Class 10: Science: Chapter 15
Our Environment - NCERT Solutions

Answer:

Trophic Levels are the hierarchical levels in an ecosystem, comprising organisms that share the same function in the food chain and the same nutritional relationship to the primary sources of energy.

Example of a Food Chain:
Grass → Grasshopper → Frog → Snake → Hawk

Trophic Levels in this Food Chain:

Trophic Level	Organism	Role
First Trophic Level (Producer)	Grass	Produces food through photosynthesis
Second Trophic Level (Primary Consumer)	Grasshopper	Herbivore that eats producers
Third Trophic Level (Secondary Consumer)	Frog	Carnivore that eats primary consumers
Fourth Trophic Level (Tertiary Consumer)	Snake	Carnivore that eats secondary consumers
Fifth Trophic Level (Quaternary Consumer)	Hawk	Top carnivore that eats tertiary consumers

Key Points:
• Energy decreases at each trophic level (10% Law)
• Producers are always at the first trophic level
• Each step represents a transfer of energy and nutrients

Answer:

Decomposers (mainly bacteria and fungi) play crucial roles in maintaining ecosystem balance:

Role	Explanation
Nutrient Recycling	Break down dead organic matter (detritus) into simpler inorganic substances that can be reused by plants
Cleaning the Environment	Decompose dead bodies and waste materials, preventing accumulation of dead matter
Energy Flow Completion	Complete the flow of energy by breaking down complex organic compounds
Soil Enrichment	Add humus to soil, improving soil fertility and structure
Carbon Cycle Maintenance	Release carbon dioxide during decomposition, essential for photosynthesis

Examples of Decomposers:
• Bacteria: Microscopic decomposers in soil and water
• Fungi: Mushrooms, molds, yeasts
• Detritivores: Earthworms, millipedes, woodlice (help in initial breakdown)

Without decomposers:
→ Dead organisms would accumulate
→ Nutrients would remain locked in dead matter
→ Ecosystem would collapse due to nutrient deficiency
→ Food chains would be incomplete

Answer:

Biodegradable substances can be broken down by biological processes (microorganisms), while non-biodegradable substances cannot.

Factor	Biodegradable Substances	Non-biodegradable Substances
Chemical Structure	Simple organic compounds (C-H bonds)	Complex synthetic compounds
Origin	Natural origin (plants, animals)	Human-made/synthetic
Molecular Size	Smaller molecules	Large polymer chains
Microbial Action	Enzymes can break them down	No natural enzymes to break them
Examples	Paper, cotton, food waste, wood	Plastic, glass, metals, DDT
Decomposition Time	Days to months	Hundreds to thousands of years

Why the Difference?
1. Chemical Bonds: Biodegradable substances have bonds that microbial enzymes can break; non-biodegradable have resistant bonds.
2. Evolution: Microorganisms evolved to decompose natural materials but not recent synthetic ones.
3. Additives: Many plastics contain stabilizers that prevent microbial attack.

Environmental Impact:
• Biodegradable: Cycle nutrients back to ecosystem
• Non-biodegradable: Accumulate, cause pollution, enter food chains

Answer:

Positive Effects of Biodegradable Substances:

1. Nutrient Recycling and Soil Fertility:
• Decomposed biodegradable waste adds organic matter (humus) to soil
• Releases essential nutrients (N, P, K) that plants can absorb
• Improves soil structure, water retention, and aeration
• Example: Compost from kitchen waste enriches garden soil

2. Natural Waste Management:
• Prevent accumulation of waste in environment
• Reduce need for landfills and incineration
• Lower greenhouse gas emissions compared to non-biodegradable waste disposal
• Example: Fallen leaves decompose naturally, fertilizing the soil

Negative Effects (if not managed properly):
1. Pollution and Health Hazards:
• Large piles can produce foul smell (anaerobic decomposition)
• Attract disease-carrying vectors (flies, mosquitoes, rodents)
• Can contaminate water sources if dumped improperly
• Example: Open dumping of food waste breeds pathogens

2. Greenhouse Gas Emissions:
• Anaerobic decomposition produces methane (CH₄), a potent greenhouse gas
• Contributes to global warming if not managed scientifically
• Example: Landfills with organic waste are major methane sources

