GSEB Class 12 Biology Solutions Chapter 16 Environmental Issues

GSEB Solutions Class 12 Biology Chapter 16 Environmental Issues

Gujarat Board Textbook Solutions Class 12 Biology Chapter 16 Environmental Issues

GSEB Class 12 Biology Environmental Issues Text Book Questions And Answers

 

Question 1. What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
Answer: Domestic sewage primarily comprises biodegradable pollutants, including animal and human excreta, dissolved organic compounds, along with nitrates, phosphates, sodium, potassium, calcium, and chloride ions. While these pollutants typically decompose rapidly, their accumulation in significant quantities in open fields can lead to environmental issues.
Sewage can also seep through the soil, reaching the water table and contaminating drinking water sources. Furthermore, its discharge into rivers can lead to the death of fish and other aquatic animals due to reduced oxygen content. It also promotes the excessive growth of microorganisms, such as algal blooms, and aquatic vegetation. This entire process is termed eutrophication. Under these circumstances, the oxygen level in the water becomes very low, leading to putrefaction and degradation of the river ecosystem. The high proliferation of microorganisms subsequently increases the water's biological oxygen demand (BOD). BOD serves as a measure of the oxygen required by bacteria to break down organic matter in a water sample over five days.
In simple words: Domestic sewage contains organic matter and nutrients that, when discharged into rivers, deplete oxygen, kill aquatic life, and cause excessive algal growth (eutrophication), ultimately degrading the water quality.

🎯 Exam Tip: When discussing sewage effects, always mention oxygen depletion (BOD), eutrophication, and contamination of water sources for comprehensive scoring.

 

Question 2. 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: Common wastes produced at home, school, or during travel include food scraps, plastic bottles and wrappers, and used clothing. Among these, plastic waste is a category that can be significantly reduced by opting for biodegradable alternatives. Other waste types are generally challenging or impossible to eliminate entirely.
In simple words: We generate wastes like food, plastic, and clothes. Plastic waste is easily reducible by using eco-friendly materials, but other waste types are harder to eliminate completely.

🎯 Exam Tip: Focus on distinguishing between easily reducible wastes (like plastics with alternatives) and those that are inherently difficult to avoid for a complete answer.

 

Question 3. Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
Answer: Global warming is primarily caused by an excessive increase in greenhouse gases, which trap infrared radiation in the atmosphere, leading to a rise in global temperatures. Carbon dioxide is the most significant greenhouse gas, contributing to 60% of global warming, with its levels constantly rising due to deforestation and fossil fuel burning. Other gases such as methane, chlorofluorocarbons (CFCs), and nitrous oxide have also increased since the 18th century. Industrialized nations have the highest per capita CO2 emissions, and rapidly developing countries like China and India are expected to contribute substantial amounts of CO2 in the future. The oceans absorb approximately 60 times the atmospheric CO2, and increased oceanic CO2 levels can lower ocean water pH, negatively impacting marine organisms.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख 1880 से 2000 तक वैश्विक तापमान के रुझान को दर्शाता है। यह ग्राफ वर्षों के साथ तापमान में लगातार वृद्धि को प्रदर्शित करता है, जो पृथ्वी के गर्म होने की प्रवृत्ति को उजागर करता है।

Drought is a severe problem resulting from climatic changes induced by greenhouse warming. A three-degree warming could lead to a 10% decrease in precipitation, and increased evaporation would further reduce water availability for agricultural, municipal, and industrial use.
International concern over global warming led to the Kyoto Protocol meeting in December 1997, where 160 nations participated. The U.S. proposed stabilizing greenhouse gas emissions to 1990 levels between 2008-2012, but developing countries raised concerns about the economic implications. Global temperature records show that the 1980s were the warmest decade, and the 1990s continued this trend, with 2000 being the warmest year on record at that time.
Another damaging consequence is the rise in sea level. Even if atmospheric gas imbalances are corrected, sea levels are projected to continue rising for an extended period. This complex phenomenon is primarily attributed to two factors:
1. **Thermal expansion of water:** As the Earth heats up, water expands. Estimates suggest that over the last 100 years, global sea levels rose by 1-2.5 mm annually, or 10-25 cm in total. This expansion is a major cause of sea level rise, and its impact is uneven across the globe due to varying water temperatures.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह ग्राफ 1990 से 2100 तक समुद्र के स्तर में अनुमानित वृद्धि को दर्शाता है। इसमें उच्च, सर्वोत्तम और निम्न वृद्धि के परिदृश्यों को दिखाया गया है, जिससे छात्रों को भविष्य में समुद्र के स्तर में बदलाव की सीमा को समझने में मदद मिलती है।

2. **Melting of glaciers:** Glaciers, particularly in the European Alps, have been retreating since the mid-20th century. Large amounts of ice from mountain tops are melting and flowing into oceans, contributing to sea level rise. Over the last century, glacier retreat added 2-5 cm to the global sea level. Many smaller glaciers are expected to disappear entirely.

**Approaches to deal with global warming:**
Mitigation strategies aim to stabilize atmospheric greenhouse gas concentrations. These include:
- Reducing greenhouse gas emissions by limiting fossil fuel use and switching to renewable energy sources like hydrogen fuel cells, wind, solar, tidal, ocean, and geothermal power.
- Adopting energy conservation methods, such as improving vehicle fuel efficiency.
- Implementing Carbon Capture and Storage (CCS) by capturing CO2 from large sources like power plants and storing it safely underground instead of releasing it.
- Practicing Carbon Sequestration, which involves removing carbon from the atmosphere through various artificial means.
- Increasing vegetation cover, especially forests, for photosynthetic utilization of CO2.
- Minimizing nitrogen fertilizer use in agriculture to reduce N2O emissions.
- Developing substitutes for chlorofluorocarbons (CFCs), such as hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs).
The melting of polar ice sheets due to global warming will directly affect sea level rise, threatening coastal cities and freshwater resources, agricultural lands, and biodiversity. Current estimates project a sea level rise of 15 cm by 2030 and about 50 cm by the end of the 21st century.
In simple words: Global warming is caused by increased greenhouse gases trapping heat, leading to rising temperatures, droughts, and sea level rise from thermal expansion and melting glaciers. Control measures involve reducing fossil fuel use, promoting renewables, carbon capture, afforestation, and efficient energy use.

