📚 GCSE WJEC Science: Ecosystems Key Points | GCSE WJEC 科学：生态系统 考点精讲
An ecosystem is a dynamic, interconnected community of living organisms interacting with each other and with the non-living components of their environment. This article breaks down the essential topics for the GCSE WJEC Science specification, covering feeding relationships, energy flow, nutrient cycles, biodiversity, and the impact of human activities. Each section is presented in clear bilingual format to help you master the concepts and prepare for your exams.
生态系统是一个由生物群落与其非生物环境相互作用而形成的动态整体。本文梳理了 GCSE WJEC 科学考试的核心主题，包括摄食关系、能量流动、物质循环、生物多样性以及人类活动的影响。每个小节均以清晰的双语对照呈现，帮助你掌握概念、备战考试。
1. What is an Ecosystem? | 什么是生态系统？
An ecosystem consists of all the organisms living in a particular area, known as the community, together with the non-living (abiotic) components such as light, temperature, water, and soil. The place where an organism lives is its habitat, while a population is all the individuals of the same species living in an area at one time. Ecology is the study of these interactions.
生态系统由生活在特定区域的所有生物（即群落）以及非生物（非生命）组分构成，例如光、温度、水和土壤。生物生活的具体地点称为栖息地，而同一物种在某一区域内所有个体的总和则是一个种群。生态学正是研究这些相互作用的学科。
2. Biotic and Abiotic Factors | 生物与非生物因素
Organisms in an ecosystem are influenced by biotic factors (living components) such as predation, competition for food and mates, disease, and human activities. They are also shaped by abiotic factors (non-living physical and chemical elements) like light intensity, temperature, pH of soil or water, wind speed, and oxygen or carbon dioxide concentration. Changes in any single factor can affect population sizes and community structure.
生态系统中的生物受到生物因素（有生命组分）的影响，如捕食、对食物和配偶的竞争、疾病以及人类活动；同时也受到非生物因素（非生命的物理和化学要素）的影响，如光照强度、温度、土壤或水的 pH、风速、氧气或二氧化碳浓度。任何一个因素的变化都可能影响种群大小和群落结构。
3. Feeding Relationships: Food Chains and Food Webs | 摄食关系：食物链与食物网
A food chain shows a simple, linear pathway of energy transfer from one organism to another, starting with a producer. A food web is a more realistic network of interconnected food chains that shows how energy flows through an ecosystem. Arrows in a food chain or web always point in the direction of energy flow, from food to feeder.
食物链表示能量从一种生物到另一种生物的简单线性传递路径，总是从生产者开始。食物网则是由多条相互关联的食物链组成的网络，能更真实地反映生态系统中能量的流动情况。无论食物链还是食物网，箭头始终指向能量流动的方向，即从食物指向取食者。
- Producer → Primary consumer → Secondary consumer → Tertiary consumer
- 生产者 → 初级消费者 → 次级消费者 → 三级消费者
4. Trophic Levels and Energy Flow | 营养级与能量流动
A trophic level is a feeding level in a food chain or web. Producers occupy the first trophic level, primary consumers the second, secondary consumers the third, and so on. Energy is transferred up the trophic levels, but the process is highly inefficient. Typically, only about 10% of the energy stored as biomass at one trophic level is passed on to the next. The rest is lost as heat from respiration, used for movement, or remains undigested.
营养级是指食物链或食物网中的摄食层级。生产者位于第一营养级，初级消费者在第二层，次级消费者在第三层，依此类推。能量在营养级之间向上传递，但这一过程效率极低。通常，某一营养级以生物量形式储存的能量，只有约 10% 会传递至下一营养级。其余能量以呼吸产热、运动消耗或未消化的形式散失。
5. Pyramids of Number, Biomass, and Energy | 数量、生物量与能量金字塔
Ecological pyramids are graphical representations of the structure of an ecosystem. A pyramid of number shows the count of organisms at each trophic level. A pyramid of biomass shows the total mass of living material (often dry mass) at each level. A pyramid of energy shows the energy content per unit area per year. Pyramids of biomass and energy are always upright, while pyramids of number can sometimes be inverted.
生态金字塔是生态系统结构的图形化表示。数量金字塔显示每个营养级的生物个体数目；生物量金字塔显示每个营养级的生物总质量（通常为干重）；能量金字塔显示单位面积每年的能量含量。生物量金字塔和能量金字塔总是正立的，而数量金字塔有时可能呈倒金字塔形。
| Pyramid type | Shape | Key characteristics |
| Number | Can be inverted | Counts individuals |
| Biomass | Always upright | Dry mass (kg/m²) |
| Energy | Always upright | Energy (kJ/m²/year) |
6. The Carbon Cycle | 碳循环
Carbon is constantly recycled between the atmosphere, living organisms, oceans, and rocks. Key processes include: photosynthesis by plants and algae removes CO₂ from the air; respiration by living organisms returns CO₂; decomposition by microorganisms releases CO₂; combustion of fossil fuels and forests adds CO₂; and ocean uptake and shell formation store carbon in limestone. Deforestation and burning fossil fuels disrupt the balance, increasing atmospheric CO₂ levels.
