📚 Food Chains in IB CCEA Biology: Key Points | IB CCEA 生物：食物链考点精讲
Food chains are the simplest way to model feeding relationships in an ecosystem. In both IB Biology and CCEA specifications, understanding how energy and matter flow from producers to consumers is essential for explaining ecological stability and change.
食物链是描述生态系统中摄食关系的最简单模型。在 IB 生物和 CCEA 考纲中，理解能量和物质如何从生产者流向消费者，对于解释生态系统的稳定与变化至关重要。
1. What is a Food Chain? | 什么是食物链？
A food chain is a linear sequence of organisms through which energy and nutrients are transferred as one organism eats another. Each step in the chain represents a feeding level, known as a trophic level.
食物链是一个线性的生物序列，能量和营养物质通过生物之间的捕食关系传递。链中的每一步代表一个摄食层次，即营养级。
Food chains always begin with a producer, typically a photosynthetic organism such as a plant or alga, that converts light energy into chemical energy.
食物链总是从生产者开始，通常是光合生物（如植物或藻类），它们将光能转化为化学能。
Arrows in a food chain point from the food source to the consumer, indicating the direction of energy flow.
食物链中的箭头从食物来源指向消费者，表示能量流动的方向。
2. Producers: The Foundation | 生产者：食物链的基础
Producers are autotrophs – organisms that can manufacture their own food using inorganic sources of energy. The majority are photoautotrophs that perform photosynthesis, using sunlight, carbon dioxide, and water to produce glucose.
生产者是自养生物——能利用无机能源制造自身食物的生物。大多数是光合自养生物，通过光合作用利用阳光、二氧化碳和水生成葡萄糖。
In aquatic ecosystems, phytoplankton are the main producers, while on land, vascular plants dominate. In IB and CCEA, you may be asked to explain the role of producers in converting light energy to chemical energy stored in biomass.
在水生生态系统中，浮游植物是主要生产者；在陆地上，维管植物占主导。IB 和 CCEA 考试可能要求你解释生产者如何将光能转化为储存在生物量中的化学能。
Without producers, there would be no energy input into an ecosystem, and all heterotrophic life would cease.
没有生产者，生态系统就没有能量输入，所有异养生命都将停止。
3. Consumers: Primary, Secondary, Tertiary | 消费者：初级、次级、三级消费者
Consumers are heterotrophs that obtain energy by feeding on other organisms. A primary consumer (herbivore) eats producers; a secondary consumer (carnivore) eats primary consumers; a tertiary consumer eats secondary consumers.
消费者是通过捕食其他生物来获取能量的异养生物。初级消费者（植食动物）吃生产者；次级消费者（肉食动物）吃初级消费者；三级消费者吃次级消费者。
Some organisms can occupy more than one trophic level depending on their diet. For example, an omnivore such as a bear can be a primary consumer when eating berries and a secondary consumer when eating fish.
有些生物根据食性可占据多个营养级。比如杂食动物熊，吃浆果时是初级消费者，吃鱼时是次级消费者。
In exam diagrams, always check the number of arrows from the food source to the consumer to determine the trophic level accurately.
在考试图表中，一定要从食物来源指向消费者的箭头数量准确判断营养级。
4. Trophic Levels and Energy Transfer | 营养级与能量传递
Each step in a food chain is a trophic level. The first trophic level is occupied by producers, the second by primary consumers, the third by secondary consumers, and so forth.
食物链的每一步都是一个营养级。第一营养级是生产者，第二是初级消费者，第三是次级消费者，以此类推。
Energy transfer between trophic levels is inefficient. Typically only about 10% of the energy in one trophic level is converted into biomass in the next level. The remainder is lost through metabolic heat, respiration, movement, and undigested material.
营养级之间的能量传递效率很低。通常只有约 10% 的能量从前一营养级转化为后一营养级的生物量。其余能量通过代谢产热、呼吸作用、运动及未消化物质而损失。
This loss explains why food chains rarely exceed four or five trophic levels – there is simply not enough energy to support higher levels.
正因为能量损失，食物链很少超过四或五个营养级——根本没有足够能量支撑更高层次。
5. Energy Loss and the 10% Rule | 能量损失与百分之十定律
The 10% rule is a generalisation stating that, on average, only 10% of the energy stored in biomass at one trophic level is passed on to the next. This value can vary between ecosystems.