🎯 Exam Tip: When explaining global warming, remember to cover both causes (greenhouse gases, deforestation) and effects (droughts, sea level rise), and list specific mitigation strategies for a complete answer.

 

Question 4. Match the items given in columns A and B:

Column A	Column 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

Answer: (a. ii b. i c. iii d. iv)

In simple words: This question matches pollution control devices and methods with the types of pollution they address. For example, catalytic converters handle vehicular emissions, and landfills manage solid waste.

🎯 Exam Tip: For matching questions, identify the core function of each item in Column A and relate it directly to the corresponding pollutant or problem in Column B.

 

Question 5. Write critical notes on the following:
a. Eutrophication
b. Biological magnification
c. Groundwater depletion and ways for its replenishment
Answer:
(a) **Eutrophication:** This phenomenon occurs when domestic sewage and agricultural fertilizers introduce large quantities of nutrients, such as nitrates and phosphates, into freshwater ecosystems. This abundant nutrient supply stimulates rapid growth of blue-green algae, green algae, and other planktons. The increased biological productivity of water bodies, driven by this nutrient enrichment, is known as eutrophication.
(b) **Biological magnification:** Certain chemicals used in biocides are not degradable or degrade very slowly. The long-term effects of these chemicals pose a significant threat to ecological security. Indiscriminate use can integrate them into the Earth's biological, geological, and chemical cycles. Once absorbed by an organism, these pollutants cannot be metabolized or excreted and accumulate in fat-containing tissues. For instance, if a non-degradable pollutant like DDT enters a pond, it moves up the food chain: from plants to zooplankton, then to fish, and finally to fish-eating birds. A concerning aspect is that DDT concentration continuously increases at successive trophic levels, a process termed biological amplification or biological magnification.
(c) **Groundwater depletion and ways for its replenishment:** Due to increasing population and urbanization, groundwater levels are steadily declining. Replenishment strategies include rainwater harvesting, protecting natural water bodies, and promoting responsible water usage to prevent over-extraction.
In simple words: Eutrophication is nutrient enrichment in water causing algal blooms. Biological magnification is the increasing concentration of toxins up the food chain. Groundwater depletion is the decline in underground water levels, which can be fixed by rainwater harvesting and protecting water sources.

🎯 Exam Tip: For descriptive notes, define the term clearly, explain its causes and effects, and for solutions, list practical and sustainable measures.

 

Question 6. Why ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?
Answer: The ozone layer, a denser form of oxygen, shields Earth from harmful ultraviolet (UV-B) radiation. Without it, the planet's inhabitants and environment would be exposed to damaging UV-B rays. Scientists observed significant seasonal variations in stratospheric ozone levels over Antarctica as early as the 1950s. In the 1970s, Sherwood Rowland and Mario Molina proposed that the decreasing wintertime ozone levels over Antarctica were due to the increasing use of chlorofluorocarbons (CFCs) in refrigerants, aerosol propellants, and plastic foam manufacturing. This finding was later confirmed by the National Academy of Sciences.
CFC molecules deplete the ozone layer by migrating to the stratosphere, accumulating over the Antarctic ice cap during the cold winter months. There, they become trapped on polar stratospheric clouds, isolated from normal atmospheric circulation. When sunlight returns to Antarctica in early spring, its ultraviolet rays initiate a chemical reaction that releases a chlorine-oxide-free radical. This radical then triggers further reactions that break down oxygen molecules, forming the ozone layer.
A global increase in CFC production and release (around 1 million tons per year) led to atmospheric CFC levels rising from 0.8 parts per billion in 1950 to at least 4 parts per billion by the end of the century. CFC gases act as catalysts, and in conjunction with UV rays, they thin the ozone layer, leading to the formation of the ozone hole.

**Effects of enhanced UV-B radiation due to ozone depletion:**
If the ozone layer is depleted, dangerous UV-B radiation penetrates to Earth, causing:
- Skin cancer, cataracts, and other severe human diseases.
- Diminished immune system function.
- Adverse effects on photosynthesis.
- Increased production of ozone in the lower atmosphere, leading to photochemical smog.
In simple words: The ozone hole forms over Antarctica primarily due to CFCs released into the atmosphere, which break down ozone when exposed to UV radiation in spring. Increased UV radiation then causes skin cancer, cataracts, weakened immunity, affects plant photosynthesis, and leads to smog.

🎯 Exam Tip: When explaining the ozone hole, remember to link CFCs, polar stratospheric clouds, and the catalytic destruction of ozone. For effects, list both human health impacts and environmental consequences.

 

Question 7. Discuss the role of women and communities in the protection and conservation of forests.
Answer:
(i) **Bishnois:** The Bishnois, followers of Guru Janbeshwar Maharaj, are a small community near Jodhpur, Rajasthan, known for their harmonious coexistence with nature. In 1731, when the King of Jodhpur needed wood for a new palace, his men attempted to cut trees in a Bishnoi village. The Bishnois resisted this effort. A Bishnoi woman, Amrita Devi, bravely hugged the trees, challenging the King's men to cut her first. Tragically, she, her three daughters, and 100 other Bishnois lost their lives protecting the trees. Today, the Amrita Devi Bishnoi Wildlife Protection Award is given to individuals or communities from rural areas demonstrating courage and dedication to wildlife and forest protection.
(ii) **Chipko movement:** In 1974, local women in the Garhwal Himalayas showed immense courage by physically embracing trees to protect them from contractors' axes. This movement highlighted community-led conservation efforts.
(iii) **Appiko movement:** This movement emphasized conservation, plantation, and the rational use of forest resources, promoting sustainable practices.
(iv) **Joint Forest Management (JFM):** The Indian government introduced the concept of JFM in the 1980s. This initiative aimed to foster collaboration between the forest department and local communities for forest protection and management. In exchange for their services, communities received various benefits, and forests were sustainably conserved, yielding products like fruits, gum, rubber, and medicine.
In simple words: Women and local communities have played a crucial role in forest conservation through movements like the Bishnoi sacrifice, Chipko, and Appiko, and through formal initiatives like Joint Forest Management, demonstrating their dedication to protecting natural resources.