Proper Management is Key:
• Composting converts biodegradable waste into useful manure
• Biogas plants produce energy from organic waste
• Segregation at source enables efficient recycling

Answer:

Negative Effects of Non-biodegradable Substances:

1. Environmental Pollution and Ecosystem Damage:
• Accumulation: Persist in environment for hundreds of years
• Soil Pollution: Reduce soil fertility, affect plant growth
• Water Pollution: Contaminate water bodies, affect aquatic life
• Visual Pollution: Litter landscapes, cities, and natural areas
• Example: Plastic bags choking drains, rivers, and oceans

2. Bioaccumulation and Biomagnification:
• Bioaccumulation: Toxic chemicals accumulate in organisms
• Biomagnification: Concentration increases at higher trophic levels
• Health Impacts: Cause diseases in animals and humans
• Example: DDT in fish → birds of prey (eagles) → reproductive failure

Non-biodegradable Substance	Environmental Impact
Plastics	Marine animal entanglement, microplastics in food chain
Glass	Injury to animals, fire hazard (acts as lens)
Metals (Aluminum cans)	Soil contamination, resource wastage
Electronic Waste	Toxic heavy metals leach into soil/water

Additional Impacts:
• Resource Depletion: Waste of finite natural resources
• Wildlife Harm: Animals ingest or get trapped in waste
• Blockage: Clog drainage systems causing floods
• Long-term Burden: Future generations inherit pollution

Answer:

Ozone (O₃) is a molecule consisting of three oxygen atoms. It exists in two layers of the atmosphere with opposite effects.

Ozone Layer	Location	Role & Effect
Good Ozone (Stratospheric)	15-35 km above Earth (stratosphere)	Protective shield against UV radiation
Bad Ozone (Tropospheric)	Ground level to 10 km (troposphere)	Harmful pollutant, component of smog

How Ozone Affects Ecosystems:

A. STRATOSPHERIC OZONE (POSITIVE EFFECTS):
1. UV Protection:
• Absorbs 97-99% of harmful UV-B radiation
• Prevents DNA damage in living organisms
• Protects phytoplankton (basis of marine food chains)

2. Ecosystem Preservation:
• Terrestrial Plants: Prevents reduced photosynthesis, growth inhibition
• Aquatic Life: Protects plankton, fish larvae, amphibians
• Animals: Prevents skin cancer, eye damage (cataracts)
• Microorganisms: Maintains soil bacteria balance

B. TROPOSPHERIC OZONE (NEGATIVE EFFECTS):
1. Plant Damage:
• Reduces photosynthesis and crop yields
• Causes leaf damage, premature aging
• Makes plants more susceptible to disease

2. Animal Health:
• Respiratory problems in animals
• Reduces lung function
• Aggravates asthma and bronchitis

Ozone Depletion Concerns:
• CFCs (chlorofluorocarbons) destroy ozone layer
• Ozone hole increases UV radiation reaching Earth
• Montreal Protocol (1987) successfully reducing CFC use

Answer:

Individual Methods to Reduce Waste Disposal Problems:

1. Practice the 3Rs: Reduce, Reuse, Recycle
A. REDUCE (Most Effective):
• Minimize consumption and waste generation at source
• Use cloth bags instead of plastic
• Avoid disposable items (plates, cups, cutlery)
• Buy products with minimal packaging
• Use both sides of paper
• Digital documents instead of printing

B. REUSE:
• Use items multiple times before discarding
• Glass jars for storage
• Old clothes as cleaning rags
• Donate usable items (books, clothes, furniture)
• Repair instead of replace

C. RECYCLE:
• Separate waste at source (wet/dry/recyclable)
• Recycle paper, glass, metals, certain plastics
• Compost biodegradable waste
• Support products made from recycled materials

2. Proper Waste Segregation and Disposal

Waste Type	Proper Disposal Method
Biodegradable (Wet)	Composting, biogas generation
Recyclable (Dry)	Send to recycling facilities (paper, plastic, metal, glass)
Hazardous	Special disposal (batteries, electronics, chemicals)
Non-recyclable	Minimize generation, safe landfill

Additional Methods:
• Community Composting: Neighborhood composting units
• E-waste Management: Proper disposal of electronics
• Public Awareness: Educate others about waste management
• Support Legislation: Follow and promote waste management laws

