NCERT Solutions for Class 12 Biology Chapter 16: Environmental Issues

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Chapter16. Environmental Issues
CategoryNCERT Solutions for Class 12

Our NCERT Solutions for Class 12 Biology is a great resource for students preparing for boards or competitive exams, such as the NEET. These Biology Class 12 Solutions are made by expert faculties, keeping the latest curriculum in mind. Besides helping students with understanding the concepts of Biology, these solutions are also helpful in writing accurate answers that are vital to score full marks in examinations. On this page, we have given the Class 12 Biology Chapter 16: Environmental Issues.

NCERT Solutions for Class 12 Biology Chapter 16

Environmental Issues Solutions

Q1) What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.

Answer) The various constituents of domestic sewage are:

  • dissolved salts such as nitrates, phosphates, etc., from detergents.
  • toxic metal ions from paints, varnishes, etc.
  • biodegradable organic matter from kitchen and toilet.
  • pathogenic microorganisms in the faecal matter.

The effects of sewage discharge on a river:

When organic wastes from the sewage enter the water bodies, it serves as a food source for micro-organisms such as algae and bacteria. As a result, the population of these micro-organisms in the water body increases. Here, they utilize most of the dissolved oxygen for their metabolism. This results in an increase in the levels of Biological oxygen demand (BOD) in river water and results in the death of aquatic organisms. Also, the nutrients in the water lead to the growth of planktonic algal, causing algal bloom. This causes deterioration of water quality and fish mortality.

Q2) List all the wastes that you generate, at home, school or during your Trips to other places, could you very easily reduce? Which would be Difficult or rather impossible to reduce?

Answer) Wastes generated at home include plastic bags, paper napkin, toiletries, kitchen wastes (such as peelings of vegetables and fruits, tea leaves), domestic sewage, glass, etc.

Wastes generated at schools include waste paper, plastics, vegetable and fruit peels, food wrappings, sewage etc.

Wastes generated at trips or picnics include plastic, paper, vegetable and fruit peels, disposable cups, plates, spoons etc.

Yes, wastes can be easily reduced by the judicious use of the above materials. Wastage of paper can be minimized by writing on both sides of the paper and by using recycled paper. Plastic and glass waste can also be reduced by recycling and re-using. Also, substituting plastics bags with biodegradable jute bags can reduce wastes generated at home, school, or during trips. Domestic sewage can be reduced by optimizing the use of water while bathing, cooking, and other household activities.

Non- biodegradable wastes such as plastic, metal, broken glass, etc are difficult to decompose because micro-organisms do not have the ability to decompose them.

Q3) Discuss the causes and effects of global warming. What measures need to be taken to control global warming?

Answer) Global warming is defined as an increase in the average temperature of the Earth’s surface.

  • Causes of global warming: Global warming occurs as a result of the increased concentration of greenhouse gases in the atmosphere. Greenhouse gases include carbon dioxide, methane, and water vapour. These gases trap solar radiations released back by the Earth. This helps in keeping our planet warm and thus, helps in human survival. However, an increase in the amount of greenhouse gases can lead to an excessive increase in the Earth’s temperature, leading to global warming. Global warming is a result of industrialization, burning of fossil fuels, and deforestation.
  • Effects of global warming: Global warming is defined as an increase in the average temperature of the Earth’s surface. It has been observed that in the past three decades, the average temperature of the Earth has increased by 0.6ºC. As a result, the natural water cycle has been disturbed resulting in changes in the pattern of rainfall. It also changes the amount of rain water. Also, it results in the melting of Polar ice caps and mountain glaciers, which has caused a rise in the sea level, leading to the inundation of coastal regions.

Control measures for preventing global warming:

  • Reducing the use of fossil fuels
  • Use of bio-fuels
  • Improving energy efficiency
  • Use of renewable source of energy such as CNG etc.
  • Reforestation.
  • Recycling of materials

Q4) Match the items given in column A and B:

Column AColumn B
(a) Catalytic converter(i) Particulate matter
(b) Electrostatic precipitator(ii) Carbon monoxide and nitrogen oxides
(c) Earmuffs(iii) High noise level
(d) Landfills(iv) Solid wastes


Column AColumn B
(a) Catalytic converter(ii) Carbon monoxide and nitrogen oxides
(b) Electrostatic precipitator(i) Particulate matter
(c) Earmuffs(iii) High noise level
(d) Landfills(iv) Solid wastes

Q5) Write critical notes on the following:

(a) Eutrophication
(b) Biological magnification
(c) Groundwater depletion and ways for its replenishment

Answer a) It is referred to the natural ageing process of a lake as a result of nutrient enrichment caused by the overflow of nutrients such as fertilizers, animal wastes and sewage from land leading to increased fertility of the lake. Consequently, there is a huge increase in the primary productivity of the ecosystem bringing about an increased growth of algae, hence in algal blooms. After some time, the decomposition of these algae reduces oxygen supply, resulting in the death of aquatic animal life.

