📚 GCSE CIE Science: Ecosystems Exam Essentials | GCSE CIE 科学：生态系统考点精讲
Ecosystems are the heart of ecology, bringing together living communities and their physical surroundings. In your CIE IGCSE Science exams (Coordinated Sciences or Biology), you will need to define key terms, explain energy flow and nutrient cycles, and describe how populations change. This article breaks down every core concept with bilingual explanations to help you master the topic.
生态系统是生态学的核心，它将生物群落与其物理环境紧密联结。在 CIE IGCSE 科学考试（协调科学或生物）中，你需要定义关键术语、解释能量流动与物质循环，并描述种群如何变化。本文以中英双语解析每一个核心概念，帮助你彻底掌握这一主题。
1. What Is an Ecosystem? | 什么是生态系统？
An ecosystem is a natural unit consisting of all the living organisms (biotic factors) and the non-living physical environment (abiotic factors) interacting in a given area. It can be as small as a pond or as large as a tropical rainforest.
生态系统是一个自然单位，由特定区域中所有生物（生物因素）和非生物物理环境（非生物因素）相互作用而成。它可以小至一个池塘，大至一片热带雨林。
Biotic factors include predators, prey, competitors and decomposers. Abiotic factors include light intensity, temperature, water availability, soil pH and mineral content. CIE questions often ask you to list biotic and abiotic factors that could affect a particular organism.
生物因素包括捕食者、猎物、竞争者与分解者。非生物因素包括光照强度、温度、水分供应、土壤 pH 和矿物质含量。CIE 考题常要求你列出可能影响某种特定生物的生物因素和非生物因素。
Ecosystems are self-supporting if they maintain a constant input of energy (usually sunlight) and efficient cycling of nutrients. The concept of interdependence is central — a change in one part of the ecosystem can affect many other organisms.
只要有持续的能量输入（通常是阳光）和高效的养分循环，生态系统就能自给自足。相互依赖是核心概念——生态系统中某一部分的变化可能会影响许多其他生物。
2. Populations, Communities, Habitats and Niches | 种群、群落、栖息地与生态位
A population is a group of individuals of the same species living in the same area at the same time. A community is made up of all the populations of different species living and interacting in a particular habitat.
种群是在同一时间生活在同一地区的同种生物个体组成的群体。群落则由栖息在特定栖息地中相互作用的不同物种种群构成。
A habitat is the place where an organism lives, providing it with food, shelter and breeding sites. The niche of an organism is its role in the ecosystem — what it eats, what it competes with, how it reproduces and how it contributes to energy flow and nutrient cycling.
栖息地是生物生活的地方，为其提供食物、庇护所和繁殖场所。生态位是生物在生态系统中的角色——它吃什么、与谁竞争、如何繁殖，以及它如何贡献于能量流动和养分循环。
CIE exam questions often test the difference between habitat and niche. Remember: a habitat is an address, a niche is a profession.
CIE 考题常考查栖息地与生态位的区别。记住：栖息地好比住址，生态位好比职业。
3. Energy Flow in Ecosystems | 生态系统中的能量流动
Nearly all ecosystems depend on energy from the Sun. Producers (green plants and algae) capture light energy during photosynthesis and convert it into chemical energy stored in organic compounds.
几乎所有生态系统都依赖太阳能。生产者（绿色植物和藻类）在光合作用中捕获光能，并将其转化为储存在有机物中的化学能。
Energy then flows through the ecosystem when consumers feed on producers or other consumers. At each transfer, a large proportion of energy is lost as heat through respiration, movement and undigested food. Only about 10% of the energy is passed on to the next trophic level.
当消费者取食生产者或其他消费者时，能量便流经生态系统。每次传递中，大部分能量通过呼吸作用、运动以及未被消化的食物以热的形式散失。只有大约 10% 的能量传递至下一个营养级。
This loss of energy explains why food chains are usually short — rarely more than four or five trophic levels — and why there are fewer top predators than producers.
这种能量损失解释了为什么食物链通常较短——很少超过四到五个营养级——也解释了为什么顶级捕食者数量远少于生产者。
4. Food Chains and Food Webs | 食物链与食物网
ss → grasshopper → frog → snake → hawk. The arrows represent the direction of energy flow.
食物链是一条线性顺序，显示能量从一个生物传递至下一个生物，始终以生产者开始。例如：草 → 蚱蜢 → 青蛙 → 蛇 → 鹰。箭头表示能量流动的方向。
A food web is a network of interconnected food chains. It provides a more realistic picture of feeding relationships because most organisms eat more than one type of food or are eaten by more than one predator.
食物网是由相互关联的食物链构成的网络。它更真实地反映了捕食关系，因为大多数生物不止吃一种食物，也不止被一种天敌捕食。
In CIE exams you may be asked to construct a food web from given information or to predict the effect of removing one organism. Always trace the connections carefully.
