Why are top predators most affected by biological magnification?

Chapter 13 of 13

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CBSE Class 10 Science★ 6-8 marks · CBSE Class 10 Science (Chapter 13)

Our Environment

Our Environment — ecosystem, food chain, food web, trophic levels, energy flow, biological magnification. Ozone layer depletion, waste management, sustainable practices. CBSE Class 10 Science Chapter 13.

⏱ 22 min readEasy difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Understand ecosystem components
2Construct food chains and food webs
3Apply 10% rule for energy flow
4Explain biological magnification
5Apply waste management principles

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Why this chapter matters

Environmental literacy. Climate change is THE issue of our time. Foundation for sustainability.

Before you start — revise these

A 5-minute refresher here will save you 30 minutes of confusion below.

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Magnetic Effects

Previous (physics)

Our Environment — Class 10 Science

"We do not inherit the Earth from our ancestors; we borrow it from our children." — Native American proverb

1. About the Chapter

This is the FINAL chapter of Class 10 Science. Covers:

Ecosystems and components
Food chains and food webs
Trophic levels
Energy flow (10% rule)
Biological magnification
Ozone depletion
Waste management

Why Important

Environmental literacy crucial for future
Climate change is THE issue of our time
India faces serious environmental challenges
Final chapter — ends class on bigger picture

2. Ecosystem

Definition

An ecosystem = community of living things + non-living environment, interacting with each other.

Components

Biotic (Living):

Producers: plants, algae (make food via photosynthesis)
Consumers: animals (eat producers or other consumers)
Decomposers: bacteria, fungi (break down dead matter)

Abiotic (Non-living):

Sunlight, water, air, soil, minerals, temperature, climate

Types of Ecosystems

Natural:

Forests, grasslands, deserts, ponds, lakes, rivers, oceans, mountains

Artificial (man-made):

Aquariums, gardens, agricultural fields, parks

3. Food Chain

Definition

The sequence of WHO EATS WHOM in an ecosystem.

Example (Grassland)

Grass → Grasshopper → Frog → Snake → Eagle

Energy Flow Direction

ONE-WAY: Sun → Producers → Consumers (Primary, Secondary, Tertiary)

Trophic Levels

First (T1): Producers (plants)
Second (T2): Primary consumers (herbivores) — eat plants
Third (T3): Secondary consumers (carnivores) — eat herbivores
Fourth (T4): Tertiary consumers (top carnivores) — eat secondary consumers
Fifth (T5): Often missing; rare

Decomposers

Special role — break down dead organisms at ALL levels, returning nutrients to soil.

4. Food Web

Definition

A NETWORK of interconnected food chains in an ecosystem.

Example

Grass eaten by grasshopper AND deer AND rabbit
Grasshopper eaten by frog AND bird
Frog eaten by snake AND owl
Snake eaten by owl AND eagle

Real ecosystems have MANY food chains overlapping.

Why Food Webs Matter

More STABLE than single chains
If one species disappears, others can fill the role
Reflect real ecological complexity

5. Energy Flow (10% Rule)

Lindeman's 10% Rule (1942)

Only about 10% of energy at one trophic level is transferred to the NEXT level.

Why So Little?

90% lost as HEAT (respiration)
Used for movement, metabolism
Cannot all transfer up

Example (Numbers)

If producers (grass) have 10,000 calories of energy:

T1 (producers): 10,000 cal
T2 (herbivores): 1,000 cal
T3 (small carnivores): 100 cal
T4 (large carnivores): 10 cal

This is why:

BASE of food chain has MANY producers
TOP of food chain has FEW top predators
Food chains rarely exceed 4-5 levels (energy too low)

Implications

VEGETARIAN diet is more energy-efficient (one step from producers)
MEAT requires more land/water (multiple steps from producers)
Affects global food sustainability

6. Biological Magnification

Definition

The concentration of POLLUTANTS (especially pesticides) INCREASES as we move up the food chain.

Why?

Pollutants don't break down easily
Stored in body fat
Animals eat MANY contaminated organisms
Each step concentrates more

Example

Pesticide spray on crops:

Water/soil: very dilute
Grass: slightly higher
Cow (eats grass): even more
Milk (from cow): concentrated
HUMAN (drinks milk): MOST concentrated

Famous Cases

DDT in birds: thinned eggshells, near-extinction of bald eagle
Mercury in fish: Minamata disease in Japan
Plastic microparticles in marine food chain

Why Humans at Risk

Humans often at TOP of food chains → accumulate highest pollutant concentrations.

