📚 IGCSE OCR Science: Environmental Science Key Concepts | IGCSE OCR 科学：环境科学 考点精讲
Environmental Science in the IGCSE OCR Science syllabus examines how living organisms interact with each other and their surroundings. It covers ecosystems, energy flow through food chains, nutrient cycles, human impact including pollution and climate change, and strategies for conservation. Mastering these topics is essential not only for the exam but also for understanding the pressing environmental challenges facing our world today.
IGCSE OCR 科学课程中的环境科学部分探讨了生物如何与彼此及其周围环境相互作用。它涵盖了生态系统、食物链中的能量流动、营养物质循环、人类影响（包括污染和气候变化）以及保护策略。掌握这些主题不仅对考试至关重要，也对理解当今世界面临的紧迫环境挑战不可或缺。
1. Understanding Ecosystems and Habitats | 理解生态系统与栖息地
An ecosystem is a natural unit consisting of all the living organisms (the community) in a particular area, interacting with each other and with their non‑living environment. The habitat is the specific place where an organism lives. Within an ecosystem, populations of different species form the community, and each species occupies a unique ecological niche that describes its role and position in the environment.
生态系统是一个自然单元，由特定区域内所有生物（群落）组成，它们彼此之间以及与非生物环境相互作用。栖息地是生物生活的具体地点。在生态系统中，不同物种种群构成群落，每个物种都占据独特的生态位，描述其在环境中的作用和位置。
- Biotic factors are the living influences such as predation, competition for resources, and disease.
- 生物因素 是指捕食、资源竞争和疾病等有生命的影响因素。
- Abiotic factors are non‑living physical and chemical elements like temperature, light intensity, water availability, pH, and mineral content of the soil.
- 非生物因素 是非生命的物理和化学元素，如温度、光照强度、水分、pH 值和土壤矿物质含量。
- Quadrats and transects are sampling tools used to estimate population size and distribution of organisms in a habitat.
- 样方和样线是用于估算栖息地中生物种群大小和分布的抽样工具。
2. Food Chains, Food Webs, and Energy Flow | 食物链、食物网与能量流动
Feeding relationships in an ecosystem can be shown by food chains and food webs. A food chain is a linear sequence showing what eats what, while a food web is a network of interconnected food chains, giving a more realistic picture of the feeding relationships in a community. Energy enters most ecosystems as sunlight and is captured by producers during photosynthesis.
生态系统中的取食关系可以用食物链和食物网来表示。食物链是显示谁吃谁的线性序列，而食物网是由相互连接的食物链组成的网络，更真实地反映出群落中的取食关系。在大多数生态系统中，能量以阳光的形式进入，并由生产者在光合作用过程中捕获。
- Producers (autotrophs) make their own food via photosynthesis, e.g., green plants and algae.
- 生产者 (自养生物) 通过光合作用制造食物，例如绿色植物和藻类。
- Consumers (heterotrophs) obtain energy by eating other organisms. Primary consumers eat producers, secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers.
- 消费者 (异养生物) 通过取食其他生物获取能量。初级消费者吃生产者，次级消费者吃初级消费者，三级消费者吃次级消费者。
- Decomposers such as bacteria and fungi break down dead organic material, recycling nutrients back into the ecosystem.
- 分解者 如细菌和真菌分解死去的有机物质，将营养物质回收回生态系统。
Energy flow is unidirectional and decreases at each trophic level. Typically, only about 10% of the energy is passed on to the next trophic level; the rest is lost as heat through respiration, movement, and undigested material. This loss limits the length of food chains.
能量流动是单向的，并且在每一营养级递减。通常只有大约 10% 的能量传递到下一个营养级；其余的能量通过呼吸作用、运动和未消化的物质以热的形式散失。这种损失限制了食物链的长度。
r efficiency = (Energy available to next level ÷ Energy available to previous level) × 100%
能量传递效率 = (下一营养级可用能量 ÷ 上一营养级可用能量) × 100%
3. Pyramids of Numbers, Biomass, and Energy | 数量金字塔、生物量金字塔和能量金字塔
Ecological pyramids are graphical representations to illustrate the trophic structure and function of an ecosystem. The three main types are pyramids of numbers, pyramids of biomass, and pyramids of energy. They can reveal important information about the efficiency and stability of the ecosystem.
