📚 IGCSE CCEA Science: Ecosystems – Key Points Review | IGCSE CCEA 科学：生态系统 考点精讲
Ecosystems are dynamic systems made up of living organisms interacting with each other and their non-living environment. In the CCEA IGCSE Science specification, understanding the flow of energy, cycling of nutrients, and the impact of human activities is essential. This revision guide covers all the key points you need, from basic terminology to practical sampling techniques.
生态系统是由生物之间以及生物与非生物环境相互作用构成的动态系统。在 CCEA IGCSE 科学大纲中，理解能量流动、养分循环以及人类活动的影响至关重要。本考点精讲涵盖了从基础术语到实用取样技巧的全部关键知识点。
1. Key Terminology in Ecosystems | 生态系统关键术语
An ecosystem includes all the organisms living in a particular area and the physical conditions with which they interact. To describe relationships, precise vocabulary is used.
生态系统包括生活在特定区域的所有生物及其相互作用的物理条件。为了描述这些关系，需要使用精确的术语。
Habitat: The specific place where an organism lives, providing food, shelter and a breeding site.
栖息地： 生物生活的具体地点，为其提供食物、庇护所和繁殖场所。
Population: All the individuals of the same species living in a particular habitat at the same time.
种群： 在同一时间生活在特定栖息地的所有同种个体。
Community: All the populations of different species living and interacting in an area.
群落： 某一区域内生活并相互作用的所有不同物种的种群。
Ecosystem: The community of organisms interacting with each other and with the abiotic (non-living) environment.
生态系统： 生物群落之间以及与非生物（非生命）环境相互作用的整体。
Biotic factors: The living components, such as predation, competition and disease.
生物因素： 如捕食、竞争和疾病等生命组成部分。
Abiotic factors: The non-living elements, including temperature, light intensity, water availability and soil pH.
非生物因素： 包括温度、光照强度、水分有效性和土壤 pH 值等非生命要素。
2. Food Chains and Food Webs | 食物链与食物网
Feeding relationships show the transfer of energy from one organism to another. A food chain is a single pathway, while a food web is a network of interconnected chains.
取食关系体现了能量从一种生物到另一种生物的传递。食物链是一条单一的路径，而食物网是由相互连接的链组成的网络。
A typical food chain: Grass → Rabbit → Fox. The arrow shows the direction of energy flow, from the organism being eaten to the organism that eats it.
一条典型的食物链：草 → 野兔 → 狐狸。箭头表示能量流动的方向，从被吃的生物指向取食者。
Producers (e.g. green plants and algae) make their own food by photosynthesis. Consumers eat other organisms; primary consumers eat producers, secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers. Decomposers (bacteria and fungi) break down dead material and return nutrients to the soil.
生产者（如绿色植物和藻类）通过光合作用制造自身食物。消费者取食其他生物；初级消费者吃生产者，次级消费者吃初级消费者，而三级消费者吃次级消费者。分解者（细菌和真菌）分解死去的物质并将养分归还土壤。
A food web gives a more realistic picture because most animals feed on more than one type of organism. If one species is removed, the whole web can be affected, sometimes leading to cascading effects.
食物网提供了更真实的图景，因为大多数动物取食不止一种生物。如果某一物种消失，整个网络都会受到影响，有时还会引发连锁效应。
3. Pyramids of Numbers and Biomass | 数量金字塔与生物量金字塔
Ecological pyramids represent the feeding structure of an ecosystem. The pyramid of numbers shows the count of organisms at each trophic level, while the pyramid of biomass shows the total mass of living material.
生态金字塔表示生态系统的取食结构。数量金字塔显示每个营养级的生物数目，而生物量金字塔显示活物质的总质量。
Pyramids of numbers can sometimes be distorted; for example, one large oak tree can support many insects, producing an inverted or unusual shape. In contrast, pyramids of biomass are almost always a true pyramid shape because they represent the dry mass, which decreases at each successive trophic level.
数量金字塔有时会变形；例如，一棵大橡树可以养活许多昆虫，形成倒置或不规则的形状。相反，生物量金字塔几乎总是正常的金字塔形状，因为它代表干质量，在每一个连续的营养级上都会减少。
Biomass is measured as dry mass per unit area (g/m² or kg/ha). Most biomass is lost at each level due to respiration, uneaten parts and waste products, typically only about 10% of energy is transferred to the next level.
生物量以单位面积干质量（克/米² 或 千克/公顷）来度量。在每个营养级，大部分生物量因呼吸作用、未被取食的部分和排泄物而损失，通常只有约 10% 的能量传递到下一级。
4. Energy Flow in Ecosystems | 生态系统中的能量流动
The sun is the principal source of energy for almost all ecosystems. Producers convert light energy into chemical energy through photosynthesis, storing it in organic compounds.