7. Ozone Layer Depletion

What is the Ozone Layer?

Layer of OZONE (O₃) gas in STRATOSPHERE (~15-35 km up)
ABSORBS harmful UV-B radiation from Sun
Protects life on Earth

Why Depleting?

Chlorofluorocarbons (CFCs) — used in:

Old refrigerators
Air conditioners
Aerosol sprays
Plastic foams

CFCs reach stratosphere, react with O₃, destroy it.

Consequences

Increased UV reaches Earth
Skin cancer, eye damage
Crop damage
Marine ecosystem disruption

Solution

Montreal Protocol (1987) — banned CFCs globally.

Most successful international environmental treaty
Ozone hole over Antarctica RECOVERING
Indian companies switched to safer alternatives

Lesson

Global action CAN solve environmental problems.

8. Waste Management

Types of Waste

Biodegradable:

Decomposed by microbes
Examples: food waste, paper, wood, cotton, animal/plant remains

Non-biodegradable:

Resist decomposition
Examples: plastics, metals, glass, certain chemicals
Stay in environment for HUNDREDS of years

Waste Disposal Methods

1. Landfills

Designated areas for burying waste
Many environmental issues (groundwater contamination)

2. Incineration

Burning waste
Some toxic emissions

3. Composting

Convert biodegradable waste to fertiliser
Eco-friendly
Done in homes, schools, communities

4. Recycling

Convert old materials to new products
Saves energy, reduces extraction
Paper, glass, metals widely recycled

5. Sewage Treatment

Treat liquid waste before release
Indian cities (Bengaluru, Delhi, Mumbai) need more plants

India's Waste Crisis

2 million tonnes of waste daily
Only 60% collected
Less than half processed
MAJOR challenge

Indian Initiatives

Swachh Bharat Abhiyan (since 2014): cleanliness mission
Plastic ban: in several states (TN, MH, Sikkim)
Solid Waste Management Rules 2016
Namami Gange: river cleaning

9. Sustainable Practices

Reduce, Reuse, Recycle (3 R's)

REDUCE: use less stuff
REUSE: use again (cloth bags, water bottles)
RECYCLE: turn old into new

Personal Actions

Save water (close tap, fix leaks, rainwater harvesting)
Save electricity (LED lights, switch off when unused)
Use bicycle/walk for short distances
Plant trees
Avoid single-use plastics
Compost kitchen waste
Buy local produce (less transport)

Community Actions

Clean-up drives
School environment clubs
Citizen science (water quality monitoring)
Tree plantation

Government Actions

Renewable energy push (500 GW by 2030)
EV promotion
Forest conservation
Pollution control

10. Worked Examples

Example 1: Food chain

Write a food chain in a pond.

Algae → Zooplankton → Small fish → Big fish → Heron
All food chains START with producers, END with decomposers (typically)

Example 2: 10% rule

If producers have 5000 calories, what energy reaches the 4th trophic level?

T1: 5000
T2: 500 (10%)
T3: 50 (10%)
T4: 5 calories

Example 3: Decomposers

What role do decomposers play in ecosystem?

Break down dead organisms
Release nutrients back to soil
Without them, dead matter would pile up; new plants couldn't grow.
Essential for nutrient cycling.

Example 4: Biological Magnification

Why are top predators most affected by pesticides?

Pesticides accumulate up food chain
Top predators eat MANY contaminated organisms
Concentration multiplies at each level
TOP gets HIGHEST pollutant levels
Examples: eagles (DDT), tigers (today's pesticides)

11. Common Mistakes

Confusing trophic levels
- T1 = producers (plants); T2 = herbivores; T3 = small carnivores; T4 = top carnivores.
Energy in cycles
- Energy flows ONE-WAY (sun → producers → consumers).
- Matter cycles (carbon, nitrogen, water).
All decomposers are bacteria
- Also fungi, some animals (earthworms).
Ozone bad in air
- Ozone in STRATOSPHERE = PROTECTIVE.
- Ozone in TROPOSPHERE (ground level) = POLLUTANT (smog).
Biodegradable = okay
- Even biodegradable waste must be properly composted, not thrown in landfills.