🎯 Exam Tip: Highlight specific historical examples like the Bishnoi and Chipko movements, along with government initiatives like JFM, to demonstrate the diverse roles of communities in forest conservation.

 

Question 8. What measures, as an individual, you would take to reduce environmental pollution?
Answer: As an individual, I would take the following measures to reduce environmental pollution:
- Encourage afforestation by planting more trees.
- Prevent deforestation by advocating against tree cutting.
- Promote controlled tapping of groundwater to prevent depletion.
- Reduce the production and use of plastics and chemical sprays.
- Use solar energy as an alternative to petroleum gases.
- Protect ponds and other water bodies from contamination.
In simple words: Individuals can reduce pollution by planting trees, avoiding deforestation, conserving groundwater, minimizing plastic and chemical use, choosing solar energy, and protecting local water sources.

🎯 Exam Tip: Provide a diverse list of actions covering different types of pollution (air, water, land) and energy sources to show a holistic understanding of individual responsibility.

 

Question 9. Discuss briefly the following:
a. Radioactive wastes
c. Municipal solid wastes
Answer:
**Radioactive wastes – Nuclear energy:** While nuclear energy is a source of non-polluting electricity, it presents two significant problems:
- Accidental leakage, as seen in incidents like Chernobyl.
- Safe disposal of radioactive waste, which remains a major challenge.
Radiations are highly detrimental to organisms, causing mutations at very high rates. High doses are lethal, while lower doses lead to various disorders such as cancer, anomalies, and genetic defects. Disposal is a critical concern. Low- and intermediate-level wastes that do not generate excessive heat or other severe environmental problems are typically managed by dumping them in suitable containers. However, high-level wastes, which release substantial heat and pose significant environmental risks, are placed in specialized containers and buried approximately 500 meters deep within stable rock formations.
(b) **Defunct ships and e-wastes:** Old ships are often dismantled in developing countries to recover scrap and other valuable materials, primarily due to lower labor costs and taxes. Workers involved in ship breaking are exposed to numerous toxicants, including asbestos, lead, and mercury. The coastal areas surrounding ship-breaking yards also become significantly polluted.
**E-wastes (electronic wastes):** The volume of e-waste is escalating rapidly due to increased use of electronic equipment and swift technological changes. Valuable metals like copper, iron, silicon, nickel, and gold are extracted from e-waste. However, the dismantling process also exposes workers to toxic substances.
(c) **Municipal solid wastes:** These include domestic waste, office waste, school waste, public sweeping debris, sludge from sewage treatment plants, and waste from vegetable and fruit markets. Municipal solid waste can be either biodegradable or non-biodegradable. It typically comprises paper (40%), food waste (7%), glass, crockery, rubber, leather, plastics, etc. Disposal methods include feeding to pigs and cattle, salvage, burning, incineration, landfills, pyrolysis (heat treatment), composting, biogas plants, and recycling.
In simple words: Radioactive wastes are harmful due to their mutational effects and pose a significant disposal challenge. Defunct ships and e-wastes involve toxic substances during dismantling and processing. Municipal solid wastes are a mix of biodegradable and non-biodegradable items disposed of through various methods like landfills, composting, and recycling.

🎯 Exam Tip: For each waste type, briefly explain its composition, highlight key hazards (e.g., radiation, toxins), and mention the common disposal or management strategies.

 

Question 10. How has Delhi Govt, succeeded in reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
Answer: Delhi has historically faced severe air pollution due to its extensive vehicular traffic, ranking among the most polluted cities globally in the 1990s. The registered vehicular population almost doubled from 2.2 million in 1994 to 4.5 million, with an annual growth rate of 10%, primarily comprising two-wheelers.
Vehicular pollution significantly contributes to Delhi’s air quality issues. According to the Central Pollution Control Board, vehicular emission load increased by nearly 50% between 1990-91 and 1995-96. However, various control measures implemented in recent years have led to a noticeable decrease in emissions. The estimated vehicular emission load reported by the Central Pollution Control Board is:

Pollutant	Pollution load (in ton/day)
Carbon Monoxide	421.84
Hydrocarbons	184.37
Nitrogen oxides	110.45
Particulate Matter	12.77
Total Pollution Load	729.43