太阳是几乎所有生态系统的主要能量来源。生产者通过光合作用将光能转化为化学能，并储存在有机化合物中。
Energy flows along food chains but is lost at each trophic level through respiration, excretion and heat. This loss limits the length of food chains – rarely more than four or five trophic levels.
能量沿食物链流动，但在每个营养级都会通过呼吸作用、排泄和散热而损失。这一损失限制了食物链的长度，很少超过四个或五个营养级。
The energy transferred can be calculated as: Energy in biomass of next level ÷ Energy in biomass of previous level × 100%. This efficiency is often low, explaining why large carnivores are relatively rare.
传递的能量可计算为：下一级生物量中的能量 ÷ 上一级生物量中的能量 × 100%。这种效率通常很低，从而解释了为何大型食肉动物相对稀少。
Understanding energy flow helps explain why short food chains are more efficient in feeding large populations, such as in agricultural systems where people eat plants directly rather than feeding plants to animals first.
理解能量流动有助于解释为何短食物链在养活大量人口时更有效，例如在农业系统中人们直接食用植物，而不是先将植物喂给动物。
5. Nutrient Cycles: The Carbon Cycle | 养分循环：碳循环
Carbon is a key element in all living organisms. The carbon cycle describes how carbon atoms move between the atmosphere, organisms, oceans and rocks.
碳是所有生物体中的关键元素。碳循环描述了碳原子在大气、生物、海洋和岩石之间如何移动。
Key processes: Photosynthesis removes CO₂ from the atmosphere; feeding passes carbon compounds along food chains; respiration by plants, animals and decomposers returns CO₂ to the atmosphere; decomposition releases carbon from dead organisms; combustion of fossil fuels and wood releases CO₂.
关键过程：光合作用从大气中吸收 CO₂；取食使碳化合物沿食物链传递；植物、动物和分解者的呼吸作用将 CO₂ 释放回大气；分解作用从死生物中释放碳；化石燃料和木材的燃烧释放 CO₂。
In oceans, CO₂ dissolves and can be stored in sediments, eventually forming carbonate rocks. Over geological time, these rocks may release carbon through weathering and volcanic activity.
在海洋中，CO₂ 溶解并可以储存在沉积物中，最终形成碳酸盐岩。在地质时间尺度上，这些岩石可能通过风化和火山活动释放碳。
Human activities, notably burning fossil fuels and deforestation, have disrupted the carbon balance, leading to an increase in atmospheric CO₂ and enhanced greenhouse effect.
人类活动，尤其是燃烧化石燃料和砍伐森林，已经破坏了碳平衡，导致大气中 CO₂ 浓度增加和温室效应增强。
6. Nutrient Cycles: The Nitrogen Cycle | 养分循环：氮循环
Nitrogen is essential for making proteins and DNA. The atmosphere contains 78% nitrogen gas (N₂), but plants cannot use it directly. The nitrogen cycle converts it into usable forms.
氮是制造蛋白质和 DNA 的必需元素。大气中含有 78% 的氮气（N₂），但植物不能直接利用它。氮循环将其转化为可利用的形式。
Key stages: Nitrogen fixation – N₂ is converted to ammonia (NH₃) by nitrogen-fixing bacteria in root nodules of legumes or free-living in soil; also by lightning. Nitrification – ammonia is oxidised to nitrite (NO₂⁻) then to nitrate (NO₃⁻) by nitrifying bacteria. Assimilation – plants absorb nitrates and use them to make proteins, which pass along food chains. Denitrification – denitrifying bacteria convert nitrates back to N₂ gas under anaerobic conditions.
关键阶段：固氮作用——N₂ 被豆科植物根瘤中的固氮菌或土壤中自由生活的固氮菌转化为氨（NH₃）；闪电也能固氮。硝化作用——氨被硝化细菌氧化为亚硝酸盐（NO₂⁻），然后变为硝酸盐（NO₃⁻）。同化作用——植物吸收硝酸盐并用于制造蛋白质，经食物链传递。反硝化作用——反硝化细菌在无氧条件下将硝酸盐还原为 N₂ 气体。
Decomposers recycle nitrogen from dead organisms and waste by breaking down proteins into ammonia (ammonification), which then enters the nitrification pathway.
分解者通过将蛋白质分解为氨（氨化作用）来循环来自死生物和排泄物的氮，氨随后进入硝化途径。
Human actions such as the use of nitrate fertilisers and leaching into waterways can disrupt the nitrogen cycle, causing eutrophication in aquatic ecosystems.
人类使用硝酸盐肥料以及淋溶进入水道的行为可能破坏氮循环，导致水生生态系统发生富营养化。
7. Population Growth and Limiting Factors | 种群增长与限制因素
A population’s size is determined by birth rate, death rate, immigration and emigration. Under ideal conditions, populations can grow exponentially, producing a J-shaped curve.
