Food Chains in IGCSE CCEA Biology | IGCSE CCEA 生物：食物链 考点精讲

📚 Food Chains in IGCSE CCEA Biology | IGCSE CCEA 生物：食物链 考点精讲

A food chain shows how energy and nutrients move through an ecosystem. For the CCEA IGCSE Biology specification, you need to understand the organisation of producers, consumers, decomposers and how energy flows from one trophic level to the next.

食物链展示了能量和营养物质如何在生态系统中流动。在 CCEA IGCSE 生物考试大纲中，你需要理解生产者、消费者和分解者的组织方式，以及能量如何从一个营养级传递到下一个营养级。

1. What is a Food Chain? | 什么是食物链？

A food chain is a linear sequence of organisms that shows ‘who eats whom’ in an ecosystem. Arrows represent the direction of energy transfer – they go from the food source to the feeder.

食物链是一条线性的生物序列，显示生态系统中“谁吃谁”。箭头表示能量传递的方向——从食物来源指向取食者。

For example, a simple grassland food chain: grass → rabbit → fox. The grass is eaten by the rabbit, and the rabbit is eaten by the fox. Energy originally captured by the grass is passed along the chain.

例如，一条简单的草原食物链：草 → 兔子 → 狐狸。草被兔子吃，兔子被狐狸吃。草最初捕获的能量沿食物链传递下去。

Every food chain begins with a producer. The number of steps in a chain rarely exceeds five because energy becomes very limited at higher levels.

每条食物链都从生产者开始。食物链的环节很少超过五级，因为在更高的营养级能量变得非常有限。

2. Producers: The Base of the Chain | 生产者：食物链的基础

Producers are organisms that make their own food using energy from sunlight through photosynthesis. Plants and algae are the main producers in most ecosystems.

生产者是利用阳光通过光合作用制造自身食物的生物。在大多数生态系统中，植物和藻类是主要的生产者。

They convert light energy into chemical energy stored in glucose. The overall equation for photosynthesis is:

它们将光能转化为储存在葡萄糖中的化学能。光合作用的总方程式为：

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Producers form the first trophic level in any food chain. Without producers, there would be no energy input for consumers.

生产者构成了任何食物链的第一个营养级。没有生产者，消费者就没有能量输入。

3. Consumers: Primary, Secondary and Tertiary | 消费者：初级、次级和三级消费者

Consumers are organisms that cannot produce their own food and must eat other organisms to obtain energy. They are classified by their feeding position in the chain.

消费者是不能自己制造食物、必须通过取食其他生物来获取能量的生物。它们按照在食物链中的取食位置进行分类。

• Primary consumers (herbivores) eat producers. Example: rabbit, caterpillar. 初级消费者（食草动物）吃生产者。例如：兔子、毛毛虫。
• Secondary consumers (carnivores or omnivores) eat primary consumers. Example: fox, robin. 次级消费者（食肉动物或杂食动物）吃初级消费者。例如：狐狸、知更鸟。
• Tertiary consumers eat secondary consumers and are often top predators. Example: hawk, killer whale. 三级消费者吃次级消费者，通常是顶级捕食者。例如：鹰、虎鲸。

An organism’s trophic level is not fixed – a bear eating berries is a primary consumer, but the same bear eating fish becomes a tertiary consumer.

一种生物的营养级并不是固定的——吃浆果的熊是初级消费者，但同只熊吃鱼时就变成了三级消费者。

4. Food Webs: Interconnected Chains | 食物网：相互连接的链

In reality, most organisms eat more than one type of food and are eaten by several different predators. A food web consists of many interconnected food chains, showing a more realistic picture of energy flow.

在现实中，大多数生物不止吃一种食物，也会被多种不同的捕食者所食。食物网由许多相互连接的食物链组成，更真实地展示了能量流动的图景。

If one species in a food web is removed, it can have a dramatic effect on other populations. This is called interdependence. For CCEA exams, you should be able to interpret a food web diagram and predict changes when a species is added or removed.

