GCSE CCEA Science: Ecosystems Revision Guide | GCSE CCEA 科学：生态系统考点精讲

📚 GCSE CCEA Science: Ecosystems Revision Guide | GCSE CCEA 科学：生态系统考点精讲

Welcome to your focused revision guide on Ecosystems, written specifically for the GCSE CCEA Science specification. This topic explores how living organisms interact with one another and their physical surroundings, forming intricate networks of energy flow and nutrient cycling. We will unpack essential concepts such as food webs, abiotic and biotic factors, pyramids of biomass, the carbon and nitrogen cycles, and the impact of human activities on natural systems. Each section is designed to break down complex ideas into manageable, exam-ready points.

欢迎阅读专门为 GCSE CCEA 科学大纲编写的生态系统考点精讲。本主题探索生物如何与彼此及其物理环境相互作用，形成复杂的能量流动和营养循环网络。我们将剖析关键概念，如食物网、非生物与生物因素、生物量金字塔、碳循环与氮循环，以及人类活动对自然系统的影响。每个小节都旨在将复杂概念拆解成易于掌握、适合考试的要点。

1. What is an Ecosystem? | 什么是生态系统？

An ecosystem is a natural unit consisting of all the living organisms (the community) in a particular area, interacting with the non-living (abiotic) components of their environment. These interactions create a stable, self-sustaining system where energy flows and nutrients cycle.

生态系统是一个自然单元，由特定区域内的所有生物（群落）与其环境中的非生物成分相互作用而构成。这些相互作用形成一个稳定、自给自足的系统，能量在其中流动，营养在其中循环。

Key terms you must know: a habitat is the place where an organism lives; a population is all the members of a single species in a habitat; a community is all the populations of different species living together in a habitat. Together, the community and the abiotic environment form the ecosystem.

你必须掌握的关键术语：栖息地是生物生活的地方；种群是栖息地中同一物种的所有成员；群落是生活在同一栖息地中所有不同物种种群的集合。群落与非生物环境一起构成生态系统。

In CCEA exams, you may be asked to give examples of ecosystems at different scales – from a rock pool or a hedgerow to a tropical rainforest or even the entire biosphere. Be ready to describe the boundaries of an ecosystem, which can be natural or defined by the investigator.

在 CCEA 考试中，你可能被要求给出不同尺度生态系统的例子 —— 从潮池或篱笆田到热带雨林，甚至整个生物圈。准备好描述生态系统的边界，这些边界可以是自然的，也可以由研究者划定。

2. Abiotic and Biotic Factors | 非生物因素与生物因素

Abiotic factors are non-living physical and chemical elements that affect the distribution and abundance of organisms. Examples include light intensity, temperature, moisture levels, soil pH, oxygen concentration in water, and wind speed.

非生物因素是指影响生物分布与数量的非生物物理和化学要素，例如光照强度、温度、湿度、土壤 pH 值、水中溶氧量以及风速。

Biotic factors are the living components of an ecosystem that influence organisms. These include competition for resources (food, mates, territory), predation, disease, and availability of food. For instance, the introduction of a new predator can dramatically reduce a prey population.

生物因素指生态系统中影响生物的生物组分，包括对资源（食物、配偶、领地）的竞争、捕食、疾病和食物供应。例如，引入新的捕食者会大幅减少猎物种群数量。

Understanding how these factors interact helps explain why certain species are found in specific environments. In a pond, dissolved oxygen (abiotic) and the presence of predators like dragonfly nymphs (biotic) both determine the number of mayfly larvae.

理解这些因素如何相互作用有助于解释为什么某些物种出现在特定环境中。在一个池塘中，溶解氧（非生物因素）和蜻蜓幼虫等捕食者的存在（生物因素）共同决定了蜉蝣幼虫的数量。

You should be able to interpret graphs showing the effect of a changing abiotic factor, such as temperature on the rate of enzyme-controlled reactions in organisms, and link this to population changes.

你应该能解读显示非生物因素变化影响的图表，例如温度对生物体内酶促反应速率的影响，并将其与种群变化联系起来。

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

A food chain is a linear sequence showing the transfer of energy from one organism to another, beginning with a producer. For example: grass → rabbit → fox. The arrow represents the direction of energy flow.