碳在大气、生物体、海洋和岩石圈之间不断循环。关键过程包括：植物和藻类的光合作用从空气中吸收 CO₂；生物的呼吸作用释放 CO₂；微生物的分解作用释放 CO₂；化石燃料和森林的燃烧增加 CO₂；海洋吸收以及贝壳的形成将碳储存在石灰岩中。森林砍伐和化石燃料的燃烧打破了平衡，导致大气 CO₂ 浓度上升。
- Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
- 光合作用：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
- Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
- 呼吸作用：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量
7. The Nitrogen Cycle | 氮循环
Nitrogen is essential for making proteins and DNA. The nitrogen cycle converts nitrogen gas (N₂) from the air into forms that plants can use. Key stages: nitrogen fixation by lightning or by bacteria in root nodules of legumes converts N₂ to ammonia (NH₃) or nitrates (NO₃⁻); nitrification by soil bacteria turns ammonium ions (NH₄⁺) into nitrites (NO₂⁻) then nitrates; plants absorb nitrates and use them to build proteins; denitrification by bacteria converts nitrates back to N₂, returning it to the air. Proper management of soil and sewage prevents excess nitrate loss.
氮是合成蛋白质和 DNA 所必需的元素。氮循环将空气中的氮气（N₂）转化为植物可利用的形式。关键阶段：闪电固氮或豆科植物根瘤中的细菌将 N₂ 转化为氨（NH₃）或硝酸盐（NO₃⁻）；土壤硝化细菌将铵离子（NH₄⁺）转化为亚硝酸盐（NO₂⁻）再转化为硝酸盐；植物吸收硝酸盐合成蛋白质；反硝化细菌将硝酸盐还原为 N₂ 返回大气。合理管理土壤和污水可防止硝酸盐过量流失。
8. Biodiversity and Conservation | 生物多样性与保护
Biodiversity is the variety of living species on Earth, measured by species richness, genetic diversity, and ecosystem diversity. High biodiversity usually indicates a healthy, stable ecosystem. Conservation efforts aim to protect species and habitats, maintain biodiversity, and use natural resources sustainably. Methods include setting up nature reserves, creating seed banks, reintroduction programmes, and controlling invasive species.
生物多样性是指地球上生物种类的丰富程度，通常用物种丰富度、遗传多样性和生态系统多样性来衡量。高生物多样性往往意味着生态系统健康稳定。保护工作的目标是保护物种和栖息地、维持生物多样性，并可持续地利用自然资源。常见保护方法包括建立自然保护区、设立种子库、实施物种再引入计划以及控制入侵物种。
9. Human Impact on Ecosystems | 人类对生态系统的影响
Human activities put enormous pressure on ecosystems. Major impacts include: habitat destruction through deforestation, urban expansion, and agriculture; overfishing, which removes top predators and destabilises food webs; introduction of alien species that outcompete native organisms; and pollution of land, water, and air. Climate change, driven by greenhouse gas emissions, alters temperature and weather patterns, further stressing ecosystems.
人类活动给生态系统带来了巨大压力。主要影响包括：森林砍伐、城市扩张和农业导致的栖息地破坏；过度捕捞使顶级捕食者消失，扰乱食物网；外来物种引入后竞争取代本地生物；以及土地、水和空气污染。由温室气体排放引发的气候变化，改变了温度和天气模式，进一步加剧了生态系统的压力。
10. Pollution: Eutrophication and Bioaccumulation | 污染：富营养化与生物累积
Eutrophication occurs when excess fertilisers (nitrates and phosphates) wash into rivers and lakes, causing rapid algae growth. This algal bloom blocks sunlight, leading to the death of aquatic plants. As algae and plants decompose, microorganisms use up dissolved oxygen, resulting in the death of fish and other aerobic organisms. Bioaccumulation is the build-up of toxic substances (e.g., pesticides like DDT) in an organism’s body. These toxins are passed along food chains and become increasingly concentrated at higher trophic levels through biomagnification, harming top predators.
富营养化是指过量化肥（硝酸盐和磷酸盐）流入河流湖泊，导致藻类疯长的现象。藻华遮挡阳光，造成水生植物死亡。藻类和植物残体分解时，微生物消耗大量溶解氧，致使鱼类及其他好氧生物死亡。生物累积是指有毒物质（如杀虫剂 DDT）在生物体内积累的过程。这些毒素沿食物链传递，并随着营养级升高不断浓缩（生物放大作用），最终危害顶级捕食者。
11. Sustainable Practices | 可持续实践
Sustainability means meeting the needs of the present without compromising the ability of future generations to meet their own needs. In ecology, this involves: using renewable resources (solar, wind) over fossil fuels; practising sustainable forestry and fishing; recycling materials; protecting peat bogs and rainforests; and reducing waste and greenhouse gas emissions. Biological control of pests and organic farming reduce reliance on chemical pesticides and fertilisers, helping to maintain soil health and water quality.
可持续性是指在满足当代人需求的同时，不损害后代人满足其自身需求的能力。在生态学中，这包括：优先使用可再生能源（太阳能、风能）替代化石燃料；实行可持续林业和渔业；回收利用材料；保护泥炭沼泽和雨林；以及减少废弃物和温室气体排放。生物防治害虫和有机农业则减少了对化学农药和化肥的依赖，有助于维持土壤健康和水质。
12. Key Definitions and Exam Tips | 关键定义与应试技巧
Make sure you can define and use these terms correctly: ecosystem, habitat, population, community, producer, consumer, decomposer, trophic level, biodiversity, eutrophication, bioaccumulation. In the exam, always refer to data provided in tables or graphs when answering questions. When describing food webs, state the direction of energy flow clearly. Use precise language, such as ‘light intensity’ instead of just ‘light’, and support your answers with specific examples, like the effect of sewage on dissolved oxygen levels.
请确保你能准确定义并运用这些术语：生态系统、栖息地、种群、群落、生产者、消费者、分解者、营养级、生物多样性、富营养化、生物累积。考试中回答问题时要充分利用表格或图表中提供的数据。描述食物网时，务必清晰说明能量流动的方向。使用精确的语言，例如说“光照强度”而不只是“光”，并用具体实例支撑作答，比如污水对溶解氧浓度的影响。
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