📚 OCR Science: Ecosystems Revision Guide | OCR 科学：生态系统 考点精讲
Ecosystems are dynamic, interconnected systems where living organisms interact with each other and their physical environment. For OCR Science, understanding the flow of energy, the cycling of materials, and the delicate balances that maintain ecosystems is essential. This guide walks you through every key specification point, from food chains to the carbon cycle, with clear explanations and exam‑focused detail.
生态系统是动态且相互联系的系统，生物与生物之间、生物与物理环境之间不断地相互作用。在 OCR 科学考试中，理解能量流动、物质循环以及维持生态系统平衡的细腻机制至关重要。这份考点精讲将带你梳理从食物链到碳循环的每一个知识要点，提供清晰的解释与紧扣考试的细节。
Published by TutorHao | OCR Science Revision Series | aleveler.com
1. Levels of Organisation in an Ecosystem | 生态系统的组织层次
An individual organism is the most basic unit. A group of individuals of the same species living in the same area forms a population. Different populations interacting with each other make up a community. The community, together with its non‑living (abiotic) environment, constitutes an ecosystem. Ecosystems can range from a small pond to a vast forest. You need to be able to define and give examples of each level: organism, population, community, ecosystem, and also habitat (the place where an organism lives).
一个单独的个体生物是最基本的单位。同一物种的多个个体生活在同一区域构成一个种群。不同种群相互影响构成一个群落。群落连同其非生物（无生命）环境一起构成一个生态系统。生态系统可以小至一个池塘，大至一片广阔的森林。你需要能够定义并举例说明每一个层次：个体、种群、群落、生态系统，以及栖息地（生物生活的地方）。
- Organism: a single living thing, e.g. a fox.
- 个体：一个活着的生物，例如一只狐狸。
- Population: all the foxes in a woodland.
- 种群：一片林地中所有的狐狸。
- Community: all the foxes, rabbits, oak trees, earthworms, and other species in that woodland.
- 群落：那片林地中所有的狐狸、兔子、橡树、蚯蚓以及其他物种。
- Ecosystem: the woodland community plus the soil, water, sunlight, and climate.
- 生态系统：林地群落加上土壤、水、阳光和气候。
2. Abiotic and Biotic Factors | 非生物因素与生物因素
Ecosystems are shaped by abiotic (non‑living) and biotic (living) factors. Abiotic factors include light intensity, temperature, moisture levels, soil pH, wind speed, and mineral content. Biotic factors include predation, competition, disease, and availability of food. Changes in any of these can affect the distribution and abundance of organisms. For OCR, you must be able to describe how specific abiotic factors affect plants and animals, and how biotic interactions like competition for resources influence population sizes.
生态系统受到非生物因素（无生命）和生物因素（有生命）的影响。非生物因素包括光照强度、温度、湿度、土壤 pH 值、风速和矿物质含量。生物因素包括捕食、竞争、疾病和食物供应。任何因素的变化都可能影响生物的分布和数量。针对 OCR 考试，你必须能够描述特定的非生物因素如何影响植物和动物，以及资源竞争等生物相互作用如何影响种群大小。
- Light intensity affects photosynthesis; plants in shade may have broader leaves.
- 光照强度影响光合作用；阴处的植物可能长出更宽的叶片。
- Competition for mates, food, or territory can limit population growth.
- 对配偶、食物或领地的竞争会限制种群增长。
3. Feeding Relationships: Food Chains and Food Webs | 营养关系：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 (usually a green plant or alga) that converts light energy into chemical energy via photosynthesis. The producer is eaten by a primary consumer, which is then eaten by a secondary consumer, and so on. A food web is a network of interconnected food chains, giving a more realistic picture of feeding relationships in a community. Knowing how to construct and interpret both is fundamental for the exam.