食物链是显示能量从一个生物转移到另一个生物的线性顺序，从生产者开始。例如：草 → 兔子 → 狐狸。箭头代表能量流动的方向。

Trophic levels describe the feeding positions in a food chain. Level 1 is always a producer (usually a green plant or alga). Level 2 is a primary consumer (herbivore), level 3 a secondary consumer (carnivore), and sometimes a tertiary consumer at level 4.

营养级描述了食物链中的摄食位置。第 1 级总是生产者（通常是绿色植物或藻类）。第 2 级为初级消费者（植食动物），第 3 级为次级消费者（肉食动物），有时还有第 4 级的三级消费者。

Food webs are more realistic representations, showing many interconnected food chains in an ecosystem. They demonstrate that most organisms eat more than one type of food and may be eaten by several different predators. A change in one species can have cascading effects on many others.

食物网是更真实的呈现方式，显示了生态系统中相互连接的众多食物链。它们表明大多数生物不只吃一种食物，且可能被多种不同捕食者捕食。一个物种的变化会对许多其他物种产生连锁效应。

When asked to analyse a food web, identify producers, herbivores, carnivores, and the number of trophic links. Be careful: removing one species might reduce competition for another, but also starve its predators.

当被要求分析食物网时，要识别生产者、植食动物、肉食动物和营养链接数量。需注意：移除一个物种可能减少另一物种的竞争，但也会使其捕食者挨饿。

4. Energy Flow and Ecological Pyramids | 能量流动与生态金字塔

Energy enters most ecosystems via sunlight and is captured by producers during photosynthesis. Only about 1% of the light energy falling on a plant is converted into chemical energy stored in biomass.

能量通过阳光进入大多数生态系统，生产者在光合作用过程中捕获能量。照射到植物上的光能只有约 1% 转化为生物量中储存的化学能。

As energy moves up a food chain, it is lost at each trophic level through respiration, heat, movement, and uneaten parts (such as bones or faeces). Typically, only around 10% of the energy is transferred from one level to the next. This limits the length of food chains.

能量沿食物链向上流动时，在每一营养级都会因呼吸、热量、运动以及未被食用的部分（如骨骼或粪便）而损失。通常只有约 10% 的能量从一个营养级传递到下一级，这限制了食物链的长度。

Ecological pyramids represent the structure of feeding relationships. The three most important types are:

生态金字塔表示摄食关系的结构。最重要的三种类型是：

Pyramid type	What it shows	CCEA note
Pyramid of numbers	Number of organisms at each trophic level, not accounting for size. Can be inverted (e.g. one tree with many insects).	Often irregular, so less useful alone.
Pyramid of biomass	Total dry mass of organisms at each level (usually g/m²). Always pyramid-shaped because mass decreases up the chain.	Preferred for GCSE; must use dry mass to eliminate water content variability.
Pyramid of energy	Energy content per unit area per year (kJ/m²/yr). Always upright, showing energy loss.	Mention efficiency calculations.

You must be able to calculate the efficiency of energy transfer: Efficiency (%) = (energy at trophic level / energy at previous level) × 100. Practice with exam data.

你必须能够计算能量传递效率：效率（%）=（某营养级能量 / 上一营养级能量）× 100。用考试数据练习。

5. The Carbon Cycle | 碳循环

Carbon is a key element in all biological molecules, including carbohydrates, proteins, and fats. The carbon cycle describes how carbon is recycled between the atmosphere, organisms, and the Earth’s crust, ensuring a constant supply for life processes.

碳是所有生物分子的关键元素，包括碳水化合物、蛋白质和脂肪。碳循环描述了碳如何在大气、生物和地壳之间循环，确保生命过程有持续的供应。

The main processes in the carbon cycle are:

Photosynthesis: Plants absorb CO₂ from the atmosphere and convert it into glucose. (6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂)
Respiration: All living organisms break down glucose, releasing CO₂ back into the atmosphere. (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy)
Combustion: Burning fossil fuels and organic matter releases stored carbon as CO₂.
Decomposition: Decomposers break down dead organic material, releasing CO₂ through respiration.
Feeding: Carbon moves through food chains when organisms consume others.