Impact of Individual Actions:
• Reduces landfill burden
• Conserves natural resources
• Saves energy
• Reduces pollution
• Creates employment in recycling industry

Answer: (a), (c), and (d) contain only biodegradable items

Analysis of each option:

Option	Items	Biodegradable?	Reason
(a)	Grass, flowers, leather	✓ All biodegradable	• Grass & flowers: Plant materials decompose naturally • Leather: Animal skin decomposes (though slowly)
(b)	Grass, wood, plastic	✗ Contains non-biodegradable	• Grass & wood: Biodegradable • Plastic: Non-biodegradable (synthetic polymer)
(c)	Fruit-peels, cake, lime-juice	✓ All biodegradable	• Fruit-peels: Organic plant matter • Cake: Food waste (flour, sugar, eggs) • Lime-juice: Organic liquid
(d)	Cake, wood, grass	✓ All biodegradable	• Cake: Food waste • Wood: Plant material • Grass: Plant material

Key Learning Points:
Biodegradable Items:
• Natural plant materials (grass, flowers, wood, fruit-peels)
• Food products (cake, lime-juice)
• Natural animal products (leather, wool, silk)
• Paper (from plant fibers)

Non-biodegradable Items:
• Synthetic plastics (all types)
• Glass
• Metals
• Most chemicals (DDT, pesticides)

Note on Leather:
• Natural leather is biodegradable but decomposes slowly
• Modern treated leathers may contain chemicals that slow decomposition
• In NCERT context, leather is considered biodegradable

Answer: (b) Grass, goat and human

What is a Food Chain?
A food chain represents the transfer of food energy from producers to consumers in a linear sequence.

Analysis of each option:

Option	Sequence	Valid Food Chain?	Explanation
(a)	Grass → Wheat → Mango	✗ Invalid	• All are producers (plants) • No consumer in sequence • Plants don't eat other plants (except carnivorous plants)
(b)	Grass → Goat → Human	✓ Valid	• Grass: Producer • Goat: Primary consumer (herbivore) • Human: Secondary consumer (omnivore) • Represents energy flow: Plant → Herbivore → Omnivore
(c)	Goat → Cow → Elephant	✗ Invalid	• All are consumers (herbivores) • Herbivores don't eat other herbivores • Missing producer at start
(d)	Grass → Fish → Goat	✗ Invalid	• Grass: Producer (terrestrial) • Fish: Consumer (aquatic) • Goat: Consumer (terrestrial herbivore) • Unrealistic: Goats don't eat fish

Characteristics of a Valid Food Chain:
1. Starts with a producer (autotroph: plant, algae)
2. Energy flows in one direction
3. Each organism eats the previous one
4. Represents feeding relationships
5. Typically has 3-5 trophic levels

More Examples of Valid Food Chains:
• Grass → Grasshopper → Frog → Snake → Hawk
• Phytoplankton → Zooplankton → Small fish → Large fish → Shark
• Leaves → Caterpillar → Bird → Fox

Note: Option (b) can be extended: Grass → Goat → Human → Decomposers

Answer:

Eliminating all organisms at one trophic level would disrupt the entire ecosystem, causing cascading effects.

Effects on Different Trophic Levels:

If this level is eliminated...	Consequences
Producers (1st trophic level)	• Ecosystem collapse • No food for herbivores • No oxygen production • All higher levels starve • Example: Deforestation kills plants → entire food chain collapses
Primary Consumers (2nd trophic level)	• Overpopulation of producers • Starvation of secondary consumers • Imbalance in plant growth • Example: Remove all deer → grass overgrows → wolves starve
Secondary Consumers (3rd trophic level)	• Overpopulation of primary consumers • Overgrazing of producers • Loss of biodiversity • Example: Remove all wolves → deer overpopulate → vegetation destroyed
Tertiary Consumers (4th trophic level)	• Overpopulation of secondary consumers • Cascade effects down the chain • Possible extinction of some species • Example: Remove all hawks → snakes increase → frogs decrease

General Consequences:
1. Trophic Cascade:
• Effects ripple through multiple trophic levels
• Both upward and downward impacts
• Can cause species extinctions

2. Population Imbalances:
• Prey populations explode without predators
• Predator populations crash without prey
• Competitive exclusion may occur

3. Ecosystem Collapse:
• Food webs disintegrate
• Nutrient cycles disrupted
• Energy flow stops
• Biodiversity loss

4. Real-world Examples:
• Wolves in Yellowstone: Their elimination caused deer overpopulation → vegetation loss → soil erosion → river changes
• DDT spraying: Killed insects → birds starved → insect pests rebounded
• Overfishing: Removes top predators → jellyfish blooms

Key Principle: All trophic levels are interconnected through food webs. Removing one level disrupts the delicate balance maintained by nature over millions of years.

