NCERT Solutions for Class 12 Biology Chapter 16 Environmental Issues to Study Online as well as download in PDF format updated for new academic session 2022-2023. Download Offline Apps following NCERT Solutions for other subjects also. Come to the world of knowledge and Share Your Thoughts via Discussion Forum of Tiwari Academy.

NCERT Solutions for Class 12 Biology Chapter 16

Chapter 16:Environmental Issues

Class 12 Biology Chapter 16 Solutions in English

NCERT Solutions for Class 12 Biology Chapter 16 in PDF form to free download based on latest NCERT Books 2022-23. All Offline Apps and NCERT Solutions 2022-2023 are based on latest CBSE Syllabus 2022-23 for UP Board, MP Board, CBSE, Gujrat Board and all other boards who are following NCERT Books as course. Join the Discussion forum to ask your doubts.

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Important Terms related to Chapter 16

1. Pollutants: Agents which cause pollution.
2. Pollution: Undesirable physical/chemical/biological characteristics of air/water/land which cause damage to the animals/plants/humans and architectural structures.
3. Reforestation: Process of restoring a forest that was removed at some point of time in the past.
4. Effluents: Something flowing over a large body of water (may be sewage or industrial effluents).

5. JFM (Joint Forest Management): Introduced by the Government of India in 1980s to work closely with local communities for protecting and managing forests.
6. Eutrophication: It is the process of nutrient enrichment of water and subsequent loss of species diversity like fishes. Excess nutrients causes algal bloom which may cover the whole surface of water body and release toxins. It causes oxygen deficiency in water that leads to the death of aquatic animals like fishes.
7. Ozone Hole: Large area of thinned ozone layer over Antarctica.


1. It refers to increase in concentration of toxic substances at successive trophic levels.
2. Harmful Effect of DDT: High concentration of DDT disturbs calcium metabolism in birds, which causes thinning of egg shell and their premature breaking, causing decline in birds population.
3. Global Warming: Increase in the level of greenhouse gases is mainly responsible for global warming, (increase in mean global temperature due to trapping of infrared radiation). Carbon dioxide, Methane, CFCs, N2O are the main gases that causes greenhouse effect.

Measures to Control Global Warming

1. Minimize the use of fossil fuel.
2. Improving efficiency of energy usage.
3. Reducing deforestation.
4. Planting trees.

Steps leading to ozone depletion

1. UV-rays split CFCs and release atomic chlorine (Cl)
2. UV-rays also split ozone into oxygen.
3. Chlorine atoms trap oxygen atoms and ozone is not formed again from oxygen. This leads to depletion of ozone in the stratosphere.
4. Electronic Wastes (e-waste): e-wastes are irreparable computer and other electronic goods.

Disposal of e-wastes

1. Burned in landfills
2. Incineration.
3. Recycling.

Important Questions on 12th Biology Chapter 16

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?

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.

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

Domestic sewage is the waste originating from the kitchen, toilet, laundry, and other sources. It contains impurities such as suspended solid (sand, salt, clay), colloidal material (faecal matter, bacteria, plastic and cloth fibres), dissolved materials (nitrate, phosphate, calcium, sodium, ammonia), and disease-causing microbes. When organic wastes from the sewage enter the water bodies, it serves as a food source for microorganisms such as algae and bacteria. As a result, the population of these microorganisms 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.

Write critical notes on Eutrophication.

Eutrophication: It is the natural ageing process of a lake caused due to nutrient enrichment. It is brought down by the runoff of nutrients such as animal wastes, fertilizers, and sewage from land which leads to an increased fertility of the lake. As a result, it causes a tremendous increase in the primary productivity of the ecosystem. This leads to an increased growth of algae, resulting into algal blooms. Later, the decomposition of these algae depletes the supply of oxygen, leading to the death of other aquatic animal life.

Why ozone hole forms over Antarctica? How will enhanced ultraviolet Radiations affect us?

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. The CFC’s magnate from the troposphere to the stratosphere, where they release chlorine atoms by the action of UV rays on them. The release of Chlorine atoms causes the conversion of ozone into molecular oxygen. One atom of chlorine can destroy around 10,000 molecules of ozone and causes ozone depletion. The formation of the ozone hole will result in an increased concentration of UV – B radiations on the Earth’s surface. 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.

Discuss briefly the Greenhouse gases.

Greenhouse gases: 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.

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

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 led 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.

NCERT Solutions for Class 12 Biology Chapter 16 Environmental Issues
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