碳循环的主要过程有：

光合作用：植物从大气中吸收二氧化碳并将其转化为葡萄糖。（6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂）
呼吸作用：所有生物分解葡萄糖，将二氧化碳释放回大气。（C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量）
燃烧：化石燃料和有机物的燃烧以二氧化碳形式释放储存的碳。
分解：分解者分解死去的有机物质，通过呼吸作用释放二氧化碳。
取食：当生物捕食其他生物时，碳沿食物链流动。

Also note that some carbon is locked up long-term in limestone (as calcium carbonate) and fossil fuels, and released slowly through geological processes and volcanic activity. For the CCEA exam, be able to draw and label a simple carbon cycle diagram showing all the key stores and fluxes.

还请注意，部分碳被长期封存在石灰岩（以碳酸钙形式）和化石燃料中，并通过地质过程和火山活动缓慢释放。在 CCEA 考试中，要能画出并标注一份简明的碳循环图，展示所有重要的库和通量。

6. The Nitrogen Cycle | 氮循环

Nitrogen is essential for making proteins and DNA, yet organisms cannot use atmospheric nitrogen gas (N₂) directly. The nitrogen cycle converts N₂ into forms plants can absorb, mainly nitrate ions (NO₃⁻). This cycle relies heavily on microorganisms.

氮对于制造蛋白质和 DNA 至关重要，但生物不能直接利用大气中的氮气（N₂）。氮循环将 N₂ 转化为植物可吸收的形式，主要是硝酸根离子（NO₃⁻）。这一循环高度依赖微生物。

The major steps are:

Nitrogen fixation: Conversion of N₂ into ammonia (NH₃) or ammonium ions (NH₄⁺), carried out by free-living soil bacteria (e.g. Azotobacter) and symbiotic Rhizobium bacteria in legume root nodules.
Nitrification: Oxidation of NH₄⁺ to nitrites (NO₂⁻) by Nitrosomonas, then to nitrates (NO₃⁻) by Nitrobacter. This requires aerobic conditions.
Assimilation: Plants absorb NO₃⁻ and use it to build proteins and nucleic acids. Consumers obtain nitrogen by eating plants or other animals.
Ammonification: Decomposers break down proteins from dead organisms and waste, releasing NH₄⁺ back into the soil.
Denitrification: Anaerobic bacteria convert NO₃⁻ back into N₂ gas, returning it to the atmosphere. This occurs in waterlogged, oxygen-poor soils.

主要步骤包括：

固氮作用：将 N₂ 转化为氨（NH₃）或铵离子（NH₄⁺），由自由生活的土壤细菌（如固氮菌）和豆科植物根瘤中的共生根瘤菌完成。
硝化作用：亚硝化单胞菌将 NH₄⁺ 氧化为亚硝酸根（NO₂⁻），然后硝化杆菌将其氧化为硝酸根（NO₃⁻）。这需要好氧条件。
同化作用：植物吸收 NO₃⁻ 并利用它构建蛋白质和核酸。消费者通过进食植物或其他动物获取氮。
氨化作用：分解者分解死去生物和废物中的蛋白质，将 NH₄⁺ 释放回土壤。
反硝化作用：厌氧细菌将 NO₃⁻ 转化回 N₂ 气体，使其返回大气。这发生在积水缺氧的土壤中。

CCEA may ask about the role of specific bacteria. Remember: Rhizobium (fixation), Nitrosomonas/Nitrobacter (nitrification), and denitrifying bacteria. Also link the nitrogen cycle to farming practices such as crop rotation with legumes to naturally enrich soil nitrate levels.

CCEA 可能会问到特定细菌的作用。记住：根瘤菌（固氮）、亚硝化单胞菌/硝化杆菌（硝化作用）以及反硝化细菌。此外，将氮循环与农耕实践联系起来，例如通过轮作豆科作物自然提高土壤硝酸盐含量。

7. Decomposers and Decay | 分解者与腐烂

Decomposers, mainly bacteria and fungi, are vital for recycling nutrients. They break down dead organic matter and waste, releasing ions such as nitrates, phosphates, and carbon dioxide back into the soil and atmosphere, making them available for producers.