百分之十定律是一个概括性规律，即平均而言，一个营养级生物量中储存的能量只有约 10% 传递到下一个营养级。该数值因生态系统而异。
Energy is lost because not all of an organism is consumed (e.g. bones, roots), and much of what is ingested is used in respiration or excreted. In IB and CCEA exams, you should be able to calculate energy transfer efficiency using the formula:
能量损失是因为并非生物的全部都被吃掉（如骨骼、根系），且摄入的能量中有很大一部分用于呼吸或排泄。在 IB 和 CCEA 考试中，你应该能使用下式计算能量传递效率：
Efficiency (%) = (Energy in biomass at higher trophic level ÷ Energy in biomass at lower trophic level) × 100
效率 (%)=（较高营养级生物量中的能量 ÷ 较低营养级生物量中的能量）× 100
You may be given data in kJ m⁻² yr⁻¹ and asked to calculate the percentage transfer. Always show your working.
题目可能以 kJ m⁻² yr⁻¹ 提供数据，要求计算传递百分比。务必展示计算过程。
6. Food Webs: Interconnected Chains | 食物网：相互关联的食物链
A food web is a network of interconnected food chains within an ecosystem. It provides a more realistic representation of feeding relationships, as most organisms eat more than one type of food and are eaten by multiple predators.
食物网是生态系统中多个食物链相互连接形成的网络。它能更真实地反映摄食关系，因为大多数生物吃多种食物，并被多种捕食者捕食。
Food webs show how stability arises: if one species declines, predators can switch to alternative prey. In contrast, a simple food chain is vulnerable to disruption.
食物网展示了生态稳定性：当某一物种减少时，捕食者可转向替代猎物。相比之下，简单的食物链更容易受到干扰。
When constructing or interpreting food webs in exams, remember that arrows still indicate energy flow. Be careful to identify producers (always at the base) and to count trophic links correctly.
在考试中构建或分析食物网时，记住箭头仍表示能量流动。要能准确识别生产者（始终在基部）并正确计算营养链接。
7. Decomposers and Detritivores | 分解者与食碎屑者
Decomposers (bacteria and fungi) break down dead organic matter and wastes, releasing inorganic nutrients back into the soil or water. Detritivores (e.g. earthworms, woodlice) feed on detritus and help fragment organic material, speeding decomposition.
分解者（细菌和真菌）分解死亡的有机质和废物，将无机养分释放回土壤或水体。食碎屑者（如蚯蚓、潮虫）以碎屑为食，帮助粉碎有机质，加速分解过程。
Although they are not always shown in simple food chain diagrams, decomposers and detritivores are essential for nutrient cycling. In CCEA and IB, you may be asked to explain their ecological role in carbon and nitrogen cycles.
虽然简单的食物链图中不一定展示，但分解者和食碎屑者对养分循环至关重要。CCEA 和 IB 可能要求解释它们在碳循环和氮循环中的生态作用。
They form a ‘detritus food chain’ that runs parallel to the grazing food chain, ensuring that energy stored in dead biomass is not completely wasted.
它们构成了与牧食食物链平行的“碎屑食物链”，确保死生物量中储存的能量不会完全浪费。
8. Pyramids of Numbers, Biomass, and Energy | 数量、生物量和能量金字塔
Ecological pyramids are graphical representations of the trophic structure. Three types are commonly examined:
生态金字塔是营养结构的图示。常考三种类型：
- Pyramid of numbers: Shows the number of organisms at each trophic level. It can be inverted (e.g. one oak tree supporting many caterpillars).
- Pyramid of biomass: Shows the total dry mass of organisms at each level. Usually upright, but can be inverted in aquatic ecosystems where phytoplankton reproduce rapidly.
- Pyramid of energy: Shows the total energy content at each level, expressed in units like kJ m⁻² yr⁻¹. Always upright because energy is lost at each transfer.
- 数量金字塔：显示每个营养级的生物个体数量。可能倒置（如一棵橡树供养许多毛虫）。
- 生物量金字塔：显示每个营养级的生物总干重。通常正立，但在浮游植物快速繁殖的水生生态系统中可能倒置。
- 能量金字塔：显示每个营养级的总能量含量，单位如 kJ m⁻² yr⁻¹。永远正立，因为每次传递都损失能量。
In IB and CCEA exams, you may be asked to interpret or sketch these pyramids and explain why the pyramid of energy is always upright.