**Steps taken by Delhi Govt, to reduce the Pollution in Delhi:**
- **Pollution Checking by Transport Department:** Mobile enforcement teams are regularly deployed to prosecute polluting vehicles and those lacking Pollution Under Control (PUC) Certificates.
- **Public Awareness:** Campaigns are conducted to raise public awareness about health hazards of air pollution and the importance of engine tuning and maintenance.
- **Catalytic Converters:** Since April 1995, all new 4-wheeled petrol-driven vehicles registered in Delhi must be fitted with catalytic converters.
- **Mass Rapid Transport System (MRTS):** The MRTS is being developed to provide a non-polluting, efficient, and affordable rail-based mass transport system for Delhi, integrated with other transport modes.
- **Phasing out of Old Commercial Vehicles:** The Supreme Court, through its orders (CWP No. 13029 of 1985), banned the operation of certain categories of vehicles in Delhi: commercial/transport vehicles older than 15 years, autos and taxis running on conventional fuels, and diesel-driven city buses.
- **Fiscal Incentives:** The Delhi government offers sales tax exemptions and interest subsidies on loans for purchasing new replacement vehicles. All Delhi buses have been converted to run on compressed natural gas (CNG).
- **Tightening of Mass Emission Standards:** New mass emission norms were introduced in 1991 and tightened further in 1996 and 2000. Currently, all vehicles (except 2- and 3-wheelers) must comply with Bharat Stage III/Euro-III emission norms, while 2- and 3-wheelers comply with Bharat Stage II/Euro-II norms for registration in Delhi.
- **Improvement in Fuel Quality:** The quality of fuel supplied in Delhi has been significantly improved in recent years.
In simple words: The Delhi Government has reduced vehicular air pollution through measures like mandatory catalytic converters, phasing out old commercial vehicles, converting buses to CNG, implementing stricter emission norms, improving fuel quality, and promoting public transport like the MRTS. These efforts have led to a noticeable improvement in air quality.

🎯 Exam Tip: When discussing government initiatives, provide specific examples of regulations (e.g., catalytic converters, emission norms), infrastructure improvements (MRTS), and awareness campaigns for a comprehensive answer.

 

Question 11. Discuss briefly the following:
a. Greenhouse gases b. Catalytic converter c. Ultraviolet B
Answer:
(a) **Greenhouse gases:** Due to overpopulation, deforestation, and industrial/domestic coal burning, significant amounts of carbon dioxide are released into the environment. Additionally, gases like carbon monoxide from automobiles, chlorofluorocarbons (CFCs), methane (CH4), and nitrous oxide (N2O) also increase in the atmosphere. These gases possess the ability to absorb infrared radiation. Known as greenhouse gases, they form an insulating layer around Earth, preventing heat re-radiation back into space. Consequently, these radiations are reflected back to Earth, contributing to global warming.
(b) **Catalytic converter:** This is a reaction chamber containing a finely divided platinum-iridium catalyst. Exhaust gases from automotive engines, mixed with excess air, pass through this converter. The catalyst oxidizes pollutants like carbon monoxide and hydrocarbons into less harmful substances: carbon dioxide and water.
(c) **Ultraviolet B (UV-B):** This refers to a range of invisible radiation wavelengths, approximately 4 nanometers (at the border of the X-ray region) to about 380 nanometers (just beyond the violet in the visible spectrum). UV-B radiation is a harmful component of sunlight that can cause damage to living organisms.
In simple words: Greenhouse gases (like CO2, CH4, N2O, CFCs) trap infrared radiation, warming the Earth. Catalytic converters use catalysts (platinum-iridium) to convert harmful vehicle exhaust gases into less toxic ones. Ultraviolet B (UV-B) is a segment of harmful invisible radiation from the sun.

🎯 Exam Tip: For definitions of scientific terms, provide a clear, concise explanation of what they are and their primary function or impact, as applicable.

GSEB Class 12 Biology Environmental Issues Additional Important Questions And Answers

 

Question 1. Name any 3 gases contributing to greenhouse effect.
Answer: Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).
In simple words: Three main gases that cause the greenhouse effect are carbon dioxide, methane, and nitrous oxide.

🎯 Exam Tip: Memorize the most prominent greenhouse gases for quick recall in short answer questions.

 

Question 2. Name an instrument used in vehicles to reduce air pollution.
Answer: Catalytic converters.
In simple words: Catalytic converters are devices in vehicles that help reduce harmful air pollution.

🎯 Exam Tip: Link specific devices to their environmental function, like catalytic converters for reducing vehicular emissions.

 

Question 3. What are ODS. Give examples.
Answer: Ozone-depleting substances (ODS) are specific compounds that react with and destroy ozone present in the stratosphere. Major examples of ODS include chlorofluorocarbons (CFCs), halons (gases used in fire extinguishers, such as bromochlorofluoromethane), nitrous oxide (N2O), methane (CH4), and chlorine (Cl).
In simple words: ODS are chemicals that destroy the ozone layer, with common examples being CFCs, halons, nitrous oxide, and methane.

🎯 Exam Tip: Define ODS by their action (destroying stratospheric ozone) and provide at least two distinct examples for full credit.

 

Question 4. Name the Act passed by the Government of India to protect and improve the quality of our environment.
Answer: Environment (Protection) Act, 1986.
In simple words: The Environment (Protection) Act of 1986 is the law enacted by the Indian government to safeguard and enhance environmental quality.

🎯 Exam Tip: Remember key environmental legislation and the year it was enacted for direct questions.

 

Question 6. What is the name given to irreparable computers and other electronic goods?
Answer: Electronic waste (e-waste).
In simple words: Broken or unusable electronic items like computers are called e-waste.

🎯 Exam Tip: Use the standard terminology for common environmental issues, such as 'e-waste' for electronic goods.

 

Question 7. Inflammation of cornea due to high dose of UV-B radiation is called
Answer: Snow blindness.
In simple words: Intense UV-B radiation can cause inflammation of the cornea, commonly known as snow blindness.

🎯 Exam Tip: Associate specific health effects with their environmental causes, like snow blindness with UV-B exposure.

 

Question 8. Motor vehicles equipped with catalytic converter should use only unleaded petrol. Justify.
Answer: Catalytic converters in motor vehicles require unleaded petrol because lead present in leaded petrol inactivates the catalyst. The catalyst (typically platinum-iridium or rhodium) in the converter works to convert harmful pollutants into less toxic substances. Lead can coat the catalyst's surface, rendering it ineffective and preventing the reduction of emissions like carbon monoxide, hydrocarbons, and nitrogen oxides.
In simple words: Catalytic converters need unleaded petrol because lead in fuel damages and deactivates the catalyst, making the converter unable to reduce harmful emissions effectively.