食物链显示能量从一个生物传递到另一个生物的单向线形路径。它总是以生产者（通常是绿色植物或藻类）开始，它们通过光合作用将光能转化为化学能。生产者被初级消费者吃掉，然后初级消费者被次级消费者吃掉，以此类推。食物网是由相互连接的食物链组成的网络，更真实地反映了群落中的营养关系。会构建、会解读食物链和食物网是考试的基本要求。
- Example chain: grass → rabbit → fox. The arrow means 'is eaten by' and shows energy flow direction.
- 示例链：草 → 兔子 → 狐狸。箭头表示“被……吃”，并显示能量流动方向。
- In a web, a single organism may have multiple prey or predators.
- 在食物网中，一种生物可能有多样猎物或天敌。
4. Energy Flow and Efficiency | 能量流动与效率
Energy enters most ecosystems as sunlight. Producers capture only about 1–3% of the available light energy. At each trophic level, energy is lost through respiration, movement, heat, and undigested materials excreted as faeces. Typically, only about 10% of the energy is transferred to the next trophic level. This explains why food chains rarely exceed four or five trophic levels and why pyramids of biomass and energy are always upright pyramids (wide at the base).
能量大多以阳光的形式进入生态系统。生产者仅能捕获大约 1–3% 的可用光能。在每一个营养级，能量会因呼吸、运动、散热以及未消化物质随粪便排出而损失。通常，只有约 10% 的能量传递到下一个营养级。这就解释了为什么食物链很少超过四五个营养级，以及为什么生物量金字塔和能量金字塔总是正立的（基部宽）。
Efficiency = (energy transferred to next level ÷ energy available at previous level) × 100%
效率 = (传递到下一营养级的能量 ÷ 上一营养级可用的能量) × 100%
You may be asked to calculate efficiency or explain ways to improve energy transfer in agriculture (e.g. reducing respiration loss in livestock by keeping them warm).
你可能会被要求计算效率，或解释如何提高农业中的能量传递效率（例如通过保暖减少牲畜的呼吸损耗）。
5. Pyramids of Biomass and Energy | 生物量金字塔与能量金字塔
A pyramid of biomass represents the dry mass of organisms at each trophic level at a given time. Because biomass can be affected by seasonal variations or water content, it is usually measured as dry mass (g/m²). A pyramid of energy shows the total energy content stored in each trophic level, measured in kJ/m²/year. Energy pyramids are always pyramid‑shaped, whereas biomass pyramids can be inverted in some aquatic ecosystems (e.g. a small phytoplankton biomass supporting a larger zooplankton biomass over time).
生物量金字塔表示在特定时间每个营养级生物的干质量。由于生物量会受到季节变化或含水量的影响，通常以外干重（克/平方米）来测量。能量金字塔表示储存在每个营养级中的总能量，单位为千焦/平方米/年。能量金字塔总是金字塔形的，而生物量金字塔在某些水域生态系统中可能是倒置的（例如少量的浮游植物生物量能支撑更大的浮游动物生物量）。
- Always label axes correctly: x‑axis = trophic level, y‑axis = biomass or energy.
- 务必正确标注坐标轴：x 轴 = 营养级，y 轴 = 生物量或能量。
- Drawing pyramids to scale is a frequent exam skill.
- 按比例绘制金字塔是考试的常见技能。
6. Material Cycles: The Carbon Cycle | 物质循环：碳循环
tion (glucose → CO₂), combustion of fossil fuels (hydrocarbons → CO₂), decomposition (organic matter → CO₂ via microorganisms), and feeding (carbon moves through food chains). For OCR, you must be able to describe and label a carbon cycle diagram, explaining the role of decomposers and the impact of human activities like deforestation and burning fossil fuels on atmospheric CO₂ levels.
碳在大气、生物体、海洋和化石储量之间循环。关键过程包括光合作用（CO₂ → 葡萄糖）、呼吸作用（葡萄糖 → CO₂）、化石燃料燃烧（碳氢化合物 → CO₂）、分解作用（有机物通过微生物分解产生 CO₂）以及捕食（碳沿食物链传递）。针对 OCR 考试，你必须能够描述并标注碳循环图，解释分解者的作用，以及毁林和燃烧化石燃料等人类活动对大气 CO₂ 浓度的影响。
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 Water Cycle | 水循环
Water evaporates from oceans, lakes, and soil, and is transpired by plants. Water vapour condenses into clouds and returns to the surface as precipitation (rain, snow, hail). Water runs off into rivers and lakes or infiltrates into underground aquifers. Animals gain water from drinking and food, and lose it through excretion, respiration, and sweating. A diagram of the water cycle should include evaporation, transpiration, condensation, precipitation, and surface run‑off.
