Ecosystem, food chains, ozone layer depletion, waste management, biodegradability
An ecosystem is all the living organisms (biotic) in an area together with the non-living (abiotic) environment — interacting as a unit.
Types: Forest, Pond, Grassland, Desert, Coral reef, Aquarium (artificial)
Biotic components: Producers, consumers, decomposers
Abiotic components: Sunlight, air, water, soil, temperature, minerals
A food chain shows the transfer of food energy from one organism to another.
Example: Grass → Grasshopper → Frog → Snake → Eagle
Arrows show direction of energy flow (from food to feeder).
Multiple interconnected food chains form a food web. More realistic than a single food chain.
Biodiversity of food web → stability of ecosystem (if one species disappears, others compensate)
Only 10% of energy is transferred from one trophic level to the next. The remaining 90% is used for metabolism and lost as heat.
Example: If grass has 10,000 J → Grasshopper gets 1,000 J → Frog gets 100 J → Snake gets 10 J → Eagle gets 1 J
This is why food chains are usually limited to 3–5 levels — very little energy reaches the top!
Since only 10% transfers at each step, eating plants directly gives you more energy than eating animals (which ate plants). If 10,000 J is in plants → you get 1,000 J if you eat them directly (as a vegetarian) but only 100 J if you eat an animal that ate the plant. So vegetarian diets support 10× more people per hectare of land!
Biological magnification (bioaccumulation/biomagnification): The increase in concentration of harmful chemicals (pesticides like DDT) at each trophic level of a food chain.
Non-biodegradable chemicals → not broken down → accumulate in organisms → concentration increases up the food chain → top predators most affected!
Water: 0.003 ppm DDT → Algae: 0.04 ppm → Small fish: 0.5 ppm → Large fish: 2 ppm → Bird (top): 25 ppm
DDT concentration increased by ~10,000× from water to top predator! This is why bald eagles (fish-eaters) nearly went extinct — DDT weakened their eggshells.
Ozone (O₃) layer in stratosphere (15–35 km altitude) absorbs harmful UV radiation from sun.
UV rays cause: skin cancer, cataracts, immune system damage, harm to aquatic life
Cause of depletion: CFCs (Chlorofluorocarbons) from refrigerators, AC, aerosols → break down ozone.
CFC → releases Cl radicals → Cl + O₃ → ClO + O₂ → ClO + O → Cl + O₂ (Cl regenerated — catalytic cycle!)
Solution: Montreal Protocol (1987) — international treaty to phase out CFCs
| Type | Examples | Disposal |
|---|---|---|
| Biodegradable | Food waste, paper, cotton, wood, vegetable peels | Composting, landfill (decomposes naturally) |
| Non-biodegradable | Plastics, glass, metals, synthetic fibres, e-waste, pesticides | Recycling, incineration, landfill (doesn't decompose — long-term problem) |
• Decomposers return minerals to ecosystem — essential for nutrient cycling
• Non-biodegradable pollutants bioaccumulate in food chains
• Only 10% energy transfers between trophic levels
• Ozone hole over Antarctica is the most severe
• CFCs are the main cause of ozone depletion
• More biodiversity = more stable ecosystem