📚 Food Chains for CIE IGCSE Biology | IGCSE CIE 生物：食物链考点精讲
A food chain is one of the most fundamental concepts in ecology. It describes how energy and nutrients flow through living organisms in an ecosystem, from producers to top consumers. Understanding food chains helps us explain the interdependence of life and the impact of environmental changes. This revision guide covers all the key points required for the CIE IGCSE Biology exam, including definitions, energy flow, trophic levels, pyramids, and bioaccumulation.
食物链是生态学中最基本的概念之一。它描述了能量和营养物质如何通过生态系统中的生物体从生产者流向顶级消费者。理解食物链有助于我们解释生命的相互依存关系以及环境变化的影响。这份考点精讲涵盖了CIE IGCSE生物考试所需的所有重点，包括定义、能量流动、营养级、金字塔和生物累积。
1. Introduction to Food Chains | 食物链简介
A food chain is a linear sequence showing the transfer of energy and nutrients between organisms. Each organism in the chain occupies a specific feeding position, called a trophic level. For example, a simple grassland food chain might be: grass → grasshopper → frog → snake → hawk.
食物链是一条线性序列，展示生物之间能量和营养物质的传递。链中的每个生物占据一个特定的摄食位置，称为营养级。例如，一条简单的草原食物链可能是：草 → 蚱蜢 → 青蛙 → 蛇 → 鹰。
Food chains always begin with a producer, an organism that makes its own food, typically through photosynthesis. The chain then moves through various consumers: primary consumers eat producers, secondary consumers eat primary consumers, and so on. The final organism in a chain is the top predator, which has no natural enemies in that ecosystem.
食物链总是从生产者开始，生产者是通过光合作用等制造自身食物的生物。然后食物链经过各种消费者：初级消费者吃生产者，次级消费者吃初级消费者，以此类推。链中最后的生物是顶级捕食者，在该生态系统内没有天敌。
2. Producers: The Foundation | 生产者：食物链的基石
Producers, also called autotrophs, are organisms that can produce their own organic nutrients using simple inorganic substances. The most common producers in terrestrial ecosystems are green plants, which use sunlight, carbon dioxide and water to carry out photosynthesis and produce glucose. In aquatic ecosystems, algae and phytoplankton are the main producers.
生产者，也称自养生物，是能够利用简单的无机物制造自身有机营养物质的生物。陆地上最常见的是绿色植物，它们利用阳光、二氧化碳和水进行光合作用产生葡萄糖。在水生生态系统中，藻类和浮游植物是主要的生产者。
Because producers convert energy from the sun (or, in some deepsea habitats, from chemicals) into food, they form the base of every food chain. Without producers, there would be no source of energy for consumers, and ecosystems would collapse. In the CIE IGCSE exam, you need to know the role of producers and the equation for photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, using light energy.
因为生产者将太阳能（或某些深海栖息地的化学能）转化为食物，所以它们构成了每条食物链的基础。没有生产者，消费者就没有能量来源，生态系统就会崩溃。在CIE IGCSE考试中，你需要知道生产者的作用和光合作用方程式：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂，利用光能。
3. Consumers: Primary, Secondary, Tertiary | 消费者：初级、次级、三级
Consumers, or heterotrophs, obtain their energy by eating other organisms. They are classified according to their position in the food chain. A primary consumer feeds directly on producers and is therefore a herbivore. Examples include grasshoppers, rabbits, and zooplankton. A secondary consumer eats primary consumers, making it a carnivore or an omnivore. An example is a frog that eats grasshoppers. A tertiary consumer eats secondary consumers, such as a snake that eats frogs. Some food chains extend to a quaternary consumer, like a hawk that eats snakes.
消费者，或异养生物，通过取食其他生物来获取能量。它们按照在食物链中的位置进行分类。初级消费者直接以生产者为食，因此是食草动物，例如蚱蜢、兔子和浮游动物。次级消费者吃初级消费者，属于食肉动物或杂食动物，例如吃蚱蜢的青蛙。三级消费者吃次级消费者，比如吃青蛙的蛇。有些食物链还有四级消费者，比如吃蛇的鹰。
It is important to remember that an organism can belong to different consumer levels depending on which food chain is being described. For instance, a robin eating a caterpillar is a secondary consumer in that chain, but the same robin eating berries acts as a primary consumer. In exam questions, always identify the trophic level based on the specific feeding relationship given.