在 IB 和 CCEA 考试中，可能要求解读或绘制这些金字塔，并解释为何能量金字塔总是正立的。
9. Bioaccumulation and Biomagnification | 生物累积与生物放大
Bioaccumulation is the build-up of a persistent chemical (e.g. DDT, heavy metals) in an organism over its lifetime. Biomagnification is the increase in concentration of such substances at successive trophic levels.
生物累积是指持久性化学物质（如 DDT、重金属）在生物一生中不断积累。生物放大则指这些物质在连续营养级中的浓度递增。
Because toxins are often fat-soluble, they are not easily excreted and become more concentrated as one predator eats many contaminated prey organisms. This explains why top predators, such as birds of prey or polar bears, can carry dangerously high toxin loads.
由于毒素通常是脂溶性的，不易排出，当一个捕食者吃掉许多受污染的猎物时，毒素浓度会随之升高。这就解释了为何顶级捕食者（如猛禽或北极熊）体内毒素负荷高得危险。
Both IB and CCEA may ask you to analyse data on toxin concentration at different trophic levels and link it to food chain dynamics.
IB 和 CCEA 都可能要求分析不同营养级毒素浓度的数据，并将其与食物链动态联系起来。
10. Trophic Cascades | 营养级联
A trophic cascade occurs when changes in the abundance of a top predator cause ripple effects down through the food web. For example, the removal of wolves can lead to an explosion in deer populations, overgrazing, and loss of vegetation.
营养级联是指顶级捕食者数量的变化通过食物网产生涟漪效应。例如，狼的消失会导致鹿群数量激增、过度啃食和植被破坏。
Conversely, the reintroduction of a keystone predator can restore balance, demonstrating the importance of top-down control in ecosystems.
相反，重新引入关键捕食者可以恢复平衡，这证明了生态系统中自上而下控制的重要性。
IB exam questions often use case studies like the Yellowstone wolves to illustrate trophic cascades; CCEA may similarly reference local examples or experimental data.
IB 考试题目常以黄石公园的狼为例说明营养级联；CCEA 也可能引用当地实例或实验数据。
11. Key Terms and Definitions | 关键术语与定义
Mastering terminology is essential for both IB and CCEA. Use the table below for quick revision.
掌握术语对 IB 和 CCEA 都至关重要。使用下表快速复习。
| Term | Definition | 中文 |
|---|---|---|
| Producer | An autotroph that synthesises organic compounds from inorganic sources | 生产者 |
| Consumer | A heterotroph that obtains energy by eating other organisms | 消费者 |
| Trophic level | The position an organism occupies in a food chain | 营养级 |
| Biomass | The total dry mass of organic matter in organisms | 生物量 |
| Decomposer | An organism that breaks down dead organic matter | 分解者 |
| Detritivore | An organism that feeds on detritus by ingesting it | 食碎屑者 |
| Bioaccumulation | The build-up of a substance in an organism over time | 生物累积 |
| Biomagnification | The increase in concentration of a toxin along a food chain | 生物放大 |
12. Exam Tips for IB and CCEA | IB与CCEA考试技巧
When tackling food chain questions, pay close attention to command terms. ‘State’ requires a brief answer, ‘explain’ demands a causal mechanism, and ‘discuss’ expects arguments for and against.
回答食物链题目时，注意指令词。“State”要求简短回答，“explain”需要因果机制，“discuss”则期待正反两面的论证。
Always draw food chains with arrows pointing from the organism being eaten to the eater. Label producers, primary consumers, etc., unless the question specifies otherwise. Use the correct units for energy flow (kJ m⁻² yr⁻¹) and biomass (g m⁻²).
绘制食物链时，箭头必须从被吃生物指向吃食者。除非题目另有要求，否则要标注生产者、初级消费者等。能量流用正确单位 (kJ m⁻² yr⁻¹)，生物量用 (g m⁻²)。
For data analysis questions, calculate percentage transfer carefully. For extended response, structure your answer around the key concepts: energy source, trophic levels, inefficiency of transfer, pyramids, and consequences for ecosystem structure.
数据分析题要仔细计算传递百分比。拓展题应围绕核心概念组织答案：能量来源、营养级、传递的低效率、金字塔以及对生态系统结构的影响。
Finally, remember that in CCEA, questions may focus on local ecosystems such as a woodland or marine environment; IB might use international contexts. Link your answer to the specific data or case study provided.
最后，注意 CCEA 可能聚焦当地生态系统（如林地或海洋环境）；IB 可能采用国际情境。答案要结合提供的具体数据或案例研究。
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