Our Environment – Case-based Questions with Answers
CBSE Class 10 Biology — Chapter 13: Our Environment — 20 Case-Based Questions
Class: CBSE Class 10
Subject: Science — Biology
Chapter: Chapter 13 — Our Environment
CBSE Board Examinations
Systematic order: Syllabus → Learning outcomes → Case-Based Q&A → Exam practice
Instructions: 20 topic-wise case-based questions (scenarios + questions) with clear, exam-focused answers. These are prepared strictly according to the NCERT Class 10 Biology chapter "Our Environment". Use them for classroom discussion, tests and board exam revision.
Case 1 — Pond with sudden fish death: A village pond received untreated sewage and agricultural runoff after heavy rains. A week later many fish were found dead.
Q1.1: Suggest the most likely ecological process responsible for fish deaths.
A: Eutrophication — nutrient overload (nitrates/phosphates) from sewage/runoff caused algal bloom; when algae died, decomposition by microbes consumed dissolved oxygen (DO) causing hypoxia and fish kills.
Q1.2: Name two control measures to prevent such incidents.
A: (1) Treat sewage before discharge and implement buffer zones/vegetative strips to reduce runoff. (2) Promote responsible fertilizer use and create constructed wetlands to filter runoff.
Case 2 — Farmer notices declining yield: A farmer observes reduced crop yields and soil that crusts after rains; groundwater tastes slightly salty.
Q2.1: What process might be causing these symptoms?
A: Soil salinisation — accumulation of soluble salts (from poor irrigation/drainage, high evaporation) reduces soil fertility and harms crops; salinised groundwater causes salty taste.
Q2.2: Suggest two remedial practices the farmer can adopt.
A: Improve drainage, apply gypsum where appropriate, use proper irrigation scheduling (avoid waterlogging), adopt salt-tolerant crop varieties and practice crop rotation.
Case 3 — Urban smog episodes: A city experiences episodes of dense smog and high respiratory complaints during winter.
Q3.1: Identify common pollutants that contribute to smog and health effects.
A: Pollutants include particulate matter (PM₂.₅/PM₁₀), NOx, SO₂, CO and VOCs. Health effects: respiratory irritation, asthma exacerbation, cardiovascular issues and reduced lung function.
Q3.2: Recommend two policy or practical actions to reduce smog.
A: Promote cleaner vehicle fuels and public transport; enforce emission norms and control open burning/industrial emissions. Encourage odd–even schemes, vehicle maintenance and awareness on reducing biomass burning.
Case 4 — Fishermen report mercury in fish: Coastal community finds high mercury in large predatory fish.
Q4.1: Which process explains high toxin levels in top predators?
A: Biomagnification — persistent toxins (like methylmercury) concentrate at higher trophic levels as predators consume contaminated prey, resulting in high levels in top predators.
Q4.2: What public health advice should be given?
A: Limit consumption of large predatory fish (especially for pregnant women/children); issue consumption advisories; identify and control pollution sources (industrial discharge) and monitor fish mercury levels.
Case 5 — Forest patch fragmentation: A large forest was converted into farmlands, leaving fragmented patches; local wildlife sightings decreased.
Q5.1: Explain how fragmentation affects biodiversity.
A: Fragmentation isolates populations, reduces habitat area, restricts movement/gene flow, increases edge effects and vulnerability to local extinction — overall biodiversity decline.
Q5.2: Suggest one landscape-level solution to help wildlife.
A: Create wildlife corridors or stepping-stone habitats to reconnect fragments, enabling migration and gene flow; promote community-based buffer zones to reduce human–wildlife conflict.
Case 6 — Decline in pollinators: Farmers notice fewer bees and reduced fruit set in orchards.
Q6.1: List two likely causes for pollinator decline.
A: Pesticide overuse (especially neonicotinoids) and habitat loss (nectar/flower scarcity, monoculture), plus diseases and climate change stressors.
Q6.2: Recommend farm practices to support pollinators.
A: Adopt integrated pest management (IPM), avoid harmful pesticides, create floral strips/hedgerows, provide nesting habitats and maintain habitat diversity (mixed cropping).
Case 7 — Sewage contamination of river: A town discharges untreated sewage into its river; downstream villagers report increase in waterborne diseases.
