📚 Energy Transfer in Ecosystems | 生态系统中的能量传递
Energy is the driving force of every ecosystem on Earth. From the sunlight captured by a blade of grass to the swift movement of a cheetah across the savannah, the flow of energy determines the structure, size and behaviour of living communities. In Edexcel IGCSE Biology, you need to understand how this energy enters the living world, how it passes from organism to organism, and why so much of it is lost at each stage.
能量是地球上每一个生态系统的驱动力。从一片草叶捕获的阳光，到猎豹在稀树草原上的快速奔跑，能量的流动决定了生物群落的结构、规模和行为。在爱德思 IGCSE 生物学中，你需要理解能量如何进入生命世界，如何在生物体之间传递，以及为什么在每个阶段都会有大量能量损失。
1. Ecosystems, Habitats and Populations | 生态系统、栖息地与种群
An ecosystem is a distinct, self-supporting system of organisms interacting with each other and with their physical environment. It includes a community of living organisms (biotic factors) together with the non-living (abiotic) components such as soil, water, temperature and light. A habitat is the specific place within an ecosystem where an organism lives, while a population refers to all the individuals of a single species living in the same habitat at the same time.
生态系统是一个由生物体之间以及生物体与物理环境相互作用而形成的、能够自我维持的独特系统。它包括生物群落（生物因素）和非生物（非生物因素）部分，如土壤、水、温度和光照。栖息地是生态系统中某个生物生存的特定场所，而种群则是指同一时间生活在同一栖息地的同一物种的所有个体。
2. Producers: The Energy Gateway | 生产者：能量的入口
er → glucose + oxygen, in the presence of light and chlorophyll. This process is the foundation of nearly every food chain.
流经生态系统的所有能量最初都来自太阳。生产者，主要是绿色植物和藻类，通过光合作用将光能转化为储存在葡萄糖和其他有机分子中的化学能。光合作用的文字方程式是：二氧化碳 + 水 → 葡萄糖 + 氧气，需要光和叶绿素参与。这个过程是几乎每一条食物链的基础。
3. Consumers and Trophic Levels | 消费者与营养级
Organisms that cannot produce their own food are called consumers. Primary consumers (herbivores) eat producers, secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers. Each step in a food chain is known as a trophic level. Decomposers, such as bacteria and fungi, break down dead matter and waste, releasing nutrients back into the soil, but they also release energy stored in organic compounds as heat through respiration.
不能自己制造食物的生物被称为消费者。初级消费者（食草动物）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。食物链中的每一步被称为一个营养级。分解者，如细菌和真菌，分解死去的生物和废物，将养分释放回土壤中，但它们也通过呼吸作用将有机化合物中储存的能量以热能的形式释放出来。
4. Food Chains and Food Webs | 食物链与食物网
t organisms eat more than one type of food, so many food chains interconnect to form a food web. Food webs give a more accurate picture of feeding relationships and show that energy can flow along multiple pathways.
食物链是显示生态系统中谁吃谁的线性序列，通常以生产者开始，以顶级捕食者结束。例如：草 → 兔子 → 狐狸。在现实中，大多数生物不止吃一种食物，因此许多食物链相互连接形成食物网。食物网更准确地呈现了捕食关系，并显示能量可以沿多条路径流动。
5. Energy Loss Between Trophic Levels | 营养级之间的能量损耗
When energy is transferred from one trophic level to the next, a large proportion is lost. On average, only about 10% of the energy in one trophic level is passed on to the next. The remaining 90% is used by the organism itself for life processes such as respiration, movement and growth, or is lost as heat to the surroundings. Some energy is also left behind in indigestible materials, such as cellulose in plant cell walls, which are egested as faeces.
当能量从一个营养级传递到下一个营养级时，很大一部分会损失掉。平均而言，一个营养级中只有大约 10% 的能量会传递到下一个营养级。剩下的 90% 被生物体自身用于呼吸、运动和生长等生命活动，或以热能的形式散失到周围环境中。部分能量还留在无法消化的物质中，比如植物细胞壁中的纤维素，这些物质会作为粪便排出体外。
6. The 10% Rule and Its Significance | 10% 法则及其意义
The so-called '10% rule' is a rough estimate. In reality, the efficiency of energy transfer can range from about 5% to 20%, depending on the organisms and ecosystem involved. Because so much energy is lost at each step, the amount of available energy decreases sharply as you move up the food chain. This explains why food chains rarely have more than four or five trophic levels — there simply is not enough energy left to support another level of consumers.
所谓的“10% 法则”只是一个粗略的估计。实际上，能量传递效率根据生物和生态系统的不同，大约在 5% 到 20% 之间。因为每一步都有大量能量损失，随着食物链上升，可用能量的数量急剧减少。这解释了为什么食物链很少有超过四到五个营养级——根本没有足够的能量来支撑更高一级的消费者。
7. Pyramids of Numbers | 数量金字塔
A pyramid of numbers shows the count of individual organisms at each trophic level in a food chain. The width of each bar is proportional to the number of organisms. Often, the producer level has the largest number, and the top predator has the smallest. However, pyramids of numbers can appear inverted or irregular in some cases, for example, a single large tree (producer) can support many insects (primary consumers), making the base appear smaller than the next level.
数量金字塔显示食物链中每个营养级的个体生物数量。每个条形图的宽度与生物数量成正比。通常情况下，生产者层级的数量最多，顶级捕食者的数量最少。然而，在某些情况下数量金字塔会呈现倒置或不规则形状，例如，一棵大树（生产者）可以支撑许多昆虫（初级消费者），导致基底看起来比上一级更窄。
8. Pyramids of Biomass | 生物量金字塔
A pyramid of biomass represents the total dry mass of living material at each trophic level, usually measured in grams per square metre (g/m²). This gives a more accurate picture of energy availability than pyramids of numbers because it considers the actual mass of organisms, not just their head count. Pyramids of biomass are almost always pyramid-shaped, with a broad producer base and progressively smaller upper levels, because biomass decreases with each energy transfer.
