12 Biology Chapter 16 Notes to study, analyse, and lighten their exam load. These notes were written by the academic professionals at Extramarks using data from the NCERT textbook and other significant sources.

Students may register on Extramarks to access the Class 12 Biology Notes Chapter 16 and CBSE Class 12 Syllabus. Along with the Syllabus, students may also refer to CBSE Revision Notes, CBSE Sample Papers, CBSE Important Questions, CBSE Extra Questions, and CBSE past years’ question papers.

Key Topics Covered In Class 12 Biology Chapter 16 Notes

Following are the topics included in Biology Chapter 16 Class 12 Notes:

  • Air Pollution and Its Control
  • Water Pollution and Its Control
  • Solid Wastes
  • Agro-chemicals and their Effects
  • Radioactive Wastes
  • Greenhouse Effect and Global Warming
  • Ozone Depletion in the Stratosphere
  • Degradation by Improper
  • Resource Utilisation and Maintenance
  • Deforestation


Extramarks Class 12 Biology Chapter 16 Notes explain that pollution is the result of undesirablechanges in the environment’s physical, chemical, or biological aspects that harm humans, living organisms, and cultural assets. 

The basic cause of pollution is man himself and is termed anthropogenic pollution, for example, industrial pollution, agricultural pollution, etc.


Pollutants are defined as substances which are present in the environment in harmful concentrations and are often the residues of  materials that are thrown away. For example, sewage, chemicals from factories, radioactive substances from nuclear plants, noise, heat, and radiation are examples of pollutants.

All pollutants are not  waste materials like nitrogen and phosphorus,which are  used in the enrichment of the soil and lead to an increase in  crop yield. Still, they are present in excess and may contribute to water pollution.

The pollutants are classified based on their persistence, existence, and natural disposal.

  1. Based on persistence, pollutants are of two types, primary, and secondary.
  • Primary pollutants always persist in the form of the environment in which they were added, like plastic goods.
  • Secondary pollutants are formed when primary pollutants interact with each other. Nitrogen oxides and hydrocarbons are the two primary pollutants, and when these interact in the presence of sunlight, they form PAN or peroxy acyl nitrate, the secondary pollutant. The secondary pollutants are more toxic than the primary pollutants. 
  1. Based on their existence, pollutants can be of two types, namely, Quantitative and Qualitative.
  • Quantitative pollutants are normally present in nature, but they can be added in large amounts by man. For example, carbon dioxide is always present in the air , but fires, industries, and automobiles can also add it.
  • Qualitative pollutants are not normally present in nature, butman adds them. For example, herbicides and insecticides are added by man.
  1. Based on natural disposal
  • Biodegradable pollutants are those which are quickly degraded by natural means.They are destroyed by microbial action and radiation. Examples of this category include sewage and heat.
  • Nondegradable pollutants degrade very slowly; some examples are DDT, arsenic salts, radioactive materials, and plastic.

Types of pollution are:

  • Atmospheric or air pollution.
  • Hydrospheric or water pollution
  • Lithospheric or land pollution
  • Radioactive pollution
  • Noise or sound pollution.

Air pollution and its control:

Air pollution is the release of material concentrations harmful to humans, animals, plants, buildings, and other objects.

The causes of air pollution are:

  • There are human activities that contribute to air pollution. These are automobiles, overpopulation, deforestation, nuclear explosions, explosives used in war, fireworks, etc.
  • Nature also contributes little to air pollution. For example, volcanic eruptions cause air pollution as they release gases and ashes into the air, which pollute it. Electric storms and solar flares lead to the production of harmful chemicals. These chemicals are also released in forest fires. Some examples of natural pollutants are pollen, spores, cysts, bacteria, marsh gases, etc., methane is formed due to the decay of vegetable matter in marshy places and coal mines. Methane is light and colourless gas.

The various sources of air pollution are:

  • Point or stationary sources include industries that add pollutants to the air at particular points via their tall chimneys and only affect restricted areas.
  • Line or mobile sources include automobiles, which add pollutants along narrow belts over long distances. If a person smokes while walking, this is also an example of a source of pollution.
  • Area sources of pollution include towns and cities, and they add smoke and gases to the air and contribute to air pollution over wide areas.