Answer b) Pesticides are used on a large scale to protect crops from various diseases and pests. When these pesticides enter the soil, they are absorbed by plant parts with minerals and water from the soil. These chemicals can enter water sources as a result of rains, furthermore into the bodies of aquatic animals and plants, hence into the food chain. As these chemicals cannot be disintegrated, at each of the trophic levels, they keep getting accumulated, wherein most of the accumulation occurs at the top carnivore’s level. This is termed as biological magnification where there is an increase in the concentration of harmful pollutants with each increasing tropic level.

For instance, high DDT concentrations were built in a pond. The producers (phytoplankton) have a DDT concentration of 0.04 ppm. As this phytoplankton was consumed by zooplankton – the consumers, the concentration of DDT in the bodies of zooplankton was noted to be 0.23 ppm. When this, in turn, is consumed by small fish, more of DDT gets collected in their bodies. Consequently, the large fish (top carnivore) feeding on different small fish tend to have a maximum concentration of DDT.

NCERT Solutions for Class 12 Biology Chapter 16

Answer c) Since the past years, the level of groundwater has decreased. Water supply from sources is declining rapidly with each passing year due to an increase in water pollution and population explosion. In order to meet the demand of water, water is being taken out from water bodies such as rivers, ponds etc. hence, the source of groundwater is fast depleting as the quantity of groundwater that is withdrawn for human utilization is more than the quantity that is being replaced by rainfall. Small quantities of water penetrate through the ground due to lack of vegetation cover. Another factor that has caused a decline in the availability of groundwater is an increase in water pollution.

Measures to replenish groundwater are as follows:

  • Over-exploitation of groundwater must be prevented
  • Water use must be optimized and water demand must be reduced
  • Promote and encourage rainwater harvesting
  • Prevent deforestation
  • Promote afforestation, plant more trees

Q6) Why does ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?

Answer) The ozone hole is more prominent over the region of Antarctica. It is formed due to an increased concentration of chlorine in the atmosphere. Chlorine is mainly released from chlorofluorocarbons (CFC’s) widely used as refrigerants.

  • When released in stratosphere, these substances drift towards poles and get accumulated on the ice clouds formed at high altitudes.
  • Ice provides a surface on which breakdown of all the CFC compounds takes place to release chlorine atom.
  • These chlorine atoms breakdown ozone resulting in thinning of the ozone layer. Normally, the ozone layer plays a protective role by absorbing harmful UV radiations but reduction in its thickness allows UV rays to reach Earth’s surface

Effects of ultraviolet radiation on humans:

  • Early ageing of skin.
  • Increased incidences of cancer of the skin.
  • Cataract of the eyes.
  • Inflammation of cornea of the eye (known as snow blindness).
  • Weakened immune system.

Q7) Discuss the role of women and communities in protection and conservation of forests.

Answer) The role of communities and women in protecting and conserving forests has been significant.

(i) The Chipko Movement
This movement was started in the Garhwal region of the Himalayas in 1974 wherein the women of the village opposed the contractors from chopping forest trees. They did so by embracing them.

(ii) Case study of the Bishnoi community
In Rajasthan, the Bishnoi community has a strict belief in the concept of peacefully co-existing with nature. The King of Jodhpur in 1731 ordered his ministers to organize wood to construct his new palace for which the King and his people visited the Bishnoi village where a Bishnoi woman known as Amrita Devi along with her daughter and hundreds of other Bishnois were courageous enough to take a step and stop them from chopping trees. They embraced the trees, losing their lives at the hands of soldiers. This conflict by the villagers forced the King to give up on the idea of chopping trees.

Q8) What measures, as an individual, you would take to reduce environmental pollution?

