生态学

An ecosystem 生态系统 is the interaction of a community of living organisms (biotic 生物因子) with the non-living (abiotic factor 非生物因子) parts of their environment. Levels of organisation: individual → population → community → ecosystem.

Competition 竞争: plants compete for light, space, water and mineral ions; animals compete for food, mates and territory. Interdependence 相互依赖: each species depends on others for food, shelter, pollination, seed dispersal — remove one species and the whole community can be affected.

Abiotic factors affecting a community: light intensity, temperature, moisture levels, soil pH and mineral content, wind intensity and direction, carbon dioxide levels (plants), oxygen levels (aquatic animals). Biotic factors : availability of food, new predators arriving, new pathogens, one species outcompeting another until numbers fall too low to breed. Explain the effect of a change in any of these from given data.

Adaptations 适应性 — features that enable survival in normal conditions — are structural (shape/body), behavioural (actions) or functional (processes, e.g. camouflage chemistry, venom). Extremophiles 极端微生物 live in extreme environments — high temperature, pressure or salt — e.g. bacteria in deep-sea vents.

Photosynthetic organisms are the producers 生产者 of biomass for life on Earth. Food chains: producer (green plant/alga making glucose by photosynthesis) → primary consumers 初级消费者 → secondary consumers 次级消费者 → tertiary consumers 三级消费者.

Predators kill and eat prey; in a stable community their numbers rise and fall in cycles — interpret the classic predator–prey graph (prey rises first, predator follows).

Sampling (RP9): transects and quadrats measure the distribution and abundance of species; calculate mean, mode, median of abundance; plot graphs with suitable scales.

Carbon cycle: returns carbon from organisms to the atmosphere as carbon dioxide for photosynthesis — respiration (plants, animals, decomposers), decay, combustion. Water cycle: evaporation and precipitation provide fresh water before it drains to the sea. Microorganisms recycle materials — returning carbon to the atmosphere as CO₂ and mineral ions to the soil. The nitrogen cycle is NOT required.

(Bio) Decomposition (RP10): temperature, water and oxygen affect the rate of decay. Gardeners and farmers provide optimum conditions for rapid decay 腐解 of waste into compost — a natural fertiliser. Anaerobic decay produces methane — biogas generators. RP10: effect of temperature on the rate of decay of fresh milk by measuring pH change.

(HT Bio) Environmental change: temperature, water availability, atmospheric-gas composition — changes may be seasonal, geographic or human-caused — shift the distribution of species.

Biodiversity 生物多样性 is the variety of all different species on Earth or within an ecosystem; it stabilises ecosystems by reducing the dependence of one species on another, and our own future relies on maintaining it.

• Waste management: population growth and living standards increase resource use and waste → pollution 污染 in water (sewage, fertiliser, toxic chemicals), air (smoke, acidic gases) and on land (landfill, toxic chemicals) — killing plants and animals.
• Land use: building, quarrying, farming and dumping waste reduce land for other species; destroying peat bogs for garden compost destroys habitat and biodiversity, and decaying or burnt peat releases CO₂.
• Deforestation in tropical areas: land for cattle and rice fields, crops for biofuels.
• Global warming: rising atmospheric CO₂ and methane contribute to global warming; describe biological consequences (distribution shifts, migration changes, biodiversity loss).

Maintaining biodiversity — programmes reducing negative human effects: breeding programmes for endangered species; protection and regeneration of rare habitats; field margins and hedgerows reintroduced in single-crop areas; reduced deforestation and CO₂ emissions; recycling rather than landfill.

Trophic levels: 1 producers (plants, algae); 2 primary consumers (herbivores); 3 secondary consumers (carnivores eating herbivores); 4 tertiary consumers (carnivores eating carnivores). Apex predators have no predators. Decomposers secrete enzymes onto dead material and absorb the small soluble food molecules.

Pyramids of biomass: trophic level 1 at the bottom; construct from data. Transfer of biomass: producers transfer ~1 % of incident light energy into biomass; only ~10 % of biomass passes from each level to the next — losses from egested faeces (not all ingested material is absorbed) and waste (CO₂ and water from respiration, water and urea in urine); glucose used in respiration. Calculate efficiency by percentage or fraction of mass.

Food security 粮食安全 — having enough food for the population — is threatened by: rising birth rate; changing diets in developed countries; new pests and pathogens; environmental changes (famine when rains fail); the cost of agricultural inputs; conflicts affecting water or food availability.

Farming techniques improve efficiency by restricting energy transfer from food animals to the environment — limiting movement and controlling temperature; high-protein feeds increase growth. Weigh these against ethical objections to intensive farming.

Sustainable fisheries: maintain fish stocks where breeding continues — control net size and fishing quotas .

Role of biotechnology: culturing microorganisms for food — Fusarium fungus grown on glucose syrup in aerobic conditions produces mycoprotein 菌蛋白 (protein-rich, vegetarian); GM bacteria produce insulin; GM crops such as golden rice add food or nutritional value.