The VIDYANKER team has thoughtfully prepared the NCERT Solutions for Class 12 Biology Chapter 16, "Environmental Issues" These solutions are designed to help you tackle the NCERT textbook questions with ease. We recommend going through the chapter's theory before diving into the solutions for a deeper understanding. Feel free to share these NCERT Solutions for Class 12 Biology with others—learning is always better when shared!
QUESTIONS FROM TEXTBOOK SOLVED
1. What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
Ans: Domestic sewage contains:
- Organic matter (human excreta, food residues),
- Inorganic substances (nitrates, phosphates, salts),
- Pathogens (bacteria, viruses),
- Suspended solids (soil, silt),
- Nutrients (nitrogen, phosphorus), and
- Toxic chemicals (pesticides, cleaning agents).
Effects of Sewage Discharge on a River
- Depletion of oxygen: Organic matter decomposition by bacteria reduces dissolved oxygen, harming aquatic life.
- Eutrophication: Excess nutrients cause algal blooms, leading to oxygen depletion.
- Pathogens: Spread waterborne diseases like cholera and typhoid.
- Toxicity: Chemicals and heavy metals harm aquatic organisms.
- Loss of biodiversity: Reduced oxygen and toxicity kill fish and aquatic plants
2. List all the wastes that you generate at home, school or during your trips to other places. Could you very easily reduce the generation of these wastes? Which would be difficult or rather impossible to reduce?
Ans: Wastes Generated
At Home:
- Kitchen waste (food scraps, vegetable peels)
- Plastic packaging (food wrappers, bottles)
- Paper (newspapers, bills)
- E-waste (old gadgets, batteries)
- Glass and metal containers
- Clothes and fabric waste
At School:
- Paper (notebooks, assignments)
- Plastic bottles and packaging
- Stationery waste (pen refills, markers)
- Food waste (lunch leftovers)
During Trips:
- Disposable items (plates, cups, cutlery)
- Plastic bottles
- Food packaging
- Ticket stubs and travel papers
Reducible Wastes:
- Plastic: Use reusable bags, bottles, and containers.
- Paper: Reduce, reuse, and recycle paper; switch to digital formats.
- Food waste: Composting and careful meal planning.
- Stationery: Use refillable pens and avoid single-use items.
Difficult to Reduce:
- E-waste: Due to technology upgrades.
- Plastic packaging: Common in many products.
- Disposable items during travel: In some cases, access to alternatives may be limited.
Some wastes, like e-waste or single-use packaging, are harder to avoid entirely due to current consumption habits and product availability.
3. Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
Ans: Increase in atmospheric concentration of green house gases has resulted in rise of atmospheric temperature by 0.6°C (global wanning) in die 20th century. This has been confirmed by intergovernmental panel on climatic change (IPCC) in its reports of 1991 and 1992. This predictable change in near future may affect climate, sea level, range of species distribution, food production as well as fisheries resources in the oceans.
Causes of global warming:
(i) Increase in concentration of greenhouse gases.
(ii) Increase of automobile and use of fossil fuel.
(iii) Deforestation and change in land use.
(iv) CFC and aerosol emission from refrigerator and aeroplane.
(v) Increased particulate matter in lower atmosphere.
Effects of global warming:
(i) CO2 fertilisation effect.
(ii )Many species of plants, being sensitive to temperature will die with sudden rise in temperature and their place will be taken over by scrub vegetation.
(iii) Loss of biodiversity.
(iv) Rise in sea level.
(v) Possibilities of drought and floods.
(vi) Erruption of plant disease and pests.
(vii) Change in rainfall pattern.
Methods that can reduce the atmospheric concentration of greenhouses gases are
(i) Reducing the greenhouse gas emission by limiting the use of fossil fuels, and by developing alternative renewable sources of energy (wind energy, solar energy etc.)
(ii) Increasing the vegetation cover, mainly the forests, for photosynthetic utilization of CO2.
(iii) Minimizing the use of nitrogen fertilizers in agriculture for reducing N2O emissions.
(iv) Developing substitutes for chlorofluorocarbons.
4. Match the items given in column A and B:
Ans: (a)-(iii),(b)-(iv),(c)-(i),(d)-(ii)
5. Write critical notes on the following:
(a) Eutrophication
(b) Biological magnification
(c) Groundwater depletion and ways for its replenishment
Ans: 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 increased fertility of the lake. As a result, it causes a tremendous increase in the primary productivity of the ecosystem. This leads to increased growth of algae, which results into algal blooms. Later on, the decomposition of these algae drains the dissolved supply of oxygen into the waters causing death of other forms of aquatic animal life.
Biological magnification: - It implies the increase in concentration of a toxic substance at successive trophic levels, in the food chain. The toxic substances that have become accumulated in an organism cannot be metabolized or excreted. When this organism is ingested by another animal at a higher trophic level, it is transferred to this and then to the next higher trophic level and so on .Biomagnification Interferes with calcium metabolism in birds, which results in thinning of egg shell and their early breaking that eventually leads to decline in bird populations.
Ground water depletion and ways for its replenishment: - The ground water level has decreased within the recent years. The source of water supply is rapidly diminishing with each passing year due to the increase of population and water pollution. In order to fulfill the demand of water, water is withdrawn from water bodies like ponds, rivers etc. As a result of this process, the source of ground water is depleting. This is because the amount of groundwater being drawn for human use is more than the amount replaced by rainfall. Lack of vegetation cover also results in very small amounts of water seeping through the ground. Another factor that has reduced the availability of ground water is an increase in water pollution.
