📚 A-Level CIE Biology: Food Chains | A-Level CIE 生物：食物链 考点精讲
In A-Level CIE Biology, food chains are fundamental to understanding how energy and nutrients move through ecosystems. A food chain is a linear sequence showing who eats whom, starting with a producer and ending with a top predator. Mastering this topic involves not just memorising definitions but also interpreting diagrams, calculating energy transfer efficiencies, and explaining ecological phenomena such as bioaccumulation.
在 A-Level CIE 生物学中，食物链是理解能量与物质如何在生态系统中流动的基础。食物链是一条直链，展示谁吃谁，从生产者开始到顶级捕食者结束。要真正掌握这个知识点，不仅需要牢记定义，还要能解读图示、计算能量传递效率，并解释生物积累等生态现象。
1. Introduction to Food Chains | 食物链简介
A food chain represents a single pathway of energy transfer through an ecosystem. It always begins with a producer, typically a photosynthetic organism like a plant or alga, and moves through a sequence of consumers. Each step in the chain is called a trophic level. The arrows in a food chain point in the direction of energy flow, from the organism being eaten to the one doing the eating.
食物链表示生态系统中能量传递的一条单一途径。它始终从生产者开始，通常是能进行光合作用的植物或藻类，然后依次经过各级消费者。链中的每一步称为一个营养级。食物链中的箭头指向能量流动的方向，即从被食者指向取食者。
A simple terrestrial food chain example: grass → grasshopper → frog → snake → hawk. In aquatic systems, a typical chain might be: phytoplankton → zooplankton → small fish → large fish → seal. Such chains are deliberately simplified; they capture only one possible route of feeding relationships.
一个简单的陆地食物链例子：草 → 蚱蜢 → 蛙 → 蛇 → 鹰。在水生系统中，典型链可能是：浮游植物 → 浮游动物 → 小鱼 → 大鱼 → 海豹。这些链是刻意简化的，它们只捕捉了捕食关系中的一条可能路径。
2. Producers, Consumers and Decomposers | 生产者、消费者与分解者
Producers (also called autotrophs) convert light energy into chemical energy via photosynthesis. They form the base of every food chain. In addition to green plants on land, cyanobacteria and algae are key producers in aquatic environments. Producers synthesise organic compounds such as glucose, which store energy in chemical bonds.
生产者（也称自养生物）通过光合作用将光能转化为化学能。它们构成每条食物链的基础。除了陆地上的绿色植物，蓝细菌和藻类也是水生环境的重要生产者。生产者合成葡萄糖等有机化合物，这些物质在化学键中储存了能量。
Consumers are heterotrophs that obtain energy by feeding on other organisms. Primary consumers (herbivores) eat producers; secondary consumers eat primary consumers; tertiary consumers eat secondary consumers. An apex predator sits at the top and has no natural enemies in that particular food web.
消费者是异养生物，通过取食其他生物获取能量。初级消费者（植食动物）吃生产者；次级消费者吃初级消费者；三级消费者吃次级消费者。顶级捕食者位于顶端，在该食物网中没有天敌。
Decomposers (saprotrophs), such as fungi and bacteria, break down dead organic matter and waste, releasing inorganic nutrients back into the environment. Although not usually depicted in simple food chain diagrams, they are vital in recycling matter and allowing producers to access essential elements like nitrogen and phosphorus.
分解者（腐生生物），如真菌和细菌，分解死去的有机物质和排泄物，将无机营养盐归还到环境中。虽然它们通常不在简单的食物链图中画出，但它们在物质循环中至关重要，让生产者能够获取氮、磷等必需元素。
3. Trophic Levels and Energy Flow | 营养级与能量流动
Each feeding position in a food chain is called a trophic level. Producers occupy the first trophic level, primary consumers the second, secondary consumers the third, and so forth. Energy flows through these levels in a unidirectional manner; it enters the system as sunlight and eventually leaves as heat. Unlike matter, energy cannot be recycled within an ecosystem.
食物链中的每一个摄食位置称为一个营养级。生产者占据第一营养级，初级消费者为第二，次级消费者为第三，依此类推。能量沿着这些营养级单向流动；它作为阳光进入系统，最终以热能的形式散失。与物质不同，能量在生态系统中无法循环利用。
The amount of energy available decreases sharply at each successive trophic level. This is because energy is lost in several ways: respiration, movement, excretion, and uneaten parts (e.g., bones, hair). Typically only about 10% of the energy stored in one trophic level is converted into biomass at the next level.