水从海洋、湖泊和土壤中蒸发，并通过植物的蒸腾作用释放水蒸气。水蒸气凝结成云，以降水的形式（雨、雪、冰雹）返回地表。水流入河流和湖泊，或下渗到地下含水层。动物通过饮水和进食获取水分，并通过排泄、呼吸和出汗失去水分。水循环示意图应包括蒸发、蒸腾、凝结、降水和地表径流。
- Transpiration is the evaporation of water from the leaves of plants.
- 蒸腾作用是水分从植物叶片蒸发的现象。
- Condensation occurs when water vapour cools and changes back to liquid droplets.
- 水蒸气冷却变回液态小水滴时即发生凝结。
8. The Nitrogen Cycle and Decomposers | 氮循环与分解者
The nitrogen cycle is driven by microorganisms. Nitrogen‑fixing bacteria in the soil or in root nodules of legumes convert atmospheric N₂ into ammonia (NH₃), which is then converted to nitrates (NO₃⁻) by nitrifying bacteria. Plants absorb nitrates to make proteins. Decomposers (fungi, bacteria) break down dead organisms and waste, returning ammonium ions to the soil. Denitrifying bacteria convert nitrates back to N₂, completing the cycle. You should know the roles of nitrogen‑fixing, nitrifying, and denitrifying bacteria, as well as decomposers.
氮循环由微生物驱动。土壤中或豆科植物根瘤中的固氮菌能将大气中的 N₂ 转化为氨（NH₃），然后经由硝化细菌转化为硝酸盐（NO₃⁻）。植物吸收硝酸盐用于制造蛋白质。分解者（真菌、细菌）分解死亡的生物和废物，将铵离子归还土壤。反硝化细菌将硝酸盐重新转化为 N₂，完成循环。考生应掌握固氮菌、硝化细菌、反硝化细菌和分解者的作用。
N₂ → NH₃ → NO₃⁻ → Plant protein → Animal protein → Decomposition → NH₃
N₂ → NH₃ → NO₃⁻ → 植物蛋白 → 动物蛋白 → 分解 → NH₃
9. Sampling Ecosystems: Quadrats and Transects | 生态系统取样：样方与样线
laced randomly to count organisms or estimate percentage cover. Random numbers can be generated to avoid bias. Transects are used to study how an abiotic factor changes across a habitat. A line transect records every organism touching the line; a belt transect uses quadrats placed at regular intervals along the line. For OCR, you must be able to explain how to use a quadrat and a transect, and how to calculate population estimates.
为了研究物种的分布和丰度，生态学家使用取样技术。样方（通常为 0.5 米 × 0.5 米或 1 米 × 1 米的方形框）被随机放置以计数生物或估算覆盖百分比。可以通过生成随机数来避免偏差。样线用于研究非生物因素在栖息地中的变化。线样线记录触及线的每个生物；带状样线则沿样线以固定间隔放置样方。针对 OCR 考试，你必须能够解释如何使用样方和样线，以及如何计算种群估算值。
- Population estimate = (mean count per quadrat × total area) ÷ quadrat area.
- 种群估算值 = （每个样方的平均数量 × 总面积） ÷ 样方面积。
- Percentage cover is useful for plants; count the number of grid squares covered.
