📚 Food Chains in GCSE CIE Biology | GCSE CIE 生物：食物链 考点精讲
In the study of ecosystems, food chains are one of the most fundamental concepts you will encounter. They illustrate the feeding relationships between organisms and show how energy flows through a community. For the CIE IGCSE Biology syllabus, you need to understand the structure of food chains, the roles of different organisms, energy transfer, and the impact of changes within a chain. This article breaks down every key point you need to master, with paired English–Chinese explanations for each concept.
在生态系统的研究中，食物链是你将遇到的最基本的概念之一。它们展示了生物之间的摄食关系，并说明了能量如何在一个群落中流动。对于 CIE IGCSE 生物学大纲，你需要理解食物链的结构、不同生物的角色、能量传递以及链内变化的影响。本文分解了你需要掌握的每一个关键点，每个概念都配有中英文对照解释。
1. What Is a Food Chain? | 什么是食物链？
A food chain is a linear sequence that shows how energy and nutrients are transferred from one organism to another in an ecosystem. It always starts with a producer, typically a green plant or alga that can make its own food via photosynthesis, and then moves through a series of consumers. Each step in the chain is called a trophic level. Food chains are usually short because energy is lost at each transfer.
食物链是一个线性序列，显示能量和营养物质如何在生态系统中从一个生物体传递到另一个生物体。它总是从生产者开始，通常是能够通过光合作用自己制造食物的绿色植物或藻类，然后经过一系列消费者。链中的每一步被称为一个营养级。食物链通常较短，因为能量在每一次传递中都会损失。
Example / 例子: grass → grasshopper → frog → snake → hawk
草 → 蚱蜢 → 青蛙 → 蛇 → 鹰
Arrows in a food chain point from the organism being eaten to the organism that eats it, indicating the direction of energy flow. Remember: the arrow means ‘is eaten by’.
食物链中的箭头从被吃的生物指向吃它的生物，表示能量流动的方向。记住：箭头意味着“被……吃”。
2. Trophic Levels in a Food Chain | 食物链中的营养级
Trophic levels are the feeding positions in a food chain. The first trophic level is always occupied by producers (autotrophs). The second trophic level consists of primary consumers, which are herbivores that eat the producers. The third trophic level includes secondary consumers, which are carnivores that eat herbivores. Tertiary consumers occupy the fourth level, and so on. In most natural food chains there are rarely more than four or five trophic levels because of the inefficiency of energy transfer.
营养级是食物链中的摄食位置。第一营养级总是由生产者（自养生物）占据。第二营养级由初级消费者组成，它们是吃生产者的食草动物。第三营养级包括次级消费者，它们是吃食草动物的食肉动物。三级消费者占据第四级，依此类推。在大多数自然食物链中，由于能量传递效率低，很少超过四到五个营养级。
Decomposers (bacteria and fungi) are not typically shown in a food chain diagram, but they play a vital role in breaking down dead matter and recycling nutrients back into the soil for producers to use.
分解者（细菌和真菌）通常不在食物链图中显示，但它们在分解死物质、将营养物质循环回土壤供生产者使用方面起着至关重要的作用。
3. Producers, Consumers and Decomposers | 生产者、消费者和分解者
Producers are organisms that can synthesise their own organic molecules using energy from sunlight (photosynthesis) or chemical reactions. In nearly all land and water food chains, green plants and algae are the dominant producers. Consumers are heterotrophs that obtain energy by feeding on other organisms. Primary consumers eat producers; secondary consumers eat primary consumers, and so on. Apex predators are at the top of the chain with no natural enemies.
生产者是能够利用太阳光能（光合作用）或化学反应来合成自身有机分子的生物。在几乎所有陆地和水域食物链中，绿色植物和藻类是主要的生产者。消费者是异养生物，通过摄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，依此类推。顶级捕食者处在食物链顶端，没有天敌。
Decomposers such as bacteria and fungi secrete enzymes to break down dead organic matter externally and then absorb the soluble products. They return mineral ions to the soil, making them available for producers. Without decomposers, ecosystems could not function because nutrients would remain locked up in dead bodies.