如果食物网中的某个物种被移除，会对其他种群产生巨大影响，这叫做相互依存。在 CCEA 考试中，你需要能够解读食物网图，推测当某个物种增加或减少时会发生什么变化。

5. Energy Flow in Food Chains | 食物链中的能量流动

Energy enters most food chains through sunlight captured by producers during photosynthesis. This chemical energy is then passed along the chain when consumers eat.

能量通过阳光被生产者在光合作用中捕获而进入大多数食物链。这些化学能随后在消费者取食时沿食物链传递。

Only about 10% of the energy stored in one trophic level is transferred to the next level. The rest is lost to the environment, mainly as heat from respiration, and also through undigested matter and waste.

大约只有 10% 储存在某个营养级中的能量能够传递到下一个营养级。其余的都散失到环境中，主要以呼吸作用产生的热量形式，也有通过未消化的物质和排泄物散失的部分。

You may be asked to draw simple energy flow diagrams using arrows of different thickness to show decreasing energy. Always label losses clearly.

你可能会被要求画出简单的能量流动图，用粗细不同的箭头表示能量递减。务必清楚地标出能量损失。

6. Energy Loss and Efficiency | 能量损失与效率

At each trophic level, energy is lost in several ways: heat from respiration, undigested food egested as faeces, nitrogenous waste (urea), and uneaten parts like bones or roots.

在每个营养级，能量会以以下几种方式散失：呼吸作用产生的热量、以粪便形式排出的未消化食物、含氮废物（尿素），以及未被吃掉的部分，如骨头或根。

Because of these losses, the amount of energy available decreases sharply at each step. This is why food chains are typically short and why top predators are rare and require large territories.

由于这些损失，每一步可用的能量总量都会急剧减少。这就是为什么食物链通常很短，以及为什么顶级捕食者很稀少并且需要大面积领地。

Efficiency of energy transfer can be calculated:
(energy in new biomass at next level ÷ energy in biomass eaten from previous level) × 100%.

能量传递效率可以这样计算：
（下一个营养级新生物量中的能量 ÷ 上一个营养级被吃掉的生物量中的能量）× 100%。

7. Pyramids of Numbers | 数量金字塔

A pyramid of numbers shows the count of individual organisms at each trophic level. The width of each bar represents the number of organisms.

数量金字塔显示每个营养级中生物的个体数量。每个横条的宽度代表生物数量。

Often the pyramid shape is upright – many producers at the bottom, progressively fewer consumers above – but there are exceptions. A single oak tree can support thousands of caterpillars, giving an inverted pyramid shape.

通常，金字塔的形状是正立的——底部有大量生产者，向上消费者数量逐渐减少——但也有例外。一棵橡树可以养活数千只毛毛虫，形成倒金字塔形状。

For CCEA, you should recognise that pyramids of numbers do not always represent biomass accurately and can be misleading when organisms vary greatly in size.

在 CCEA 考试中，你需要知道数量金字塔并不总能准确代表生物量，当生物个体大小差异很大时可能会产生误导。

8. Pyramids of Biomass | 生物量金字塔

A pyramid of biomass represents the total dry mass of living matter at each trophic level. This gives a more reliable picture of energy stored than numbers alone.

生物量金字塔表示每个营养级中活物质的总干质量。与单纯的数量相比，这能更可靠地反映储存的能量。

Biomass pyramids are almost always upright because the total mass of producers needed to support the next level must be greater. Even large trees can be dried and weighed to give a true biomass figure.

生物量金字塔几乎总是正立的，因为要支撑下一个营养级，生产者的总质量必须更大。即使是大树，也可以通过干燥称重得出真实的生物量数值。

When drawing, remember that the area of each block should be proportional to the biomass. Always label the trophic levels and the units, e.g. g/m².

画图时，要记住每个方块的面积应与生物量成正比。始终标注营养级和单位，例如 g/m²。

9. Pyramids of Energy | 能量金字塔

Pyramids of energy show the rate of energy flow (productivity) at each trophic level, usually in units of kJ m⁻² year⁻¹. They are always upright because energy is always lost at each transfer.