Answer:

Part 1: Impact varies for different trophic levels
Yes, the impact differs significantly depending on which trophic level is removed.

Trophic Level Removed	Severity of Impact	Reason
Producers (1st level)	⭑⭑⭑⭑⭑ (Maximum)	• Energy entry point of ecosystem • All other levels depend on them • Ecosystem cannot survive without producers
Primary Consumers (2nd level)	⭑⭑⭑⭑ (High)	• Disconnects producers from higher levels • Causes producer overpopulation • Starves secondary consumers
Secondary Consumers (3rd level)	⭑⭑⭑ (Moderate-High)	• Causes primary consumer explosion • Overgrazing of producers • May lead to ecosystem imbalance
Tertiary Consumers (4th level)	⭑⭑ (Moderate)	• May cause temporary imbalance • Ecosystem may adjust over time • Other predators may fill the niche

Part 2: Can any level be removed without damage?
NO, removing any complete trophic level will cause damage to the ecosystem, though the extent varies.

Why No Trophic Level Can Be Removed Safely:
1. Interconnectedness:
• All levels are linked through food webs
• Each has specific ecological functions
• Energy flow depends on all levels

2. Ecological Functions:
• Producers: Convert solar energy, produce oxygen
• Consumers: Control populations, aid decomposition
• Decomposers: Recycle nutrients, clean environment

3. Buffer Capacity:
• Ecosystems have some resilience
• But complete removal exceeds this capacity
• Leads to irreversible changes

Possible Exceptions (Partial Removal):
1. Redundant Species: If multiple species occupy same niche, removing one might have less impact
2. Invasive Species: Removing non-native species can help restore balance
3. Overpopulated Levels: Controlled reduction (not elimination) may benefit ecosystem

Real-world Analogy:
Removing a trophic level is like removing a floor from a building – the entire structure becomes unstable or collapses.

Conservation Implication:
This understanding highlights why biodiversity conservation is crucial – every species, at every trophic level, plays a role in maintaining ecosystem health.

Answer:

Part 1: What is Biological Magnification?
Biological Magnification (Biomagnification) is the process where the concentration of toxic substances increases at successive trophic levels in a food chain.

Key Characteristics:
• Affects non-biodegradable substances (DDT, mercury, PCBs)
• Toxins accumulate in fatty tissues of organisms
• Not excreted or broken down easily
• Concentration increases up the food chain

Part 2: Different levels at different trophic levels
YES, the levels of magnification are different at different trophic levels, increasing at each step.

Example: DDT in Aquatic Food Chain

Trophic Level	Organism	DDT Concentration	Increase Factor
Water (Non-living)	–	0.003 ppm	Baseline
1st (Producers)	Phytoplankton	0.04 ppm	13×
2nd (Primary Consumers)	Zooplankton	0.5 ppm	167×
3rd (Secondary Consumers)	Small fish	2 ppm	667×
4th (Tertiary Consumers)	Large fish	5 ppm	1,667×
5th (Top Consumers)	Fish-eating birds	10-25 ppm	3,333-8,333×

Why Magnification Increases at Higher Levels:
1. Consumption Ratio:
• Each predator consumes many prey organisms
• Toxins from all prey accumulate in predator
• Example: Eagle eats 100 fish → gets toxins from all 100

2. Fat Solubility:
• Most toxins are lipid-soluble (dissolve in fats)
• Stored in fatty tissues, not excreted
• Concentration builds up over lifetime

3. Slow Decomposition:
• Non-biodegradable toxins don't break down
• Remain in organism until death
• Then transferred to next consumer

Real-world Example: Minamata Disease
• Mercury discharged in water → algae → small fish → large fish → humans
• Mercury concentration increased at each level
• Humans at top suffered neurological damage

Mathematical Representation:
If each trophic level magnifies toxin by 10×:
Water: 1 unit → Producer: 10 units → Primary consumer: 100 units → Secondary consumer: 1,000 units → Tertiary consumer: 10,000 units

Prevention: Control use of persistent toxic chemicals, proper waste disposal, monitoring food chains.