诸如细菌和真菌之类的分解者分泌酶在体外分解死有机物质，然后吸收可溶性产物。它们将矿物质离子返回土壤，使其可供生产者使用。如果没有分解者，生态系统将无法运作，因为营养物质将滞留在死尸中。
4. Food Webs | 食物网
In a real community, organisms rarely eat just one type of food. A food web is a network of interconnected food chains that shows all the possible feeding relationships in an ecosystem. It gives a more realistic picture of energy flow and predator–prey interactions. A change in the population of one species can affect many others through the web.
在真实的群落中，生物很少只吃一种食物。食物网是由相互连接的食物链组成的网络，显示了一个生态系统中所有可能的摄食关系。它给出了能量流动和捕食者-猎物互动的更真实图像。一个物种种群的变化可以通过网络影响许多其他物种。
When constructing a food web, you need to correctly orient the arrows to show energy flow. For example, if a fox eats rabbits and mice, arrows go from rabbit to fox and from mouse to fox. A typical exam question may ask you to identify all the food chains present, name a producer, or predict the effect of removing one species.
构建食物网时，你需要正确放置箭头以显示能量流动。例如，如果狐狸吃兔子和老鼠，箭头从兔子指向狐狸，从老鼠指向狐狸。典型的考题可能要求你识别所有存在的食物链，说出一个生产者，或预测移除某一个物种的影响。
5. Energy Flow and Energy Loss | 能量流动与能量损失
Energy enters most ecosystems in the form of sunlight. Producers convert only about 1–2% of the light energy reaching them into chemical energy through photosynthesis. When a primary consumer eats a producer, only about 10% of the energy stored in the producer’s biomass is transferred to the consumer. The rest is lost as heat from respiration, used in movement, or remains in undigested material (egested as faeces).
能量以阳光的形式进入大多数生态系统。生产者仅能将到达它们的约 1–2% 的光能通过光合作用转化为化学能。当初级消费者吃生产者时，只有大约 10% 储存在生产者生物量中的能量被传递给消费者。其余能量以呼吸热的形式损失，用于运动，或留在未消化的物质中（作为粪便排出）。
This is known as the 10% rule, although the actual percentage varies. The low efficiency of energy transfer explains why food chains are short and why producers are always the most abundant organisms in an ecosystem in terms of biomass.
这被称为 10% 法则，尽管实际比例有所不同。能量传递的低效率解释了为什么食物链很短，以及为什么在生物量方面生产者总是生态系统中数量最丰富的生物。
Energy lost = heat from respiration + movement + undigested material
能量损失 = 呼吸热 + 运动 + 未消化物质
6. Pyramids of Energy | 能量金字塔
A pyramid of energy represents the amount of energy present at each trophic level per unit area per unit time (e.g., kJ m⁻² yr⁻¹). The bars are drawn to scale and the pyramid is always a true pyramid shape – upright and getting smaller at higher levels. This is because energy is always lost between trophic levels, never gained, so less energy is available to support the next level.
能量金字塔表示单位面积单位时间内每个营养级存在的能量数量（例如，kJ m⁻² yr⁻¹）。条形按比例绘制，金字塔总是真正的金字塔形状——直立，在较高级别变小。这是因为能量在营养级之间总是损失，从不会增加，所以可用来维持下一级的能量更少。
Energy pyramids are the most accurate way to represent feeding relationships as they take time and productivity into account. They are never inverted. A drawing of a pyramid of energy might show the producer level with a bar of 10,000 kJ, primary consumers at 1,000 kJ, secondary consumers at 100 kJ, and tertiary consumers at only 10 kJ.
能量金字塔是代表摄食关系的最准确方式，因为它考虑了时间和生产力。它们从不颠倒。能量金字塔的绘图可能显示生产者级条形为 10000 kJ，初级消费者为 1000 kJ，次级消费者为 100 kJ，三级消费者仅 10 kJ。
7. Pyramids of Numbers and Biomass | 数量金字塔与生物量金字塔
A pyramid of numbers shows the count of individual organisms at each trophic level. It is usually broad at the bottom but can be distorted. For example, one large oak tree (producer) can support thousands of insects, so the pyramid appears inverted with a small base. Similarly, a pyramid of biomass shows the dry mass of living material. While generally upright, a pyramid of biomass can also be inverted in some aquatic ecosystems where phytoplankton reproduce very rapidly and are consumed as quickly, having a small standing biomass compared to the zooplankton that eat them.