种群的大小由出生率、死亡率、迁入和迁出决定。在理想条件下，种群呈指数增长，产生 J 型曲线。
In reality, limiting factors slow growth, resulting in a sigmoid (S-shaped) curve. These factors include competition for resources (food, water, space), predation, disease and accumulation of wastes.
在现实中，限制因素会减缓增长，导致 S 型（逻辑斯谛）曲线。这些因素包括对资源（食物、水、空间）的竞争、捕食、疾病和废物积累。
Carrying capacity is the maximum population size an environment can sustain indefinitely. When a population approaches carrying capacity, environmental resistance increases, and the growth rate slows and stabilises.
环境容纳量是环境能够持续维持的最大种群数量。当种群接近容纳量时，环境阻力增大，增长率减慢并趋于稳定。
Density-dependent factors (e.g. food shortage, disease) have a greater effect when the population is large. Density-independent factors (e.g. natural disasters, extreme weather) affect populations regardless of their size.
密度依赖因素（如食物短缺、疾病）当种群数量大时影响更大。密度非依赖因素（如自然灾害、极端天气）无论种群大小都会产生影响。
8. Human Impact on Ecosystems: Pollution | 人类对生态系统的影响：污染
Pollution is the introduction of harmful materials into the environment. It can affect air, water and land, disrupting ecosystems and harming organisms.
污染是将有害物质引入环境。它会影响空气、水和土地，破坏生态系统并危害生物。
Air pollution: Burning fossil fuels releases sulfur dioxide (SO₂) and nitrogen oxides (NOₓ), which cause acid rain. Acid rain lowers soil pH, damages plant leaves and leaches toxic aluminium ions into water bodies, killing fish.
空气污染： 燃烧化石燃料释放二氧化硫（SO₂）和氮氧化物（NOₓ），导致酸雨。酸雨降低土壤 pH 值，损害植物叶片，并将有毒铝离子淋洗入水体，杀死鱼类。
Water pollution: Fertilisers and sewage can cause eutrophication. Nitrates and phosphates stimulate rapid algae growth (algal bloom). When the algae die, their decomposition by bacteria uses up dissolved oxygen, killing aquatic animals. Pesticides can bioaccumulate and become concentrated through food chains (biomagnification).
水污染： 肥料和污水可导致富营养化。硝酸盐和磷酸盐刺激藻类迅速生长（水华）。当藻类死亡时，其被细菌分解消耗大量溶解氧，杀死水生动物。农药会生物累积并沿食物链浓缩（生物放大作用）。
Land pollution: Solid waste, including plastics, can persist for hundreds of years, leaching toxins and entangling wildlife. Landfill sites generate methane, a potent greenhouse gas.
土地污染： 固体废物，包括塑料，可以存续数百年，淋出毒素并缠绕野生动物。填埋场产生甲烷，一种强效温室气体。
9. Deforestation and Its Consequences | 森林砍伐及其后果
Deforestation is the large-scale removal of forests, often for timber, agriculture or urban expansion. It has severe ecological consequences on a local and global scale.
森林砍伐是大规模清除森林，通常用于木材、农业或城市扩张。它在局部和全球范围内产生严重的生态后果。
Local impacts include soil erosion because tree roots no longer hold the soil, leading to loss of nutrients and desertification. Biodiversity is drastically reduced as habitats are destroyed, pushing many species to extinction. The water cycle is disrupted: less evapotranspiration reduces rainfall, causing drier climates.
局部影响包括土壤侵蚀，因为树根不再固土，导致养分流失和荒漠化。随着栖息地被破坏，生物多样性急剧下降，许多物种濒临灭绝。水循环被扰乱：蒸散作用减少，降低了降雨量，造成气候变干。
Globally, deforestation contributes to climate change. Trees are carbon sinks; removing them releases stored carbon and reduces CO₂ absorption. Burning forests releases huge amounts of CO₂ directly into the atmosphere.
在全球范围内，森林砍伐加剧气候变化。树木是碳汇；砍伐树木会释放储存的碳并减少 CO₂ 的吸收。焚烧森林直接向大气释放大量 CO₂。
Peat bogs are also destroyed by drainage and burning, releasing stored carbon and destroying a unique habitat. Sustainable management, such as selective logging and replanting, can mitigate these effects.
泥炭沼也因排水和焚烧而遭到破坏，释放储存的碳并摧毁独特的栖息地。可持续管理，如择伐和重新种植，可以减轻这些影响。
10. The Greenhouse Effect and Climate Change | 温室效应与气候变化
The natural greenhouse effect is vital for life: greenhouse gases (CO₂, methane, water vapour) trap some of the Sun’s heat, keeping Earth’s average temperature at about 15 °C rather than -18 °C.