生物量金字塔表示每个营养级生命物质的总干质量，通常以克每平方米（g/m²）计量。这比数量金字塔更准确地反映了能量的可利用性，因为它考虑了生物体的实际质量，而不仅仅是数量。生物量金字塔几乎总是呈金字塔形，具有宽阔的生产者基部，而上层逐渐变小，因为生物量随着每次能量传递而减少。
9. Pyramids of Energy | 能量金字塔
A pyramid of energy shows the total amount of energy present at each trophic level, typically measured in kilojoules per square metre per year (kJ/m²/year). Unlike pyramids of numbers or biomass, energy pyramids are never inverted. They always have a wide base and progressively narrower upper levels because energy is lost at each transfer. These pyramids give the best representation of energy flow through an ecosystem.
能量金字塔显示每个营养级中存在的总能量，通常以千焦每平方米每年（kJ/m²/年）计量。与数量金字塔或生物量金字塔不同，能量金字塔永远不会倒置。它们总是具有宽阔的底部和逐渐变窄的上层，因为每次传递都会损失能量。这些金字塔最能代表通过生态系统的能量流动。
10. Calculating the Efficiency of Energy Transfer | 能量传递效率的计算
In Edexcel IGCSE Biology, you may be asked to calculate the percentage of energy transferred from one trophic level to the next. The formula is:
Efficiency (%) = (energy in higher trophic level ÷ energy in lower trophic level) × 100
nd primary consumers receive 2000 kJ/m²/year, the efficiency is (2000 ÷ 20 000) × 100 = 10% is simple calculation highlights how little energy is actually available to top predators.
在爱德思 IGCSE 生物学中，你可能会被要求计算从一个营养级传递到下一个营养级的能量百分比。公式是：
效率 (%) =（较高营养级的能量 ÷ 较低营养级的能量）× 100
例如，如果生产者捕获 20 000 kJ/m²/年，而初级消费者获得 2000 kJ/m²/年，则效率为 (2000 ÷ 20 000) × 100 = 10%。这个简单的计算突出了顶级捕食者实际上能获得的能量非常少。
11. Comparing Pyramids of Numbers, Biomass and Energy | 数量、生物量与能量金字塔的比较
| Feature | Pyramid of Numbers | Pyramid of Biomass | Pyramid of Energy |
|---|---|---|---|
| What it shows | Number of individuals | Total dry mass (g/m²) | Energy content (kJ/m²/year) |
| Shape | Can be upright, inverted or irregular | Almost always upright | Always upright |
| Accuracy for energy flow | Low — does not account for size | Better — accounts for mass, but not time | Most accurate — accounts for energy loss over time |
| Limitation | Misleading when organisms vary greatly in size | Must measure dry mass; does not show rate of production | Data collection is complex and time-consuming |
Understanding the strengths and weaknesses of each type of pyramid helps you interpret ecological data correctly, which is a key skill examined in Edexcel IGCSE Biology.
了解每种金字塔的优缺点有助于你正确解读生态数据，这是爱德思 IGCSE 生物学考试中考察的一项关键技能。
12. Why Food Chains Are Short | 为什么食物链很短
The inefficiency of energy transfer is the main reason why you rarely find a food chain with more than five trophic levels. If only 10% of energy is passed on, the total energy available at the fifth trophic level is just 0.01% of what the producers originally captured. Such a tiny amount of energy cannot sustain a viable population of large predators. In addition, the loss of energy as heat at each level ensures that ecosystems are dependent on a constant input of solar energy.
能量传递的低效率是食物链很少超过五个营养级的主要原因。如果只有 10% 的能量被传递，第五营养级可用的总能量仅为生产者最初捕获能量的 0.01%。如此微小的能量无法维持一个能够存活的大型捕食者种群。此外，每个层级以热能形式损失的能量确保生态系统依赖持续不断的太阳能输入。
13. Impact of Humans on Energy Flow | 人类对能量流动的影响
Human activities can drastically alter energy flow in ecosystems. When forests are cleared for agriculture, the removal of large, long-lived producers reduces the total biomass and energy available at the base of the food web. Intensive farming, where crops are harvested and fed directly to livestock, can artificially shorten food chains, making energy transfer more efficient for human food production. However, this often comes at the cost of biodiversity and ecosystem stability.
人类活动会极大地改变生态系统中的能量流动。当森林被砍伐用于农业时，移除大量长寿的生产者减少了食物网基部的总生物量和可用能量。集约化农业中，作物被收割并直接喂养牲畜，可以人为缩短食物链，从而让人类食物生产的能量传递效率更高。然而，这往往以牺牲生物多样性和生态系统稳定性为代价。
14. Key Points for Edexcel IGCSE Examinations | 爱德思 IGCSE 考试要点
Whenever you tackle a question on energy transfer, remember to use precise terminology: producers, primary consumers, trophic levels, biomass, and efficiency. Always explain that energy is lost through respiration, heat, movement and egestion. When drawing pyramids, label each trophic level clearly and use a scale if given numerical data. Practice calculating efficiency using the formula, and be ready to suggest why a food chain might be limited to just a few levels.
每当你解答有关能量传递的问题时，记住使用准确的术语：生产者、初级消费者、营养级、生物量和效率。要始终解释能量通过呼吸、散热、运动和排遗而损失。在绘制金字塔时，清楚地标注每个营养级，如果给出了数值数据则使用比例尺。练习使用公式计算效率，并准备好解释为什么一条食物链可能只限于几个层级。
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