NCERT Solutions for Class 12 Biology Chapter 16 - Environmental Issues

Aakash NCERT Solutions for Chapter 16 explains in detail the problems that are posing a threat to the ecological balance in nature such as pollution, global warming, deforestation as included in the chapter. The solution for the chapter has also mentioned measures to be taken to control such kind of pollution. Effects of pollution on human life is the most important topic in the chapter and is explained in an easy and simple language in the Aakash NCERT Solutions.

Q1. What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river?
Answer: Domestic sewage refers to the wastewater coming from toilets, kitchens, and washings which is passed into sewer systems. Domestic sewage contains soaps, grit, colloidal particles, fecal matter, small-sized food leftovers, pathogens, nitrates, phosphates, and other salts, etc.
The effects of sewage discharge on a river
1. Sewage discharge causes rise in BOD or biological oxygen demand thus reducing the amount of dissolved oxygen in the river.
2. Sewage discharge cause the disappearance of fishes and some other aquatic animals in the river.
3. Water becomes turbid, odorous and unfit for human drinking.

Q2. List all the waste that you generate, at home, school or during your trips to other places. Could you very easily reduce the generation of these waste? Which would be difficult or rather impossible to reduce?
Answer:
1. In our daily life, we generate a lot of waste at our home, schools, during trips etc. Waste generated at homes- waste paper, old clothes, leather articles, broken crockery, cartons, food leftovers, kitchen wastes etc.
2.Waste generated in schools- paper, discarded pencils, pen refills, cardboards, polyethene bags, fruit peels, wrappers, etc.
3. Waste generated during trips are papers, plastic glasses, plastic bags, fruit bottles, old clothes, eatables, cartons, food wrappers, Aluminium foils, thermocol plates etc.
- Among these waste products, electronic crockery, plastic items, pet bottles and metal cans cannot be reduced. In fact, they are difficult or rather impossible to reduce. They can be sorted by recycling them or dumping them in open landfills. On the other hand, the paper pencil wastes, food items, etc. can be easily reduced by dumping them as they are biodegradable and get degraded by decomposers with time.

Q3. Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
Answer: Global warming can be defined as a rise in the mean temperature of the earth. Global warming is mainly caused due to the increased amounts of greenhouse gases in the atmosphere. These gases allow long wave radiation to enter into the atmosphere but do not let them leave, so these radiations remain trapped in the atmosphere and cause the mean temperature to rise. This is similar to the effect of glass walls in a greenhouse on the plants. The main greenhouse gases are:
1. Carbon dioxide - 60% of global warming is caused by carbon dioxide. The atmospheric concentration of carbon dioxide has risen to 280 ppm in1750 to 380 ppm in 2007 and until 2019 it has risen to above 400. The main reason for the increase in greenhouse gases is the combustion of fossil fuels and deforestation.
2. Methane- It contributes to 20% of global warming. The main reason for increase in greenhouse gases includes incomplete combustions, anaerobic decomposition, gas released from chimneys, paddy fields, etc.
3. Chlorofluorocarbons- These are compounds of carbon and halogens used as propellants in aerosols, refrigerants, fire extinguishers, plastic foams, jet fuels etc.
4. Nitrous oxide- They are responsible for causing 6 % of global warming. It is formed during the combustion of nitrogen-rich fuels.
Effects of global warming
1. Melting of snow- Due to the increase in global temperature, the polar ice caps and snow mountains are melting.
2. Sea level rise- Due to the melting of snow, the sea level will rise leading to submerging of coastal areas.  
3. Odd climatic changes- Global warming will lead to odd climatic changes such as a reduction in precipitation, rise in El Nino effect, more floods and droughts, change in the global air current etc.
4. Vegetation- Forest will be turned into scrub vegetation, tropic will have more deserts.
5. Food production- Global warming may lead to a reduction in food production.
Measures to control global warming
1. Reduction in CFCs production.
2. Increase in forest areas.
3. Reduce fossil fuel exploitation.
4. Checking population growth.