The various air pollutants and their effects are as follows:

  1. Gaseous pollutants:
  • Oxides of carbon include carbon monoxide and carbon dioxide. They are produced from cigarette smoking and fuel burning in houses, industries, power houses and automobiles. Carbon dioxide is also released by plants and animals during respiration and is produced due to the decay of organic matter.
  • Carbon monoxide is a very poisonous gas resulting from the incomplete combustion of fuels. It accounts for 50 % of the total air pollutants. If this harmful gas is inhaled, it combines with haemoglobin and reduces its oxygen-carrying capacity. The manifestations produced are giddiness, laziness, exhaustion, reduced vision, and nervous and cardiovascular disorders which may even lead to the person’s death. Just 10 ppm of CO is sufficient to cause severe illness.
  • Carbon dioxide in the air has increased due to excessive fuel burning, which manifests as headache and nausea. Carbon dioxide in the air also leads to a rise in the atmospheric temperature and may lead to the melting of the polar ice, rising ocean water levels, and flooding.
  • Nitrogen monoxide and nitrogen dioxide are nitrogen oxides, and they are released by automobiles and the chemical industry as waste gases. The nitrogen monoxide reduces the oxygen-carrying capacity of the blood. Nitrogen dioxide irritates the eyes, nose, bronchial tubes, and lungs and is fatal at high concentrations. These are also responsible for photochemical smog.
  • Sulphur dioxide and sulphur trioxide are the oxides of sulphur and are produced as a result of fossil fuels like coal and oil, industries, thermal plants, etc., they are harmful to  buildings, clothing, animals, and plants. They can cause many respiratory diseases in men, like asthma, bronchitis and emphysema. Sulphur dioxide and sulphur trioxide react with water to form sulphurous acid and sulphuric acid, which irritate the eyes, nose, and throat. They also harm aquatic life and produce acid rain or acid precipitation. They also have mutagenic properties.
  • Hydrocarbons like methane and ethylene are composed of hydrogen and carbon and are produced due to the incomplete combustion of fuel in automobiles. These hydrocarbons are carcinogenic and can cause cancer. 
  • Photochemical oxidants include peroxyacyl nitrate (PAN), ozone and aldehydes.

PAN irritates the eyes, produces respiratory troubles, and affects plants like spinach and lettuce.

The ozone layer formed in the troposphere by photochemical reactions as a result of  human activity is harmful. It produces chest pain, cough, and eye irritation at a low level, but at higher concentrations, it can even kill plants and animals. In plants, it is identified as marking on leaves, premature yellowing, and falling. 

Smog is a dark fog formed due to condensing water vapour, dust, and smoke particles. It can be classical or photochemical.

Aldehydes irritate both the digestive and respiratory tracts.

  1. Particulate pollutants: these are added to the air by industries, automobiles, and operations like blasting, drilling, crushing, grinding and mixing. Some of these are also added by living organisms, including pollen, spores, cysts and bacteria.

The various types of particulates are aerosol, mist, dust, smoke, fume, plumes, fog and smog.

  1. Radioactive pollutants: They are released by nuclear explosions and war explosives. They kill the living tissues they happen to enter.

Effects of air pollution:

Air pollution is a serious problem in big, congested, industrialised cities with heavy traffic. The major source of air pollution in Delhi is automobiles, as there are more cars. In the 1990s. The air pollution in Delhi was so severe that it was ranked 4th among the 41 most polluted cities in the world. To combat this, the following measures were taken by the Government of Delhi. They are:

  • To switch from Diesel to compressed natural gases (CNG) by the end of 2002.
  • To phase out old vehicles.
  • Use of unleaded petrol
  • To use petrol and Diesel with low sulphur
  • To use the catalytic converter in vehicles
  • Application of Euro II norms for vehicles.

Some of the effects of air pollution on humans are mentioned below:

  • Increased incidence of asthma, emphysema, tuberculosis and lung cancer.
  • Eye irritation.
  • Throat and respiratory diseases
  • Liver damage
  • Impaired vision
  • Changes in skin pigmentation

Control of air pollution:

  1. To separate pollutants:
  • More trees should be planted as it purifies the air.
  • Plants like Phaseolus vulgaris,Coleus blumei, and Ficus variegata, can fix carbon monoxide.
  • Plants like Pinus, Juniperus, Quercus, Pyrus and Vitis can metabolise nitrogen oxides.
  • Use good quality fuel in motor vehicles, including low sulphur, sulphur free or lead-free fuel.
  1. To control particulate matter:
  • Use of arresters which are the controlling devices and separate particulate pollutants.
  • Gravity settling tanks are used to remove large particles up to 50 m in size.
  • Porous filters
  • Electrostatic precipitators remove gaseous pollutants.
  • Cyclonic separators in which polluted air is rotated.
  • Trajectory separators separate heavier particulates.
  • Catalytic converters are installed in automobiles to reduce gas emissions.
  1. To control gaseous pollutants.
  • The combustion method controls oxidizable pollutants in the petrochemical, fertiliser, paint, and varnish industries.
  • Absorption method: dry or wet scrubbers have packed materials where gaseous pollutants are absorbed.
  • Adsorption technique: this method removes toxic gases, vapours and inflammable compounds from the polluted air by the use of very fine solid particles, which can include activated charcoal, etc.
  1. To use tall chimneys in factories.
  2. Filtering of industrial smoke
  3. Afforestation of mining areas.