能量金字塔显示每个营养级的能量流动速率（生产力），通常以 kJ m⁻² year⁻¹ 为单位。它们总是正立的，因为每次传递都会有能量损失。

In CCEA papers, you might be asked to explain why an energy pyramid never appears inverted. The answer is based on the second law of thermodynamics: energy transfers are never 100% efficient.

在 CCEA 试卷中，你可能会被要求解释为什么能量金字塔永远不会倒置。答案基于热力学第二定律：能量传递永远不会达到 100% 的效率。

Energy pyramids are the most accurate way to compare different ecosystems because they are not affected by organism size or seasonal changes in biomass.

能量金字塔是比较不同生态系统最准确的方式，因为它们不受生物个体大小或生物量季节性变化的影响。

10. Biological Magnification (Bioaccumulation) | 生物放大（生物累积）

Biological magnification is the process by which toxic substances become increasingly concentrated in the tissues of organisms at higher trophic levels. This is especially important for persistent pesticides like DDT.

生物放大是指有毒物质在更高营养级生物的组织中浓度不断升高的过程。这对于像 DDT 这样的持久性杀虫剂尤为重要。

In water, a low concentration of a toxin in phytoplankton can build up in zooplankton, then small fish, then larger fish, and finally reach dangerous levels in birds of prey or humans at the top of the chain.

在水中，浮游植物内低浓度的毒素会在浮游动物体内积累，再到小鱼、大鱼，最终在食物链顶端的猛禽或人类体内达到危险水平。

The CCEA specification expects you to be able to interpret data on toxin concentrations in organisms from different trophic levels and to explain the trend.

CCEA 大纲要求你能够解读不同营养级生物体内毒素浓度的数据，并解释这一趋势。

11. Role of Decomposers | 分解者的作用

Decomposers, such as bacteria and fungi, break down dead organisms and waste materials. They release enzymes onto the organic matter and absorb the breakdown products, returning mineral ions to the soil.

分解者，如细菌和真菌，能够分解死亡生物和废弃物。它们将酶释放到有机物上，吸收分解产物，并将矿物质离子归还到土壤。

This recycling of nutrients is essential for maintaining soil fertility so that producers can continue to grow. Without decomposers, essential elements would remain locked in dead matter and the ecosystem would collapse.

这种营养物质的循环对于保持土壤肥力至关重要，这样生产者才能持续生长。如果没有分解者，重要元素就会被困在死亡物质中，生态系统将会崩溃。

Food chain diagrams often include decomposers as a separate box or arrow showing that they break down organisms from all trophic levels. Make sure you can draw and label this clearly.

食物链示意图通常会用一个单独的方框或箭头来表示分解者，说明它们分解所有营养级的生物。确保你能清楚地画出并标出这一点。

12. CCEA Exam Tips | CCEA 考试技巧

When tackling questions on food chains in CCEA Biology papers, always start by identifying the producer and the top consumer. Look carefully at the direction of arrows – they must point from eaten to eater.

在应对 CCEA 生物试卷中食物链相关题目时，始终从识别生产者和顶级消费者开始。仔细观察箭头的方向——必须从被吃的生物指向取食者。

Data analysis questions may give you figures on energy content or pesticide levels at different trophic levels. Practise calculating percentage energy transfers and drawing pyramids with correct labelling.

数据分析题可能会给出不同营养级的能量含量或杀虫剂水平数据。练习计算能量传递百分比，并画出标注正确的金字塔图。

Remember the key reasons for energy loss: movement, heat from respiration, uneaten parts and excretion. If asked ‘why short food chains’, link back to energy inefficiency.

记住能量损失的关键原因：运动、呼吸作用产热、未被吃掉的部分以及排泄物。如果被问到“为什么食物链很短”，要联系回能量利用的低效。

Use precise language: ‘energy is lost as heat’, not just ‘energy is lost’. Mention decomposers and omnivores where relevant to show deeper understanding.

使用精确的语言：“能量以热的形式散失”，而不仅仅是“能量散失”。在相关的地方提及分解者和杂食动物，以展示更深入的理解。

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