Answer:

Non-biodegradable wastes cause multiple environmental, health, and economic problems:

Problem Category	Specific Problems	Examples
Environmental Pollution	• Soil contamination • Water pollution • Air pollution (burning plastics) • Visual pollution • Marine ecosystem damage	• Plastic bags in soil reduce fertility • Microplastics in oceans • Dioxins from burning plastic • Landscapes littered with waste
Health Hazards	• Toxic chemical exposure • Disease vectors breeding grounds • Respiratory problems • Cancer risks • Reproductive issues	• Lead from batteries • Mosquitoes in discarded tires • Asthma from particulate matter • DDT causing cancer • BPA in plastics affecting hormones
Ecosystem Damage	• Wildlife harm (ingestion, entanglement) • Soil fertility reduction • Water body clogging • Coral reef destruction • Bioaccumulation in food chains	• Sea turtles eating plastic bags • Aluminum cans affecting soil pH • Plastic blocking rivers • Sunscreen chemicals killing coral • Mercury in fish
Resource Management	• Landfill space consumption • Resource wastage • Energy consumption for production • Recycling challenges • Long-term storage problems	• Mountains of e-waste • Metals not recovered • High energy to make new plastic • Mixed plastics hard to recycle • Nuclear waste storage for millennia
Economic Costs	• Waste management expenses • Healthcare costs • Tourism revenue loss • Agricultural productivity loss • Cleanup operations	• Municipal solid waste management • Treating pollution-related diseases • Dirty beaches deter tourists • Contaminated farmland • Ocean cleanup projects

Specific Examples by Waste Type:

1. Plastics:
• Microplastics: Enter food chain, found in human blood
• Marine debris: 1 million seabirds, 100,000 marine mammals killed annually
• Landfill persistence: Take 400-1000 years to decompose

2. Electronic Waste (E-waste):
• Toxic metals: Lead, mercury, cadmium leach into soil/water
• Informal recycling: Health risks to workers (especially in developing countries)
• Rapid generation: Fastest growing waste stream globally

3. Chemical Wastes:
• Persistent Organic Pollutants (POPs): DDT, PCBs remain for decades
• Heavy metals: Mercury, arsenic accumulate in organisms
• Radioactive waste: Dangerous for thousands of years

4. Construction Debris:
• Concrete, bricks: Consume landfill space
• Asbestos: Carcinogenic when disturbed
• Paints: Contain toxic solvents and metals

Long-term Implications:
• Future generations inherit pollution
• Irreversible damage to some ecosystems
• Cumulative effects may be catastrophic
• Climate change linkages (plastic production emits GHGs)

Solutions: Reduce use, improve recycling, develop biodegradable alternatives, proper disposal systems, public awareness.

Answer:

NO, even if all waste were biodegradable, it would still have significant environmental impacts if not managed properly.

Problems with Biodegradable Waste (if unmanaged):

Impact Type	Problem	Mechanism
Greenhouse Gas Emissions	Methane production	Anaerobic decomposition in landfills produces CH₄ (25× more potent than CO₂)
Water Pollution	Eutrophication	Nutrient runoff causes algal blooms → oxygen depletion → dead zones
Air Pollution	Odor, particulates	Decomposition releases foul smells, airborne bacteria, fungal spores
Health Hazards	Disease vectors	Attracts flies, mosquitoes, rodents that spread diseases (malaria, dengue, plague)
Soil Contamination	Leachate formation	Decomposing waste produces toxic liquids that contaminate groundwater
Aesthetic Issues	Visual pollution	Uncollected waste creates unsightly conditions, reduces property values

Specific Scenarios:

1. Large-scale Agriculture Waste:
• Crop residues burning causes air pollution (PM2.5, CO)
• Stubble burning in North India creates severe smog
• Sugar mill effluents pollute rivers

2. Food Waste in Landfills:
• 8-10% of global greenhouse gases from food waste
• Methane from landfills contributes to climate change
• Attracts pests and creates public health risks