🎯 Exam Tip: Explain the mechanism of catalyst deactivation by lead to justify the use of unleaded petrol with catalytic converters.

 

Question 9. Many villagers near Industrial are sufferers from "blue baby syndrome! How is this problem caused?
Answer: Villagers residing near industrial areas often suffer from "blue baby syndrome" (methemoglobinemia). This condition is caused by water pollution, specifically when industrial discharges introduce nitrate-containing impurities into the water supply. When individuals, particularly infants, consume this nitrate-contaminated water, the nitrites convert into nitrates in the body. Nitrates then enter the bloodstream and oxidize the ferrous iron in hemoglobin to ferric iron, forming methemoglobin. Methemoglobin cannot effectively carry oxygen, thus reducing the blood's oxygen-carrying capacity. This oxygen deprivation leads to cyanosis, manifesting as a bluish discoloration of the skin in infants, commonly known as blue baby syndrome.
In simple words: Blue baby syndrome is caused by drinking water contaminated with industrial nitrates. These nitrates convert hemoglobin into methemoglobin, which cannot carry oxygen, leading to the baby's skin turning blue due to lack of oxygen.

🎯 Exam Tip: Detail the chemical process (nitrate to nitrite, ferrous to ferric iron) and its physiological consequence (reduced oxygen carrying capacity) for a comprehensive explanation of blue baby syndrome.

 

Question 10. We have got used to associating loud sounds with pleasure and entertainment not realising that noise causes psychological and physiological disorders in humans. Comment on the various ill effects of noise in human.
Answer: While loud sounds are often associated with pleasure and entertainment, excessive noise can have severe psychological and physiological effects on humans.
**Various ill effects of noise in humans include:**
- Brief exposure to extremely high sound levels (150 dB or more) can cause irreversible damage to eardrums.
- Chronic exposure to relatively lower noise levels, common in urban areas, can permanently impair human hearing ability.
- Noise contributes to sleeplessness, increased heart rate, altered breathing patterns, and elevated stress levels.
In simple words: Constant exposure to loud noise can cause ear damage, permanent hearing loss, and lead to stress, sleep problems, and heart rate changes.

🎯 Exam Tip: Categorize noise effects into acute (eardrum damage) and chronic (hearing loss, stress, sleep issues) for a structured answer.

 

Question 11. Briefly explain the different measures to reduce noise pollution.
Answer: Measures to reduce noise pollution include:
- Reducing industrial noise by using sound-absorbent materials or by muffling machinery.
- Establishing horn-free zones around sensitive areas like hospitals and schools.
- Limiting the use of loudspeakers, especially during late hours (e.g., from 9 pm – 9 am).
- Restricting the use of crackers to permissible sound levels.
In simple words: Noise pollution can be reduced by using sound-absorbing materials in industries, creating horn-free zones, limiting loudspeaker use, and restricting firecracker noise.

🎯 Exam Tip: Provide practical and implementable measures, differentiating between source control (industries, crackers) and regulatory actions (horn-free zones, loudspeaker limits).

 

Question 12. CNG is better than other conventionally used fossil fuels. Comment.
Answer: Compressed Natural Gas (CNG) is considered superior to other conventional fossil fuels due to several advantages:
- CNG burns more efficiently, resulting in very little unburnt residue.
- It is generally cheaper than petrol or diesel.
- CNG cannot be siphoned off by thieves, enhancing security.
- It is difficult to adulterate CNG, ensuring better fuel quality.
In simple words: CNG is a better fossil fuel because it burns cleanly, is cheaper, cannot be stolen easily, and is hard to adulterate, making it more efficient and reliable.

🎯 Exam Tip: Focus on the economic (cheaper), environmental (efficient burning), and practical (security, no adulteration) benefits of CNG compared to other fossil fuels.

 

Question 13. What is meant by algal bloom?
Ans: Algal bloom refers to the excessive growth of certain phytoplankton in water bodies, facilitated by the abundant presence of nutrients.
In simple words: An algal bloom is when too many nutrients in water cause a rapid overgrowth of algae or phytoplankton, making the water look discolored.

🎯 Exam Tip: Define algal bloom by mentioning excessive phytoplankton growth and nutrient enrichment as the primary cause.

 

Question 14. Write a short note on algal bloom.
Answer: Algal bloom occurs when an excess of nutrients, particularly nitrates and phosphates, enters water bodies. These nutrients promote the rapid proliferation of planktonic algae, which impart a distinct color to the water. While algal blooms are a natural phenomenon, human activities such as agricultural runoff and sewage discharge often exacerbate them. Excessive algal growth can severely deteriorate water quality, deplete dissolved oxygen as the algae decompose, and lead to the mortality of fish and other aquatic organisms. Some bloom-forming algae can also produce toxins, posing risks to human beings and animals that consume contaminated water.
In simple words: Algal bloom is the rapid growth of algae due to excess nutrients in water, which can deplete oxygen, harm aquatic life, and produce toxins, degrading water quality and impacting ecosystems.

🎯 Exam Tip: A comprehensive note on algal bloom should include its cause (nutrient excess), visual characteristic (discoloration), and its negative impacts on water quality and aquatic life, including toxicity.

Question 15. Sewage treatment can be done by integrating artificial and natural processes. Explain this using the example of Areata town.
Answer: The residents of Arcata, in collaboration with biologists, developed an integrated wastewater treatment system operating within a natural framework. The water purification process occurs in two distinct stages. Initially, conventional treatments involving sedimentation, filtration, and chlorine are applied. Subsequently, remaining pollutants are addressed in the second phase. Biologists established a sequence of six interconnected marshes spanning over 60 hectares of marshland. Specific plants, algae, fungi, and bacteria were introduced into this area, designed to neutralize, absorb, and assimilate pollutants. As the water flows through these marshes, it undergoes natural purification.
In simple words: Arcata developed a two-stage sewage treatment system. First, traditional methods like filtration and chlorination are used. Then, the water flows through constructed marshes with special plants and microbes that naturally clean the remaining pollutants.

🎯 Exam Tip: When explaining integrated waste-water treatment, ensure you detail both the conventional (physical/chemical) and ecological (biological/natural) stages, highlighting the role of each in purification and mentioning key examples like Arcata's project.

 

Question 16. Are sanitary landfills a practical solution to dispose solid waste? Why?
Answer: Sanitary landfills are not truly a sustainable solution because the volume of garbage produced, especially in metropolitan areas, has increased to such an extent that these sites quickly fill up. Furthermore, there is a significant risk of chemicals leaching from these landfills, potentially contaminating underground water sources.
In simple words: No, sanitary landfills are not very practical because they quickly get full with too much garbage, and chemicals from them can leak and pollute our groundwater.

🎯 Exam Tip: For questions on waste management, always discuss both the advantages (e.g., immediate disposal) and disadvantages (e.g., land use, pollution risk) of methods like landfills. Focus on the long-term sustainability aspect.

 

Question 17. Enumerate some important measures for controlling global warming.
Answer: Key measures to mitigate global warming include:
- Reducing the consumption of fossil fuels.
- Enhancing energy usage efficiency.
- Decreasing deforestation rates.
- Engaging in extensive tree planting.
In simple words: To control global warming, we need to burn fewer fossil fuels, use energy more efficiently, stop cutting down forests, and plant more trees.

🎯 Exam Tip: When listing measures for environmental issues, categorize them into broad areas like energy, land use, and individual actions for a comprehensive answer. Prioritize impactful solutions.

 

Question 18. Global warming is due to the greenhouse effect. Explain both the greenhouse effect and global warming.
Answer: The greenhouse effect refers to the natural phenomenon where specific atmospheric gases, such as CO\(_{2}\), CH\(_{4}\), NO\(_{2}\), and CFCs, trap infrared radiation, causing the Earth's surface to warm. Global warming, on the other hand, is the observed increase in the Earth's average global temperature, primarily driven by an amplified greenhouse effect resulting from increased concentrations of these greenhouse gases due to human activities.
In simple words: The greenhouse effect is when gases in our atmosphere trap heat, naturally warming the Earth. Global warming is the additional, man-made increase in Earth's temperature because we've added too many of these heat-trapping gases.

🎯 Exam Tip: Clearly differentiate between the natural "greenhouse effect" and the human-enhanced "global warming." Emphasize the role of specific greenhouse gases and the impact of human activities on their atmospheric concentration.

 

Question 19. "Eutrophication can lead to the death of a lake” Discuss.
Answer: Eutrophication can indeed lead to the death of a lake through a series of detrimental processes.
- The primary pollutants in sewage, industrial discharges, and agricultural runoff are nitrates and phosphates.
- These abundant nutrients stimulate rapid proliferation of algae, often resulting in dense algal blooms.
- The excessive growth and subsequent decomposition of these algae by bacteria consume a large amount of dissolved oxygen in the water bodies, creating hypoxic or anoxic conditions. This severe reduction in oxygen levels causes the death of aquatic organisms like fish.
- Additionally, other toxic substances that flow into the lake can further harm and kill fish and other aquatic life.
- The decomposition of these dead organisms further depletes oxygen levels in the water, exacerbating the problem.
- Ultimately, this cascade of events leads to the ecological demise of the lake.
In simple words: Eutrophication kills lakes by overfeeding algae with pollutants. The algae grow excessively, then die and decompose, using up all the oxygen in the water. This lack of oxygen suffocates and kills fish and other aquatic life, eventually leading to the lake's ecological death.

🎯 Exam Tip: When discussing eutrophication, detail the complete cause-and-effect chain: nutrient input -> algal bloom -> oxygen depletion -> aquatic life mortality -> lake degradation. Mention key nutrients like nitrates and phosphates.

 

Question 20. You have been appointed as the minister for food, agriculture, and the environment. Write down 6 laws you would like to implement in order to save our environment (write in the order of priority).
Answer: As minister, I would propose the following laws to protect our environment, prioritized for maximum impact:
- Encourage widespread afforestation through national programs.
- Implement strict measures to prevent deforestation and illegal logging.
- Establish regulations for controlled tapping of groundwater to ensure sustainable use.
- Mandate the reduction in production and use of non-biodegradable plastics and chemical sprays.
- Promote the widespread adoption of solar energy as a replacement for petroleum gases.
- Enact laws for the protection and restoration of all natural ponds and water bodies.
In simple words: As minister, I'd prioritize planting more trees, stopping deforestation, managing groundwater, reducing plastic and chemical use, switching to solar energy, and protecting natural water bodies to save our environment.

🎯 Exam Tip: When suggesting policy measures, aim for a balanced approach that covers different aspects of environmental protection, such as resource management, pollution control, and biodiversity conservation. Justify your prioritization if asked.

 

Question 21. What would be the impact on the environment around a thermal power plant if its electrostatic precipitator stops functioning? Give a reason.
Answer: An electrostatic precipitator is highly efficient, capable of removing approximately 99% of particulate matter from the exhaust gases of a thermal power plant. If it ceases to function, a massive amount of fine particulate matter will be released into the atmosphere. This will lead to significant air pollution in the surrounding environment, causing breathing and respiratory issues, irritation, inflammation, and damage to the lungs in humans and animals, and potentially resulting in premature deaths.
In simple words: If an electrostatic precipitator at a thermal power plant stops working, a lot of harmful tiny particles will be released into the air. This will cause severe air pollution, leading to breathing problems, lung damage, and increased health risks for people and animals nearby.

🎯 Exam Tip: When discussing pollution control devices, explain their function (what they remove and how effectively) and then detail the specific environmental and health impacts that would occur if they fail. Focus on the direct consequences.

