Energy Transfer in Ecosystems | 生态系统中的能量传递

📚 Energy Transfer in Ecosystems | 生态系统中的能量传递

All living organisms require energy to survive, grow and reproduce. In an ecosystem, energy is transferred from one organism to another through feeding relationships. This transfer starts with the Sun and flows through producers to consumers and eventually to decomposers, with a significant portion of energy being lost at each trophic level. Understanding this flow helps explain why food chains are short and why populations at higher trophic levels are relatively small.

所有生物都需要能量来生存、生长和繁殖。在生态系统中，能量通过摄食关系从一个生物体传递到另一个生物体。这种传递从太阳开始，流经生产者到消费者，最后到分解者，每个营养级都有大量能量被损耗。理解这一能量流动有助于解释为什么食物链通常很短，以及为什么更高营养级的种群数量相对较少。

1. Ecosystems and Energy Flow | 生态系统与能量流动

An ecosystem is a community of living organisms interacting with each other and their non‑living environment. All ecosystems depend on a continuous input of energy, which originates almost entirely from the Sun. Solar energy is captured by producers and converted into chemical energy stored in organic compounds. This chemical energy is then passed along the food chain as organisms consume one another.

生态系统是生物群落与周围非生物环境相互作用的系统。所有生态系统都依赖持续的能量输入，这些能量几乎全部来自太阳。生产者捕获太阳能，将其转化为储存在有机物中的化学能。当生物彼此摄食时，化学能便沿着食物链传递下去。

2. Producers – the Starting Point | 生产者——能量流动的起点

Producers are organisms that can make their own food using energy from sunlight (or, in rare cases, from chemical reactions). In most ecosystems, green plants and algae are the main producers. They carry out photosynthesis, which can be summarised as:

生产者是指能利用阳光（或在少数情况下利用化学反应能量）自己制造食物的生物。在大多数生态系统中，绿色植物和藻类是主要生产者。它们进行光合作用，概括公式为：

Carbon dioxide + Water → Glucose + Oxygen

二氧化碳 + 水 → 葡萄糖 + 氧气

Only a small percentage of the sunlight that reaches a plant is actually used in photosynthesis. The rest is reflected, transmitted or lost as heat. The chemical energy stored in the biomass of producers is the total energy available to the rest of the ecosystem.

到达植物的阳光中只有一小部分真正用于光合作用，其余的被反射、透射或作为热量散失。生产者生物质中储存的化学能是生态系统中可供其他生物使用的总能量。

3. Consumers and Trophic Levels | 消费者与营养级

Consumers are organisms that obtain energy by eating other organisms. They are classified into trophic levels according to their position in the food chain:

消费者是通过摄食其他生物来获取能量的生物。根据它们在食物链中的位置，消费者被划分为不同的营养级：

• Trophic level 1: Producers (e.g. grass, phytoplankton)

  营养级1：生产者（例如草、浮游植物）

• Trophic level 2: Primary consumers – herbivores that eat producers (e.g. rabbits, zooplankton)

  营养级2：初级消费者——以生产者为食的草食动物（例如兔子、浮游动物）

• Trophic level 3: Secondary consumers – carnivores that eat primary consumers (e.g. foxes, small fish)

  营养级3：次级消费者——以初级消费者为食的肉食动物（例如狐狸、小鱼）

• Trophic level 4: Tertiary consumers – carnivores that eat secondary consumers (e.g. eagles, sharks)

  营养级4：三级消费者——以次级消费者为食的肉食动物（例如鹰、鲨鱼）

A typical food chain rarely exceeds four or five trophic levels because the amount of available energy decreases sharply at each step.

典型的食物链很少超过四到五个营养级，因为每上升一级，可供利用的能量会显著减少。

4. The 10% Rule of Energy Transfer | 能量传递的10%法则

As energy moves from one trophic level to the next, only about 10% of the energy is transferred. The remaining 90% is lost to the environment, mainly as heat from respiration, and through uneaten parts, egestion (faeces) and excretion (urine). This general pattern is known as the 10% rule and it explains the pyramid shape of energy distribution.

当能量从一个营养级传递到下一个营养级时，只有约10%的能量被转移。剩余的90%散失到环境中，主要是呼吸作用产生的热量，以及未被食用的部分、排遗（粪便）和排泄（尿液）造成的损失。这一普遍规律被称为10%法则，它解释了能量分布呈现的金字塔形状。

For example, if producers fix 20 000 kJ m⁻² year⁻¹ of energy, primary consumers might receive only about 2 000 kJ m⁻² year⁻¹, secondary consumers about 200 kJ m⁻² year⁻¹, and tertiary consumers merely 20 kJ m⁻² year⁻¹.