每个连续的营养级可用能量大幅减少。这是因为能量以多种方式损失：呼吸作用、运动、排泄以及未被食用的部分（如骨骼、毛发）。通常，一个营养级中储存的能量只有大约10%转化为下一营养级的生物量。
4. The 10% Rule and Energy Loss | 10%定律与能量损失
Ecologists often estimate the efficiency of energy transfer between trophic levels using the 10% rule. The actual value varies, but is generally between 5% and 20%. Energy transfer efficiency can be calculated using the formula:
生态学家常使用10%定律来估算营养级之间的能量传递效率。实际数值有所波动，但通常在5%至20%之间。能量传递效率可用以下公式计算：
Ecological efficiency (%) = (Energy in biomass at trophic level n+1 ÷ Energy in biomass at trophic level n) × 100
生态效率 (%) = (第 n+1 营养级生物量所含能量 ÷ 第 n 营养级生物量所含能量) × 100
It is crucial to understand why energy losses occur. During respiration, organic molecules are oxidised to release energy for movement, growth and maintenance of body temperature, with heat given off as a by‑product. In addition, not all parts of an organism are consumed or digested; faeces and dead tissue are passed to decomposers rather than to higher trophic levels.
理解能量损失的原因至关重要。在呼吸过程中，有机分子被氧化以释放能量，用于运动、生长和维持体温，同时以热的形式散失。此外，并非生物体的所有部分都被取食或消化；粪便和死亡组织被传递到分解者，而不是进入更高的营养级。
Eventually, these energy losses limit the length of food chains. Most natural food chains rarely exceed five trophic levels because there is simply insufficient energy left to support an additional level.
最终，这些能量损失限制了食物链的长度。大多数自然食物链很少超过五个营养级，因为剩下的能量不足以支撑额外的营养级。
5. Food Webs | 食物网
A food web is a network of interconnected food chains. Real ecosystems are far more complex than single chains because most organisms feed on more than one species. A food web gives a more realistic picture of energy flow and feeding relationships. It also increases ecosystem stability—if one species declines, organisms can switch to alternative prey.
食物网是由相互连接的食物链组成的网络。真实生态系统远比单一食物链复杂，因为大多数生物以多个物种为食。食物网能更真实地反映能量流动和捕食关系。它也增加了生态系统的稳定性——如果某一物种数量下降，生物可转而捕食其他替代猎物。
When drawing or analysing a food web, always remember that arrows represent energy transfer. They point from the eaten to the eater. In a CIE exam, you may be asked to identify a producer, a primary consumer, or to construct a chain from a given web. Practice extracting the longest possible chain and identifying organisms that occupy more than one trophic level.
在绘制或分析食物网时，始终记住箭头表示能量传递。它们从被食者指向取食者。在CIE考试中，你可能会被要求找出生产者、初级消费者，或从给定的食物网中构建一条食物链。建议练习提取最长的可能链，并识别占据不止一个营养级的生物。
6. Pyramids of Numbers, Biomass and Energy | 数量、生物量与能量金字塔
Ecological pyramids are graphical representations of the trophic structure in an ecosystem. There are three main types: pyramids of numbers, pyramids of biomass, and pyramids of energy. Each has a different shape and conveys different information.
生态金字塔是生态系统中营养结构的图示。主要有三种类型：数量金字塔、生物量金字塔和能量金字塔。它们的形状各有不同，传达的信息也不一样。
| Pyramid type | What it shows | Typical shape |
|---|---|---|
| Numbers | Number of organisms at each trophic level | Can be inverted (e.g. one tree supports many insects) |
| Biomass | Total dry mass of organisms (g/m²) | Almost always upright, except in aquatic systems where phytoplankton may have small standing biomass but rapid turnover |
| Energy | Energy content (kJ/m²/yr) | Always upright, because energy is always lost at each transfer |
A pyramid of energy is the most accurate representation of energy relationships because it accounts for the loss of energy as heat. It is always pyramid-shaped, never inverted. In CIE exams, you are often asked to explain why a pyramid of numbers might be inverted but a pyramid of energy never is.
能量金字塔是能量关系最准确的表示，因为它考虑了能量以热的形式损失。它始终保持正金字塔形，永不倒置。在CIE考试中，经常要求解释为何数量金字塔可能倒置，而能量金字塔绝不会倒置。
7. Bioaccumulation and Biomagnification | 生物积累与生物放大
Bioaccumulation is the build-up of persistent, fat-soluble chemicals in an organism’s body over its lifetime. Biomagnification is the increase in concentration of such substances as they pass up a food chain. A classic example is DDT, a pesticide used in the mid‑20th century that caused thinning of eggshells in birds of prey.
生物积累是指一种持久性、脂溶性的化学物质在生物体一生中体内逐渐累积。生物放大是这类物质随食物链上升浓度不断增加的现象。一个经典例子是 DDT，这种 20 世纪中期使用的杀虫剂导致了猛禽蛋壳变薄。
In a typical aquatic chain: phytoplankton absorb trace amounts of DDT from water → zooplankton eat large quantities of phytoplankton, concentrating the toxin in their bodies → small fish eat many zooplankton → large fish consume many small fish. At each step the concentration increases, sometimes by a factor of millions at the top predator level. This explains why top carnivores suffer the most severe toxic effects.