 

Question 2. The figure given below shows the relative contributions of various greenhouse gases to total global warming.
i. Name the gases (a) and (b).
ii. Explain how an increase in greenhouse gases in the earth's atmosphere leads to the melting of ice caps.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख वैश्विक तापन में विभिन्न ग्रीनहाउस गैसों के सापेक्ष योगदान को दर्शाता है। इसमें CO\(_{2}\) और CH\(_{4}\) जैसी गैसों के प्रतिशत योगदान को ग्राफ के रूप में प्रस्तुत किया गया है ताकि उनके प्रभाव की तुलना की जा सके।
i. a. N\(_{2}\)O
b. Methane (CH\(_{4}\))
ii. The increased concentration of greenhouse gases such as CO\(_{2}\), CFCs, CH\(_{4}\), and N\(_{2}\)O in the Earth's atmosphere enhances the greenhouse effect. This process leads to a rise in the planet's surface temperature, a phenomenon known as global warming. This elevated temperature, in turn, causes significant climatic changes, directly contributing to the accelerated melting of polar ice caps and other glaciers, including those in the Himalayan region.
In simple words: More greenhouse gases like CO\(_{2}\) and methane trap more heat, increasing Earth's temperature (global warming). This extra heat then melts ice caps and glaciers faster, causing sea levels to rise.

🎯 Exam Tip: For diagram-based questions, accurately identify the components shown. When explaining the melting of ice caps, link the increase in greenhouse gases directly to temperature rise, which then causes the physical change of ice melting.

 

Question 3. Microbes play a dual role when used for sewage treatment as they not only help to retrieve usable water but also generate fuel. ‘Write how this happens?
Answer: Microbes are integral to sewage treatment, performing a dual function: purifying water and generating energy.
- **Primary treatment:** This initial stage is a physical process that involves removing large and small particles through filtration and sedimentation.
- **Secondary treatment:** Following primary treatment, this biological process employs heterotrophic bacteria naturally present in the sewage. These bacteria consume the organic matter in the wastewater.
- As the bacterial flocs settle, they form activated sludge. A significant portion of this sludge is then pumped into large anaerobic sludge digesters.
- During anaerobic digestion, different types of bacteria break down the organic matter in the sludge in the absence of oxygen. This process generates a mixture of gases, primarily methane, carbon dioxide, and hydrogen sulfide, collectively known as biogas.
- This biogas is an inflammable fuel that can be used as an energy source, thus demonstrating the dual role of microbes in both water purification and fuel production.
In simple words: In sewage treatment, microbes first break down waste to clean water. Then, some of these microbes in special tanks produce biogas, which is a useful fuel, playing a dual role in cleaning water and making energy.

🎯 Exam Tip: When describing the dual role of microbes in sewage treatment, clearly explain both their function in biodegrading organic matter for water purification (secondary treatment) and their role in anaerobic digestion to produce biogas (fuel generation).

 

Question. The above diagram shows a simplified biogeochemical cycle.
i. Name the compound whose cycle is depicted.
ii. In what way do vehicles add this compound to the atmosphere?
iii. What adverse effect does its excess have on the environment?
iv. Cite an event that depicts this effect in modern times.
v. Suggest two ways of reducing this effect.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख कार्बन चक्र को दर्शाता है, जिसमें पौधे श्वसन के माध्यम से CO\(_{2}\) छोड़ते हैं, जीवाश्म ईंधन जलाने और जंगल की आग से भी CO\(_{2}\) का उत्सर्जन होता है, और वायुमंडलीय कार्बन से संबंधित विभिन्न प्रक्रियाएँ दिखायी गयी हैं।
i. The compound depicted in the cycle is carbon, and this is known as the carbon cycle.
ii. Vehicles contribute to the atmosphere by emitting various poisonous gases, including carbon monoxide and unburnt hydrocarbons, which add to atmospheric pollution. These emissions are particularly harmful to respiratory organs, such as the lungs.
iii. An excessive concentration of carbon gases in the air poses significant challenges for living organisms, especially concerning respiration. Given that carbon constitutes 71% of the total global carbon, its imbalance has widespread environmental repercussions.
iv. Human activities have profoundly altered the carbon cycle. Rapid deforestation and the extensive burning of fossil fuels for energy and transportation have led to a substantial increase in carbon dioxide levels in the atmosphere, intensifying the greenhouse effect.
v. Two effective strategies for mitigating this effect are:
- Halting deforestation efforts.
- Significantly reducing the massive combustion of fossil fuels.
In simple words: This diagram shows the carbon cycle. Vehicles add carbon to the air through exhaust, which pollutes and harms breathing. Too much carbon in the atmosphere causes breathing problems and strengthens the greenhouse effect. We can reduce this by stopping deforestation and burning fewer fossil fuels.

🎯 Exam Tip: For cycle-based questions, identify the cycle accurately and trace the element's movement. When discussing environmental impacts, connect human activities directly to imbalances in the cycle and suggest specific, actionable solutions.

