Ecology Revision Guide: Key Concepts for IGCSE WJEC Biology | 生态学考点精讲：IGCSE WJEC 生物学核心概念

📚 Ecology Revision Guide: Key Concepts for IGCSE WJEC Biology | 生态学考点精讲：IGCSE WJEC 生物学核心概念

Ecology is the study of interactions between living organisms and their environment. For IGCSE WJEC Biology, this topic covers everything from feeding relationships and energy flow to nutrient cycles and human impacts. Mastering ecology means understanding how energy and matter move through ecosystems, how to sample populations accurately, and why biodiversity and conservation matter for a sustainable future.

生态学是研究生物与环境之间相互作用的科学。在IGCSE WJEC 生物考纲中，生态学涵盖从食物关系、能量流动到养分循环和人类影响的所有内容。掌握生态学意味着理解能量和物质如何在生态系统中移动，如何准确取样调查种群，以及为什么生物多样性与保护对可持续发展的未来至关重要。

1. Introduction to Ecology | 生态学导论

Ecology examines the distribution and abundance of organisms, the interactions that shape communities, and the flow of energy and cycling of nutrients within ecosystems. Key terms include habitat, population, community, ecosystem, and niche. The habitat is the place where an organism lives, while a population is all the individuals of a species in that habitat. A community consists of all populations living together, and an ecosystem includes the community plus the abiotic environment. The niche describes an organism's role, including what it eats, where it feeds, and how it interacts with other species.

生态学研究生物的分布与数量、塑造群落的相互作用，以及生态系统中的能量流动和养分循环。关键术语包括栖息地、种群、群落、生态系统和生态位。栖息地是生物生活的地方；种群是栖息地中同一物种的全部个体；群落包括共同生活的所有种群；生态系统则由群落与非生物环境组成。生态位描述了生物的“角色”，包括其食性、取食位置以及与其他物种的相互关系。

WJEC exams often test the definition of these terms and ask you to identify them from a scenario. For example, a rock pool contains seaweed, crabs, and fish living in saltwater – this whole system is an ecosystem.

WJEC 考试常考查这些术语的定义，并要求从情境中识别它们。例如，一个潮池中有海藻、螃蟹和鱼类生活在海水里，这整个系统就是一个生态系统。

2. Levels of Organisation | 组织层次

anism is a single living individual. A population is a group of organisms of the same species living in a specific area. A community is formed by multiple interacting populations. An ecosystem comprises the community and its physical environment. The biosphere is the global sum of all ecosystems.

生命系统按照层级组织：个体 → 种群 → 群落 → 生态系统 → 生物圈。个体是单一生命体；种群是特定区域内同一物种的一群生物；群落由多个相互作用的种群构成；生态系统包括群落及其物理环境；生物圈则是地球上所有生态系统的总和。

This hierarchical thinking helps biologists design studies and analyse data. For instance, to understand a decline in a butterfly species, you might first examine its population size, then its community interactions with food plants and predators, and finally abiotic factors like temperature and soil moisture within the ecosystem.

这种层级思维有助于生物学家设计研究和分析数据。例如，要理解某种蝴蝶数量下降，你需要先考察其种群大小，然后看它与食物植物、捕食者的群落相互作用，最后还要考虑生态系统中的非生物因素，如温度和土壤湿度。

3. Food Chains and Food Webs | 食物链和食物网

nd is followed by primary, secondary, and tertiary consumers. Arrows point in the direction of energy flow, i.e. from the eaten to the eater. For example: grass → rabbit → fox.

食物链显示能量从一个生物传递到另一个生物的单一路径。它总是从生产者（通常是绿色植物）开始，然后依次是初级消费者、次级消费者和三级消费者。箭头指向能量流动的方向，即从被食者指向捕食者。例如：草 → 兔子 → 狐狸。

A food web is a network of interconnected food chains, providing a more realistic picture of feeding relationships. If one species declines, the web shows alternative food sources that may buffer the impact. Predators often occupy higher trophic levels, and omnivores can feed at several levels.

食物网是由相互连接的食物链构成的网络，更真实地反映了取食关系。如果某个物种数量下降，食物网能显示替代食物来源，这可能会缓冲冲击。捕食者通常占据较高的营养级，而杂食动物可以在多个营养级取食。

In WJEC exams, you may be given a food web and asked to name producers, consumers, predators, and prey, or to predict the consequences of removing a species.

在 WJEC 考试中，你可能会被要求根据食物网指出生产者、消费者、捕食者和猎物，或预测移除某一物种的后果。

4. Energy Flow and Trophic Levels | 能量流动与营养级

Energy enters most ecosystems as sunlight and is captured by producers during photosynthesis. This energy is converted into biomass. At each trophic level, a large proportion of energy is lost to the environment as heat from respiration, used for movement and growth, or lost in uneaten parts and excretion. Only about 10% of the energy is transferred to the next trophic level.