生态金字塔是图解表示，用于说明生态系统的营养结构和功能。主要有三种类型：数量金字塔、生物量金字塔和能量金字塔。它们可以揭示关于生态系统效率和稳定性的重要信息。
- A pyramid of numbers shows the count of organisms at each trophic level. It can be upright, inverted, or partly inverted depending on the size of the organisms.
- 数量金字塔显示各营养级的生物数量。根据生物的大小，它可以是正立的、倒立的或部分倒立的。
- A pyramid of biomass is a representation of the total dry mass of organisms. It is normally upright because biomass decreases at higher trophic levels, but aquatic systems can show an inverted pyramid due to rapid producer turnover.
- 生物量金字塔表示生物的总干重。因为在较高的营养级生物量减少，它通常呈正立，但由于生产者更新快，水生系统可能呈现倒金字塔形。
- A pyramid of energy is always upright because energy is lost at each transfer. It depicts the amount of energy stored in each trophic level per unit area per unit time.
- 能量金字塔总是正立的，因为每次转移都有能量损失。它描绘了单位面积单位时间内各营养级储存的能量。
4. The Carbon Cycle | 碳循环
Carbon is a key element in all living organisms and the environment. The carbon cycle describes how carbon moves between the atmosphere, living organisms, oceans, and the Earth's crust. The main processes involved are photosynthesis, respiration, combustion, decomposition, and feeding.
碳是所有生物体及环境中的关键元素。碳循环描述了碳如何在大气、生物体、海洋和地壳之间移动。主要涉及的过程包括光合作用、呼吸作用、燃烧、分解和摄食。
| Process / 过程 | Role in cycle / 循环中的作用 |
| Photosynthesis | Removes CO₂ from the atmosphere and converts it into glucose. / 从大气中吸收CO₂并将其转化为葡萄糖。 |
| Respiration | Releases CO₂ back into the atmosphere as organisms break down glucose for energy. / 生物分解葡萄糖获取能量时将CO₂释放回大气。 |
| Combustion | Burning of fossil fuels and biomass releases CO₂. / 燃烧化石燃料和生物质释放CO₂。 |
| Decomposition | Microorganisms break down dead matter, releasing CO₂ and returning nutrients to soil. / 微生物分解死物质，释放CO₂并将养分返回土壤。 |
| Feeding | Carbon passes along food chains when consumers eat producers or other consumers. / 当消费者吃生产者或其他消费者时，碳沿食物链传递。 |
| Fossilisation | Dead organisms buried under pressure form fossil fuels or carbonate rocks, storing carbon for millions of years. / 被埋藏并承受压力的死生物形成化石燃料或碳酸盐岩，将碳储存数百万年。 |
Human activities such as deforestation and the burning of fossil fuels increase atmospheric CO₂, enhancing the greenhouse effect and global warming.
砍伐森林和燃烧化石燃料等人类活动增加了大气中的CO₂，加剧了温室效应和全球变暖。
5. 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 nitrogen into forms usable by plants and animals through processes including nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.
氮对于制造蛋白质和 DNA 至关重要。尽管大气中 78% 是氮气 (N₂)，但大多数生物不能直接利用。氮循环通过固氮作用、硝化作用、同化作用、氨化作用和反硝化作用等过程，将氮转化为植物和动物可利用的形式。
- Nitrogen fixation: conversion of N₂ gas into ammonia (NH₃) or ammonium ions (NH₄⁺) by nitrogen‑fixing bacteria (e.g., Rhizobium in root nodules of legumes) or by lightning.
- 固氮作用：通过固氮细菌（例如豆科植物根瘤中的根瘤菌）或闪电将氮气转化为氨 (NH₃) 或铵离子 (NH₄⁺)。
- Nitrification: soil bacteria oxidise ammonium ions into nitrites (NO₂⁻) and then into nitrates (NO₃⁻).