Electrostatic Precipitator:

This removes 99 % of the particulate matter present in the exhaust from a thermal power plant. Several thousand volts maintain the electrode wires of an electrostatic precipitator. This produces a corona, which releases the electrons.

These released electrons attach to the dust particles, giving them a net negative charge.The collected plates are grounded, and they attract the charged dust particles.

Between the plates, there must be a low velocity of air so as to allow the dust to fall.


This removes gases such as sulphur dioxide.The exhaust is sprayed with water or lime.

Acid rain:

Robert August, in the year 1872, first coined the term acid rain. This is a man-made phenomenon. The meaning of acid rain is precipitation with a pH of less than 5. It is a mixture of H2SO4 and HNO3.

The oxides are produced from the combustion of fossil fuels, industries, power plants, automobiles, domestic fires, etc., in the atmosphere, sulphur oxide, and nitric oxide are converted into sulphuric acid and nitric acid after they combine with oxygen and water. These acids are deposited over the earth in two forms: wet and dry.

Wet deposition occurs in the form of rain, snow, or fog. The settling down of wind-blown acidic gases is referred to as dry decomposition.The effects of acid rain are:

  • Increase in acidity of the soil.
  • Terrestrial flora and fauna are affected.
  • Chlorosis, necrosis, and defoliation in plants at the growing tips.
  • Acidification of water bodies.
  • A pH of less than 5 affects aquatic life and kills plankton, molluscs, and fish in water bodies.
  • Corrodes metals, marbles, painted surfaces, etc.



Water pollution is defined as the addition of harmful or foreign substances like organic, inorganic, biological, or radiological waste to water. It causes a change in the physical property of the water, which makes it unfit for use and is a hazard to human health.

Types of pollutants:

They are of three types: physical, chemical and biological.

  • Heat and oil spills are examples of physical pollutants.
  • Chemical pollutants include organic waste, pesticides like DDT and BHC, polychlorinated biphenyls, and inorganic chemicals like arsenic, cadmium, mercury, lead, nickel, phosphates, nitrates, and fluorides. Radioactive wastes are also included in this category.
  • Pathogens like viruses, bacteria, protozoa, helminths, and algae are examples of biological pollutants.

Organic vs inorganic water pollutants:

The organic water pollutants are insecticides and herbicides, bacteria from sewage or livestock operations, food processing waste, volatile organic compounds, trees and bush debris, etc.

The inorganic water pollutants are heavy metals including acid mine drainage, industrial byproducts, fertilisers like nitrates and phosphates, etc.

Sources of water pollution:

They are of two types: natural and anthropogenic, or man-made.

  • Examples of natural resources can be explained as soil erosion making soil particles enter the water, minerals getting dissolved in water from rocks and soil, and falling animal waste and dead leaves into the water sources. Organic matter decay is also associated with water pollution.
  • Anthropogenic or man-made resources include organic wastes like domestic waste, sewage, industrial waste, animal waste, etc. agricultural waste like pesticides and fertilisers are also responsible for water pollution.


Detergents are present in bathroom water. In surface water, the major pollutants are phosphorus and nitrates. When dissolved in water, these accelerate the growth of algae as it provides nutrition to them. These algae may form an accelerated mat on the surface of the water. This is known as eutrophication.

The algae use oxygen at night, deoxygenating the water enough to kill the fish. These mats on the surface of the water block the light from reaching the submerged plants.


Industrial waste is released in water and contains toxic substances like arsenic, cadmium, lead, zinc, copper, mercury, and cyanides.hese chemicals are very harmful to health. They can reach the human body directly and indirectly, and their concentration may increase at each food chain level. This is known as biomagnification.

River water may have a low concentration of DDT, but the carnivorousfish in it may have a higher concentration of DDT. This fish is unfit for a man when it comes to eating. Mercury which is discharged into lakes and rivers is converted to the neurotoxic form by the bacteria called methylmercury. This is a highly poisonous chemical, and the fish may directly absorb it.

Thermal pollution:

Heat causes deoxygenation in water, and the dissolved oxygen content of water decreases due to an increase in temperature.

The temperature rise also speeds up the metabolism in aquatic organisms, due to which their requirement for oxygen increases.