重要的是要记住，根据不同食物链的描述，同一种生物可能属于不同的消费者级别。例如，一只知更鸟吃毛毛虫时是次级消费者，但同一只鸟吃浆果时则是初级消费者。在考试中，始终要根据给出的具体摄食关系来确定营养级。
4. Decomposers: Nature’s Recyclers | 分解者：自然的循环者
Decomposers are organisms, mainly bacteria and fungi, that break down dead remains and waste materials from all trophic levels. They secrete enzymes onto dead organic matter and absorb the soluble products. Through the process of decomposition, they release inorganic nutrients back into the environment, which can then be reused by producers. This recycling of nutrients is essential for the sustainability of ecosystems.
分解者主要是细菌和真菌等生物，它们分解所有营养级的尸体和废物。它们向死去的有机物上分泌酶，并吸收可溶性产物。通过分解过程，它们将无机养分释放回环境中，供生产者再次使用。这种养分的循环利用对生态系统的可持续性至关重要。
Although decomposers are often not drawn in food chain diagrams, they play a critical role. Without decomposers, nutrients would remain locked in dead organisms and waste, and the soil would become depleted. When constructing food chains, you may be asked to add a decomposer or explain why they are represented separately. CIE often expects you to know that decomposers use organic compounds as their energy source and release carbon dioxide and minerals.
虽然分解者在食物链图中通常不画出来，但它们起着关键作用。如果没有分解者，养分就会被锁死在生物残体和废物中，土壤会变得贫瘠。在构建食物链时，可能会要求添加分解者或解释为什么分解者被单独表示。CIE通常希望你知道分解者利用有机化合物作为能源，并释放二氧化碳和矿物质。
5. Direction of Energy Flow and Arrows | 能量流动方向与箭头
In a food chain diagram, the arrow points from the organism being eaten to the organism that eats it. The arrow therefore represents the direction of energy transfer, not just ‘who eats whom’. Energy flows from the producer through each successive consumer. A common mistake is to reverse the arrow, pointing from the predator to the prey. Always remember: arrows follow the energy, and energy moves from the food to the feeder.
在食物链图中，箭头从被吃的生物指向吃它的生物。因此，箭头代表能量传递的方向，而不仅仅是“谁吃谁”。能量从生产者流向每一个后续消费者。一个常见错误是把箭头方向弄反，从捕食者指向猎物。始终记住：箭头跟随能量流动，能量从食物移向取食者。
For example, in the chain grass → rabbit → fox, the first arrow means that energy stored in the grass is transferred to the rabbit when it eats the grass. The second arrow means that energy from the rabbit is transferred to the fox when it eats the rabbit. The arrows never point backwards because energy cannot flow from a consumer back to a producer in a feeding relationship.
例如，在草 → 兔 → 狐狸的食物链中，第一个箭头意味着草中储存的能量在兔子吃草时传给了兔子。第二个箭头意味着兔子的能量在狐狸吃兔子时传给了狐狸。箭头从不指向后方，因为在摄食关系中能量不能从消费者流回生产者。
6. Trophic Levels | 营养级
A trophic level is the position an organism occupies in a food chain. Level 1 is always a producer. Level 2 is a primary consumer, level 3 a secondary consumer, level 4 a tertiary consumer, and so on. Each trophic level depends on the level below it for energy, and the number of trophic levels in a food chain is usually limited to four or five because of energy losses at each transfer.
营养级是指生物在食物链中所处的位置。第1级始终是生产者。第2级是初级消费者，第3级次级消费者，第4级三级消费者，以此类推。每个营养级依靠其下一级获得能量，由于每次传递都有能量损失，一条食物链的营养级数量通常限制在四到五个。
When answering exam questions, always refer to organisms by their trophic level number or name (e.g., ‘the frog is at the third trophic level and is a secondary consumer’). Be careful not to confuse trophic level and consumer order: a secondary consumer is at trophic level 3, not level 2. Counting trophic levels correctly is vital for interpreting ecological pyramids and energy flow.