Q7.1: Which pathogens or hazards are commonly linked to untreated sewage?
A: Bacteria (E. coli, Vibrio), viruses (hepatitis A), protozoa (Giardia), and parasites causing diarrhoea, cholera, typhoid and other waterborne illnesses.
Q7.2: Give two infrastructure or community measures to reduce risks.
A: Build/upgrade sewage treatment plants and promote household-level sanitation (toilets, safe disposal). Educate communities on boiling/treated water and safe hygiene practices.
Case 8 — Wetland conversion: A wetland is drained for housing development and later the area floods often during monsoon.
Q8.1: How did destroying the wetland increase flooding?
A: Wetlands act as natural sponges that absorb and slowly release floodwaters. Draining/removing them reduces water-storage capacity, increases runoff and raises flood risk downstream.
Q8.2: Propose a nature-based solution to reduce flooding.
A: Restore or create wetlands and floodplains, implement green infrastructure (permeable pavements, rain gardens) and preserve upstream vegetation to improve infiltration and reduce peak runoff.
Case 9 — Noise complaints near airport: Residents report sleep disturbance and stress due to frequent flights.
Q9.1: What are common health impacts of chronic noise exposure?
A: Sleep disruption, increased stress and blood pressure, impaired cognitive performance (in children), and potential hearing impairment at high levels.
Q9.2: Mention two mitigation measures airports can implement.
A: Enforce flight curfews/quiet hours, use noise abatement procedures and sound insulation programs for nearby buildings; design flight paths to minimize populated area overflights.
Case 10 — Household waste pile: A neighbourhood dumps mixed household waste openly; flies and rodents increase and local groundwater seems polluted.
Q10.1: Identify environmental and health hazards of open dumping.
A: Disease vectors (flies/rodents) spread illnesses; leachate from waste can percolate and pollute groundwater; odour and air pollution; breeding ground for mosquitoes increasing vector-borne diseases.
Q10.2: Recommend a simple community-level waste management plan.
A: Implement source segregation (wet/dry/hazardous), establish community composting for organic waste, arrange regular collection linking to municipal recycling and educate residents on reducing and reusing materials.
Case 11 — River island development: Construction upstream changed river flow causing siltation and fewer breeding grounds for fish.
Q11.1: How does siltation affect aquatic life?
A: Siltation buries spawning grounds, reduces light penetration affecting plants, clogs fish gills, reduces dissolved oxygen and alters habitat structure reducing biodiversity.
Q11.2: What engineering or ecological measures can reduce siltation?
A: Use upstream soil conservation (contour bunding, reforestation), sediment traps/retention ponds, controlled construction practices and riparian buffer restoration to reduce erosion and silt load.
Case 12 — Excess fertilizer use in fields: Fields show high weed growth and pest outbreaks despite heavy fertiliser use.
Q12.1: Explain how excessive fertiliser can worsen pest problems.
A: Excess nutrients can create lush plant growth that attracts herbivores and pests; imbalance in soil microbes may reduce natural pest predators; runoff also harms aquatic ecosystems leading to secondary ecological effects.
Q12.2: Suggest sustainable agricultural practices to address this.
A: Use soil testing for targeted fertiliser application, adopt integrated nutrient management (organic manures + chemical fertilisers), introduce IPM to control pests and use crop rotation and biological control agents.
Case 13 — City introduces tree-planting drive: After planting native trees along roads, air quality and shade improved.
Q13.1: List environmental benefits of urban tree planting.
A: Trees filter particulates and gaseous pollutants, sequester CO₂, reduce urban heat island effect through shade and evapotranspiration, increase biodiversity and improve mental well-being of residents.
Q13.2: Why are native species preferred over exotic ones for urban greening?
A: Native species are adapted to local climate/soil, support local fauna (pollinators, birds), require less maintenance and reduce risk of becoming invasive compared to some exotics.
Case 14 — Coastal mangrove clearance: Area cleared for shrimp farms; storms later caused severe coastal erosion and property loss.
Q14.1: Explain how mangroves protect coasts.
A: Mangroves stabilise sediments with complex root systems, reduce wave energy and storm surge impacts, trap sediments and provide habitat for fish and crustaceans — acting as natural coastal defence.