- 硝化作用：土壤细菌将铵离子氧化成亚硝酸盐 (NO₂⁻)，然后再氧化成硝酸盐 (NO₃⁻)。
- Assimilation: plants absorb nitrates from the soil and use them to build proteins. Animals obtain nitrogen by eating plants or other animals.
- 同化作用：植物从土壤中吸收硝酸盐，用于合成蛋白质。动物通过吃植物或其他动物获得氮。
- Ammonification: decomposers break down dead organisms and waste, releasing ammonium ions back into the soil.
- 氨化作用：分解者分解死去的生物和废物，将铵离子释放回土壤。
- Denitrification: denitrifying bacteria convert nitrates back into N₂ gas under anaerobic conditions, completing the cycle.
- 反硝化作用：在缺氧条件下，反硝化细菌将硝酸盐转化回氮气，完成循环。
6. Population Growth and Factors Affecting Population Size | 种群增长及影响种群大小的因素
A population is a group of organisms of the same species living in a particular area at the same time. Population size can change due to births, deaths, immigration, and emigration. Environmental factors ultimately limit population growth, leading to a carrying capacity.
种群是同一时间生活在特定区域的同种生物群体。种群大小会因出生、死亡、迁入和迁出而改变。环境因素最终限制种群增长，形成环境容纳量。
The growth pattern often follows a sigmoid (S‑shaped) curve: a lag phase of slow growth, a log (exponential) phase of rapid increase, a deceleration phase as resources become limited, and finally a stationary phase where the carrying capacity is reached. The carrying capacity is the maximum population size that an environment can support indefinitely.
增长模式通常呈 S 形曲线：缓慢增长的迟滞期、快速增长的指数期、资源受限时的减速期，最后达到环境容纳量的稳定期。环境容纳量是环境能持续支撑的最大种群规模。
- Limiting factors include food availability, water, shelter, disease, predation, and build‑up of wastes. These can be density‑dependent (effect increases with population density) or density‑independent (e.g., natural disasters).
- 限制因素 包括食物供应、水分、栖息地、疾病、捕食和废物积累。这些因素可以是密度制约的（随种群密度增加效应增强）或非密度制约的（如自然灾害）。
Human population growth is currently exponential, raising concerns about resource depletion and environmental degradation.
当前人类人口呈指数增长，引发了人们对资源枯竭和环境退化的担忧。
7. Pollution: Air, Water, and Land | 污染：空气、水和土地
Pollution is the introduction of harmful materials into the environment. IGCSE Science covers three main types: air pollution, water pollution, and land pollution. Each has serious consequences for ecosystems and human health.
污染是指有害物质进入环境。IGCSE 科学涵盖三种主要类型：空气污染、水污染和土地污染。每种都对生态系统和人类健康造成严重后果。
- Air pollution: Key pollutants include sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) which cause acid rain; carbon monoxide from incomplete combustion; particulates; and greenhouse gases. Acid rain damages plants, acidifies lakes (killing fish), and corrodes buildings.
- 空气污染：主要污染物包括导致酸雨的二氧化硫 (SO₂) 和氮氧化物 (NOₓ)；不完全燃烧产生的一氧化碳；颗粒物；以及温室气体。酸雨损害植物，使湖泊酸化（杀死鱼类），并腐蚀建筑物。
- Water pollution: Sewage and fertilisers lead to eutrophication — excess nutrients cause algal bloom, which blocks sunlight and depletes oxygen when algae decompose, killing aquatic life. Toxic chemicals and oil spills also contaminate water.
- 水污染：污水和化肥导致富营养化——过量营养物质引起藻华，遮蔽阳光，并在藻类分解时耗尽氧气，杀死水生生物。有毒化学物质和石油泄漏也污染水域。
- Land pollution: Improper disposal of solid waste, pesticides, and industrial chemicals can destroy soil structure and biodiversity. Landfill sites generate methane and leachate that pollute groundwater.
