Ecology studies the relationships between living organisms and their environment. This section covers energy flow through ecosystems, nutrient cycling, human impact on the environment, and conservation efforts.
Ecosystem: community of organisms + their physical environment. Habitat: where an organism lives. Population: group of same species. Community: all populations in an area. Food chain: producer → primary consumer → secondary consumer → tertiary consumer. Producer: makes own food (photosynthesis). Energy lost at each trophic level (respiration, heat, excretion, not all eaten). Pyramid of energy shows this loss. Typically only ~10% of energy passes to next level.
Carbon cycle: CO₂ → plants (photosynthesis) → animals (feeding) → CO₂ (respiration, combustion, decomposition). Fossil fuels: carbon stored millions of years, released by burning. Deforestation reduces CO₂ absorption. Nitrogen cycle (Supplement): N₂ in air → nitrogen-fixing bacteria → NH₃ → nitrifying bacteria → NO₃⁻ (absorbed by plants) → proteins → decomposition → NH₃ → denitrifying bacteria → N₂. Legumes have root nodules with nitrogen-fixing bacteria.
Pollution: CO₂/methane cause greenhouse effect → global warming → climate change. SO₂/NOₓ cause acid rain → damage to forests, lakes. Water pollution: fertiliser runoff → eutrophication (excess algae → algae die → decomposers use up O₂ → fish die). Deforestation: habitat loss, reduced biodiversity, soil erosion, more CO₂. Conservation: maintaining biodiversity through: protected areas, captive breeding, seed banks, sustainable development, education. Sampling: quadrats (plants), pitfall traps, sweep nets.
Biodiversity (variety of species in an ecosystem) is important for: (1) ecosystem stability — more species means more food web connections, so the ecosystem can recover from changes; (2) food security — diverse crops are more resistant to disease; (3) medical resources — many medicines come from plants and animals; (4) ecosystem services — pollination, water purification, nutrient cycling; (5) ethical reasons — all species have a right to exist. Loss of biodiversity (through habitat destruction, pollution, overexploitation) reduces ecosystem resilience and can have cascading effects through food webs.
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