自然温室效应对生命至关重要：温室气体（CO₂、甲烷、水蒸气）捕获部分太阳热量，使地球平均温度保持在约 15 °C，而非 -18 °C。
The enhanced greenhouse effect is caused by increased concentrations of these gases due to human activities. Major sources: combustion of fossil fuels (CO₂), agriculture (methane from cattle and rice paddies), and landfill (methane). Deforestation reduces CO₂ absorption.
增强的温室效应是由于人类活动造成这些气体浓度增加。主要来源：化石燃料燃烧（CO₂）、农业（牛和水稻田产生的甲烷）、以及填埋场（甲烷）。森林砍伐减少了 CO₂ 的吸收。
Consequences include global warming, melting polar ice caps and glaciers, rising sea levels, more frequent extreme weather events (storms, droughts), changes in species distribution, and disturbances to farming patterns.
后果包括全球变暖、极地冰盖和冰川融化、海平面上升、更频繁的极端天气事件（暴风雨、干旱）、物种分布变化以及农业格局受干扰。
International efforts such as the Paris Agreement aim to limit temperature rise by reducing emissions and investing in renewable energy. Individual actions, including reducing energy consumption and recycling, also contribute.
国际努力如《巴黎协定》旨在通过减少排放和投资可再生能源来限制温升。包括减少能源消耗和回收在内的个人行动也发挥了一定的作用。
11. Conservation and Sustainability | 保育与可持续发展
Conservation is the protection and management of species and ecosystems to maintain biodiversity. Sustainability means meeting the needs of the present without compromising the ability of future generations to meet their own needs.
保育是对物种和生态系统进行保护与管理，以维持生物多样性。可持续性意味着满足当代需求，而不损害后代满足自身需求的能力。
Strategies include establishing protected areas like national parks and marine reserves, captive breeding programmes for endangered species, seed banks, and habitat restoration (e.g. reforestation).
策略包括建立国家公园和海洋保护区等保护地、濒危物种的人工繁殖计划、种子库以及栖息地恢复（如重新造林）。
Sustainable resource use: fish quotas and net sizes prevent overfishing; sustainable forestry ensures replanting; crop rotation and organic farming maintain soil fertility and reduce chemical inputs.
可持续资源利用：渔业配额和网目大小防止过度捕捞；可持续林业确保重新种植；轮作和有机农业保持土壤肥力并减少化学品投入。
Encouraging ecotourism can provide economic benefits while raising awareness of conservation needs. International laws like CITES regulate trade in endangered species.
鼓励生态旅游可以在提高对保育需求认知的同时带来经济利益。像 CITES 这样的国际法律规范了濒危物种贸易。
12. Practical Skills: Sampling Techniques | 实验技能：取样技术
Studying ecosystems requires sampling methods to estimate population sizes and distribution. The choice of technique depends on the organisms being studied and the habitat.
研究生态系统需要取样方法来估算种群大小和分布。技术选择取决于所研究的生物和栖息地。
For stationary organisms like plants, quadrats are used. A quadrat is a square frame placed randomly in the area. Counting individuals or estimating percentage cover allows calculation of population density per square metre. Line transects can show how species distribution changes across a habitat, such as from a woodland into a field.
对于像植物这样的静止生物，使用样方。样方是随机放置在区域内的正方形框架。计算个体数量或估算覆盖度百分比，可以计算每平方米的种群密度。样线可以显示物种分布如何沿栖息地变化，例如从林地到田野。
To ensure reliability, a large number of random samples should be taken. Randomness is achieved using random number coordinates. Mean values are calculated, and the population size is estimated by multiplying mean density by total habitat area.
为了确保可靠性，应采集大量随机样本。使用随机数坐标实现随机性。计算平均值，并通过平均密度乘以总栖息地面积来估算种群大小。
For mobile animals, the capture-mark-recapture method is used. Example calculation: In the first capture, 30 animals are marked and released. Later, 40 animals are captured, of which 10 are marked. Estimated population = (30 × 40) ÷ 10 = 120. Assumptions include: no migration, no births or deaths, and marks are not lost during the interval.
对于移动的动物，使用标志重捕法。示例计算：第一次捕捉，30 只动物被标记并释放。稍后，40 只被捕获，其中 10 只有标记。估计种群 = (30 × 40) ÷ 10 = 120。假设包括：无迁移、无出生或死亡，且标记在间隔期间不会脱落。
Environmental factors such as light, temperature, soil moisture and pH are often measured alongside biological sampling to relate distribution to abiotic conditions.
环境因素如光照、温度、土壤湿度和 pH 值通常与生物取样同时测量，以便将分布与非生物条件关联起来。
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