CBSE Class 12 Biology Chapter 16: Environmental Issues NCERT Solutions

Solution: Domestic sewage is the wastewater generated from households, including contributions from kitchens, toilets, and laundry. Its primary constituents are impurities such as:

1. Suspended solids: These are insoluble particles like sand, silt, and salts.

2. Colloidal material: These include fine particles that do not settle easily, such as fecal matter, bacteria, and fibers from cloth and paper.

3. Dissolved materials: Various inorganic salts (like nitrates, phosphates, calcium, sodium) and organic compounds are dissolved in the sewage.

4. Disease-causing microbes: Pathogens like bacteria and viruses can be present, posing health risks.

Effects of sewage discharge on a river: When domestic sewage is discharged into a river, it significantly impacts the aquatic ecosystem:

• Increased microbial activity: The organic matter in sewage serves as a food source for microorganisms (bacteria, algae). Their population increases rapidly.
• Oxygen depletion: These microorganisms consume large amounts of dissolved oxygen from the river water during the decomposition of organic waste. This process increases the Biological Oxygen Demand (BOD) of the water.
• Harm to aquatic life: The depletion of dissolved oxygen makes it difficult for fish and other aquatic organisms to survive, often leading to their death.
• Algal blooms: The excess nutrients (like nitrates and phosphates) from sewage can cause rapid growth of algae and plankton, forming an algal bloom. This further reduces light penetration and oxygen levels when the algae die and decompose.
• Deterioration of water quality: The overall quality of the river water degrades, making it unsuitable for drinking, recreation, and supporting a healthy aquatic environment.

Solution: We generate various types of waste in our daily lives from different locations: Wastes generated at home: Plastic bags, paper napkins, toiletries, kitchen waste (vegetable/fruit peels, tea leaves), domestic sewage, glass bottles, food packaging. Wastes generated at school: Waste paper, plastic wrappers, food scraps, disposable items, domestic sewage. Wastes generated during trips/picnics: Plastic bottles and wrappers, disposable cups and plates, food packaging, paper napkins. Wastes that can be easily reduced:

• Paper waste: By using both sides of the paper for writing, opting for recycled paper, and reducing unnecessary printing.
• Plastic waste: By reducing the use of single-use plastics, carrying reusable bags, bottles, and containers.
• Kitchen waste: By composting organic waste (peels, leaves) and minimizing food wastage.
• Domestic sewage: By optimizing water usage in daily activities like bathing, washing, and cooking.

Wastes that are difficult or impossible to reduce:

• Non-biodegradable wastes: Materials like certain plastics, metals, and broken glass are difficult to decompose naturally. While they can be recycled or reused, completely eliminating their generation is challenging with current technologies and lifestyles.
• Industrial and medical waste: These often require specialized treatment and disposal methods and are difficult to reduce significantly without major technological or policy changes.

The key to reducing waste lies in the principles of Reduce, Reuse, and Recycle (3Rs), along with conscious consumption and opting for biodegradable alternatives whenever possible. Substituting plastic bags with jute or cloth bags is a practical step towards reducing plastic waste. Optimizing water use helps minimize domestic sewage generation.

Solution: Global warming refers to the gradual increase in the average temperature of the Earth's surface over time. Causes of Global Warming: Global warming is primarily caused by the enhanced greenhouse effect, resulting from an increase in the concentration of greenhouse gases (GHGs) in the atmosphere. These gases include:

• Carbon dioxide (CO2)
• Methane (CH4)
• Water vapor (H2O)
• Nitrous oxide (N2O)

These gases trap the heat radiated from the Earth's surface, preventing it from escaping into space. While this natural greenhouse effect is essential for maintaining a habitable temperature, an excessive increase in GHG concentrations, mainly due to human activities like burning fossil fuels (coal, oil, natural gas), deforestation, industrial processes, and agriculture, leads to an abnormal rise in global temperatures. Effects of Global Warming: The consequences of global warming are far-reaching and include:

• Rising global temperatures: An average increase of about 0.6°C has been observed in the Earth's temperature over the past few decades.
• Changes in climate patterns: This leads to unpredictable and extreme weather events, such as altered rainfall patterns (floods and droughts) and increased frequency of heatwaves.
• Melting of ice caps and glaciers: Polar ice sheets and mountain glaciers are melting at an accelerated rate.
• Sea-level rise: The melting ice contributes to a rise in sea levels, threatening coastal regions with inundation and erosion.
• Impact on ecosystems: Changes in temperature and precipitation affect biodiversity, leading to habitat loss and species extinction.

Measures to Control Global Warming: To mitigate global warming, several measures need to be implemented:

• Reduce fossil fuel consumption: Transitioning to cleaner energy sources is crucial.
• Promote renewable energy: Increasing the use of solar, wind, and hydroelectric power.
• Improve energy efficiency: Using energy more wisely in homes, industries, and transportation.
• Use biofuels and cleaner fuels: Such as Compressed Natural Gas (CNG) where appropriate.
• Reforestation and afforestation: Planting more trees helps absorb CO2 from the atmosphere.
• Recycling and waste reduction: Minimizing waste reduces the energy required for production and disposal.
• Sustainable agriculture and land management practices.

Solution: Here is the correct matching of the items from Column A and Column B:

1. Catalytic converter is matched with (ii) Carbon monoxide and nitrogen oxides. Catalytic converters in vehicles help reduce harmful emissions by converting toxic gases like CO and NOx into less harmful substances.
2. Electrostatic precipitator is matched with (i) Particulate matter. Electrostatic precipitators are devices used in industries to remove fine particulate matter from exhaust gases using an electric charge.
3. Earmuffs are matched with (iii) High noise level. Earmuffs are personal protective equipment designed to reduce the impact of high noise levels on hearing.
4. Landfills are matched with (iv) Solid wastes. Landfills are sites used for the disposal of solid wastes by burying them.