在回答考试问题时，始终要用营养级编号或名称来描述生物（例如，“青蛙处于第三营养级，是次级消费者”）。注意不要混淆营养级和消费者级别：次级消费者在营养级3，而不是2。正确数清营养级对于解读生态金字塔和能量流动至关重要。
7. Food Webs: Interconnected Chains | 食物网：相互连接的食物链
A food web is a network of many interconnected food chains within an ecosystem. While a food chain shows a single, direct feeding relationship, a food web shows that most organisms have more than one food source and are preyed upon by more than one predator. Food webs provide a more realistic representation of energy flow and feeding relationships in nature.
食物网是一个生态系统内许多相互连接的食物链组成的网络。食物链只显示单一直接的摄食关系，而食物网表明大多数生物有不止一种食物来源，也被不止一种捕食者取食。食物网更真实地体现了自然界中的能量流动和摄食关系。
Food webs contribute to ecosystem stability. If one species disappears, organisms that relied on it can switch to alternative food sources, preventing a total collapse. In CIE exams, you may be given a diagram of a food web and asked to identify a food chain within it, name producers, herbivores, carnivores, or predict the effect of removing a particular species.
食物网有助于生态系统的稳定。如果一个物种消失，依赖它的生物可以转向其他食物来源，从而避免整个系统的崩溃。在CIE考试中，可能会给出一个食物网图，让你从中找出一条食物链，指出生产者、食草动物、食肉动物，或者预测移除某一物种的影响。
8. Ecological Pyramids: Numbers, Biomass, Energy | 生态金字塔：数量、生物量、能量
Ecological pyramids are graphical representations of the trophic structure of an ecosystem. There are three main types: pyramid of numbers, pyramid of biomass, and pyramid of energy. Each type uses bars of different lengths to represent the quantity at each trophic level, with producers at the base.
生态金字塔是生态系统营养结构的图形表示。主要有三种类型：数量金字塔、生物量金字塔和能量金字塔。每种类型用不同长度的条形来表示每个营养级的数量，生产者位于底部。
A pyramid of numbers shows the number of individual organisms at each level. This pyramid can sometimes be inverted, for instance when a single large tree supports many aphids, which in turn support a smaller number of ladybirds. A pyramid of biomass shows the total dry mass of organisms at each level. It is usually upright, but can also be inverted in aquatic ecosystems, where the mass of phytoplankton can be less than that of zooplankton at certain times. A pyramid of energy always has an upright shape, because energy is always lost as it moves up trophic levels through respiration, waste and uneaten material.
数量金字塔表示每个营养级中生物个体的数量。这种金字塔有时会倒置，例如一棵大树养活许多蚜虫，这些蚜虫又养活较少数量的瓢虫。生物量金字塔表示每个营养级中生物的总干重。它通常是正立的，但在水生生态系统中也可能倒置，比如在某一时期浮游植物的生物量可能小于浮游动物。能量金字塔总是正立的，因为能量沿着营养级向上流动时，总会通过呼吸、废物和未被食用的物质而损失。
In the IGCSE exam, you need to be able to draw, label and interpret these pyramids, and explain why the pyramid of energy is always upright. Remember that energy is measured in kilojoules per square metre per year (kJ m⁻² yr⁻¹) when constructing energy pyramids.
在IGCSE考试中，你需要能够绘制、标注并解读这些金字塔，并解释为什么能量金字塔总是正立的。记住，构建能量金字塔时，能量的单位是千焦每平方米每年（kJ m⁻² yr⁻¹）。
9. Energy Loss and Efficiency | 能量损失与效率
At each step in a food chain, a large proportion of the energy is lost. On average, only about 10% of the energy from one trophic level is transferred to the next. The remaining 90% is lost mainly through respiration (heat), egestion (faeces), excretion (urine) and uneaten parts such as bones or roots. This explains why food chains rarely have more than five trophic levels – there simply is not enough energy left to support another level.
在食物链的每个环节，大部分能量都会损失。平均而言，一个营养级中只有大约10%的能量传递到下一级。其余90%的能量主要通过呼吸作用（热）、排遗（粪便）、排泄（尿液）以及未被食用的部分（如骨头或根）而损失。这就解释了为什么食物链很少超过五个营养级——根本没有足够的剩余能量来支撑更高的营养级。
The efficiency of energy transfer can be calculated using the formula: efficiency (%) = (energy available to the next level ÷ energy available to the previous level) × 100. CIE may ask you to carry out such calculations from data provided. Understanding this loss is crucial for evaluating the efficiency of different farming methods, such as feeding livestock directly on plant material rather than feeding them animal protein.