能量通过阳光进入大多数生态系统，由生产者在光合作用中捕获，并转化为生物量。在每个营养级，大部分能量会以呼吸热、用于运动与生长，或随未食部分和排泄物而散失。通常只有大约 10% 的能量传递到下一个营养级。

This low efficiency explains why food chains rarely have more than four or five trophic levels; there simply is not enough energy to support another level. Energy is not recycled, unlike nutrients.

这种低效率解释了为什么食物链很少超过四到五个营养级；根本没有足够的能量支撑更多层级。能量不像养分那样可以循环再利用。

5. Pyramids of Numbers, Biomass and Energy | 数量、生物量和能量金字塔

Pyramids of numbers show the count of organisms at each trophic level. Their shape can be irregular; for example, a single oak tree may support thousands of insects, giving an inverted pyramid. Pyramids of biomass show the total living mass (dry mass) at each level and are almost always upright, because mass decreases along the chain. Pyramids of energy show the energy content (kJ per m² per year) and are always upright, reflecting the laws of thermodynamics.

数量金字塔显示每个营养级的生物个体数，形状可能不规则；例如，一棵橡树可能支撑数千只昆虫，形成倒金字塔。生物量金字塔显示每级的干物质量，几乎总是正立的，因为生物量沿食物链递减。能量金字塔展示能量含量（千焦/平方米/年），总是正立的，这反映了热力学定律。

WJEC expects you to interpret and sometimes draw these pyramids, paying attention to labels, scale, and the units of measurement. Remember that biomass pyramids must state dry mass to avoid the effect of water content.

WJEC 考试要求你能解读、有时还要绘制这些金字塔，注意标签、比例尺和单位。记住，生物量金字塔必须使用干质量，以去除水分含量的影响。

6. Nutrient Cycles: The Carbon Cycle | 养分循环：碳循环

cks. Key processes include photosynthesis (CO₂ → glucose), respiration (glucose → CO₂), decomposition (organic matter → CO₂ by microorganisms), combustion (fossil fuels → CO₂), and ocean uptake and release.

碳是生命的基本构造单元。碳循环描述了碳原子如何在大气、生物、海洋和岩石之间移动。关键过程包括光合作用（CO₂ → 葡萄糖）、呼吸作用（葡萄糖 → CO₂）、分解作用（微生物将有机物转化为 CO₂）、燃烧（化石燃料 → CO₂），以及海洋的吸收与释放。

Deforestation and fossil fuel burning increase atmospheric CO₂, contributing to the enhanced greenhouse effect and climate change. You should be able to label a carbon cycle diagram and explain the role of each process.

森林砍伐和化石燃料燃烧增加了大气中的 CO₂，加剧了温室效应与气候变化。你需要能够标注碳循环图，并解释每个过程的作用。

7. The Nitrogen Cycle | 氮循环

orm. The nitrogen cycle converts N₂ into usable compounds. Nitrogen fixation, carried out by free‑ ammonia). Ammonia can then be oxidised to nitrites (NO₂⁻) and nitrates (NO₃⁻) by nitrifying bacteria (Nitrosomonas and Nitrobacter). Plants absorb nitrates for protein synthesis. Decomposition and denitrification return nitrogen to the atmosphere.

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氮是蛋白质和核酸必需的元素，但生物无法直接利用大气中的 N₂。氮循环将 N₂ 转化为可用的化合物。固氮作用由自由生活的细菌（如固氮菌）和豆科植物根瘤中的共生细菌（根瘤菌）进行，反应为 N₂ → NH₃（氨）。氨随后被硝化细菌（亚硝酸菌和硝酸菌）氧化成亚硝酸盐（NO₂⁻）和硝酸盐（NO₃⁻）。植物吸收硝酸盐用于合成蛋白质。分解作用和反硝化作用则将氮送回大气。

WJEC may ask you to identify the role of bacteria in the nitrogen cycle or to explain how farming practices like crop rotation with legumes improve soil fertility by increasing nitrate content.

WJEC 可能会要求你指出细菌在氮循环中的作用，或解释轮作豆科植物等农业实践如何通过增加硝酸盐含量来提高土壤肥力。

8. Sampling Techniques | 取样技术

To study ecosystems, ecologists use sampling methods to estimate population size and distribution. For stationary organisms (plants, slow‑moving animals), quadrats are used. A quadrat is a square frame of a known area (e.g. 0.25 m²). Random sampling with many quadrats gives an estimate of species frequency, density, or percentage cover. A transect – a line along which quadrats are placed – is used to investigate distribution changes across a gradient.

研究生态系统时，生态学家使用取样方法来估算种群大小和分布。对于静止生物（植物、移动缓慢的动物），使用样方。样方是一个已知面积（例如 0.25 m²）的方框。用许多样方进行随机取样可以估算物种的频度、密度或盖度。样线——即一条放置样方的直线——用于研究分布随环境梯度的变化。

For mobile animals, the capture‑mark‑ ptured and marked in the first sample, C is the total number captured in the second sample, and R is the number of marked individuals recaptured. This method assumes that marking does not affect survival, marked individuals mix evenly, and the population is closed.