Q4. Write critical notes on the following:
a.Eutrophication
b.Biological magnification
c.Groundwater depletion and ways for its replenishment 
Answer: a.Eutrophication- The term eutrophication is used to refer to the excessive growth of algae, plants in water bodies due to the nutrient enrichment of the water body with nitrogen and phosphorus. Eutrophication can be natural or accelerated. In the case of natural eutrophication, natural ageing causes nutrient enrichment of the water body. This is a slow process that is not detectable in a human lifetime. A young the water body is clear, cold water with no nutrient enrichment. The nutrients are added via runoff and streams draining into it. Gradually the water becomes shallower and accelerated eutrophication, nutrient enrichment is due to human activities like the passage of sewage, industrial effluents and run-off rich in nitrates and phosphates from fertilized fields. These nutrients cause dense growth of plants and planktonic algae over the water body.
Answer: b.Biological magnification
Biological magnification refers to the increase in the concentration of a persistent chemical with the rise in trophic level. The chemical becomes hazardous when its concentration becomes very high. For example, a DDT concentration of 0.003 ppb becomes 0.003 ppm in phytoplankton, 0.04 ppm in zooplankton, 0.5 ppm in small fish, 2.0 ppm in larger fish and 5 ppm in fish-eating birds.

Answer: (c) Groundwater depletion and ways for its replenishment
Groundwater is being pumped out at an enormous rate for its use in agricultural and urban areas resulting in the fall of the water table by 10 m to 30m and depletion of groundwater. Ways of replenishment of groundwater:
1. Rainwater harvesting
2. Sprinkler and sub-surface irrigation techniques
3. Afforestation

Q5. Match the items given in column A and B:

Answer: The correct matching is as follows

Q6. Why does the ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?
Answer: The countries like USA, Japan, and other European countries, emit a lot of ozone-depleting substances such as CFCs, nitrogen oxides, halogens, methane, etc. These chemicals are released in the stratosphere and they drift towards poles before the onset of winters. During winter, ice clouds are formed over Antarctica with no sunrise. It catalyzes the release of Cl from CFCs. During springs, the Cl reacts with ozone and converts it into free oxygen using it for depletion of ozone and formation of the ozone hole.
Effects of enhanced UV radiations
1. Snow blindness
2. Inflammation of cornea
3. Damage of skin cells and development of skin cancer
4. Increased incidence of herpes
5. Damage to nucleic acids and proteins
6. Increased blindness in animals
7. Reduced immunity
8. Reduction in photosynthesis

Q7. Discuss the role of women and communities in protection and conservation of forests.
Answer: The role of women and communities in the protection and conservation of forests can be understood by following two case studies:
1. Bishnoi community- The Bishnoi community in Bishnoi village of Rajasthan fought with the king and his army for the protection of trees. Amrita Devi, a woman of Bishnoi lead this movement and with her daughter and hundreds of other members of her community, embraced the trees and lost their lives in the hands of soldiers. Ultimately the king had to drop this idea of cutting trees for his palace.
2. Chipko movement- In 1974, in the Garhwal region of Himalayas, the Chipko movement was started. During this movement, the villagers hugged the trees and stopped contractors from cutting the trees.
Thus, by means of these two case studies, we can conclude that women and social communities have a very large role to play in the prevention of forests.

Q8. What measures, as an individual, would you take to reduce environmental pollution?
Answer: The following measures can be taken to reduce environmental pollution
1. Planting a greater number of trees.
2. We can reduce the use of fossil fuels by not using our own vehicles for travelling short distances.
3.We should use clean fuel such as CNG in our cars which is environment-friendly as well as pocket-friendly.
4. We must segregate the wastes into biodegradable and non-biodegradable waste products. So that wastes can be easily sorted out.
5. Encourage the practice to reduce, reuse, recycle
6. We must use catalytic converters in vehicles.
7. We should avoid burning crackers.
8. Reduce the use of plastics. We can replace plastic bags with jute bags.