在典型的水生食物链中：浮游植物从水中吸收微量 DDT → 浮游动物大量取食浮游植物，在其体内浓缩毒素 → 小鱼吃许多浮游动物 → 大鱼捕食许多小鱼。每一步浓度都在增加，在顶级捕食者体内有时可放大数百万倍。这解释了为何顶级肉食动物受到最严重的中毒影响。
Other examples of biomagnifying substances include mercury (as methylmercury) and PCBs. CIE expects you to be able to explain the process using the terms bioaccumulation and biomagnification and to relate it to food chain length and energy flow.
其他具有生物放大效应的物质包括汞（甲基汞）和多氯联苯（PCBs）。CIE 希望你能用“生物积累”和“生物放大”这两个术语解释这一过程，并将其与食物链长度和能量流动联系起来。
8. Common Misconceptions | 常见误区
- Misconception: Arrows in a food chain show the direction of predation. Correct understanding: Arrows indicate the flow of energy and biomass, from prey to predator.
- 误区：食物链中的箭头表示捕食方向。正确理解：箭头表示能量和生物量的流动方向，从猎物到捕食者。
- Misconception: Decomposers are not part of food chains. Correct understanding: Decomposers are involved in all trophic levels, recycling nutrients, even though they are often omitted from simplified diagrams.
- 误区：分解者不属于食物链。正确理解：分解者参与所有营养级，回收养分，尽管常被简化图示忽略。
- Misconception: The 10% rule is a fixed law. Correct understanding: It is an approximate average; real efficiency varies widely and is affected by the organisms and environment.
- 误区：10%定律是一条固定法则。正确理解：它是一个近似的平均值，实际效率变化很大，并受生物和环境因素影响。
- Misconception: A pyramid of biomass is always upright. Correct understanding: In some aquatic ecosystems, the biomass of phytoplankton can be smaller than that of zooplankton at a given instant due to high turnover rates, creating an inverted pyramid.
- 误区：生物量金字塔总是正立的。正确理解：在某些水生生态系统中，由于浮游植物周转率极高，某一瞬间其生物量可能小于浮游动物，从而形成倒置金字塔。
9. Exam Tips and Key Terms | 考试技巧与关键词汇
When tackling CIE questions on food chains, be precise with terminology. Use ‘producer’ not ‘plant’ (some producers are not plants). Distinguish clearly between ‘food chain’ and ‘food web’. In calculations, always show your working and state the formula. For extended response questions, provide a logical sequence: define, explain with an example, then relate to wider ecological principles.
在回答 CIE 食物链相关问题时，术语要精准。使用“生产者”而不是“植物”（有些生产者不是植物）。清楚区分“食物链”与“食物网”。计算题要列出计算步骤并写出公式。对于扩展简答题，提供逻辑顺序：下定义、举例解释，然后联系更广泛的生态原理。
Key vocabulary to memorise:
需要记忆的关键词汇：
| English term | 中文术语 | Definition cue |
|---|---|---|
| Trophic level | 营养级 | Feeding level in a chain |
| Producer / Autotroph | 生产者/自养生物 | Makes own food via photosynthesis |
| Consumer / Heterotroph | 消费者/异养生物 | Eats other organisms |
| Decomposer / Saprotroph | 分解者/腐生生物 | Breaks down dead matter externally |
| Biomass | 生物量 | Total dry mass of organisms |
| Bioaccumulation | 生物积累 | Build-up of toxin in an organism |
| Biomagnification | 生物放大 | Increasing concentration along a food chain |
| Ecological efficiency | 生态效率 | Percentage of energy transferred between trophic levels |
10. Summary and Connections | 总结与知识关联
Food chains are not isolated facts; they integrate with topics such as photosynthesis, respiration, energy transfers, and human impact on the environment. Understanding the low efficiency of energy transfer helps explain why short food chains are more efficient for feeding the human population—a concept linking to agriculture and sustainability. Similarly, the principles of bioaccumulation underpin many environmental regulations concerning pesticides and heavy metals.
食物链并非孤立的知识点；它与光合作用、呼吸作用、能量传递以及人类对环境的影响等主题紧密关联。理解能量传递的低效率有助于解释为何短食物链在养活人口方面更高效——这一概念与农业和可持续发展相联系。同样地，生物积累的原理为许多关于杀虫剂和重金属的环境法规提供了科学依据。
For revision, practise drawing and labelling food chains and webs. Solve past paper questions that ask you to calculate trophic efficiency or to explain why top predators are especially vulnerable to pollutants. Always link your answers back to core biological principles: energy is never created or destroyed, only transferred; and toxic substances can become concentrated in living tissues.
复习时，要练习绘制并标注食物链和食物网。完成历年真题中要求计算营养效率或解释为何顶级捕食者特别容易受到污染物威胁的题目。始终将答案与核心生物学原理联系起来：能量既不会创生也不会消失，只是不断传递；而有毒物质能够在生物组织中浓缩。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply