Ans: Unmanaged garbage causes: soil, water, and air pollution; spread of diseases; blockage of drains; release of greenhouse gases (methane from rotting waste); harm to wildlife. Methods of waste disposal: (1) Landfills — waste buried underground; not ideal due to leaching of toxins and methane production. (2) Composting — biodegradable waste decomposed into manure by microbes; enriches soil. (3) Incineration — burning waste; reduces volume but releases pollutants. (4) Recycling — processing waste (paper, glass, metal, plastic) into new products; most sustainable. (5) Biogas plants — organic waste converted to methane gas for fuel. (6) Vermicomposting — earthworms decompose organic waste. Segregation of waste at source (biodegradable vs non-biodegradable) is essential.

Ans: Excessive fertilisers (containing nitrates and phosphates) run off from fields into nearby rivers, lakes, and ponds — a process called eutrophication: (1) Nitrates and phosphates cause explosive growth of algae (algal bloom) on the water surface. (2) Algae blocks sunlight from reaching aquatic plants below, killing them. (3) When algae die, bacteria decompose them using large amounts of dissolved oxygen (BOD — Biological Oxygen Demand increases). (4) Dissolved oxygen in water drops drastically. (5) Fish and other aquatic animals die due to lack of oxygen (hypoxia/dead zones). Additionally: nitrates in drinking water cause methemoglobinemia (blue baby syndrome) in infants; pesticides bioaccumulate in food chains.

Ans: Decomposers (mainly bacteria and fungi) are organisms that break down dead and decaying organic matter (dead plants, animals, feces, etc.) into simpler inorganic substances. Their roles: (1) Nutrient cycling — they release minerals (nitrogen, phosphorus, potassium) back into the soil, making them available for plants again. Without decomposers, dead matter would accumulate and nutrients would be locked up, starving producers. (2) Soil formation — decomposition of organic matter creates humus, improving soil fertility and structure. (3) Energy flow — they obtain energy from dead organic matter, completing the energy flow in the ecosystem. They are essential for the sustainability of all ecosystems.

Ans: A food chain is a series of organisms in an ecosystem where each organism eats the previous one, transferring energy and nutrients. Example: Grass → Grasshopper → Frog → Snake → Eagle. 10% law (Lindeman's Rule): Only 10% of the energy at one trophic level is available to the next trophic level — 90% is lost as heat during metabolism, movement, and other life processes. Example: If producers (grass) have 10,000 J of energy: Herbivores get 1,000 J (10%). Carnivores I get 100 J (10% of 1,000). Carnivores II get 10 J. This is why food chains rarely have more than 4–5 levels — too little energy remains at higher levels.