Other effects of high temperatures include fish death, disrupted spawning, changes in the composition of flora and fauna, and so on.Effects of water pollutants:

Contamination of water directly affects the health and economy of man. The effects are explained by Class 12 Biology Chapter 16 Notes as follows:

    • Water becomes turbid when fine, solid suspended particles or colloidal substances are added.
  • Organic wastes promote decomposition, deoxygenation,  and the death of animals. Anaerobic bacteria produce foul gases.
  • Pathogens produce disease in humans and domestic animals.
  • Phosphates and nitrates in fertilisers produce algal growth, which causes deoxygenation and death of the animals. Sit, and decaying matter may fill up the water bodies.
  • Toxic chemicals reach animals and the human body through contaminated food, which may cause poisoning and death due to harmful chemicals like mercury, arsenic, and lead.
  • Oil reduces oxygen.
  • Radioactive wastes reach human and animal bodies via the food chain and cause death.
  • Solid particles cause turbidity, which reduces the light available for photosynthesis.
    • Heat causes an insufficiency of oxygen to sustain life.
  • Non Degradable pesticides affect the nervous system.
  • Broad-spectrum pesticides cause damage to aquatic life on a large scale.
  • Fluorides in water cause fluorosis.
  • Dyes change the colour of the water.
  • Iron, chloride, manganese and phenol make the water distasteful.
  • Hydrogen sulphide and ammonia add an unpleasant odour to the water.
  • Detergents and soap cause foam formation.
  • Organic sulphur hampers nitrification.
  • Excessive chemicals make water lose its productivity.

Control of water pollution:

The water can be controlled in the following ways as explained by Class 12 Biology Chapter 16 Notes:

  • There should be a prohibition on taking baths and washing clothes directly in ponds, tanks, and rivers, as these are the sources from which the water is supplied for drinking.
  • There should be a reservation of separate ponds and tanks for supplying water to the tanks.
  • Treatment of domestic and farmyard water before disposing of it into the water.
  • Pesticides and fertilisers should not be used in excess.
  • Hot water should be cooled before being released into the water.
  • Recycling of solid waste wherever possible.
  • Sewage treatment could make the polluted water harmless.
  • Water hyacinths can take up heavy metals and purify water.

Soil pollution:

The soil’s productivity is reduced due to the addition and removal of materials. This is known as soil pollution.

The soil pollutants are chemicals, pesticides, fertilisers, radioactive wastes, discarded materials, etc.

The chemicals include iron, lead, tin, copper, mercury, aluminium, zinc, cadmium, cyanides, acids, and alkalis. These chemicals enter the soil as a result of weathering rocks and mining operations.Pesticides include insecticides, fungicides, and herbicides. The pesticides sprayed fall on the soil and penetrate it.

Fertilisers and manures are added to increase crop yield. Still, when used excessively, it reduces the productivity of the soil as the bacterial population is reduced and the salt content is increased.

Radioactive dust from mining and uranium processing finds its way into the water, reaching the soil through irrigation.

Discarded materials include waste food, paper, clothes, bottles, cans, plastic, and carcasses.

Solid waste:

In the section below, Extramarks Class 12 Biology Chapter 16 Notes explains the topic of Solid Waste. 

The landscape is polluted with solid waste. This includes a variety of solid waste like peels of vegetables and fruits, ashes, leftovers of eatables, discarded clothes and papers, etc.

The waste produced from offices, homes, stores, school, hospitals, which are collected and disposed of by the municipality is known as the municipal solid waste. This waste contains paper, food, plastic, glass, metals, rubber, etc. When these are burned, the volume of the waste reduces, but the waste cannot be burned completely, and It becomes a breeding ground for rats and flies.

Sanitary landfills are substitutes for open-burning dumps. The waste is dumped in a depression after compaction, and then it is covered with dirt every day. This is becoming increasingly crowded in metropolitan areas.There is a high risk of underground water sources polluting underground water resources.Hospitals also generate a lot of waste, like harmful chemicals, syringes, cotton, bandages, and pathogenic microorganisms. Defunct ships are also adding to the solid waste. Computers and electronic goods are irreparable and are called electronic waste, or e-waste. Workers are also exposed to toxic substances in e-waste.

This is a serious problem; the land where the material is discarded becomes barren. Some organic waste decomposes and and fouls the air, whileothers do not, aggravating the problem of solid waste disposal. If the waste is burned, it will pollute the air, and if it is left, it will create unhygienicliving conditions.

The following are some methods for controlling soil and land pollution:

1.Recycling of waste:

  • Agricultural waste is converted into paper and board.
  • Waste paper is converted into new paper by paper mills.
  • The changing of jute waste into hardboard.
  • Cattle dung is used to cook gas-enricheddung manure.
  • Composting
  • Sludge burning
  • Treatment of sewage and industrial waste.

2.Highly judicious use of chemical fertilisers and pesticides.

3.To reduce chemical fertilisers by replacing them with manures and biofertilisers.

4.Employment of biological methods of pest control.

5.Soil erosion should be checked by deforestation.

6.Improvement in mining techniques.

7.Proper crop patterns can eliminate weeds.