3. Animal Waste from Livestock:
• Manure runoff contaminates water with nitrates, pathogens
• Ammonia emissions affect air quality
• Antibiotics in manure create drug-resistant bacteria

4. Human Sewage:
• Pathogens (bacteria, viruses, parasites) in untreated sewage
• Nutrient overload causes eutrophication
• Oxygen demand depletes aquatic oxygen

Quantitative Impacts:
• Methane: 1 ton food waste ≈ 0.5 tons CO₂-equivalent
• Water: 1 kg biodegradable waste pollutes 1000 L water
• Land: Organic waste occupies 60-70% landfill space

Proper Management Required:
Beneficial Processing Methods:
1. Composting: Produces organic fertilizer
2. Vermicomposting: Using earthworms for faster decomposition
3. Biogas Production: Anaerobic digestion for energy
4. Incineration with Energy Recovery: Waste-to-energy plants

Conclusion:
While biodegradable waste is preferable to non-biodegradable waste, it still requires proper management to prevent environmental harm. The key is not just what waste we generate, but how we manage it.

Answer:

Part 1: Why ozone layer damage is concerning
Ozone layer depletion allows more harmful UV radiation to reach Earth, causing multiple problems:

Impact Area	Specific Concerns	Mechanism
Human Health	• Skin cancers (melanoma, non-melanoma) • Cataracts and eye damage • Weakened immune system • Premature skin aging	UV-B damages DNA, proteins, and cells
Ecosystems	• Reduced phytoplankton productivity • Coral bleaching • Plant growth inhibition • Amphibian population decline	UV affects photosynthesis, reproduction, development
Agriculture	• Reduced crop yields • Poor quality produce • Increased vulnerability to diseases	UV damages plant tissues, reduces photosynthesis
Materials	• Faster degradation of plastics • Fading of paints and dyes • Reduced lifetime of outdoor materials	UV breaks chemical bonds in materials
Climate	• Altered atmospheric circulation • Potential climate change effects • Changed precipitation patterns	Ozone affects temperature distribution in stratosphere

Quantitative Risks:
• 1% decrease in ozone → 2-3% increase in skin cancer
• UV-B increases 10% for every 4% ozone loss
• Phytoplankton productivity reduced by 6-12% under ozone hole

Part 2: Steps taken to limit damage

1. International Agreements:
• Montreal Protocol (1987): Global treaty to phase out ozone-depleting substances
• Vienna Convention (1985): Framework for ozone protection
• London (1990), Copenhagen (1992) Amendments: Accelerated phase-out schedules

2. Phasing Out Ozone-Depleting Substances:

Substance	Use	Phase-out Status
CFCs (Chlorofluorocarbons)	Refrigerants, aerosols, foam blowing	Phased out globally (developed: 1996, developing: 2010)
Halons	Fire extinguishers	Phased out (emergency uses only)
Carbon Tetrachloride	Solvents, chemical production	Phased out globally
Methyl Chloroform	Industrial solvent	Phased out globally
HCFCs (Hydrochlorofluorocarbons)	Transitional substitutes for CFCs	Phasing out (complete by 2030 in developing countries)

3. Technological Solutions:
• Development of ozone-friendly alternatives (HFCs, hydrocarbons, ammonia)
• Recovery and recycling of existing CFCs
• Modification of equipment to use alternatives

4. Monitoring and Research:
• Satellite monitoring (NASA, ESA)
• Ground-based ozone measurement stations
• Atmospheric research on ozone chemistry
• Assessment reports every 4 years

5. National Actions:
• India: Ozone Rules (2000), Ozone Cell in Ministry of Environment
• USA: Clean Air Act amendments
• EU: Regulations exceeding Montreal Protocol requirements

Success Story:
• 99% of controlled ozone-depleting substances phased out
• Ozone hole showing signs of recovery
• Expected to heal completely by 2060s
• Prevented millions of skin cancer cases

Current Challenges:
• Illegal trade in CFCs
• Rising use of HFCs (potent greenhouse gases)
• New threats from unregulated chemicals
• Climate change effects on ozone recovery

Kigali Amendment (2016): Extension of Montreal Protocol to phase down HFCs, addressing both ozone and climate change.