CIE 考试可能会让你根据给定信息构建一个食物网，或预测移除某种生物后的影响。务必仔细追踪每一种联系。
5. Trophic Levels and Energy Transfer | 营养级与能量传递
Trophic levels describe the position an organism occupies in a food chain. Level 1: producers; Level 2: primary consumers (herbivores); Level 3: secondary consumers (carnivores that eat herbivores); Level 4: tertiary consumers, and so on.
营养级描述了生物在食物链中所处的位置。第一级：生产者；第二级：初级消费者（植食动物）；第三级：次级消费者（捕食植食动物的肉食动物）；第四级：三级消费者，以此类推。
÷ energy available in lower trophic level) × 100. CIE papers often provide data in kJ and ask for a percentage efficiency.
营养级之间的能量传递效率很低。你需要会用公式计算：效率 = (消费者摄入能量 ÷ 低营养级可获得的能量) × 100%。CIE 试卷中常给出以千焦为单位的数据，要求计算能量传递效率百分比。
Decomposers, such as bacteria and fungi, break down dead organic matter and return nutrients to the soil. They are not usually shown in simple food chains but are essential for recycling.
分解者（如细菌和真菌）分解死亡的有机物，将养分归还土壤。它们通常不在简单食物链中显示，但对物质循环至关重要。
6. Ecological Pyramids | 生态金字塔
Ecological pyramids are graphical representations of the number, biomass or energy at each trophic level. Pyramid of numbers counts individuals, pyramid of biomass measures the dry mass of living material, and pyramid of energy shows the energy content (always pyramid-shaped due to energy loss).
生态金字塔是各营养级数量、生物量或能量的图示。数量金字塔统计个体数量，生物量金字塔衡量活体干重，能量金字塔则展示能量含量（由于能量损失，总是呈金字塔形）。
Pyramids of biomass and energy are generally more accurate than pyramids of numbers, which can be inverted (e.g. one oak tree supports thousands of insects). CIE expects you to interpret and draw simple pyramids from data.
生物量金字塔和能量金字塔通常比数量金字塔更准确，后者可能倒置（例如一棵橡树支撑着成千上万只昆虫）。CIE 要求你能够根据数据解读并绘制简单的金字塔图。
7. The Carbon Cycle | 碳循环
Carbon is the key element in all organic molecules. The carbon cycle describes how carbon moves between the atmosphere, living organisms, oceans and rocks.
碳是所有有机分子的关键元素。碳循环描述碳如何在大气、生物体、海洋与岩石之间流动。
Carbon dioxide (CO₂) is removed from the atmosphere by photosynthesis in plants and algae. It is returned to the atmosphere through respiration by all organisms, decomposition by microorganisms, and combustion of fossil fuels.
二氧化碳 (CO₂) 通过植物与藻类的光合作用从大气中移除，又通过所有生物的呼吸作用、微生物的分解以及化石燃料的燃烧返回大气。
Feeding passes carbon compounds along food chains. When organisms die, decomposers break down their bodies, releasing CO₂ during respiration. In the oceans, CO₂ can dissolve and form carbonates used by marine organisms to build shells.
取食过程将含碳化合物沿食物链传递。生物死亡后，分解者将其身体分解，在呼吸过程中释放 CO₂。在海洋中，CO₂ 可溶解并形成碳酸盐，被海洋生物用来构建外壳。
Exam questions often ask you to name the processes that add or remove CO₂ from the atmosphere. Be able to label a diagram of the carbon cycle with terms like photosynthesis, respiration, combustion, decomposition and fossilisation.
考试常问哪些过程会增加或减少大气中的 CO₂。要能为碳循环示意图标注光合作用、呼吸作用、燃烧、分解和化石形成等术语。
8. The Nitrogen Cycle | 氮循环
Nitrogen is essential for making proteins and DNA. Although the atmosphere is 78% nitrogen gas (N₂), most organisms cannot use it directly. The nitrogen cycle converts N₂ into usable forms.
氮对制造蛋白质和 DNA 至关重要。虽然大气中含有 78% 的氮气 (N₂)，但大多数生物无法直接利用。氮循环将 N₂ 转化为可用的形式。
Key processes include nitrogen fixation (by lightning or nitrogen-fixing bacteria in root nodules of legumes converting N₂ to ammonium compounds), nitrification (ammonium ions NH₄⁺ converted to nitrites NO₂⁻ then to nitrates NO₃⁻ by nitrifying bacteria), assimilation (plants absorb nitrates to make proteins), and denitrification (denitrifying bacteria convert nitrates back to N₂ gas in anaerobic conditions).
关键过程包括固氮（通过闪电或豆科植物根瘤中的固氮菌将 N₂ 转变成铵化合物）、硝化作用（硝化细菌将铵离子 NH₄⁺ 转变为亚硝酸盐 NO₂⁻，再转为硝酸盐 NO₃⁻）、同化作用（植物吸收硝酸盐制造蛋白质）以及反硝化作用（反硝化细菌在缺氧条件下将硝酸盐转化为 N₂ 气体）。
Decomposers break down proteins and urea from dead organisms and waste, releasing ammonium ions back into the soil — a process called ammonification.