12. Indian Context

India's Environmental Heroes

Sundarlal Bahuguna: Chipko Movement
Vandana Shiva: environmental activist
Saalumarada Thimmakka: planted 8,000+ trees
Jadav Payeng: 'Forest Man of India' (grew forest single-handedly)

India's Environmental Laws

Wildlife Protection Act 1972
Forest Conservation Act 1980
Environment Protection Act 1986
National Green Tribunal (2010)

Major Challenges

Air pollution (Delhi #1 worst city)
Water pollution (Yamuna, Ganga in places)
Deforestation
Plastic waste
Climate change effects (erratic monsoon, glacier melt)

Government Initiatives

Swachh Bharat (cleanliness)
Namami Gange (Ganga cleaning)
Renewable energy push
Mission LiFE (Lifestyle for Environment, launched 2022)

13. Conclusion

Our Environment is the FOUNDATION of all life:

Ecosystems sustain all species
Food chains describe energy flow
10% rule explains why food chains are short
Biological magnification explains why pollutants reach humans
Ozone depletion showed global cooperation works
Waste management is critical for sustainability

Master:

Ecosystem components
Food chains and webs
Trophic levels
10% rule
Biological magnification
Sustainability principles

Class 10 Science ends here. The most important lesson: WE are part of the environment. Caring for it is caring for OURSELVES.

For Class 11-12, you'll specialise in Physics, Chemistry, Biology. For now, master the basics across all three.

Earth is our home. Be its guardian.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Ecosystem

Biotic + Abiotic components

Trophic levels

T1 (Producers) → T2 (Herbivores) → T3 → T4 (Top carnivores)

10% rule

Only 10% energy transfers to next trophic level

90% lost as heat

Biological magnification

Pollutants concentrate UP food chain

Montreal Protocol

1987 — banned CFCs to protect ozone

3 R's

Reduce, Reuse, Recycle

⚠️

Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Energy cycles in ecosystem

✓ Energy FLOWS ONE-WAY (sun → producers → consumers). MATTER cycles (carbon, water).

WATCH OUT

✗ Ozone is always harmful

✓ Stratospheric ozone PROTECTS (absorbs UV). Tropospheric ozone (ground level) is POLLUTANT.

WATCH OUT

✗ Biodegradable = no problem

✓ Biodegradable waste must be PROPERLY COMPOSTED. Mixed in landfills, it can produce methane (greenhouse gas).

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· Food chain

Write a food chain in a grassland.

▶ Show solution

✦ Answer: Grass → Grasshopper → Frog → Snake → Eagle. (Many variations possible.)

Q2EASY· Ozone

Why is the ozone layer important?

▶ Show solution

✦ Answer: Ozone layer (in stratosphere) ABSORBS harmful UV-B radiation from Sun. Without it, UV would cause skin cancer, eye damage, harm crops and marine life.

Q3MEDIUM· 10% rule

Explain the 10% rule with an example.

▶ Show solution

Step 1 — Statement of 10% Rule.
  Only 10% of energy at one trophic level is transferred to the NEXT level. 90% is lost as heat (respiration, movement).

Step 2 — Example numbers.
  Producers (grass): 10,000 calories
  Primary consumers (deer): 1,000 cal (10%)
  Secondary consumers (lion): 100 cal (10%)
  Tertiary consumers (top predator): 10 cal (10%)

Step 3 — Implications.
  • Food chains rarely exceed 4-5 levels (energy too low)
  • TOP predators are FEW in number (need many prey)
  • Vegetarian diet is more energy-efficient

Step 4 — Lindeman discovered (1942).
  Raymond Lindeman first formalised this — basis of ecology.

Step 5 — Why so much loss?
  • Heat from respiration
  • Movement
  • Reproduction
  • Not all parts edible/digestible

✦ Answer: 10% rule: only 10% of energy at one trophic level transfers to the next; 90% lost as heat. Example: 10,000 cal in producers → 1,000 cal in herbivores → 100 cal in carnivores → 10 cal in top predator. This explains why food chains are short and why there are few top predators.

Q4HARD· Application

Discuss the problem of plastic pollution in India and possible solutions.

▶ Show solution

Step 1 — Plastic problem.
  India produces ~10 million tonnes of plastic waste annually. Only ~60% collected. Less than half properly processed. Rest ends up in landfills, rivers, oceans.

