Chapter 13 — Our Environment

Chapter 13 of the Class 10 Science NCERT textbook, "Our Environment", explains how ecosystems function through food chains, energy flow, biological magnification of pesticides, ozone layer depletion by CFCs, and the environmental impact of biodegradable versus non-biodegradable waste.

• How an ecosystem is organised — An ecosystem combines living biotic components with non-living abiotic ones. Its organisms play roles as producers, consumers, or decomposers, and this structure lets energy and matter cycle through forests, ponds, and fields.
• Energy flow and food chains — Energy passes along food chains but only about ten percent transfers between trophic levels, which is why chains rarely exceed three or four steps. Non-degradable pesticides instead build up through biological magnification toward the top.
• Human impact on the environment — CFCs thinned the protective ozone layer until international action curbed them. Waste that is biodegradable breaks down naturally, whereas non-biodegradable plastics and disposables persist and increasingly harm ecosystems.

1. 01An ecosystem consists of biotic components (living organisms) and abiotic components (temperature, rainfall, wind, soil, minerals); examples include forests, ponds, gardens, and crop-fields.
2. 02Organisms are classified as producers (green plants and certain bacteria using photosynthesis), consumers (herbivores, carnivores, omnivores, parasites), and decomposers (bacteria and fungi that break down dead matter).
3. 03Only about 10% of energy at one trophic level is transferred to the next; green plants capture only about 1% of sunlight, which limits food chains to three or four trophic levels.
4. 04Biological magnification occurs when non-degradable pesticide chemicals accumulate progressively at each trophic level, reaching maximum concentration in humans at the top of the food chain.
5. 05The ozone layer (O₃) shields Earth from harmful UV radiation; synthetic chemicals called CFCs (used in refrigerants and fire extinguishers) caused a sharp drop in ozone levels from the 1980s, leading to a 1987 UNEP agreement to freeze CFC production.
6. 06Waste is classified as biodegradable (broken down by biological processes) or non-biodegradable (persists in the environment and may harm ecosystems); increased use of disposable and plastic items has worsened non-biodegradable waste problems.