8.Low-lying areas unfit for agriculture can be used for dumping discarded material and garbage


  • A solution to the increasing problem of plastic waste has been found by the Plastic sack manufacturer in Bangalore.
  • Plastic sacks as a real problem were identified by one of the men, Ahmed Khan, aged 57 years old. This man has been producing plastic sacks for nearly 20 years.
  • TThis business created a polyblend, which is a fine powder made from recycled modified plastic.
  • This mixture is mixed with bitumen, and then it is used to lay roads.
  • Ahmad Khan demonstrated in collaboration with the R.V. College of Engineering and the Bangalore City Corporation that this mixture improves the water repellent properties of the road and increases its shelf life by a factor of three.



  • Inorganic fertilisers and pesticides enhance the productivity of crops.
  • There is increased use of pesticides, herbicides and fungicides.
  • There are non-target organisms present in the soil ecosystem and they are the important components.
  • The chemicals also target these organisms.
  • Fertiliser is causing serious problems in agriculture because it is harmful to the environment.


  • One of the zero-waste procedures is integrated organic farming.
  • Waste products are converted into nutrients in this manner from one process to the next.
  • This type of farming makes the best use of available resources.
  • There is increased efficiency in production in this type of farming.
  • One of the farmers in Sonipat, called Ramesh Chandra Dagar, is doing this. Bee – keeping, dairy management, water harvesting, composting, agriculture are the chains that support each other.
  • These are all kept by Ramesh Chandra Dagar.
  • There is no need to use chemical fertilisers on crops.
  • Manure is used to enhance crop production.
  • Natural fertiliser is created by using crop waste. The energy needs of the farm are met by the natural gas that is generated.
  • Haryana Kisan Welfare is the club that has members who are all farmers, and thisclub was created by the farmers.


The effect of radiation on humans was first reported in the year 1909. It was when the uranium miners suffered from skin burns and cancer.

Radioactive pollution is the physical pollution of air, water, and soil with radioactive materials. Radioactivity is the property of elements like radium, thorium, uranium, alpha particles, electrons, and gamma rays.

Radioactive pollution can be natural or man-made. 

Natural radiation refers to the cosmic rays that reach the earth from outer space and the terrestrial radiation from nuclides of radioactive elements present in the rock, soil, and water. Natural radiation, also known as “background radiation,” is not a health hazard because of its low concentration.Man-made radiation includes mining and refining plutonium and thorium, atomic explosions, atomic reactors, and nuclear fuel. The atomic explosion, atomic reactors and nuclear fuel, radioactive isotopes, radiation therapy, and occupational exposure are how man is exposed to such radiation. Such radiations cause molecular damage to the cells.

The ways to control radioactive pollution are:

  • The leakage from the nuclear reactors, laboratories, and industries should be checked.
  • Strict enforcement of safety measures.
  • Regular checking of the level of radiation pollution.
  • Safety limit check.
  • Workers should use protective garments.

Greenhouse effect and Global warming:

The greenhouse is a building made chiefly of gases for growing delicate plants or exotic plants. The air in the greenhouse is warmer than the outside air, even though it receives less solar radiation. This is known as the greenhouse effect.

Three factors contribute to the greenhouse effect. They are:

  • Glass walls of the greenhouse.
  • Carbon dioxide contents
  • Water vapour contents.

The gases present in the atmosphere to keep the earth’s surface warm are carbon dioxide, methane, chlorofluorocarbons, nitrous oxide, and water vapours. These are greenhouse gases.

Due to man’s activities like burning fossil fuels in homes, industries, and automobiles, he is adding a large amount of carbon dioxide to the atmosphere. Methane is produced by marshes, paddy fields, cattle sheds, and biogas plants.

Refrigerators and air conditioners emit chlorofluorocarbons. Nitrogen oxides are produced as a result of organic matter and fertilisers by denitrifying bacteria, as well as automobile exhausts and industries. The concentrations of these gases in the atmosphere are increasing, affecting the global climate.

The effects of greenhouse gases are:

  • The response of plants to the increased concentration of carbon dioxide is called the carbon dioxide fertilisation effect. As a result of an increase in carbon dioxide concentration, the rate of photosynthesis in C3 plants will increase. If the rising trend of carbon dioxide continues, then the atmospheric carbon dioxide concentration will be between 540 ppm and 970 ppm by the end of the 21st century.
  • An increased rise in the earth’s temperature has adversely affected the climate and the weather. This can adversely affect the sea level, range of species distribution, food production, and fisheries resources in the ocean.
  • Global warming may increase the sea level due to the thermal expansion of the seawater and the melting of glaciers.
  • Adverse effect on the range of species distributions. The various species that are sensitive to temperature stress, may die as a result of this sudden rise in temperature, and their place would be taken by the scrub vegetation.The explosive growth of weeds and increased plant disease incidence are the consequences of global warming. All these factors will collectively lead to decreased crop productivity.