分解者，主要是细菌和真菌，对营养循环至关重要。它们分解死去的有机物和废物，将硝酸盐、磷酸盐和二氧化碳等释放回土壤和大气，供生产者重新利用。

The rate of decay depends on several factors: temperature (enzyme activity increases with warmth up to an optimum, then denatures), moisture (microorganisms need water to dissolve food and for metabolic reactions), and oxygen availability (most decomposers respire aerobically).

腐烂的速率取决于几个因素：温度（酶活性随温度升高而增加，直至最适温度，然后变性）、水分（微生物需要水来溶解食物和进行代谢反应），以及氧气供应（大多数分解者进行有氧呼吸）。

In the lab, you may investigate decay using milk and a pH indicator such as cresol red, or by measuring the volume of CO₂ produced. The process can be slowed by refrigeration, drying, or vacuum packing, which are used in food preservation.

在实验室中，你可能用牛奶和甲酚红等 pH 指示剂，或通过测量产生的 CO₂ 体积来研究腐烂过程。该过程可通过冷藏、干燥或真空包装来减缓，这些方法被用于食品保存。

Detritivores (earthworms, woodlice, maggots) are often confused with decomposers. They break down material into smaller pieces, increasing the surface area for bacterial and fungal decomposition. In an exam, clearly distinguish between the two roles.

食碎屑动物（蚯蚓、鼠妇、蛆）常与分解者混淆。它们将有机物质碎化，增大表面积便于细菌和真菌分解。在考试中，要清晰区分这两类角色。

8. Population Growth and Competition | 种群增长与竞争

A population grows when the birth rate exceeds the death rate, but growth is eventually limited by environmental resistance. The sigmoid (S-shaped) population growth curve shows distinct phases: lag phase (slow growth, acclimatisation), log phase (rapid exponential growth), and stationary phase (carrying capacity reached).

当出生率超过死亡率时，种群数量增长，但增长最终受环境阻力限制。S 形种群增长曲线显示出明显阶段：延滞期（缓慢增长，适应环境）、对数期（快速指数增长）和稳定期（达到环境容纳量）。

Carrying capacity is the maximum steady population size an environment can support, determined by available resources (food, water, shelter) and other limiting factors. Around carrying capacity, the birth rate roughly equals the death rate.

环境容纳量是一个环境能稳定支持的最大种群数量，由可利用的资源（食物、水、栖息地）和其他限制因素决定。在容纳量附近，出生率大致等于死亡率。

Competition occurs either between members of the same species (intraspecific) or between different species (interspecific). Animals compete for food, mates, and territory; plants compete for light, water, minerals, and space. Interspecific competition often leads to one species being less successful, a concept linked to predator-prey cycles.

竞争既可发生在同一物种成员之间（种内竞争），也可发生在不同物种之间（种间竞争）。动物竞争食物、配偶和领地；植物竞争光、水、矿物质和空间。种间竞争常导致一个物种处于劣势，这与捕食者-猎物循环概念相关。

Predator-prey cycles show regular oscillations: a rise in prey numbers leads to an increase in predators, which then reduces prey, causing a predator crash, and the cycle repeats. Be able to interpret such graphs and explain the time lag between the two curves.

捕食者-猎物循环表现出有规律的波动：猎物数量上升导致捕食者增加，随后减少猎物数量，捕食者随之下降，如此循环往复。要能解读这类图表并解释两条曲线之间的时间滞后。

9. Bioaccumulation and Pesticides | 生物累积和杀虫剂

Bioaccumulation is the build-up of persistent, fat-soluble toxic substances in an organism’s body, because they cannot be broken down or excreted. Substances like DDT and heavy metals accumulate in fatty tissues over an organism’s lifetime.