能量传递效率可以用公式计算：效率（%）=（下一营养级可用的能量 ÷ 上一营养级可用的能量）× 100。CIE可能会要求根据提供的数据进行此类计算。理解这种能量损失对于评估不同农业方法的效率至关重要，比如用植物饲料直接喂养牲畜，而非用动物蛋白喂养。
10. Bioaccumulation and Biomagnification | 生物累积与生物放大
Some toxic substances, such as certain pesticides (e.g., DDT, C₁₄H₉Cl₅) and heavy metals, do not break down easily in the environment. When these substances enter a food chain, they are absorbed and stored in the tissues of organisms. Bioaccumulation refers to the build-up of a toxin within a single organism over time, as it takes in the substance faster than it can excrete it.
某些有毒物质，如特定的杀虫剂（例如DDT，C₁₄H₉Cl₅）和重金属，在环境中不易分解。当这些物质进入食物链，就会被生物体吸收并储存在组织里。生物累积指的是毒素在单个生物体内随时间积累，因为吸收的速度快于排出的速度。
Biomagnification (or biological magnification) is the increase in concentration of a toxin as it passes up through successive trophic levels. Typically, producers have a low concentration, but at each higher level the concentration becomes greater because predators eat many contaminated prey from the level below. Top predators, therefore, often suffer the most severe effects, such as the thinning of eggshells in birds exposed to DDT, which led to declining populations.
生物放大（或生物放大作用）是指毒素随着营养级不断上升，浓度不断增加的现象。通常生产者体内毒素浓度较低，但每上升一个营养级，浓度就会增加，因为捕食者会吃掉许多来自下级的受污染猎物。因此，顶级捕食者往往遭受最严重的影响，例如接触DDT的鸟类蛋壳变薄，导致种群数量下降。
CIE IGCSE questions often require you to explain how bioaccumulation affects organisms at the top of a food chain and to interpret data showing concentrations at different trophic levels. Always link the increase in concentration to the fact that the toxin is persistent and not easily excreted or metabolised.
CIE IGCSE考题常要求解释生物累积如何影响食物链顶端的生物，并要求解读显示不同营养级浓度的数据。始终要将浓度增加与毒素持久且不易排出或代谢这一事实联系起来。
11. Exam Tips and Common Mistakes | 考试技巧与常见错误
When constructing a food chain, always start with a producer and use arrows correctly (→) to show energy flow. Label organisms clearly as producer, primary consumer, etc., if asked. A very common error is to draw the arrow pointing away from the organism that is eaten. Remember: the arrow goes into the mouth of the organism that does the eating.
构建食物链时，总是从生产者开始，并正确使用箭头（→）来表示能量流动。如果题目要求，要清楚地标注生产者、初级消费者等。一个非常常见的错误是把箭头从被吃的生物指向外。记住：箭头指向取食者的口中。
Do not forget decomposers when discussing energy flow or nutrient cycling, even if they are not always drawn in the chain. When describing pyramids, make sure you can explain why the pyramid of energy is always a true pyramid, while the pyramid of numbers can be inverted. If a question provides data, practise calculating the percentage energy transfer and stating the amount of energy lost at each step.
在讨论能量流动或养分循环时，不要忘记分解者，即使它们不一定被画在食物链中。描述金字塔时，确保你能解释为什么能量金字塔始终是真正的金字塔，而数量金字塔可能倒置。如果题目提供了数据，要练习计算能量传递的百分比，并说明每一步损失的能量数量。
For the food web questions, read the diagram carefully. Predict the consequences of species removal or introduction using the concept of alternative prey and competition. Use specific examples you have studied, such as the effect of DDT on birds of prey, to support longer answer questions. Finally, always use scientific terminology like ‘trophic level’, ‘biomass’, ‘bioaccumulation’ and ‘energy transfer’ to gain full marks for communication.
遇到食物网的题目，要仔细阅读图表。利用替代猎物和竞争的概念，预测物种移除或引入的后果。运用你学过的具体例子，比如DDT对猛禽的影响，来支撑较长的简答题。最后，要始终使用科学术语，如“营养级”、“生物量”、“生物累积”和“能量传递”，以便在表达上拿到满分。
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