Answer) Listed below are some measures that can be taken to prevent environmental pollution:

To prevent air pollution-

  • Clean and renewable energy sources to be used such as bio-fuels and CNG
  • Afforestation – promote planting
  • Limit usage of fossil fuels
  • Catalytic converters to be used in automobiles

To prevent water pollution-

  • Use of water to be optimized
  • For gardening and other related chores, switch to using kitchen wastewater

To prevent noise pollution-

  • Plant more trees
  • Reduce/avoid bursting of crackers

Measures to decrease solid waste generation-

  • Different types of wastes to be separated
  • Reuse and recycle paper and plastic
  • Plastic usage must be reduced and eventually avoided completely
  • Biodegradable kitchen waste must be composted

Q9) Discuss briefly the following:

(a) Radioactive wastes
(b) Defunct ships and e-wastes
(c) Municipal solid wastes

Answer a) Radioactive wastes are generated during the process of generating nuclear energy from radioactive materials. Nuclear waste is rich in radioactive materials that generate large quantities of ionizing radiations such as gamma rays. These rays cause mutation in organisms, which often results in skin cancer. At high dosage, these rays can be lethal. Safe disposal of radioactive wastes is a big challenge. It is recommended that nuclear wastes should be stored after pre-treatment in suitable shielded containers, which should then be buried in rocks.

Answer b) Defunct ships are dead ships that are no longer in use. Such ships are broken down for scrap metal in countries such as India and Pakistan. These ships are a source of various toxicants such as asbestos, lead, mercury etc. Thus, they contribute to solid wastes that are hazardous to health. E-wastes or electronic wastes generally include electronic goods such as computers etc. Such wastes are rich in metals such as copper, iron, silicon, gold etc. These metals are highly toxic and pose serious health hazards. People of developing countries are involved in the recycling process of these metals and therefore, get exposed to toxic substances present in these wastes.

Answer c) Municipal solid wastes are generated from schools, offices, homes, and stores. It is generally rich in glass, metal, paper waste, food, rubber, leather, and textiles. The open dumps of municipal wastes serve as a breeding ground for flies, mosquitoes, and other disease-causing microbes. Hence, it is necessary to dispose municipal solid waste properly to prevent the spreading of diseases. Sanitary landfills and incineration are the methods for the safe disposal of solid wastes.

Q10) What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?

Answer) Delhi has been categorized as the fourth most polluted city of the world in a list of 41 cities. Burning of fossil fuels has added to the pollution of air in Delhi.

Various steps have been taken to improve the quality of air in Delhi.

  • Introduction of CNG (Compressed Natural Gas):By the order of the supreme court of India, CNG-powered vehicles were introduced at the end of year 2006 to reduce the levels of pollution in Delhi. CNG is a clean fuel that produces very little unburnt particles.
  • Phasing out of old vehicles
  • Use of unleaded petrol
  • Use of low-sulphur petrol and diesel
  • Use of catalytic converters
  • Application of stringent pollution-level norms for vehicles
  • Implementation of Bharat stage I, which is equivalent to euro II norms in vehicles of major Indian cities.

The introduction of CNG-powered vehicles has improved Delhi’s air quality, which has lead to a substantial fall in the level of CO2 and SO2. However, the problem of suspended particulate matter (SPM) and respiratory suspended particulate matter (RSPM) still persists.

Q11) Discuss briefly the following:

(a) Greenhouse gases
(b) Catalytic converter
(c) Ultraviolet B

Answer a) The greenhouse effect refers to an overall increase in the average temperature of the Earth due to the presence of greenhouse gases. Greenhouse gases mainly consist of carbon dioxide, methane, and water vapour. When solar radiations reach the Earth, some of these radiations are absorbed. These absorbed radiations are released back into the atmosphere. These radiations are trapped by the greenhouse gases present in the atmosphere.. This helps in keeping our planet warm and thus, helps in human survival. However, an increase in the amount of greenhouse gases can lead to an excessive increase in the Earth’s temperature, thereby causing global warming.

Answer b) Catalytic converters are devices fitted in automobiles to reduce vehicular pollution. These devices contain expensive metals such as platinum, palladium, and rhodium that act as catalysts. As the vehicular discharge passes through the catalytic converter, the unburnt hydrocarbons present in it get converted into carbon dioxide and water. Carbon monoxide and nitric oxide released by catalytic converters are converted into carbon dioxide and nitrogen gas (respectively).

Answer c) Ultraviolet-B is an electromagnetic radiation which has a shorter wavelength than visible light. It is a harmful radiation that comes from sunlight and penetrates through the ozone hole onto the Earth’s surface. It induces many health hazards in humans. UV −B damages DNA and activates the process of skin ageing. It also causes skin darkening and skin cancer. High levels of UV −B cause corneal cataract in human beings.

That’s it. These were the solutions of NCERT Class 12 Biology Chapter 16 – Environmental Issues. Our team hopes that you have found these solutions helpful for you. If you have any doubt related to this chapter then feel free to comment your doubts below. Our team will try their best to help you with your doubts.

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