📚 IGCSE OCR Biology: Ecology Key Revision Notes | IGCSE OCR 生物：生态学 考点精讲
Ecology is the study of how organisms interact with each other and their environment. This revision guide covers all essential topics for the IGCSE OCR Biology exam, including key terms, energy flow, cycles, populations, human impacts and fieldwork techniques.
生态学研究生物体如何彼此相互作用并与环境相互作用。本复习指南涵盖 IGCSE OCR 生物学考试所有基本主题，包括关键术语、能量流动、循环、种群、人类影响和实地调查技术。
1. Key Terminology in Ecology | 生态学关键术语
An ecosystem consists of a community of organisms interacting with the non-living (abiotic) components of their environment, such as a pond or a forest.
生态系统由生物群落与其环境中的非生物成分相互作用而形成，例如池塘或森林。
A habitat is the specific place where an organism lives, providing it with food, shelter and a breeding site.
栖息地是生物体居住的具体地方，为其提供食物、庇护和繁殖场所。
A population includes all organisms of the same species living in a particular area at the same time, while a community is made up of all populations of different species interacting in that area.
种群是同一物种在同一时间同一区域的所有个体，群落则由该区域所有不同物种种群相互作用组成。
A niche describes the role an organism plays in its ecosystem, including its habitat, feeding relationships and interactions with other species.
生态位描述生物在生态系统中的角色，包括其栖息地、食性以及与其他物种的相互作用。
Producers are autotrophs that synthesise organic molecules from inorganic sources; consumers are heterotrophs that feed on other organisms; decomposers break down dead organic matter.
生产者是自养生物，从无机物合成有机分子；消费者是异养生物，以其他生物为食；分解者分解死有机物质。
2. Energy Flow and Trophic Levels | 能量流动与营养级
Energy enters most ecosystems as light energy captured by producers (plants and algae) during photosynthesis, converting it into chemical energy stored in biomass.
在大多数生态系统中，能量以光能形式进入，由生产者（植物和藻类）在光合作用中捕获，转化为储存在生物量中的化学能。
In a few deep-sea ecosystems, energy originates from chemical compounds released by hydrothermal vents, supporting chemosynthetic bacteria.
在少数深海生态系统中，能量来源于热液喷口释放的化学物质，支持化能合成细菌。
Energy is transferred along the food chain from producers to primary consumers, then to secondary and tertiary consumers, but large losses occur at each trophic level.
能量沿食物链从生产者传递到初级消费者，再到次级和三级消费者，但每经过一个营养级都有大量损失。
Energy is lost mainly through respiration, movement, heat and undigested waste; typically only about 10% is passed on, which limits the number of trophic levels.
能量主要通过呼吸作用、运动、热量和未消化废物散失；通常只有约10% 传递到下一级，因此限制了营养级的数目。
3. Food Chains and Food Webs | 食物链与食物网
A food chain shows a single linear pathway of energy transfer, for example: grass → rabbit → fox. Arrows always point in the direction of energy flow.
食物链显示能量传递的单一线性途径，例如：草 → 兔 → 狐狸。箭头总是指向能量流动的方向。
A food web is a network of interconnected food chains, representing the complex feeding relationships and stability within an ecosystem.
食物网是由相互关联的食物链组成的网络，代表生态系统内复杂的食性关系和稳定性。
If one species in a food web disappears, alternative food sources are often available, making the ecosystem more resilient than one relying on a single food chain.
如果食物网中一个物种消失，通常有其他食物来源，这使生态系统比依赖单一食物链的更富弹性。
Top predators are found at the highest trophic level, and their numbers are small because of the progressive loss of energy through the chain.
顶级捕食者处于最高营养级，由于能量沿链逐步损耗，它们的数量很少。
4. Ecological Pyramids | 生态金字塔
Pyramids of numbers show the count of individual organisms at each trophic level. They can be irregular if a large tree supports many insects.