数量金字塔显示每个营养级的个体数量。它通常在底部较宽，但可能变形。例如，一棵大橡树（生产者）可以养活数千只昆虫，所以金字塔呈现倒置，底部较小。同样，生物量金字塔显示的是干生物量。虽然通常直立，但在一些水生生态系统中，浮游植物繁殖非常快且被迅速消耗，其现有生物量相对摄食它们的浮游动物较小，生物量金字塔也可能倒置。
Despite these limitations, pyramids of numbers and biomass are often used because they are easier to collect data for than energy pyramids. The CIE exam expects you to be able to interpret and sketch these pyramids, and to explain why certain shapes occur.
尽管有这些局限性，数量金字塔和生物量金字塔仍常被使用，因为比能量金字塔更容易收集数据。CIE 考试期望你能够解释和绘制这些金字塔，并解释为什么会出现某些形状。
| Pyramid type / 金字塔类型 | Shape / 形状 | Always upright? / 总是正立？ |
|---|---|---|
| Energy / 能量 | Upright / 正立 | Yes / 是 |
| Biomass / 生物量 | Usually upright / 通常正立 | No (e.g., aquatic) / 否（如水域） |
| Numbers / 数量 | Variable / 可变 | No / 否 |
8. Bioaccumulation and Biomagnification | 生物积累与生物放大
Some substances, such as pesticides (e.g., DDT) or heavy metals, are not easily broken down or excreted by organisms. When a consumer eats many contaminated prey, the toxin accumulates in its tissues over time – a process called bioaccumulation. If this toxin passes up the food chain, its concentration increases at each successive trophic level, a phenomenon known as biomagnification.
一些物质，如杀虫剂（例如 DDT）或重金属，不易被生物分解或排出。当消费者吃下许多受污染的猎物时，毒素会随时间在其组织中积累——这一过程称为生物积累。如果这种毒素沿着食物链向上传递，其浓度在每一个连续营养级中都会增加，这一现象被称为生物放大。
A classic example is the use of DDT to control mosquitoes. DDT entered water bodies, was absorbed by microscopic algae, then concentrated in small fish, larger fish, and finally reached toxic levels in birds of prey like ospreys, causing thinning of eggshells and population decline. This is why certain pesticides are now banned.
一个经典例子是使用 DDT 控制蚊子。DDT 进入水体，被微型藻类吸收，然后在小鱼、大鱼中浓缩，最终在鱼鹰等猛禽体内达到毒性水平，导致蛋壳变薄和种群下降。这就是为什么某些杀虫剂现在被禁止的原因。
Bioaccumulation: toxin builds up in one organism over time.
生物积累：毒素随时间在一个生物体内积累。
Biomagnification: toxin concentration increases along a food chain.
生物放大：毒素浓度沿食物链增加。
9. Predator–Prey Relationships | 捕食者-猎物关系
Predator and prey populations are closely linked in a cycle. When prey numbers increase, there is more food available for predators, so predator numbers rise after a short delay. However, as predators increase, they eat more prey, causing the prey population to fall. With less food, predator numbers then decline, allowing the prey population to recover. This results in regular fluctuations, often represented by graphs with two overlapping waves.
捕食者和猎物种群在一个周期中紧密相连。当猎物数量增加时，捕食者有更多食物可用，因此捕食者数量在短暂延迟后上升。然而，随着捕食者增加，它们吃掉更多猎物，导致猎物种群下降。由于食物减少，捕食者数量随后下降，使猎物种群得以恢复。这导致有规律的波动，通常用两个重叠波形的图表表示。
In an exam, you might be asked to interpret such a graph and identify which line represents predator and which prey. Remember: the prey peak always comes slightly before the predator peak. This is because the change in prey abundance drives the change in predator abundance, not the other way around.
