Our Environment — Class 10 Science
What CBSE examines here (2026-27). Verified against
jesc113.pdf, Reprint 2026-27 — the chapter's own core content (ecosystems, food chains/webs, trophic levels, the 10% energy rule, biological magnification, ozone depletion, biodegradable/non-biodegradable waste) is intact and unchanged. Its real structure is three in-text "QUESTIONS" sets (2 + 3 + 2 = 7 questions) plus one end-of-chapter Exercise of 9 questions — not the 8/13 an older manifest claimed. Two things needed fixing: a fabricated fifth trophic level and an unverified "Lindeman (1942)" attribution to the 10% rule, neither of which is in the book (fixed below); and a batch of content on Chipko, Vandana Shiva, and India's forest/wildlife laws that actually belongs to "Sustainable Management of Natural Resources" — the old Chapter 16, entirely dropped from the current 13-chapter book — kept in the appendix as background, not as this chapter's own content.
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
The book itself stops at four trophic levels and says why: so little usable energy remains after four steps that food chains "generally consist of only three or four steps" — a fifth level isn't described as rare, it simply isn't part of the pattern the chapter teaches.
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)
The Book's Own Numbers
Green plants in a terrestrial ecosystem capture only about 1% of the solar energy falling on their leaves. Of the food a consumer eats, an average of only 10% is turned into its own body and made available to the next trophic level — the chapter gives this as an average value, not attributed to a named rule or scientist.
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. 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)
10. 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.
11. Indian Context
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)
12. 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
- Biodegradable vs non-biodegradable waste
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.
Appendix — beyond the current syllabus
Not examinable in CBSE 2026-27, as part of this chapter. Everything below is genuine, accurate environmental content — but it belongs to "Sustainable Management of Natural Resources," the old Chapter 16 of the pre-rationalisation NCERT book, which covered forest and wildlife conservation, dams and water harvesting, and the conservation of coal and petroleum. That chapter was dropped entirely when the book was rationalised down to 13 chapters — none of its content, or the names below, appear anywhere in the current "Our Environment" chapter (confirmed by full-text search). It's kept here as background, since it's still useful civics and general knowledge, just not what this specific chapter examines.
Reduce, Reuse, Recycle (3 R's)
- REDUCE: use less stuff
- REUSE: use again (cloth bags, water bottles)
- RECYCLE: turn old into new
Personal, Community and Government Action
- Personal: save water and electricity, use a bicycle or walk for short distances, plant trees, avoid single-use plastics, compost kitchen waste, buy local produce
- Community: clean-up drives, school environment clubs, citizen science (water quality monitoring), tree plantation
- Government: renewable energy push, EV promotion, forest conservation, pollution control
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)