Step 2 — Why plastic is problematic.
  • NON-BIODEGRADABLE: takes 100-1000+ years to break down
  • Choking marine life: turtles, whales, fish eat plastic
  • Microplastics enter food chain (BIOLOGICAL MAGNIFICATION)
  • Found in human blood, breast milk (2020s research)
  • Air pollution when burnt
  • Soil contamination

Step 3 — Sources.
  • Single-use plastics (bags, bottles, straws, packaging)
  • Industrial waste
  • Synthetic textiles (microfibres)
  • Construction waste

Step 4 — Indian initiatives.
  • PLASTIC BAN: many states (Tamil Nadu, Maharashtra, Sikkim, etc.) banned single-use plastics
  • EXTENDED PRODUCER RESPONSIBILITY (EPR): companies must collect and recycle their packaging
  • SWACHH BHARAT: cleanliness mission
  • NAMAMI GANGE: river cleaning programme

Step 5 — Individual solutions.
  • USE CLOTH/JUTE BAGS instead of plastic
  • Carry your own water bottle (refillable)
  • Refuse single-use straws, cutlery
  • Buy products with minimal packaging
  • Buy local (less transport packaging)
  • Compost biodegradable waste
  • Separate dry/wet waste

Step 6 — Community solutions.
  • Beach clean-ups
  • Waste segregation drives
  • Plant trees
  • Educate others
  • Support local recycling

Step 7 — Industry solutions.
  • Bioplastics (made from corn, sugarcane)
  • Recycling industries
  • Refill shops (Bring Your Own Container)
  • Cassava and seaweed packaging
  • Reduce packaging

Step 8 — Government policy.
  • Stricter enforcement of plastic bans
  • Tax on plastic
  • Investment in waste processing infrastructure
  • Awareness campaigns

Step 9 — Indian success stories.
  • Sikkim: largely plastic-free state
  • Kerala: strong waste segregation
  • Many startups developing biodegradable alternatives

Step 10 — Global context.
  • Indian Ocean is heavily polluted (5 ocean gyres of plastic)
  • India is signatory to UN plastic treaty (2022)
  • Global cooperation needed

✦ Answer: India produces ~10M tonnes plastic waste/year; only 60% collected. Plastic is non-biodegradable, harming marine life, entering food chain, contaminating soil. Solutions: (1) Personal (cloth bags, refillable bottles, refuse single-use); (2) Community (clean-ups, education); (3) Industry (bioplastics, recycling); (4) Government (bans, EPR, infrastructure). Indian successes: Sikkim plastic-free, Kerala segregation. Global treaty signed 2022. Individual action multiplied by 1.4B Indians = massive impact.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Ecosystem: biotic + abiotic components
•Trophic levels: T1 (producer) to T4 (top consumer)
•Food chain: linear; Food web: interconnected
•10% rule (Lindeman): only 10% energy to next level
•Biological magnification: pollutants concentrate UP
•Producers: plants (autotrophs)
•Decomposers: bacteria, fungi
•Ozone layer: stratosphere; absorbs UV
•CFCs destroy ozone
•Montreal Protocol (1987): banned CFCs
•Biodegradable: composts (paper, food)
•Non-biodegradable: plastic, metals, glass
•3 R's: Reduce, Reuse, Recycle
•Indian initiatives: Swachh Bharat, Namami Gange, Mission LiFE

CBSE marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 6-8 marks

Question type	Marks each	Typical count	What it tests
MCQ	1	3	Ecosystem terms
Short	2-3	2	Food chains, ozone
Long	5	0-1	Environmental issues

Prep strategy

Memorise trophic levels
Master 10% rule
Understand biological magnification
Know Indian initiatives

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Indian wildlife reserves

Project Tiger (1973), elephant corridors. Ecosystem protection for species survival.

Mission LiFE

Indian global initiative (2022) for sustainable lifestyles. Now adopted by UN.

Swachh Bharat

₹62,000+ crore cleanliness mission. 100,000+ public toilets built.

Sikkim plastic-free

First Indian state to ban single-use plastics (1998). Model for others.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Memorise food chain examples
Master 10% rule
Connect environmental issues
Know Indian government initiatives

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Biogeochemical cycles
Climate change in detail
Biodiversity hotspots
Read 'Silent Spring' by Rachel Carson

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

CBSE Class 10 BoardVery High

Science OlympiadVery High

Environmental StudiesVery High

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

Pollutants don't break down; they accumulate in body fat. As we go up the food chain, predators eat MANY contaminated organisms. Each step CONCENTRATES the pollutant. Top predators (tigers, eagles, killer whales) get HIGHEST concentrations. Humans, often at top, also affected. Classic example: DDT thinning bald eagle eggshells nearly extinct them.

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