数量金字塔显示各营养级生物个体的数目。如果一棵大树供养许多昆虫，金字塔形状可能不规则。
Pyramids of biomass present the total dry mass of living material at each level. They usually show a pyramid shape, except in some aquatic ecosystems where phytoplankton reproduce quickly.
生物量金字塔展示各营养级活物质的总干质量。除了某些浮游植物快速繁殖的水生系统外，通常呈现金字塔形。
Pyramids of energy always show a decreasing pattern because energy is lost at each transfer; they are never inverted and best represent ecosystem structure.
能量金字塔总是呈递减模式，因为每次传递都有能量损耗；它们绝不倒置，最能代表生态系统结构。
5. The Carbon Cycle | 碳循环
Carbon is continuously recycled through ecosystems via photosynthesis, respiration, decomposition, combustion and other processes, linking the atmosphere, biosphere and geosphere.
碳通过光合作用、呼吸作用、分解、燃烧等过程在生态系统中不断循环，将大气圈、生物圈和岩石圈联系起来。
Producers absorb CO₂ from the air and convert it into glucose (C₆H₁₂O₆) during photosynthesis. Consumers obtain carbon by feeding on plants or other animals.
生产者从空气中吸收 CO₂，在光合作用中将其转化为葡萄糖 (C₆H₁₂O₆)。消费者通过吃植物或其他动物获得碳。
All organisms release CO₂ back into the atmosphere through respiration. Decomposers break down dead organic matter, returning nutrients and CO₂ to the soil and air.
所有生物通过呼吸作用将 CO₂ 释放回大气。分解者分解死有机物，将养分和 CO₂ 归还土壤和空气。
Fossil fuels (coal, oil, gas) formed from ancient organisms; their combustion rapidly releases stored carbon, increasing atmospheric CO₂ and contributing to global warming.
化石燃料（煤、石油、天然气）由远古生物形成；其燃烧快速释放储存的碳，增加大气 CO₂，导致全球变暖。
6. Population Dynamics and Predator-Prey Relationships | 种群动态与捕食者-猎物关系
Population size is influenced by biotic factors such as predation, competition and disease, as well as abiotic factors like temperature, light, water and pH.
种群大小受捕食、竞争、疾病等生物因素以及温度、光照、水、pH 等非生物因素影响。
Predator and prey populations show cyclical fluctuations: when prey numbers rise, predators have more food and their numbers increase; high predation then reduces prey numbers, causing a subsequent decline in predators.
捕食者和猎物种群呈现周期性波动：猎物数量上升时，捕食者食物充足而增多；高捕食率降低猎物数量，随后捕食者减少。
Competition for limited resources can be intraspecific (within a species) or interspecific (between species), both of which limit population growth.
对有限资源的竞争可以是种内竞争或种间竞争，两者都限制种群增长。
Population growth often follows a logistic model: exponential at first, then slowing as resources become scarce, until it stabilises at the carrying capacity.
种群增长常遵循逻辑斯蒂模型：起初呈指数增长，随着资源短缺而减缓，直至在环境容纳量处趋于稳定。
7. Fieldwork Techniques: Quadrats and Transects | 田野调查技术：样方与样带
Quadrat sampling estimates the abundance and distribution of organisms in a uniform habitat. Randomly placed quadrats eliminate sampling bias.
样方取样用于估算均匀栖息地中生物的数量和分布。随机放置样方可消除取样偏差。
A belt transect places quadrats at regular intervals along a line, often used to study how distribution changes across an environmental gradient, such as from shade to full sunlight.
样带法是沿线等间距放置样方，常用于研究分布沿环境梯度的变化，例如从阴暗处到全日照。
A continuous transect records every organism touching the line, giving a detailed profile of species distribution along the gradient.
连续样带记录接触线的每个生物，提供物种沿梯度分布的详细剖面。
Population size of mobile organisms can be estimated by the capture-mark-recapture method: (number caught first time × number caught second time) ÷ number of marked individuals recaptured.