- 土地污染：固体废物、农药和工业化学品的不当处置会破坏土壤结构和生物多样性。垃圾填埋场产生甲烷和渗滤液污染地下水。
8. The Greenhouse Effect and Climate Change | 温室效应与气候变化
The greenhouse effect is a natural process that warms the Earth's surface. Short‑wave solar radiation passes through the atmosphere, warms the Earth, and the Earth radiates long‑wave infrared radiation. Greenhouse gases (such as CO₂, methane, water vapour) absorb some of this outgoing radiation and re‑radiate it back, keeping the planet habitable.
温室效应是使地球表面变暖的自然过程。短波太阳辐射穿过大气层使地球变暖，地球再发射长波红外辐射。温室气体（如 CO₂、甲烷、水蒸气）吸收部分向外辐射并将其重新辐射回来，使地球保持适宜居住。
Human activities have intensified the greenhouse effect by increasing the concentration of greenhouse gases, leading to an enhanced greenhouse effect and global warming. Sources include burning fossil fuels for transport and electricity, deforestation (reducing CO₂ absorption), agriculture (methane from cattle, rice paddies), and industrial processes.
人类活动通过增加温室气体浓度强化了温室效应，导致了增强的温室效应和全球变暖。来源包括交通和发电燃烧化石燃料、砍伐森林（减少 CO₂ 吸收）、农业（牛、稻田产生的甲烷）以及工业过程。
Observed effects of climate change include rising global temperatures, melting ice caps and glaciers, sea level rise, more frequent extreme weather events, changes in precipitation patterns, and shifts in species distributions. Without mitigation, these impacts threaten food security, water supply, and biodiversity.
观测到的气候变化影响包括全球气温上升、冰盖和冰川融化、海平面上升、更频繁的极端天气事件、降水模式变化以及物种分布变化。若不加以缓解，这些影响威胁到粮食安全、水资源供应和生物多样性。
9. Deforestation and Its Impacts | 森林砍伐及其影响
Deforestation is the large‑scale removal of trees from forests. It occurs mainly for timber, agricultural land (including palm oil plantations), and urban expansion. This has multiple environmental consequences that are often tested in the IGCSE OCR examination.
森林砍伐是指大规模清除森林中的树木。主要为了获取木材、农业用地（包括棕榈油种植园）和城市扩张。这会产生多种环境后果，在 IGCSE OCR 考试中常被考查。
- Increased atmospheric CO₂: Trees act as carbon sinks. Removing them releases stored carbon and reduces CO₂ absorption, contributing to global warming.
- 大气 CO₂ 增加：树木是碳汇。清除树木会释放储存的碳并减少 CO₂ 吸收，导致全球变暖。
- Loss of biodiversity: Forests host a huge variety of species. Habitat destruction can lead to extinction.
- 生物多样性丧失：森林是大量物种的家园。栖息地破坏可能导致物种灭绝。
- Soil erosion: Tree roots bind soil. Without them, heavy rain washes away topsoil, leading to loss of fertility and desertification.
- 土壤侵蚀：树根固定土壤。没有它们，暴雨会冲走表土，导致肥力丧失和荒漠化。
- Disruption of the water cycle: Less transpiration reduces rainfall and increases the risk of drought.
- 水循环破坏：蒸腾作用减少会降低降雨量并增加干旱风险。
10. Conservation and Sustainable Development | 保护与可持续发展
Conservation is the sensible management of the biosphere to maintain habitats and biodiversity while allowing human activity. Sustainable development meets the needs of the present without compromising the ability of future generations to meet their own needs. Several strategies are important to learn for the syllabus.
保护是对生物圈的明智管理，以维持栖息地和生物多样性，同时允许人类活动。可持续发展在满足当代人需求的同时，不损害后代人满足其需求的能力。课程要求学习几种重要策略。
- Protected areas: National parks, nature reserves, and marine protected areas help preserve critical habitats and endangered species.
- 保护区：国家公园、自然保护区和海洋保护区有助于保护关键栖息地和濒危物种。
- Captive breeding and reintroduction: Breeding animals in zoos or botanical gardens and releasing them into the wild can boost endangered populations (e.g., golden lion tamarin).
- 人工繁殖与再引入：在动物园或植物园繁殖动物并将它们放归野外可增加濒危种群（例如金狮面狨）。
- Reforestation and afforestation: Planting trees to restore or create forests helps absorb CO₂, prevent erosion, and restore habitats.
