Ecology is the study of relationships between organisms and their environment. Ecosystem = biotic (living) + abiotic (non-living) components. Food chain: Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer. Food webs show interconnected food chains. Energy flows; matter cycles (carbon, nitrogen, water cycles). Biodiversity is the variety of life in an area. Threats: deforestation, pollution, climate change. Conservation: protected areas, captive breeding.