生物累积是指难以分解的脂溶性有毒物质在生物体内积累，因为它们无法被分解或排出。像 DDT 和重金属这类物质会在生物一生中不断在脂肪组织中积累。

Biomagnification (or biological amplification) describes how the concentration of these toxins increases at successive trophic levels in a food chain. A top predator may have tissue concentrations millions of times higher than the environment, which can cause reproductive failure, thin eggshells, or death.

生物放大（或生物扩增）描述了这些毒素的浓度如何沿食物链营养级逐级升高。顶级捕食者的组织浓度可能比环境中高出数百万倍，这会导致繁殖失败、蛋壳变薄甚至死亡。

The classic example is DDT, a pesticide that washed into water systems, was absorbed by microscopic algae, consumed by zooplankton, small fish, large fish, and finally birds of prey like ospreys. This nearly wiped out some raptor populations before the chemical was banned.

经典例子是 DDT，这种杀虫剂冲入水体后被微藻吸收，浮游动物取食藻类，小鱼吃浮游动物，大鱼吃小鱼，最后鱼鹰等猛禽捕食大鱼。在该化学品被禁用前，几乎导致某些猛禽种群灭绝。

In CCEA, you might need to calculate the concentration factor using simple data tables, or suggest ways to reduce pesticide impact (biological control, biodegradable pesticides, integrated pest management).

在 CCEA 考试中，你可能需要使用简单的数据表计算浓缩系数，或者提出减少杀虫剂影响的方法（生物防治、可生物降解的杀虫剂、综合害虫管理）。

10. Sampling and Investigating Ecosystems | 取样与生态系统调查

To study ecosystems objectively, ecologists use sampling techniques that give representative data without counting every organism. The choice of technique depends on the habitat and the type of organism being studied.

为了客观研究生态系统，生态学家使用取样技术在不计数每个生物的情况下获得代表性数据。技术的选择取决于栖息地和所研究生物的类型。

Common apparatus and methods:

Quadrat: A square frame (e.g. 0.5 m × 0.5 m) placed randomly in a habitat to count plant species or estimate percentage cover. Random placement can be achieved by generating coordinates.
Transect: A line (line transect) or belt (belt transect) laid across a habitat to investigate how species distribution changes with an environmental gradient (e.g. from the sea edge into sand dunes).
Pooter: A handheld device used to suck up small invertebrates from leaves or soil for identification and counting.
Pitfall trap: A container buried in the ground to catch ground-dwelling invertebrates. Must be checked regularly and protected from rain.
Sweep net: A sturdy net swept through vegetation to collect insects.

常用器材和方法：

样方：一个正方形框架（例如 0.5 m × 0.5 m），随机放置在栖息地中以计数植物物种或估算覆盖百分比。可通过生成坐标实现随机放置。
样条：在栖息地中布设一条线（线样条）或带（带样条），以考察物种分布如何随环境梯度（例如从海边到沙丘）变化。
吸虫器：一种手持装置，用于从叶片或土壤中吸取小型无脊椎动物进行鉴定和计数。
陷坑诱捕器：埋在地下的容器，用于捕捉地面无脊椎动物。必须定期检查并防止雨水进入。
扫网：一个坚固的网，在植被中挥扫以收集昆虫。

When estimating population size, you may use the capture-mark-recapture method. The Lincoln index formula can be applied: Population size = (Number in first sample × Number in second sample) / Number of marked recaptured. You should be able to discuss the assumptions (no migration, marking does not affect survival, enough time for mixing).

当估算种群大小时，您可能会使用标记-重捕法。可应用林肯指数公式：种群大小 =（首次样本数 × 第二次样本数）/ 标记个体重捕数。你应该能够讨论其假设（没有迁移、标记不影响生存、有足够时间混合）。

Also, be able to evaluate experimental designs: why sample size matters, the importance of random sampling to avoid bias, and how to calculate mean, median, and mode from ecological data.

同时，要能评估实验设计：为什么样本量很重要，随机取样为何能避免偏差，以及如何根据生态数据计算平均数、中位数和众数。

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GCSE CCEA Science: Ecosystems Revision Guide | GCSE CCEA 科学：生态系统 考点精讲