- 覆盖百分比对植物很有用；数一数被覆盖的网格格子数。
10. Biodiversity and Conservation | 生物多样性与保护
Biodiversity refers to the variety of species, genetic variation within species, and the variety of ecosystems in a given area. High biodiversity often indicates a healthy, stable ecosystem. Human activities — deforestation, pollution, urbanisation — reduce biodiversity. Conservation efforts include breeding programmes, protected areas, reforestation, and sustainable resource use. In the OCR exam, you may be asked to evaluate methods of conserving biodiversity or to explain why maintaining biodiversity is important for ecosystem services such as pollination, water purification, and climate regulation.
生物多样性指一个区域内物种的多样性、物种内的遗传变异以及生态系统的多样性。高生物多样性通常表明生态系统健康且稳定。人类活动——砍伐森林、污染、城市化——会降低生物多样性。保护措施包括繁育计划、保护区、重新造林和资源的可持续利用。在 OCR 考试中，你可能会被要求评价保护生物多样性的方法，或解释为什么维持生物多样性对授粉、净化水源和调节气候等生态系统服务至关重要。
- Keystone species: a species that has a disproportionately large effect on its environment.
- 关键种（基石物种）：对环境产生不成比例巨大影响的物种。
- Ex situ conservation: off‑site, e.g. seed banks, zoos.
- 迁地保护：在原生地之外，例如种子库、动物园。
- In situ conservation: on‑site, e.g. nature reserves.
- 就地保护：在原栖息地，例如自然保护区。
11. Predator–Prey Relationships | 捕食者与被捕食者关系
Predator and prey populations are interlinked in a cyclical pattern. An increase in prey leads to an increase in predator numbers after a time lag; then, as predators consume more prey, the prey population declines, which eventually causes a decline in predators. These cyclical fluctuations can be seen in data like the classic lynx–snowshoe hare cycle. Be prepared to interpret graphs showing these oscillations and to explain the reasons behind the time lag — predators take time to reproduce after an increase in food availability.
捕食者种群与被捕食者种群以周期性模式相互关联。猎物数量增加后，捕食者数量经过一段时滞后也会增加；随着捕食者吃掉更多猎物，猎物种群下降，最终导致捕食者数量下降。这种周期性波动可以在经典数据中看到，比如猞猁–雪鞋兔的周期。请准备好解读展示这些波动的图表，并解释时滞背后的原因——捕食者在食物增加后需要一段时间才能繁殖。
The lag typically occurs because predator reproduction depends on the number of surviving young, which is influenced by food availability several months earlier.
时滞通常是因为捕食者的繁殖取决于存活幼崽的数量，而这受到数月前食物供应的影响。
12. Human Impact on Ecosystems: Eutrophication and Bioaccumulation | 人类对生态系统的影响：富营养化与生物累积
Two exam‑focused consequences of human activity are eutrophication and bioaccumulation. Eutrophication occurs when fertilisers or sewage enter water bodies, causing an algal bloom. The algae block sunlight, causing aquatic plants to die. Aerobic bacteria decompose the dead plants, using up oxygen, leading to the death of fish and other aerobic organisms. Bioaccumulation is the build‑up of a non‑biodegradable substance (e.g. pesticides such as DDT) in an organism. Biomagnification is the increase in concentration along the food chain, causing top predators to accumulate toxic levels. OCR often asks for the sequence of events in eutrophication and the dangers of persistent pesticides.
两种考试常考的人类活动后果是富营养化和生物累积。富营养化发生在肥料或污水进入水体时，引起藻华。藻类遮蔽阳光，导致水生植物死亡。好氧细菌分解死亡植物，消耗氧气，导致鱼类和其他好氧生物死亡。生物累积是指不可生物降解的物质（如滴滴涕等杀虫剂）在生物体内积累。生物放大是指浓度沿食物链逐级升高，导致顶级捕食者积累到毒性水平。OCR 考试常要求叙述富营养化的事件顺序以及持久性杀虫剂的危害。
gal bloom → Sunlight blocked → Plants die → Bacteria multiply → Oxygen depleted → Fish die
肥料 → 藻华 → 阳光被遮蔽 → 植物死亡 → 细菌大量繁殖 → 氧气耗尽 → 鱼类死亡
Published by TutorHao | OCR Science Revision Series | aleveler.com
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