The strategies to deal with the greenhouse effect are:

  • Increasing vegetation for photosynthetic carbon dioxide utilisation
  • Chlorofluorocarbon substitute replacement
  • Fossil fuel usage limitations.
  • Alternate renewable energy sources like solar energy and wind energy should be developed.
  • The use of nitrogen fertiliser should be minimised.
  • Increased reliability in nitrogen fixation.

Ozone depletion:

  • The good ozone is formed in the upper part of the atmosphere, called the stratosphere.
  • This acts like a shield.
  • DNA and proteins of living organisms absorb UV radiation and these are very injurious as the chemical bond within these molecules is broken.
  • Dobson units or DU is used to measure the thickness of the ozone in the column of air from the ground to the top of the atmosphere.
  • The action of UV rays on molecular oxygen forms ozone gas continuously.
  • There is also degrading ozone in the stratosphere.
  • Chlorofluorocarbons of CFCs disrupt this balance as they degrade the ozone.
  • CFC are widely used as refrigerants.
  • CFCs reach the stratosphere after they are discharged in the lower part of the atmosphere, and they move upward.
  • UV rays act on them in the stratosphere and release Cl atoms.
  • Ozone, which releases molecular oxygen, is degraded by Cl atoms. These atoms act as catalyst.
  • Cl atoms are not consumed in the reaction.
  • When CFCs are added to the stratosphere, they have permanent and continuing effects on the Ozone levels.

Ozone hole:

In the stratosphere, ozone depletion has occurred widely, and this depletion is more marked over the Antarctic region. The decline in the thickness of the ozone layer over a restricted area is called an ozone hole. In the stratosphere, chlorofluorocarbons are mainly responsible for the depletion of ozone.

The effects of ozone depletion are

  • The rise in cataract cases, diminishing eyesight, and diminished immune system functioning.
  • Increased incidence of skin cancer.
  • Mortality of animals.
  • Mutations.
  • Inhibition of photosynthesis.
  • Disturbance of aquatic and terrestrial food chains.

SNOW-Given that the ozone layer is intact, UV radiation with a shorter wavelength than UV-B is completely absorbed by the earth’s atmosphere.

  • UVB causes damage to the DNA.
  • This causes many changes in the skin, such as ageing and cell damage, and it also increases the risk of various types of skin cancer.

UVB radiation is absorbed by the cornea of the human eye.

  • When the cornea is exposed to high doses of UVB radiation,  inflammation of the cornea. This leads to many conditions like snow – blindness, cataract, etc., which cause permanent damage to the cornea.


  • This was done in recognition of the deleterious effect of ozone depletion.
  • This was signed in 1987, Canada.
  • This was signed to control the emission of substances that deplete ozone.
    • Several efforts have been made to reduce CFC emissions.



Extramarks Class 12 Biology Chapter 16 Notes explains the action of pollutants and the improper utilisation of resources is contributing to the degradation of the natural resources.

  • Soil Erosion: The damage to the topsoil reduces the fertility of the soil. The main factors that cause soil erosion are deforestation and a lack of protection against the wind and water. The soil cleared of the forest is eroded by the water in hilly areas, and on plains, even strong winds erode the soil.

The topsoil is fertile soil, and it takes centuries to develop fertile soil. Human activities such as over-cultivation, unrestricted grazing, poor irrigation practices, deforestation, or forest cutting can easily remove this.These activities result in arid patches of land.

  • Water logging and soil salinity: This occurs when irrigation without proper drainage of water leads to waterlogging in the soil. The most important harmful fact is that waterlogging draws salt to the surface of the soil. On the surface of the land, a thin crust of salt is deposited. Then this salt collection also occurs at the root of the plant. When the plants are exposed to this increasing content of salt, it is detrimental to their growth and also damages agriculture. Water logging and  salinity are some of the problems that have come in the wake of the Green Revolution.
  • Sand shifting: The strong wind shifts the sand from deserts into fertile lands and converts it into deserts. The desert was once fertile land, formed in this manner.
  • Urbanisation: These are developmental activities. Other activities include mining, dams, canals, playgrounds, industries, etc.

The land degradation can be controlled by taking the following necessary steps:

  • Restoration of the forest.
  • Shifting cultivation can be reduced by crop rotation, mixed cropping, and plantation cropping. These productive methods will replace shifting cultivation and improve soil fertility, which can enhance productivity and support a larger population.
  • Salinity can be checked by improving drainage. If the groundwater table is not high, it is possible to recover salinity-rich land by leaching it with more water.
  • To check the advancement of deserts.
  • Suitable vegetation.