在考试中，你可能被要求解读这样的图表，并识别哪条线代表捕食者，哪条代表猎物。记住：猎物高峰总是稍微早于捕食者高峰。这是因为猎物丰度的变化驱动捕食者丰度的变化，而不是相反。
10. The Impact of Change on Food Chains | 食物链变化的影响
Removing or adding a species to a food chain can have dramatic knock-on effects throughout the ecosystem. For example, if a disease kills all the rabbits in a meadow, the grass population may increase because there are fewer herbivores eating it. Meanwhile, foxes that relied on rabbits for food would either starve, move away, or switch to alternative prey, affecting other species.
在食物链中移除或添加一个物种可能在整个生态系统中产生巨大的连锁效应。例如，如果一种疾病杀死了草地上所有的兔子，草的数量可能会增加，因为吃草的动物少了。同时，依赖兔子为食的狐狸要么饿死，要么迁走，要么转而捕食其他猎物，从而影响其他物种。
This concept is linked to the idea of interdependence within a community. All organisms depend on each other for food, shelter, pollination, seed dispersal, and more. Human activities such as deforestation, overfishing, and introducing alien species can disrupt these delicate balances.
这个概念与群落内相互依存的观点相联系。所有生物在食物、栖息地、授粉、种子传播等方面相互依赖。人类活动，如砍伐森林、过度捕捞和引入外来物种，会破坏这些微妙的平衡。
A common exam question: ‘Explain the possible consequences of removing the secondary consumer from this food web.’ You must discuss both the increase in primary consumers and the subsequent decline in producers, as well as any alternative pathways in the web.
一个常见的考题：“解释从该食物网中移除次级消费者的可能后果。”你必须讨论初级消费者的增加以及随后的生产者减少，以及食物网中的替代途径。
11. Typical CIE Exam Questions and How to Answer | CIE 典型考题及如何作答
CIE IGCSE Biology frequently asks students to: draw and label a food chain or food web; state the source of energy for a food chain (always the Sun); name the trophic levels of given organisms; explain why food chains rarely have more than five trophic levels; interpret pyramids of numbers, biomass, and energy; describe the consequences of removing a species; explain bioaccumulation using a named example; and analyse predator–prey graphs.
CIE IGCSE 生物学经常要求考生：绘制并标注食物链或食物网；说出食物链的能量来源（总是太阳）；说出给定生物的营养级；解释为什么食物链很少有超过五个营养级；解读数量、生物量和能量金字塔；描述移除一个物种的后果；用一个具体例子解释生物积累；分析捕食者-猎物图表。
When answering, be precise with terminology. Use phrases like ‘trophic level’, ‘producer’, ‘primary consumer’, and ‘energy is lost as heat during respiration’. For bioaccumulation, always link a named persistent toxin (e.g., DDT) to a specific top predator and state the harmful effect. For energy loss, quote the 10% rule and mention respiration, movement, and undigested food.
作答时，术语要精确。使用诸如“营养级”“生产者”“初级消费者”以及“能量在呼吸作用中以热的形式损失”等短语。对于生物积累，总是将一种命名的持久性毒素（例如 DDT）与特定的顶级捕食者联系起来，并说明有害影响。对于能量损失，引用 10% 法则，并提及呼吸、运动和未消化的食物。
12. Summary and Key Points to Remember | 总结与关键点记忆
Food chains always start with a producer and show energy flow with arrows pointing from food to feeder. Trophic levels are numbered starting with producers (level 1). Energy is lost at each level, mainly as heat, meaning pyramids of energy are always upright. Food webs are more realistic than single chains. Bioaccumulation and biomagnification explain why toxins become concentrated in top predators. Predator–prey cycles show interconnected population dynamics.
食物链总是从生产者开始，用箭头从食物指向摄食者来表示能量流动。营养级从生产者开始编号（第一级）。能量在每一级都会损失，主要以热的形式，意味着能量金字塔总是正立的。食物网比单一链条更真实。生物积累和生物放大解释了为何毒素在顶级捕食者体内浓缩。捕食者-猎物循环显示了相互关联的种群动态。
Master these fundamentals, practise interpreting data from graphs and pyramids, and you will be well prepared for any food chain question on the CIE IGCSE Biology paper.
掌握这些基础知识，练习解读图表和金字塔中的数据，你将为 CIE IGCSE 生物学试卷上的任何食物链问题做好充分准备。
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