CBSE Class 12 Biology Chapter 16: Environmental Issues NCERT Solutions

Solution: Domestic sewage is the wastewater generated from households, originating from sources like kitchens, toilets, and laundry. It contains a complex mixture of impurities. These include suspended solids such as sand, salt, and clay; colloidal materials like fecal matter, bacteria, and fibers from cloth and plastic; and dissolved substances including nitrates, phosphates, and various ions like calcium and sodium. It also harbors disease-causing microbes.

When this organic-rich sewage enters a river, it provides a food source for microorganisms, particularly algae and bacteria. This leads to a rapid increase in their populations. These microorganisms consume large amounts of dissolved oxygen from the water during their metabolic processes. Consequently, the Biological Oxygen Demand (BOD), which measures the amount of oxygen required by these organisms, increases significantly in the river water. This depletion of dissolved oxygen is detrimental to aquatic life, leading to the death of fish and other organisms. Furthermore, the excess nutrients (like nitrates and phosphates) in the sewage can stimulate excessive growth of planktonic algae, causing an 'algal bloom'. This bloom not only deteriorates the water quality but also contributes to fish mortality by further reducing oxygen levels and blocking sunlight.

Solution:

Wastes generated at home include items like plastic bags, used paper napkins, toiletries, kitchen scraps (vegetable and fruit peels, tea leaves), domestic sewage, glass bottles, and packaging materials.

At school, common wastes include waste paper from notebooks and printing, discarded plastic items, food wrappers, vegetable and fruit peels from lunch, and domestic sewage from restrooms.

During trips or picnics, wastes typically consist of disposable plastic items (cups, plates, cutlery), food wrappings, plastic bottles, and organic waste like fruit peels.

Wastes that can be easily reduced:

Paper waste: By writing on both sides of the paper, using recycled paper, and minimizing unnecessary printing.

Plastic waste: By opting for reusable containers, bags, and bottles instead of single-use plastics. Recycling and proper disposal also help.

Kitchen waste: Composting fruit and vegetable peels can significantly reduce organic waste.

Domestic sewage: Optimizing water usage in daily activities like bathing, washing, and cooking can reduce the volume of sewage generated.

Disposable items: Choosing reusable alternatives for plates, cups, and cutlery during picnics or events.

Wastes that are difficult or impossible to reduce:

Non-biodegradable materials: Items like certain plastics, metals, and broken glass are difficult to decompose naturally. While recycling is possible, complete elimination of their generation is challenging with current consumption patterns.

Industrial by-products: Some industrial processes inherently generate waste that is hard to eliminate or recycle effectively.

Medical waste: Certain types of medical waste require specific disposal methods and cannot be easily reduced without impacting healthcare services.

Solution: Global warming refers to the gradual increase in the average temperature of the Earth's surface over time.

Causes of Global Warming: The primary cause of global warming is the increased concentration of greenhouse gases in the Earth's atmosphere. These gases, including carbon dioxide (CO2), methane (CH4), and water vapor (H2O), naturally trap some of the heat radiated back from the Earth's surface, maintaining a habitable temperature. However, human activities have significantly increased the levels of these gases. Major contributing factors include:

Industrialization: Burning of fossil fuels (coal, oil, natural gas) in industries releases large amounts of CO2.

Deforestation: Trees absorb CO2 during photosynthesis. Large-scale deforestation reduces this absorption capacity and often involves burning, releasing stored carbon.

Agriculture and Livestock: Methane is released from rice paddies and livestock digestion.

Use of certain chemicals: Some industrial chemicals also contribute to the greenhouse effect.

Effects of Global Warming: The consequences of global warming are far-reaching and severe:

Rising Global Temperatures: The average global temperature has already increased by approximately 0.6°C in the last few decades.

Disturbance of Water Cycle: Changes in temperature patterns alter rainfall, leading to more extreme weather events like droughts and floods.

Melting 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.

Impact on Ecosystems: Changes in climate can disrupt habitats, affect species survival, and alter agricultural productivity.

Measures to Control Global Warming:

Reduce Fossil Fuel Consumption: Transitioning to cleaner energy sources and improving energy efficiency in homes and industries.

Promote Renewable Energy: Increasing the use of solar, wind, and hydroelectric power. Using cleaner fuels like Compressed Natural Gas (CNG).

Reforestation and Afforestation: Planting more trees to increase CO2 absorption.

Sustainable Agriculture: Implementing practices that reduce methane and nitrous oxide emissions.

Recycling and Waste Reduction: Minimizing waste generation and maximizing recycling reduces the energy needed for production and disposal.

International Cooperation: Global agreements and policies to limit greenhouse gas emissions.

Solution: The correct matching of the items from Column A and Column B is as follows:

1. Catalytic converter is used to convert harmful gases like carbon monoxide and nitrogen oxides into less harmful substances. So, it matches with (ii) Carbon monoxide and nitrogen oxides.
2. Electrostatic precipitator is a device used to remove particulate matter from exhaust gases by using an electric charge. So, it matches with (i) Particulate matter.
3. Earmuffs are used to protect the ears from high noise levels. So, it matches with (iii) High noise level.
4. Landfills are sites used for the disposal of solid wastes. So, it matches with (iv) Solid wastes.

Therefore, the complete matching is:

a) (ii), b) (i), c) (iii), d) (iv)