6. Why ozone hole forms over Antarctica? How will enhanced ultraviolet radiation affect us?
Ans: Chlorofluorocarbons, mainly released by developed nations to the stratosphere, under the influence of winds move slowly to the poles. Environmental conditions in Antarctica during the winter months; there is no sunlight at Antarctica and the temperature is extremely low at ( – 85°C) which helps in developing ice clouds. In winter, natural circulation of wind (polar vertex) completely cuts off Antarctic air from the rest of the world.
The degradation of ozone takes place with the return of solar radiations to Antarctica during spring (September and October). The catalytic surface for the reaction of chlorine atoms and then ozone is provided by the ice clouds. This causes the thinning of the ozone layer every year over most of Antarctica. This hole disappears in summer due to warming up of air and the mixing up of Antarctic air with that of the rest of the world.
For more intense UV radiations on earth, the impact it would have on humans and other animals would be:
- Skin cancer
- Blindness and increased chances of cataract in eyes.
- Malfunctioning of immune system.
- Higher number of mutations.
7. Discuss the role of women and communities in protection and conservation of forests.
Ans: Amrita Bishnoi Wildlife protection project Known for its peaceful co-existence with nature. And it was in 1730 AD. Amrita Devi protested against the king's men's attempt to cut trees because it was prohibited in Bishnoi religion. A party of Maharaja Abhay Singhji, Rular of Marwar (Jodhpur) state who wanted to fell green khejdali trees. Amrita Devi fy her three daughter & more than 360 of other Bishnois lost their lives in saving trees & became martyers. Later 'Chipko' movement' was started by Sunderlal Bahuguna and others to prevent cutting of trees. The people showed enormous bravery in protecting trees from the axe of contractors by hugging them.
8. What measures, as an individual, would you take to reduce environmental pollution?
Ans: To reduce environmental pollution we should take following measures:
(i) Reducing use of CFC.
(ii) Disposing off waste safely.
(iii) Reducing use of polythene.
(iv) Not disposing off waste in water bodies.
(v) Making automobiles pollution free.
(iv) Prevention of noise pollution by using fire crackers/TV/musical instruments at permissible limits.
(vii) Tree plantation in school, around residence.
9. Discuss briefly the following:
(a) Radioactive wastes
(b) Defunct ships and e-wastes
(c) Municipal solid wastes
Ans: Radioactive wastes: - Radioactive wastes are produced in the production of nuclear energy from radioactive materials. Nuclear waste is rich in radioactive materials that emit enormous amounts of ionizing radiations such as gamma rays. These rays induce mutation in organisms, which often results in skin cancer. At a high dosage, these rays could become lethal. Safe disposal of radioactive wastes poses the greatest challenge. Nuclear wastes must be stored in shielded containers after pretreatment and then buried into rocks.
Defunct ships and e-wastes: - Dead ships are those which are out of commission. They are scrupped in countries like India and Pakistan. Such ships are a source of different toxicants like asbestos, lead, mercury, etc. Thus, they contribute to hazardous solid wastes. E-wastes or electronic wastes generally include electronic goods which include computers, etc. Such wastes are rich in metals like copper, iron, silicon, gold, and so on. These metals are quite toxic. Severe health hazards are caused by such toxic metals. People of the developing countries get engaged in recycling these metals, thus exposing them to the toxic contents available in these wastes.
Municipal solid wastes: - These are called trash or garbage. It encompasses items like packaging of products, furniture, clothes, bottles, food waste, newspapers, and much more.
Several of the municipal social waste management sources to reduction, recycling and compositing. Source reduction changes the design, manufacture or use of products & materials to reduce the amount and toxicity of what gets thrown away. Recycling sends items such as paper, glass, plastic & metals into anew products. Composting breaks up organic waste such as food scraps & yard trimmings with micro-organisms, resulting in a humus-like substance. Examples of source reduction include consumers' purchasing smaller appliances, paints, batteries etc.
10. What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
Ans: The initiatives were taken for reducing vehicular air pollution in Delhi are :-
(i) Introduction of CNG
(ii) Enforcement of pollution control law
(iii) Introduction of green zones
(iv) Use of unleaded fuels
(v) Replacement of old vehicle with new one. The result is that the air quality of Delhi has improved considerably with a substantial fall in pollutant gases.
(vi)Use of catalytic converters in vehicles.
(vii)Application of Euro II norms for vehicle.
11. Discuss briefly the following:
(a) Greenhouse gases
(b) Catalytic converter
(c) Ultraviolet B
Ans: Greenhouse gases: - Thegreenhouse effect is a general rise in the average temperature of the Earth caused by the presence of greenhouse gases. Mainly, greenhouse gases include carbon dioxide, methane, and water vapour. When the solar radiations struck the Earth, some of these radiations are absorbed. These absorbed radiations are released back into the atmosphere. These radiations get trapped by the greenhouse gases present in the atmosphere. This helps in keeping the Earth warm and therefore contributes to the preservation of humanity. On the other hand, an increase in the concentration of greenhouse gases leads to exaggerated warming of the Earth, which causes global warming.
Catalytic converter: - Catalytic converter 'are used to reduce emission of poisonous gases like nitrogen oxides, carbon monoxide & un reacted hydrocarbon in automotive emission. It is made of platinum, palladium and rhodium and is used as catalyst. It converts unbumt hydrocarbons into CO2. The only precaution required is not to use gasoline having lead as lead inactivates the catalysts of the converter.
Ultraviolet-B: - Ultraviolet-B is electromagnetic radiation that has a shorter wavelength than visible light. It is a harmful radiation which occurs from sunlight and penetrates through the ozone hole onto the surface of the Earth. It triggers many health problems in human beings. 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.