Q14.2: Propose restoration or policy steps to prevent future damage.
A: Enforce protection of remaining mangroves, restore degraded mangrove areas through community-based planting, regulate shrimp farm siting and promote sustainable aquaculture practices with environmental safeguards.
Case 15 — School pond becomes eutrophic: School pond used to teach biology now has green scum and few tadpoles.
Q15.1: As a student, list immediate steps to revive the pond.
A: Reduce nutrient inputs (stop fertiliser runoff), remove excessive algae mechanically, aerate water (fountains) to raise DO, introduce aquatic plants that uptake nutrients and involve local environmental agency for further testing and remediation.
Q15.2: What educational value does pond restoration offer?
A: Hands-on learning in ecology, nutrient cycles, biodiversity, conservation practices and community action; fosters stewardship and practical science skills.
Case 16 — Illegal dumping of e-waste near a settlement: Residents report skin irritation and odd smells after months of informal e-waste burning.
Q16.1: Identify hazards associated with informal e-waste burning.
A: Release of toxic metals (lead, cadmium), persistent organic pollutants and harmful fumes causing skin, respiratory and neurological effects; soil and groundwater contamination is possible.
Q16.2: Recommend an action plan for authorities.
A: Enforce e-waste regulations, set up authorised collection and recycling centres, run public awareness campaigns, provide protective facilities for informal workers and remediate contaminated sites.
Case 17 — River deoxygenation downstream of factory: A factory discharges warm effluent; DO downstream is low and sensitive aquatic species decline.
Q17.1: Name two effects of thermal effluent on river ecology.
A: Warm effluent reduces dissolved oxygen (lower solubility), alters species composition favouring tolerant species, and can disrupt breeding cycles of temperature-sensitive organisms.
Q17.2: Suggest technological measures for the factory to mitigate impacts.
A: Install cooling ponds/towers to reduce effluent temperature before discharge, recycle/process cooling water internally, and ensure effluent treatment to remove contaminants.
Case 18 — Introduction of invasive plant: A fast-growing ornamental plant escapes gardens and spreads, replacing native grasses and reducing grazing area.
Q18.1: What ecological problems arise when an invasive plant dominates?
A: Loss of native species, reduced forage for herbivores, altered soil chemistry and hydrology, decreased biodiversity and disruption of food webs.
Q18.2: Outline an integrated management approach to control the invasive species.
A: Mechanical removal combined with controlled burning where appropriate, targeted herbicide application with care, restoration planting of native species and community monitoring to prevent reinvasion.
Case 19 — Decline of an apex predator: Local reports show fewer sightings of a top carnivore, and mesopredator (mid-sized predator) numbers have surged.
Q19.1: Explain trophic cascade that can arise from apex predator loss.
A: Apex predator decline can lead to mesopredator release — increase in mid-level predators that overconsume prey species (e.g., herbivores), causing imbalance, vegetation loss and cascading ecosystem changes affecting many trophic levels.
Q19.2: Suggest conservation actions to restore balance.
A: Protect and restore habitat to support apex predators, reduce human–predator conflicts (compensation, livestock protection), and consider managed reintroduction where feasible under scientific guidance.
Case 20 — Community facing groundwater depletion: Wells are drying earlier each year while population and irrigation demands grow.
Q20.1: Identify human activities that commonly cause groundwater depletion.
A: Over-extraction for irrigation and domestic use, inefficient irrigation (flooding), reduction in recharge due to urbanisation and loss of vegetation, and prolonged drought exacerbated by climate change.
Q20.2: Propose a combination of immediate and long-term measures to restore groundwater levels.
A: Immediate: restrict extraction, promote water-saving practices (drip irrigation), repair leaks and encourage rainwater harvesting (storage tanks, percolation pits). Long-term: recharge structures (check-dams), afforestation, land-use planning to increase infiltration and sustainable groundwater management policies.
Tip: When answering case-based questions in exams, (1) quickly identify the core environmental process(s) in the scenario, (2) explain cause–effect relationships concisely, and (3) propose practical, exam-appropriate solutions (policy/technical/community) — conclude with one-line significance.