对于移动的动物，采用标记‑重捕法。林肯指数估算种群数量：N = (M × C) / R，其中 M 是第一次捕捉并标记的数量，C 是第二次捕捉的总数，R 是重捕到的标记个体数。该方法假设标记不影响生存、标记个体均匀混合，并且种群是封闭的。

N = (M × C) / R

WJEC practical tasks often involve using quadrats to compare two habitats or applying the Lincoln index to a simulated animal population. Be prepared to calculate means, percentages, and estimate total population size.

WJEC 实验任务常涉及使用样方比较两个栖息地，或对模拟动物种群应用林肯指数。准备好计算平均值、百分比和估算种群总数。

9. Population Dynamics | 种群动态

birth rate + immigration = death rate + emigration. Populations often follow a sigmoid (S‑ lowing phase as limiting factors act, and finally a stationary phase at carrying capacity.

种群大小受出生率、死亡率、迁入和迁出的影响。在稳定种群中，出生率+迁入 = 死亡率+迁出。当资源有限时，种群常呈现 S 形增长曲线：滞后期、指数增长期（对数期）、随限制因素作用而减缓的时期，最后在环境容纳量达到平稳期。

Limiting factors such as food supply, predation, disease, and shelter prevent indefinite growth. These factors can be density‑dependent (effect intensifies with population size) or density‑independent (natural disasters).

食物供应、捕食、疾病和庇护所等限制因素会阻止无限增长。这些因素可以是密度制约的（影响随种群规模增大而加剧）或非密度制约的（如自然灾害）。

10. Biodiversity and Conservation | 生物多样性与保护

Biodiversity refers to the variety of life at all levels: genetic diversity within a species, species diversity in a community, and ecosystem diversity. High biodiversity increases ecosystem resilience, providing essential services like pollination, climate regulation, and nutrient cycling.

生物多样性指各个层次的生命多样性：物种内部的遗传多样性、群落中的物种多样性，以及生态系统多样性。高生物多样性增强生态系统恢复力，提供授粉、气候调节和养分循环等关键服务。

Conservation aims to protect and sustainably manage biodiversity. Strategies include establishing protected areas, captive breeding programmes, seed banks, and legislation to prevent overharvesting and habitat destruction. The WJEC syllabus may reference examples like the protection of the Snowdonia National Park or marine conservation zones.

保护旨在保护并可持续管理生物多样性。策略包括建立保护区、异地繁殖计划、种子库以及防止过度捕捞和栖息地破坏的立法。WJEC 考纲可能引用斯诺登尼亚国家公园或海洋保护区的保护实例。

11. Human Impact on Ecosystems | 人类对生态系统的影响

Human activities significantly alter ecosystems. Deforestation reduces biodiversity, disrupts carbon and water cycles, and leads to soil erosion. Burning fossil fuels releases CO₂ and SO₂, causing acid rain that damages forests and aquatic habitats. Agricultural practices, including overuse of fertilisers, cause eutrophication: excess nitrates and phosphates run into water bodies, triggering algal blooms, oxygen depletion, and death of aquatic life.

人类活动显著改变生态系统。砍伐森林降低生物多样性，扰乱碳循环和水循环，并导致土壤侵蚀。燃烧化石燃料释放 CO₂ 和 SO₂，引起酸雨，损害森林与水生栖息地。包括过度使用化肥的农业实践造成富营养化：过量的硝酸盐和磷酸盐流入水体，引发藻华、缺氧和水生生物死亡。

Pollution from plastics, insecticides, and industrial waste accumulates in food chains through bioaccumulation and biomagnification. Understanding these impacts is crucial for evaluating sustainable solutions such as renewable energy, organic farming, and recycling.

塑料、杀虫剂和工业废物造成的污染通过生物积累和生物放大作用在食物链中积累。理解这些影响对于评估可再生能源、有机农业和循环利用等可持续解决方案至关重要。

12. Practical Skills and Data Analysis | 实验技能与数据分析

WJEC ecology questions frequently test your ability to interpret data from tables, graphs, and diagrams. You should be proficient in calculating rates, percentages, means, and population estimates; describing trends; and drawing conclusions based on evidence. When writing about experiments, always refer to controlled variables, reliability (repetition), and sources of error, such as edge effects when using quadrats or marking that makes animals more visible to predators.

WJEC 生态学考题经常测试你解读表格、图表和示意图数据的能力。你应熟练计算速率、百分比、平均值和种群估计量；描述趋势；并基于证据得出结论。在描述实验时，务必提及控制变量、可靠性（重复）和误差来源，例如使用样方时的边缘效应，或标记使得动物更容易被天敌发现。

In a typical exam question, you might be given a graph showing the growth of a bacterial population in nutrient broth. You could be asked to identify the exponential phase, explain why growth slows, and calculate the mean division rate. Always use precise biological vocabulary and show your working clearly.

在典型的考题中，可能会给出细菌在营养液中生长的曲线图。你可能需要指出指数期、解释生长为何减慢，并计算平均分裂速率。务必使用准确的生物学术语，并清晰展示计算步骤。

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