Quick Revision

An ecosystem is a self-sustaining system of living organisms interacting with each other and with their physical environment. Two components: 1. Biotic (living) — Producers, consumers, decomposers. 2. Abiotic (non-living) — Sunlight, temperature, water, soil, air, minerals. Examples: Forest ecosystem, pond ecosystem, desert ecosystem.

The 10% law (proposed by Lindemann) states that only 10% of the energy available at each trophic level gets transferred to the next trophic level. The remaining 90% is used by the organism for life processes (respiration, digestion, growth) and lost as heat. This is why food chains usually have 3-4 trophic levels.

Biological magnification (biomagnification) is the increase in concentration of harmful non-biodegradable chemicals (like pesticides such as DDT) at each successive trophic level in a food chain. Example: DDT sprayed on crops → absorbed by plants → eaten by insects (low concentration) → eaten by frogs (higher) → eaten by birds (highest concentration). Top predators like eagles have the highest concentration. This can cause reproductive failure and population decline in top predators.

Biodegradable waste: Can be broken down by biological processes (bacteria, fungi). Examples: food waste, paper, cotton, wood, cow dung. They decompose naturally and return nutrients to the soil. Do not cause long-term pollution. Non-biodegradable waste: Cannot be broken down by biological processes. Examples: plastic, glass, aluminium, DDT, heavy metals. They persist in the environment for very long periods. Cause pollution, harm wildlife (plastic in oceans), and accumulate in food chains (biomagnification). Solutions: Reduce, Reuse, Recycle. Segregate waste at source. Compost biodegradable waste.

The ozone (O₃) layer is a region in the stratosphere (about 15-35 km above Earth) with high concentration of ozone molecules. Importance: It absorbs harmful ultraviolet (UV) radiation from the sun, protecting life on Earth. UV radiation can cause: 1. Skin cancer and sunburns. 2. Cataracts (eye damage). 3. Damage to immune system. 4. Harm to crops and marine phytoplankton. Ozone depletion: CFCs (chlorofluorocarbons) from refrigerators, ACs, and aerosol sprays break down ozone. One CFC molecule can destroy thousands of ozone molecules. The ozone hole over Antarctica was discovered in 1985. UNEP led efforts — Montreal Protocol (1987) banned CFCs.