📚 IGCSE Science: Ecosystem Essentials | IGCSE 科学：生态系统考点精讲
An ecosystem is a fundamental concept in IGCSE Science, combining the interactions between living organisms and their physical environment. This article highlights the key points you need to master, from feeding relationships and energy flow to nutrient cycles and human impacts. Each section is clearly structured with core facts to help you revise efficiently.
生态系统是IGCSE科学的基础概念，它涵盖了生物与其物理环境之间的相互作用。本文精讲你需要掌握的核心考点，从摄食关系、能量流动到物质循环和人类影响。每个部分都结构清晰，用核心事实帮助你高效复习。
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 community) in a particular area, interacting with the non-living (abiotic) components of their environment. These interactions form a stable, self-sustaining system. A pond, a forest, and even a rotting log can be considered ecosystems.
生态系统是一个自然单元，由特定区域内的所有生物（生物群落）和环境中非生物（非生物）组分相互作用而构成。这些相互作用形成了一个稳定、自给自足的系统。一个池塘、一片森林，甚至一段腐烂的木头都可以被视为生态系统。
The concept includes the flow of energy and the cycling of nutrients. Organisms within an ecosystem are dependent on each other and on the physical conditions surrounding them. Studying ecosystems helps us understand the delicate balance of nature.
这个概念包括能量流动和物质循环。生态系统中的生物彼此依赖，也依赖周围的物理条件。研究生态系统有助于我们理解自然界微妙的平衡。
2. Biotic and Abiotic Factors | 生物与非生物因素
Biotic factors are the living components of an ecosystem. They include plants, animals, fungi, bacteria, and any other organisms. These factors interact through relationships such as predation, competition for resources, and symbiosis (e.g., mutualism).
生物因素是指生态系统中的生命组成部分，包括植物、动物、真菌、细菌以及所有其他生物。这些因子通过捕食、竞争资源以及共生（例如互利共生）等关系相互作用。
Abiotic factors are the non-living physical and chemical elements that influence the ecosystem. Key examples are sunlight intensity, temperature range, water availability, soil composition, and pH level. These factors determine which species can survive in a habitat and how abundant they become.
非生物因素是指影响生态系统的非生命物理和化学元素。主要例子有光照强度、温度范围、水分供应、土壤成分和酸碱度。这些因素决定了哪些物种能够在某个栖息地中生存以及它们的丰富度。
3. Feeding Relationships: Food Chains and Food Webs | 摄食关系：食物链与食物网
A food chain shows a single, linear pathway of energy transfer from one organism to another. It always starts with a producer (e.g., grass) that captures sunlight energy through photosynthesis. Arrows represent the direction of energy flow from eaten to eater.
一条食物链显示能量从一个生物传递到另一个生物的单一线性途径。它总是从生产者（如草）开始，生产者通过光合作用捕获太阳能。箭头表示能量从被食者流向取食者的方向。
Most organisms eat more than one type of food, so many food chains interconnect to form a food web. A food web gives a more realistic picture of the complex feeding relationships in an ecosystem. If one species is removed, the entire web can be affected.
大多数生物不只吃一种食物，因此许多食物链交织在一起形成食物网。食物网更真实地展示了生态系统中复杂的摄食关系。如果一个物种消失，整个网络都可能受到影响。
4. Trophic Levels and Energy Transfer | 营养级与能量传递
Each step in a food chain is called a trophic level. The first level is occupied by producers (plants and algae). Primary consumers (herbivores) form the second level, secondary consumers (carnivores that eat herbivores) form the third, and tertiary consumers form the fourth. Decomposers break down dead matter at all levels.
食物链中的每一级称为营养级。第一级由生产者（植物和藻类）占据。初级消费者（食草动物）构成第二级，次级消费者（以食草动物为食的肉食动物）构成第三级，三级消费者构成第四级。分解者则在所有级别分解死去的物质。
At each transfer between trophic levels, a large amount of energy is lost. Typically, only about 10% of the energy is passed on to the next level. Energy is lost mainly through respiration, movement, heat, and undigested materials in faeces. This inefficiency limits the length of food chains.
在营养级之间的每一次传递中，都有大量能量损失。通常只有大约10%的能量传递到下一级。能量主要通过呼吸作用、运动、散热和粪便中未消化的物质而损失。这种低效率限制了食物链的长度。
5. Ecological Pyramids | 生态金字塔
A pyramid of numbers shows the count of individual organisms at each trophic level. It can be upright (many producers, few top consumers) or occasionally inverted, such as when one large tree supports numerous insects.
数量金字塔显示每个营养级的生物个体数量。它可能是正立的（许多生产者，很少的顶级消费者），偶尔也会倒置，例如一棵大树支撑着无数昆虫。
A pyramid of biomass represents the total dry mass of living material at each level. It is almost always upright because the mass of producers must be greater than that of consumers to support them. Measuring dry mass removes the variable of water content.
生物量金字塔代表每个营养级活体物质的总干重。它几乎总是正立的，因为生产者的生物量必须大于消费者的生物量才能支撑它们。测量干重可以排除水分含量的影响。
A pyramid of energy illustrates the rate of energy flow from one level to the next, always drawn to scale. It is always upright and never inverted because energy is lost at each transfer. It is the most accurate way to represent the structure of an ecosystem.
能量金字塔描绘了能量从一级流向下一级的速率，总是按比例绘制。它始终是正立的，绝不会倒置，因为能量在每次传递中都会损失。这是展示生态系统结构最准确的方式。
6. The Carbon Cycle | 碳循环
Carbon is a vital element found in all organic molecules. It cycles between the atmosphere (as CO₂), organisms, oceans, and fossil fuels. The main processes are photosynthesis, respiration, decomposition, and combustion. The balanced carbon cycle sustains life on Earth.
