NCERT Solutions for 12th Class Biology Chapter 16: Environmental Issues

Answer: Air pollutants are categorized as:

Primary Pollutants: Directly emitted from sources including particulate matter (causes respiratory problems), sulfur dioxide (causes respiratory issues and acid rain), nitrogen oxides (creates smog), carbon monoxide (reduces oxygen delivery to tissues), and hydrocarbons (contribute to smog formation).

Secondary Pollutants: Formed in atmosphere through reactions, including ground-level ozone (from NOx and VOCs), acid rain (from SO2 and NOx reactions), and photochemical smog.

Effects include respiratory diseases, reduced visibility, plant damage, and climate change contribution.

Answer:

Causes of Water Pollution:

• Industrial effluents containing toxic chemicals
• Sewage and domestic waste
• Agricultural runoff containing fertilizers and pesticides
• Oil spills from ships and pipelines
• Thermal pollution from power plants
• Radioactive waste from nuclear facilities

Effects of Water Pollution:

• Water-borne diseases like cholera, typhoid, and dysentery
• Biomagnification of toxins in the food chain
• Eutrophication leading to algal blooms and oxygen depletion
• Destruction of aquatic ecosystems
• Reduced availability of clean drinking water
• Accumulation of harmful substances in fish and other aquatic organisms

Answer: Biomagnification (or biological magnification) is the process where concentration of toxic substances increases at each successive trophic level in a food chain.

Example of biomagnification:

• Water contaminated with mercury is consumed by phytoplankton (low concentration accumulates)
• Small fish feeding on these phytoplankton consume higher concentrations
• Larger predatory fish eating smaller fish accumulate even higher concentrations
• Birds or humans at the top of this food chain receive the highest concentration, which can be harmful

The Minamata disease in Japan is a well-known example of mercury poisoning through consumption of contaminated fish.

Answer: The greenhouse effect is the trapping of heat by certain gases in Earth's atmosphere. Enhanced greenhouse effect refers to increased trapping due to higher concentrations of these gases, primarily from human activities.

Causes:

• Burning fossil fuels (coal, oil, natural gas) for electricity and transportation
• Deforestation reducing carbon sinks
• Industrial processes and manufacturing
• Agricultural activities (rice cultivation, cattle rearing)
• Waste generation in landfills

Consequences:

• Global warming and rising average temperatures
• Melting ice caps and glaciers
• Rising sea levels threatening coastal areas
• More frequent extreme weather events
• Ecosystem disruption and biodiversity loss
• Ocean acidification affecting marine life
• Impacts on agriculture and food security

Answer: The ozone layer in stratosphere absorbs harmful UV radiation. CFCs, halons, and other chemicals break down ozone molecules, causing thinning (ozone holes).

Causes: Release of CFCs (used in refrigerants, aerosols), halons (fire extinguishers), methyl chloroform, and carbon tetrachloride into the atmosphere.

Effects: Increased UV-B radiation reaching Earth's surface results in:

• Higher skin cancer and cataract rates
• Immune system suppression
• Damage to plant life affecting photosynthesis
• Disruption of aquatic ecosystems
• Degradation of synthetic polymers

The Montreal Protocol (1987) was an international agreement to phase out ozone-depleting substances, which has shown positive results in ozone layer recovery.

Answer: The 3R principle stands for:

Reduce: Minimize waste generation at source by:

• Using products with minimal packaging
• Choosing durable, long-lasting items
• Avoiding single-use products
• Bulk purchasing to reduce packaging waste

Reuse: Use items multiple times before discarding by:

• Repairing instead of replacing
• Using reusable bags and containers
• Donating items that can be used by others
• Repurposing items for different uses

Recycle: Process used materials into new products by:

• Properly segregating waste
• Supporting community recycling programs
• Purchasing products made from recycled materials
• Creating new products from recycled materials

The 3R principle helps minimize waste, conserve resources, and reduce environmental impact.

Answer:

Causes of Deforestation:

• Conversion of forest land to agricultural land
• Logging for timber and wood products
• Urbanization and infrastructure development
• Mining activities
• Cattle ranching and livestock grazing
• Forest fires (natural and human-made)

Effects of Deforestation:

• Loss of biodiversity and habitat destruction
• Soil erosion and degradation
• Disruption of water cycles
• Contribution to climate change (reduced carbon sequestration)
• Displacement of indigenous communities
• Reduced rainfall and desertification
• Air quality deterioration

Answer: Eutrophication is the process where water bodies become enriched with minerals and nutrients, leading to excessive growth of algae and plants, which results in oxygen depletion. When these organisms die and decompose, they consume oxygen, creating dead zones where aquatic life cannot survive.

Example: Agricultural runoff containing fertilizers rich in nitrogen and phosphorus enters a lake. These nutrients stimulate the rapid growth of algae (algal bloom). When these algae die, bacteria decompose them, consuming oxygen in the process. This reduces oxygen levels in the water, killing fish and other aquatic organisms. The Mississippi River delta's dead zone in the Gulf of Mexico is a prominent example of eutrophication.