  • This means clearing forests to claim land for human use.
  • This is the conversion of the forest area to a non-forest area.
  • In the tropics, 40 % of the forest has been lost to deforestation.
  • The scenario is grim in India.
  • In the beginning of the 20th century, the total percentage of land covered by forest was 30 %.
  • This area will shrink to 21.54 % by the end of the century.
  • The National Forest Policy of 1988 recommended that the plains receive 33% of the forest cover, while the hills receive 67%.

Causes of deforestation:

There are many causes of deforestation. They are:

  • The explosion of population:  As a result of rising population, man has cut down forests to reclaim land for housing, agriculture, forests, roads, and rail tracks. There is rising demand for timber, fuel, wood, wooden crates, and paper, all of which are associated with the large-scale felling of trees. The forest is seriously affected by industries and mining.
  • Fires: The fire is the biggest enemy of the forest, and it destroys both full-grown and young trees. This endangers both animal and human life.
  • Pests: The pest destroys the trees as they eat up the leaves and further spread the disease by boring into the shoots. It is very difficult to spray the entire forest.
  • Grazing: The animals eat the young leaves of the trees.
  • Weather: The storm and snow damage the forest, and this is beyond human control.
  • Dam
  • Jhuming cultivation

Jhum cultivation:

    • Shifting cultivation, a peculiar practise of slash-and-burn agriculture is prevalent among tribal communities of Africa, Asia, and Oceania.
    • Slash and burn agriculture is known as Jhum cultivation. 
    • This has been observed in the North-eastern states of India and has contributed a lot to deforestation.
    • In this, the trees are cut down from the forest by the farmers, and the plant remains are burned.
    • The ash obtained by burning is used as fertiliser.
    • The land is then used for farming and grazing cattle.
    • After cultivation, the area is left for years to recover.
    • This process is repeated by the farmers in the other areas.
  •  It is not harmful, as the cycles are longer than ten years. 
  • Short cycles are harmful and destroy the forest, causing soil erosion. Then, it is accompanied by complications from soil erosion.
  • Previously, in the early days, when the prevalence of Jhum cultivation was higher, a sufficient time gap was provided so that the land recovered from the effects of cultivation.
  • Due to the continuous increase in population and the increased repetition of cultivation, the recovery phase has been done away with. So this leads to deforestation.

Effects/Consequences of deforestation:

The effects of deforestation are explained by Class 12 Biology Chapter 16 Notes:

  • Decrease in percolation and groundwater discharge.
  • Loss of biodiversity.
  • Habitat destruction.
  • Desertification increases in extreme cases due to deforestation.
  • Hydrologic cycles are disturbed.
  • Increase in soil erosion
  • Increased frequency of floods and droughts.
  • The imbalance between carbon dioxide and oxygen. There is an increased concentration of carbon dioxide in the atmosphere. This is due to the fact that trees hold a lot of carbon in their biomass, and with deforestation, since the trees are lost, there is an increased concentration of carbon dioxide.
  • Extinction of forest-dwelling species
  • Changed pattern of rainfall
  • Warming of climate
  • Increase in landslides.


  • Prohibition of indiscriminate deforestation.
  • Reforestation
  • Afforestation
  • Prevention of forest fires
  • Control of pests and diseases in the forest
  • Discouraged grazing of cattle in the forest
  • Adoption of modern techniques in forestry
  • Improvement cutting and selective cutting are used.


  • This is a process in which the forest that was once cleared is restored.
  • This may occur naturally in  areas of deforestation.
  • The process can be speeded up by planting more trees.


  • The history dates back to 1731.
  • The king of Jodhpur asked his men to arrange wood for the construction of a new palace.
  • The Bishnois thwarted the king’s order to cut down the trees for wood to make a palace.
  • There was a woman called Amrita Devi, she showed a lot of courage by hugging a tree. She asked the king’s men to cut her down first before cutting the tree. This shows how much trees were important to her more than her own life.
  • The Bishnoi is a community of people who are known for their peace and love of nature. 
  • Amritas Devi’s plea was not heard, and the king’s men cut down the tree along with her.
  • Many Bishnois, including her three daughters, Amrita Devi, followed her, and many people died while saving the tree.
  • There is no mention of such people in history who  lost their lives while saving the trees. There are many people who have sacrificed their lives for the cause of the environment.
  • The Amrita Devi Bishnoi Wildlife Protection Award is given to rural communities that have demonstrated extraordinary courage and dedicated their lives to wildlife protection.
  • The award is given by the Government of India.

Chipko movement:

  • The Chipko movement dates back to 1974, when the local women displayed enormous bravery by protecting the trees from the axe of the contractor by hugging them.
  • The Chipko movement is acclaimed by people all over the world.