分解者分解死生物和废物中的蛋白质与尿素，将铵离子释放回土壤，这一过程称为氨化作用。
In CIE, you may be asked to describe the roles of different bacteria and explain why crop rotation with legumes can improve soil fertility.
CIE 考试可能要求你描述不同细菌的作用，并解释为什么与豆类轮作能提高土壤肥力。
9. Population Growth and Limiting Factors | 种群增长与限制因素
A population grows when births exceed deaths and immigration is higher than emigration. The maximum population size an environment can sustain is called the carrying capacity, determined by limiting factors.
当出生率大于死亡率且迁入大于迁出时，种群增长。环境能持续供养的最大种群数量被称为环境容纳量，它由限制因素决定。
Limiting factors are environmental resources or conditions that restrict population growth. They include food supply, water, shelter, disease, predators and competition. For plants, light, mineral ions and space are crucial.
限制因素是指限制种群增长的环境资源或条件，包括食物供应、水、庇护所、疾病、捕食者和竞争。对植物而言，光照、矿质离子和空间至关重要。
The typical sigmoid (S-shaped) growth curve has a lag phase, exponential (log) phase, stationary phase and sometimes a death phase. CIE candidates should be able to interpret such curves and identify where limiting factors come into play.
典型的 S 型生长曲线包含延缓期、指数（对数）生长期、稳定期，有时还有死亡期。CIE 考生应能解读这类曲线，并指出限制因素在哪个阶段发挥作用。
10. Human Impacts on Ecosystems | 人类对生态系统的影响
Human activities can disrupt ecosystems through deforestation, pollution, overfishing and introduction of invasive species. Deforestation, for example, reduces biodiversity, destroys habitats and increases CO₂ levels.
人类活动如森林砍伐、污染、过度捕捞和引入入侵物种，都可能破坏生态系统。例如森林砍伐会降低生物多样性、破坏栖息地并提高 CO₂ 水平。
Bioaccumulation is the build-up of toxic substances (e.g. DDT, mercury) in an organism's body. Biomagnification is the increasing concentration of these toxins at higher trophic levels. Top predators can suffer reproductive failure or death as a result.
生物累积指有毒物质（如 DDT、汞）在生物体内累积。生物放大作用则指这些毒素在更高营养级中浓度不断增加。顶级捕食者可能因此出现繁殖障碍或死亡。
Eutrophication is another common CIE topic. Excess nitrates and phosphates from fertilisers run off into water bodies, causing algal blooms. The algae block light and, when they die, decomposition by bacteria uses up oxygen, killing fish and other aquatic life.
富营养化是另一个常见的 CIE 考点。化肥中过量的硝酸盐和磷酸盐流入水体，导致藻华。藻类遮光，死后被细菌分解消耗氧气，导致鱼类和其他水生生物死亡。
11. Conservation and Sustainability | 保护与可持续性
Conservation aims to protect species, habitats and genetic diversity. Sustainable practices allow humans to use resources without depleting them for future generations.
保护旨在保护物种、栖息地和遗传多样性。可持续实践允许人类利用资源，却不会耗尽它们而影响后代。
Examples include replanting forests, using renewable energy, installing fish quotas, setting up national parks and using biological control instead of chemical pesticides to reduce bioaccumulation.
例子包括植树造林、使用可再生能源、设定捕鱼配额、建立国家公园，以及使用生物防治替代化学农药以减少生物累积。
CIE often links sustainability to the carbon footprint and the importance of maintaining biodiversity for stable ecosystems. You should be able to evaluate the advantages and disadvantages of different conservation strategies.
CIE 常将可持续性与碳足迹以及维持生物多样性对稳定生态系统的重要性相联系。你应能评估不同保护策略的优缺点。
12. Exam Tips for CIE Science | 考试技巧
Use precise scientific vocabulary: say 'limiting factor' rather than 'something that stops growth'. Distinguish clearly between a food chain and a food web, habitat and niche, pyramid of numbers and pyramid of energy.
使用准确的科学术语：使用“限制因素”而不是“阻碍生长的东西”。清晰区分食物链与食物网、栖息地与生态位、数量金字塔与能量金字塔。
For data-based questions, always include units and show your working when calculating energy transfer efficiency. If a question asks you to 'describe' a cycle, name the steps in order and mention the organisms or processes involved.
在数据题中，务必注明单位，计算能量传递效率时展示运算步骤。如果题目要求“描述”一个循环，请按顺序说出各步骤，并提及所涉及的生物或过程。
In conservation and human impact questions, structure your answer around causes, effects and solutions. Compare alternatives using phrases like 'whereas', 'on the other hand' and 'this leads to'.
在保护与人类影响的题目中，围绕原因、影响和解决方案搭建你的答案。使用诸如“而”、“另一方面”、“这导致”等短语进行比较。
Finally, practice with past CIE papers. Look for recurring command words like 'state', 'explain', 'suggest' and 'evaluate', and tailor your answers to the number of marks available.
最后，多练习 CIE 历年真题。注意反复出现的指令词，如“陈述”、“解释”、“建议”和“评估”，并根据所给分值调整答案的详略程度。
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