Use and Abuse of Biology
Ecosystems and Food Chains/Webs
An ecosystem is a community of organisms interacting with their abiotic (non-living) and biotic (living) environment.
Food chain: shows energy transfer. Producers (plants) → Primary consumers (herbivores) → Secondary consumers (carnivores) → Tertiary consumers.
Food web: multiple interconnected food chains. Removing one species can affect many others (e.g. removing a predator → prey population explodes → plant population crashes).
Trophic levels: each level in a food chain. Energy is lost at each trophic level (as heat, movement, waste) — only ~10% passes to the next level. This is why food chains rarely have more than 4–5 links.
Biodiversity and Its Importance
Biodiversity = the variety of life in an area (species richness + genetic diversity + ecosystem diversity).
High biodiversity:
- More stable ecosystems (many food web connections)
- Source of medicines (e.g. aspirin from willow bark; penicillin from fungi)
- Genetic resources for agriculture and biotechnology
- Intrinsic and ethical value
Threats to biodiversity: habitat destruction, climate change, pollution, invasive species, over-exploitation (hunting/fishing), disease.
Food Security
Food security = having reliable access to sufficient nutritious food.
Threats to food security:
- Population growth → more food demand
- Climate change → altered rainfall, extreme weather → crop failure
- Pests and disease → crop losses
- Water shortages → less irrigation
Strategies to improve food security:
- Selective breeding: higher yield, pest/disease resistant crops
- Genetic modification: GM crops (pest resistance, drought tolerance)
- Fertilisers: increase plant growth but risk eutrophication
- Pesticides: reduce crop losses but kill non-target species
- Biological control: using natural predators (avoids chemical pesticides)
- Hydroponics: growing plants without soil (controlled environment; year-round)
- Sustainable fishing (quotas, mesh size regulations)
Environmental Pollution
Eutrophication:
- Fertilisers (nitrates/phosphates) leach into waterways from agricultural land.
- Rapid algal growth (algal bloom) → algae block light.
- Plants below surface die → decomposers break down dead material.
- Decomposers use up dissolved O₂ (aerobic decomposition).
- Fish and other organisms die from lack of oxygen.
Pesticide accumulation (bioaccumulation/biomagnification): persistent pesticides (e.g. DDT) accumulate in fat tissue and concentrate at each trophic level. Predators at top of food chain receive highest doses → reproductive failure, death.
Acid rain: caused by SO₂ and NOₓ (from burning fossil fuels); dissolves in rain → dilute acids → damages leaves, acidifies lakes (kills aquatic life), corrodes limestone buildings.
Conservation
Reasons to conserve species and habitats: ecological stability, medicinal value, food security, aesthetic/ethical reasons, tourism.
Methods:
- In situ conservation: protected areas (nature reserves, national parks, marine protected areas).
- Ex situ conservation: captive breeding programmes (zoos, seed banks, gene banks).
- Legislation: international treaties (CITES — trade in endangered species); national endangered species acts.
- Education and ecotourism: raise awareness; provide economic incentives to local communities.
- Habitat restoration: rewilding, reforestation.
⚠Common mistakes
- Eutrophication kills fish because O₂ is depleted by decomposers — NOT because the algae directly poison the fish.
- Bioaccumulation concentrates toxins at HIGHER trophic levels — top predators are worst affected.
- Biodiversity is NOT just about the number of species — it includes genetic diversity and ecosystem diversity.
- Biological control uses living organisms (predators/parasites), not chemicals.
AI-generated · claude-opus-4-7 · v3-wjec-biology