Q9. Discuss briefly the following:
a. Radioactive waste
b. Defunct ships and e-waste
c. Municipal solid waste
Answer: (a) Radioactive Wastes-
These waste products include non-usable discards that possess radioactivity. Radioactive wastes are of three types-
1. Wastes with low-level radioactivity- Include coolant water of atomic reactors, pond water for cooling spent fuel in reactors, etc. They emit very small amounts of radioactivity. Irradiation centers, radiotherapy units, and laboratories also produce wastes with low radioactivity.
2. Wastes with an intermediate level of radioactivity- These include radioactive wastes of many ores which are separated during the refinement of minerals.
3. Wastes with high levels of radioactivity- These include spent fuel of cosmic reactors and leakage from reactors that have a very high level of radioactivity. The radioactive wastes have to be handled very carefully and should be dumped 500 m deep in the earth or inside the sea after placing them inside very thick protective closed containers. These wastes are very dangerous to human beings, animals, microorganisms, etc. High exposure to these radioactive materials can cause mutations and they can even be lethal.
Answer: (b) Defunct ships and e-waste
The dead ships which are not in use are called defunct ships. Defunct ships can be broken down for scrap metal in some countries. Defunct ships can act as a source of heavy metals such as asbestos, lead, mercury etc. E- wastes also called electronic wastes include waste products generated from electronic goods such as computers, televisions, refrigerators etc. These wastes are highly toxic and can pose serious threats to humans and animals.
Answer: (c) Municipal solid waste
The solid waste generated from schools, offices, homes, stores, etc. is known as municipal solid wastes. The municipal solid wastes include food, articles, stationery, rubber, leather, textiles etc. The municipal solid waste is necessary to dispose properly as it acts as a breeding site for mosquitoes thus leading to diseases like dengue, malaria etc. The methods used for safe disposal of solid wastes include sanitary landfills and incineration.

Q10. What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
Answer: Delhi is considered to be one of the most polluted cities. The major reasons for Delhi being polluted include increased fossil fuel consumption, increased number of industries etc. Government s taken several steps in order to minimize vehicular air pollution. Some of these steps are as follows:
1. Introduction of CNG- The supreme court of India in the year 2006, in order to reduce the air pollution, decided that all the public transports such as buses, autos etc. will have to use CNG (compressed natural gas). This is a clean fuel that spreads less pollution.
2. Use of unleaded petrol and non-Sulphur petrol and diesel.
3. Phasing out of old vehicles because they cause more pollution.
4. Use of catalytic converters in automobiles.
5. Implementation of BHARAT stage I in order to control pollution levels
All these steps led to a reduction in the pollution levels in Delhi. The air quality has improved after this as there is a fall in carbon dioxide and sulfur oxide levels in the air.

Q11. Discuss briefly the following:
a.Greenhouse gas
b.Catalytic converter
c.Ultraviolet B
Answer: a.Greenhouse Gases-
The gases which cause the greenhouse effect are called greenhouse gases e.g., carbon dioxide, methane, chlorofluorocarbon, nitrous oxide etc. Greenhouse gases allow long wave radiation to enter into the atmosphere but do not let them leave, so these radiations remain trapped in the atmosphere. This causes the greenhouse effect. This is similar to the effect of glass walls in a greenhouse on the plants. The contribution of Carbon dioxide, methane, chlorofluorocarbons, and nitrous oxide in causing global warming is 60%, 20%,14%, and 6% respectively.
1. Carbon dioxide- The atmospheric concentration of carbon dioxide has risen from 280 ppm in 1750 to 380 ppm in 2007 and until 2019 it has risen to above 400. The main reason for the increase in the combustion of fossil fuels and deforestation.
2. Methane- The main reason for increase includes incomplete combustions, anaerobic decomposition, chimneys, paddy fields, etc.
3. Chlorofluorocarbons- These are compounds of carbon and halogens used as propellants in aerosols, refrigerants, fire extinguishers, plastic foams, jet fuels.
4. Nitrous Oxide-It is formed during the combustion of nitrogen-rich fuels.
Answer: b.Catalytic converter
Catalytic converter refers to a device co tai g platinum, palladium and rhodium that is fitted in the automobiles. The major functions of catalytic converters in the automobile are:
1.Complete oxidation of unburnt hydrocarbons
2. Oxidation of carbon monoxide into carbon dioxide
3. Conversion of nitrogen oxides into nitrogen
While using catalytic converters, we must not use gasoline with lead as lead inactivates the catalysis of the converter.
Answer: c.Ultraviolet B
The part of ultraviolet radiation having a wavelength of 280-320 nm. UV-B is harmful to organisms. The ozone layer in the stratosphere absorbs 50% of total UV-B. Due to depletion of ozone, mostly UV-B radiations reach the Earth. In humans, UV radiation causes snow blindness, cataract, skin cancer, skin ageing, mutations etc.