Joint Forest Management:

    • Joint forest management is a concept introduced by the Government of India, and it dates back to 1980. 
    • This began as a result of the significant participation of local communities and people in saving the environment.
    • JFM began to work closely with such people in the communities in order to protect the forest.The communities benefit from products obtained from the forest, like fruits, gum, rubber, medicine, etc. This is a reward offered to them in return for the services they provide to save the environment.
  • In this way, the forest is conserved in a sustainable manner.

Class 12 Biology Chapter 16 Notes: Exercises & Solutions

 Students in Class 12 can swiftly comprehend every Chapter of the entire Biology Syllabus by using the educational study resources that Extramarks offers. Once students have access to the most recent syllabus, chapter notes, question and answer solutions, etc., learning biology will be simple. The Class 12 Biology Chapter 16 Notes are available to students who sign up for Extramarks at any time and from any location.

Simple explanations were used to write the Class 12 Biology Chapter 16 Notes on Environmental Issues. The Notes, which are based on the CBSE Syllabus, may be very helpful to students. By clicking on the links below, students can access the exercises and solutions for particular chapters.

  • Chapter 16: Exercise 16.1 Solutions       
  • Chapter 16: Exercise 16.2 Solutions 
  • Chapter 16: Exercise 16.3 Solutions
  • Chapter 16: Exercise 16.4 Solutions      
  • Chapter 16: Exercise 16.5 Solutions
  • Chapter 16: Exercise 16.6 Solutions
  • Chapter 16: Exercise 16.7 Solutions
  • Chapter 16: Exercise 16.8 Solutions
  • Chapter 16: Exercise 16.9 Solutions
  • Chapter 16: Exercise 16.10 Solutions
  • Chapter 16: Exercise 16.11 Solutions

 Extramarks offers excellent, detailed, and accurate study materials for Class 12 Biology Chapter 16. These study materials can help students understand the major Chapter’s subject matter and interpret its exam questions. The goal of these study aids is to help students comprehend the Chapters in the CBSE Class 12 textbooks so they can do well on their Class 12 exams.

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  • NCERT Solutions     
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  • CBSE Past Year Question Papers 
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NCERT Exemplar Class 12 Biology

Biology demands ongoing research and study. The length of the class 12 Biology course requires students to attempt a large number of questions.

Students can utilise the NCERT Exemplar for Class 12 Biology to build questions and solutions from previous year exam papers. The Exemplar has multiple choice, long answers, and short answers among its question types.

Our study guides for Class 12 Biology Chapter 16 Notes now include thorough justifications for the solutions created by Extramarks. Students can improve their problem-solving and critical thinking skills by using the solutions to the exemplar problems. Students who complete these projects will have a better understanding of the numerous subjects presented in Chapter 16.In addition to the sample solutions, our Class 12 Biology Chapter 16 Notes and Study Materials include CBSE revision notes, questions from previous year exams, and additional study tools.

Key Features of Class 12 Biology Chapter 16 Notes

The key features of Class 12 Biology Chapter 16 Notes provided by Extramarks are listed below:

  • It offers accessible information that is very clear.
  • It improves time management capabilities.
  • Each topic is thoroughly covered while still being easily understood.
  • It uses the CBSE curriculum.
  • These comments were written by Extramarks faculty members, all of whom hold doctorate degrees.
  • Each subject is completely explained.It emphasises the creation of detailed, short Notes.

We strongly advise students to sign up on the Extramarks website in order to access all of the study materials for the Class 12 Biology Chapter 16 Notes.

FAQs (Frequently Asked Questions)

1. Biological Magnification: What Does It Mean?

Intoxicant buildup causes biological amplification. These are the pesticides that are found in the organism’s tolerant tissues. These organisms are at the top of the food chain. Refer to Extramarks Class 12 Biology Chapter 16 Notes for an in-depth knowledge of the same.

2. Discover Some Environmental Issues Solutions.

Listed below are a few ways to help with environmental:

  •       Recycling of waste
  •       Conserving water and electricity.
  •       Recycling.
  •       Refraining from using plastic.

3. What does the term "Eutrophication" mean?

When water bodies are too enriched with nutrients and minerals, it is known as Eutrophication. This results in an excess of algae development. As a result, the water body’s oxygen levels become low. Refer to Extramarks Class 12 Biology Chapter 16 Notes for an in-depth knowledge of the same.

4. What does "Organic Farming" mean?

Organic farming is a waste-free, circular process in which leftovers from one step are recycled as nutrients for use in subsequent steps. As a result, resources can be used more efficiently, and manufacturing efficiency also rises. In this procedure, no chemical fertilisers are used. Refer to Extramarks Class 12 Biology Chapter 16 Notes for an in-depth knowledge of the same.