活动生物的种群大小可用标记重捕法估算：(第一次捕获数 × 第二次捕获数) ÷ 重捕的标记个体数。
8. Human Impacts on Ecosystems | 人类对生态系统的影响
Deforestation destroys habitats, reduces biodiversity, and disrupts water and carbon cycles. Burning trees releases CO₂ and removes carbon sinks that absorb CO₂.
森林砍伐破坏栖息地、降低生物多样性，扰乱水循环和碳循环。焚烧树木释放 CO₂，并移除吸收 CO₂ 的碳汇。
Agricultural pollution from fertilisers and pesticides can lead to eutrophication: excess nutrients cause algal blooms that block light and deplete dissolved oxygen when decomposers break down the algae.
农业污染（化肥和农药）可导致富营养化：过量的养分引发藻华，遮蔽光照，当分解者分解藻类时消耗溶解氧。
Burning fossil fuels increases atmospheric CO₂ and other greenhouse gases, enhancing the natural greenhouse effect and driving climate change, sea level rise and extreme weather.
燃烧化石燃料增加大气中 CO₂ 和其他温室气体，增强自然温室效应，引发气候变化、海平面上升和极端天气。
Acid rain, caused by dissolving sulfur dioxide and nitrogen oxides in rainwater, damages forests, acidifies lakes and soils, and corrodes buildings.
酸雨由二氧化硫和氮氧化物溶解在雨水中形成，损害森林，酸化湖泊和土壤，腐蚀建筑物。
9. Biodiversity and Conservation | 生物多样性与保护
Biodiversity encompasses species diversity, genetic diversity and ecosystem diversity. High biodiversity increases ecosystem resilience and productivity.
生物多样性包括物种多样性、遗传多样性和生态系统多样性。高生物多样性可增强生态系统的恢复力和生产力。
Human activities such as habitat destruction, overexploitation, pollution and introduction of invasive species are the main threats to biodiversity.
栖息地破坏、过度开发、污染和外来物种入侵等人类活动是生物多样性的主要威胁。
Conservation strategies include establishing protected areas (national parks), captive breeding programmes, seed banks, and legislation to control pollution and trade in endangered species.
保护策略包括建立保护区（国家公园）、圈养繁殖计划、种子库，以及控制污染和濒危物种贸易的立法。
Monoculture farming reduces genetic diversity, making crops vulnerable to pests and diseases; preserving wild relatives helps maintain genetic resources for future breeding.
单一作物种植降低遗传多样性，使作物易受病虫害侵袭；保护野生近缘种有助于保存遗传资源，用于未来育种。
10. Nutrient Cycling: The Role of Decomposers | 营养物质循环：分解者的作用
Decomposers such as bacteria and fungi break down dead organisms and organic waste, releasing mineral ions (nitrates, phosphates) back into the soil for absorption by plant roots.
分解者（如细菌和真菌）分解死生物和有机废物，将矿物离子（硝酸盐、磷酸盐）释放回土壤，供植物根部吸收。
Without decomposers, nutrients would remain locked in dead matter, stopping plant growth and collapsing the ecosystem.
没有分解者，养分将被禁锢在死物中，植物停止生长，生态系统崩溃。
In the nitrogen cycle, nitrogen-fixing bacteria convert atmospheric N₂ into ammonia, which is then oxidised to nitrites and nitrates by nitrifying bacteria. Decomposers return organic nitrogen to the soil as ammonium.
在氮循环中，固氮细菌将大气 N₂ 转化为氨，随后由硝化细菌氧化为亚硝酸盐和硝酸盐。分解者将有机氮以铵盐形式归还土壤。
Denitrifying bacteria convert nitrates back into N₂ gas, completing the cycle and maintaining the balance of nitrogen in the atmosphere.
反硝化细菌将硝酸盐转化回 N₂ 气体，完成循环，维持大气中的氮平衡。
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