- 重新造林与植树造林：植树以恢复或建立森林有助于吸收 CO₂、防止侵蚀并恢复栖息地。
- Renewable energy: Switching to solar, wind, hydroelectric, and geothermal power reduces the reliance on fossil fuels and cuts greenhouse gas emissions.
- 可再生能源：改用太阳能、风能、水电和地热可减少对化石燃料的依赖并削减温室气体排放。
- Sustainable agriculture and fishing: Methods such as crop rotation, organic farming, and setting fishing quotas prevent over‑exploitation of resources.
- 可持续农业与渔业：轮作、有机农业和设定捕鱼配额等方法防止资源过度开发。
11. Eutrophication in Detail | 富营养化详解
Eutrophication is a common focus of questions linking water pollution to ecosystem change. It is a process driven by the enrichment of water bodies with nutrients, particularly nitrates and phosphates from fertilisers and sewage.
富营养化是将水污染与生态系统变化联系起来的常见考题焦点。这是一个由水体富含营养物质，特别是化肥和污水中的硝酸盐和磷酸盐驱动的过程。
- Rain washes excess fertilisers or untreated sewage into a river or lake, increasing nutrient levels.
- 雨水将多余的肥料或未经处理的污水冲入河流或湖泊，使营养物水平升高。
- The high nutrient concentration causes rapid growth of algae and surface plants (algal bloom).
- 高浓度营养物质导致藻类和表面植物快速生长（藻华）。
- The dense algal layer blocks sunlight from reaching deeper water, causing plants below to die.
- 浓密的藻层阻挡阳光到达较深水域，导致下方植物死亡。
- Aerobic bacteria decompose the dead plants and algae, using up dissolved oxygen as they respire.
- 需氧细菌分解死去的植物和藻类，在呼吸过程中消耗溶解氧。
- Oxygen levels plummet, leading to the death of fish and other aerobic organisms. Anaerobic bacteria take over, producing foul‑smelling gases.
- 氧气含量骤降，导致鱼类和其他需氧生物死亡。厌氧细菌取而代之，产生有臭味的气体。
- Biodiversity diminishes, and the ecosystem becomes severely degraded.
- 生物多样性下降，生态系统严重退化。
Preventing eutrophication involves reducing fertiliser use, treating sewage before release, and creating buffer strips alongside waterways to absorb excess nutrients.
预防富营养化包括减少化肥使用、在排放前处理污水，以及在河道旁设立缓冲带以吸收过量营养物质。
12. Case Study: Bioaccumulation and Pesticides | 案例研究：生物累积与农药
Bioaccumulation is the accumulation of substances, such as pesticides (e.g., DDT) or heavy metals, in an organism. Biomagnification occurs when the concentration of these persistent toxins increases at higher trophic levels in a food chain. A classic example is the effect of DDT on birds of prey.
生物累积是指物质（如农药 DDT）或重金属在生物体内积累。生物放大作用是指这些持久性毒素在食物链较高营养级中浓度增加。一个经典例子是 DDT 对猛禽的影响。
- DDT was widely used to control insect pests. It is non‑biodegradable and remains in the environment for many years.
- DDT 曾被广泛用于控制害虫。它不可生物降解，在环境中存留多年。
- Rain washes DDT into water bodies, where it is absorbed by microscopic producers and accumulates in their tissues.
- 雨水将 DDT 冲入水体，被微型生产者吸收并在其组织中积累。
- Primary consumers eat many producers, concentrating the DDT further. Secondary and tertiary consumers eat many prey, resulting in very high concentrations at the top of the food chain.
- 初级消费者吃掉许多生产者，进一步浓缩 DDT。次级和三级消费者捕食大量猎物，导致食物链顶端的浓度极高。
- In birds of prey, high DDT levels cause thinning of eggshells, so eggs break easily during incubation, leading to population decline. This evidence has led to bans on DDT in many countries.
- 在猛禽体内，高浓度 DDT 导致蛋壳变薄，孵化时蛋易破碎，导致种群数量下降。这一证据促使许多国家禁用 DDT。
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