 

Question 5. Create an aquatic food chain in a water body into which effluents flow from a pesticide factory. Diagrammatically represent biomagnification in this food chain.
Answer: Certain toxic substances, frequently found in industrial wastewater, can undergo biological magnification within an aquatic food chain. Biomagnification refers to the progressive increase in the concentration of a toxicant at successive trophic levels. This occurs because a toxic substance, once accumulated by an organism, cannot be metabolized or excreted and thus gets passed on to the next higher trophic level. This phenomenon is well-documented for mercury and DDT.
The figure illustrates the biomagnification of DDT in an aquatic food chain. If DDT starts at a concentration of 0.003 ppb (parts per billion) in water, its concentration progressively increases through the trophic levels, eventually reaching up to 25 ppm (parts per million) in fish-eating birds. This elevated DDT concentration disrupts calcium metabolism in birds, leading to the thinning of eggshells and their premature breakage, ultimately causing a decline in bird populations.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक जलीय खाद्य श्रृंखला में DDT के जैविक आवर्धन (biomagnification) को दर्शाता है। इसमें दिखाया गया है कि पानी से लेकर मछलियों और फिर मछली खाने वाले पक्षियों तक, DDT की सांद्रता कैसे बढ़ती जाती है, जिससे पक्षी आबादी पर नकारात्मक प्रभाव पड़ता है।
- **Water** (DDT 0.003 ppm)
- **Zooplankton** (DDT 0.04 ppm)
- **Small fish** (DDT 0.5 ppm)
- **Large fish** (DDT 2 ppm)
- **Fish-eating birds** (DDT 25 ppm)
In simple words: When a pesticide factory releases toxic chemicals like DDT into water, these toxins move up the food chain. Organisms cannot get rid of them, so the concentration gets higher at each step, like in fish-eating birds, causing harm such as weak eggshells.

🎯 Exam Tip: When illustrating biomagnification, clearly show the increasing concentration of the toxicant at each successive trophic level. Use a quantitative example (like DDT ppm values) to demonstrate the amplification effect, and explain the specific ecological consequences.

 

Question 6. What is the greenhouse effect? Discuss the effect of increased levels (between 540 and 970ppm.) of carbon dioxide gas on the growth of C3 plants.
Answer: The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases and is re-radiated in all directions. This effect causes the Earth's surface temperature to increase. With rising levels of greenhouse gases like CO\(_{2}\), CFCs, CH\(_{4}\), and N\(_{2}\)O, the environmental temperature at the surface rises, intensifying this process. CO\(_{2}\) is the most abundant greenhouse gas. An increase in atmospheric CO\(_{2}\) levels (e.g., between 540 and 970 ppm) leads to what is known as CO\(_{2}\) fertilization. This can result in an increased growth rate, potentially up to 30%, for C3 plants, as CO\(_{2}\) is a key substrate for photosynthesis.
In simple words: The greenhouse effect is when gases in the atmosphere trap heat, making Earth warmer. More CO\(_{2}\) in the air, a major greenhouse gas, can actually boost the growth of C3 plants because they use CO\(_{2}\) for photosynthesis.

🎯 Exam Tip: Define the greenhouse effect clearly. When discussing CO\(_{2}\) fertilization, specifically mention its positive impact on C3 plant growth due to increased substrate availability for photosynthesis, but also briefly acknowledge the broader negative implications of rising CO\(_{2}\) levels.

 

Question 7. What is meant by ozone hole? When does it develop every year? How are CFCs responsible for this?
Answer: The ozone hole refers to the significant thinning of the ozone layer in the stratosphere, most notably observed over the Antarctic region. This phenomenon typically develops annually between late August and early October. Chlorofluorocarbons (CFCs) are highly responsible for this depletion. In the stratosphere, ultraviolet (UV) rays catalyze the breakdown of CFCs, releasing chlorine atoms. These chlorine atoms then act as catalysts to degrade ozone molecules (O\(_{3}\)) into oxygen (O\(_{2}\)). Since the chlorine atom is not consumed in the reaction, it can continuously destroy numerous ozone molecules, perpetuating and intensifying the ozone depletion effect.
In simple words: The ozone hole is a thin patch in the ozone layer over Antarctica, appearing yearly in late summer/early autumn. CFCs cause it because UV light breaks them down into chlorine atoms, which then destroy ozone molecules repeatedly.

🎯 Exam Tip: Define the ozone hole's location and timing. Crucially, explain the catalytic role of chlorine atoms released from CFCs in ozone destruction, emphasizing that chlorine is not consumed in the reaction, leading to ongoing damage.

 

Question 8. Study the graph given below and answer the questions that follow.
i. What is the relationship between dissolved oxygen and biochemical oxygen demand (BOD)?
ii. Mention their effect on aquatic life in the river.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह ग्राफ एक नदी में सीवेज डिस्चार्ज के बाद घुली हुई ऑक्सीजन (Dissolved Oxygen) और जैव रासायनिक ऑक्सीजन मांग (BOD) के बीच के संबंध को दर्शाता है। इसमें दिखाया गया है कि जैसे-जैसे BOD बढ़ता है, घुली हुई ऑक्सीजन घटती है और फिर धीरे-धीरे दोनों अपने सामान्य स्तर पर लौट आते हैं।
i. The relationship between dissolved oxygen (DO) and biochemical oxygen demand (BOD) is inversely proportional. When the biochemical oxygen demand (BOD) in a water body increases, it indicates a higher concentration of biodegradable organic matter. Microorganisms decompose this organic matter, consuming a significant amount of dissolved oxygen in the process. Consequently, an elevated BOD directly leads to a sharp decline in the dissolved oxygen levels of the water.
ii. The impact on aquatic life in the river is severe. A sharp decline in dissolved oxygen levels, caused by high BOD, creates hypoxic or anoxic conditions (low or no oxygen). Most aquatic organisms, including fish, require sufficient dissolved oxygen to survive. Under such conditions, fish and other aquatic creatures cannot respire adequately, leading to widespread mortality downstream from the point of sewage discharge. The overall biodiversity and health of the aquatic ecosystem are severely compromised.
In simple words: When sewage enters a river, the Biochemical Oxygen Demand (BOD) goes up, meaning more oxygen is needed to break down pollutants. This causes the Dissolved Oxygen (DO) to drop. Low DO harms aquatic life, leading to fish and other creatures dying as they can't breathe.

🎯 Exam Tip: For graphs showing DO and BOD, explain their inverse relationship. Emphasize that high BOD indicates pollution, which consumes oxygen, directly affecting the survival and diversity of aquatic organisms. Relate these concepts to water quality indicators.