碳是存在于所有有机分子中的重要元素。它在大气（以CO₂形式）、生物、海洋和化石燃料之间循环。主要过程是光合作用、呼吸作用、分解作用和燃烧。平衡的碳循环维持着地球上的生命。
Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light energy)
光合作用：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂（光能）
Plants absorb CO₂ from the air and convert it into glucose. Animals obtain carbon by eating plants or other animals. Respiration in all living things returns CO₂ to the atmosphere. Decomposers break down dead organisms and waste, releasing CO₂ back into the air.
植物从空气中吸收CO₂并将其转化为葡萄糖。动物通过食用植物或其他动物获取碳。所有生物的呼吸作用将CO₂归还到大气中。分解者分解死去的生物和废物，将CO₂释放回空气中。
Some carbon is stored for long periods in fossil fuels or carbonaceous rocks. When we burn fossil fuels (combustion), locked-away carbon is rapidly released as CO₂, disrupting the natural balance. Deforestation also reduces the number of trees available to absorb CO₂.
一些碳长期储存在化石燃料或碳质岩石中。当我们燃烧化石燃料（燃烧作用）时，被封存的碳会迅速以CO₂的形式释放出来，破坏自然平衡。森林砍伐也会减少可吸收CO₂的树木数量。
7. The Role of Decomposers | 分解者的作用
Decomposers, mainly bacteria and fungi, are essential for recycling nutrients. They secrete enzymes onto dead organic matter and absorb the soluble products. This process releases inorganic nutrients, such as nitrates and phosphates, back into the soil for plants to use again.
分解者，主要是细菌和真菌，对于物质循环至关重要。它们向死的有机物分泌酶，并吸收可溶性产物。这个过程将无机养分，如硝酸盐和磷酸盐，释放回土壤中，供植物重新利用。
Without decomposers, dead material would accumulate and nutrients would remain locked away. They complete the cycle of matter, ensuring that elements like carbon and nitrogen are continuously available. Detritivores (e.g., earthworms, woodlice) also assist by breaking materials into smaller pieces.
如果没有分解者，死去的物质将不断累积，养分也将被禁锢。它们完成了物质循环，确保碳和氮等元素持续可用。食碎屑动物（如蚯蚓、潮虫）也通过将物质破碎为更小的碎屑来协助分解。
8. Population Dynamics | 种群动态
Population size in an ecosystem is affected by the availability of food, water, shelter, disease, and predation. In a typical predator-prey cycle, an increase in prey allows the predator population to grow, which then reduces prey numbers, leading to a crash in the predator population. This cycle repeats over time.
生态系统中的种群大小受食物、水、庇护所、疾病和捕食等因素的影响。在典型的捕食者-猎物循环中，猎物数量增加促使捕食者种群增长，随后猎物数量减少，导致捕食者种群崩溃。这个循环会随着时间重复。
Environmental resistance factors, such as competition and climate, prevent populations from growing indefinitely. The carrying capacity is the maximum population size an environment can sustain. Human intervention, through habitat destruction or introduction of alien species, can drastically alter these natural dynamics.
环境阻力因素，例如竞争和气候，阻止种群无限增长。环境容纳量是指环境能够维持的最大种群数量。人类通过破坏栖息地或引入外来物种进行的干预，能极大地改变这些自然动态。
9. Human Impact on Ecosystems | 人类对生态系统的影响
Human activities have a profound impact on ecosystems. Deforestation for agriculture or urbanisation destroys habitats, reduces biodiversity, and disrupts the carbon and water cycles. It also leads to soil erosion and can change local climates.
人类活动对生态系统产生深远影响。为农业或城市化而进行的森林砍伐破坏了栖息地，降低了生物多样性，并扰乱了碳循环和水循环。它还会导致土壤侵蚀，并可能改变局部气候。
Burning fossil fuels increases greenhouse gases (e.g., CO₂, methane), enhancing the greenhouse effect and causing global warming. Water pollution from fertilisers causes eutrophication: excess nutrients lead to algal blooms, which block light and deplete oxygen when they decompose, killing aquatic life.
燃烧化石燃料增加了温室气体（如CO₂、甲烷），加剧温室效应并引起全球变暖。化肥造成的水污染导致富营养化：过多的养分引起藻华，藻类腐烂分解时遮蔽光线并耗尽氧气，杀死水生生物。
Bioindicators such as lichens are sensitive to air pollution (sulfur dioxide), and their presence or absence helps scientists monitor ecosystem health. Sustainable practices are urgently needed to minimise further damage.
生物指示物如地衣对空气污染（二氧化硫）敏感，它们的存在或缺失帮助科学家监测生态系统健康。迫切需要可持续的实践来减少进一步的损害。
10. Conservation and Sustainability | 保护与可持续性
Conservation aims to maintain biodiversity, protect endangered species, and use natural resources wisely. Sustainable development meets present needs without compromising the ability of future generations to meet their own needs. Examples include replanting forests, establishing marine protected areas, and using renewable energy.
保护旨在维持生物多样性、保护濒危物种以及明智地利用自然资源。可持续发展在满足当代人需求的同时，不损害后代满足其自身需求的能力。例子包括植树造林、建立海洋保护区和利用可再生能源。
Captive breeding programs and seed banks help preserve genetic diversity. Education and legislation, such as fishing quotas and bans on hunting, are crucial. Every individual can contribute by reducing, reusing, and recycling waste, and by making informed choices as consumers.
圈养繁殖计划和种子库有助于保存遗传多样性。教育和立法，如渔业配额和狩猎禁令，至关重要。每个人都可以通过减少、重复使用和回收废物，以及作为消费者做出明智选择来贡献力量。
Published by TutorHao | IGCSE Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导