CBSE Class 10 Science: Our Environment — Complete Notes 2026

Ecosystem Components

• Biotic: producers (plants), consumers (animals), decomposers (bacteria, fungi)
• Abiotic: sunlight, temperature, humidity, pH, soil; drive energy flow and nutrient cycling
• Types: terrestrial (forest, desert, grassland), aquatic (marine, freshwater), artificial (crop fields)

Food Chains and Food Webs

• Food chain: linear sequence of who eats whom; each organism is a trophic level
• Grassland: grass → grasshopper → frog → snake → hawk; aquatic: phytoplankton → zooplankton → fish → shark
• Food web: interconnected food chains; more stable than single food chains

Energy Flow and 10% Law

• 10% law (Lindemann, 1942): only 10% of energy transferred from one trophic level to next
• Example: if grass has 10,000 J, herbivore gets 1,000 J, carnivore gets 100 J, top predator 10 J
• Implication: food chains rarely exceed 4–5 levels; shorter chain = more energy available

Biological Magnification

• Some substances (DDT, mercury) accumulate in organisms; concentration increases at each trophic level
• DDT concentration: water → plankton → small fish → large fish → osprey (10 million × increase)
• Human health risk: highest concentration in top predators; humans at top of food chain most affected

Ozone Layer Depletion

• Ozone (O₃) in stratosphere (15–35 km): absorbs harmful UV-B and UV-C radiation from sun
• CFCs (chlorofluorocarbons) from refrigerants, aerosols: break down ozone in stratosphere
• Effects: increased UV radiation → skin cancer, cataracts, damage to phytoplankton, reduced crop yields

Waste Management

• Biodegradable: paper, food waste, cotton — decomposed by microbes; non-biodegradable: plastic, glass, metals
• Reduce-Reuse-Recycle: reduce consumption first; reuse products; recycle materials into new products
• E-waste: fastest growing waste stream; contains toxic lead, cadmium, mercury; needs special recycling

CBSE Exam Focus Points

• 10% law calculation: always asked with a food chain — calculate energy at each level
• Ozone depletion: CFCs mechanism asked in 3-mark questions; UV radiation effects
• Define: biodegradable vs non-biodegradable; food chain vs food web