例如，如果生产者每年每平方米固定20 000千焦的能量，那么初级消费者可能只获得约2 000 千焦，次级消费者约200 千焦，而三级消费者仅有约20 千焦。

5. Food Chains and Food Webs | 食物链与食物网

A food chain is a linear sequence showing the transfer of energy from one organism to another. In reality, most organisms eat more than one type of food and are eaten by several different predators, forming a complex network called a food web. Food webs provide a more accurate picture of energy flow in an ecosystem because they show multiple feeding relationships.

食物链是显示能量从一个生物体传递到另一个生物的线性序列。在现实中，大多数生物吃多种食物，并被多种捕食者取食，形成复杂的网络，称为食物网。食物网能更准确地展示生态系统中的能量流动，因为它显示了多种摄食关系。

Despite this complexity, the basic principle remains the same: energy is transferred from producers to consumers, with significant losses at every link. Disruptions to one species can affect energy flow throughout the entire web.

尽管结构复杂，基本规律依然相同：能量从生产者传递给消费者，并且每个环节都有大量损耗。一个物种的变动可能影响整个食物网中的能量流动。

6. Pyramids of Energy, Numbers and Biomass | 能量金字塔、数量金字塔和生物量金字塔

Ecologists use ecological pyramids to represent the structure of ecosystems. The three main types are pyramids of numbers, pyramids of biomass and pyramids of energy. They can be compared as follows:

生态学家使用生态金字塔来表示生态系统的结构。三种主要类型是数量金字塔、生物量金字塔和能量金字塔，对比如下：

Type of Pyramid	What it shows	Shape	Limitations	金字塔类型	显示内容	形状	局限性
Pyramid of numbers	Number of organisms at each trophic level	Can be inverted (e.g. one large tree supports many insects)	Does not account for size or mass of organisms	数量金字塔	每个营养级的生物个体数量	可能倒置（如一棵大树支撑许多昆虫）	未考虑生物的体型或质量
Pyramid of biomass	Total dry mass of organisms at each trophic level	Usually pyramid‑shaped, but can be inverted in aquatic ecosystems (e.g. phytoplankton have low biomass at a given moment)	Does not show rate of energy transfer	生物量金字塔	每个营养级生物的总干质量	通常为金字塔形，但在水生生态系统中可能倒置（如某一时刻浮游植物生物量很小）	不显示能量传递速率
Pyramid of energy	Energy content at each trophic level over a period of time	Always upright pyramid	Data can be difficult to collect	能量金字塔	一段时间内各营养级的能量含量	总是正立的金字塔	数据较难收集

The pyramid of energy is considered the most accurate representation of ecosystem structure because it shows the actual flow of energy and can never be inverted – energy always decreases at higher trophic levels.

能量金字塔被认为最能准确反映生态系统结构，因为它显示了实际的能量流动，且永远不会倒置——在更高的营养级上能量总是递减的。

7. Energy Losses in Detail | 能量损耗的详细分析

Energy is lost at every stage of a food chain for several reasons:

能量在食物链的每个阶段都会损耗，原因如下：

Not all of an organism is consumed. Bones, roots and other indigestible parts are often left uneaten, so the energy stored in them is not transferred to the next level.

并非生物体的所有部分都被食用。骨骼、根系和其他难以消化的部分常常被留下，其中的能量没有被传递到下一营养级。

Of the food that is eaten, not all is digested and absorbed. Energy is lost in faeces (egestion). In herbivores, cellulose is difficult to digest, resulting in considerable energy loss.

在被取食的食物中，并非全部被消化和吸收。能量通过粪便（排遗）流失。草食动物消化纤维素较困难，导致大量能量损耗。

A large proportion of the absorbed energy is used in respiration to release energy for movement, growth, repair and maintaining body temperature (in mammals and birds). The energy released during respiration is eventually lost to the surroundings as heat.

被吸收的能量中有很大一部分用于呼吸作用，以释放能量用于运动、生长、修复以及维持体温（哺乳动物和鸟类）。呼吸作用中释放的能量最终以热的形式散失到环境中。

Energy is also lost through excretion, mainly as urea in urine. These losses mean that only a small fraction of the original energy captured by producers is available to top predators.

能量还会通过排泄作用流失，主要是尿液中的尿素。这些损耗意味着生产者最初捕获的能量中，只有极小一部分可供顶级捕食者使用。

8. Calculating Energy Transfer Efficiency | 计算能量传递效率

To quantify how efficiently energy moves between trophic levels, ecologists calculate the percentage efficiency of energy transfer using the formula:

为了量化能量在营养级之间传递的效率，生态学家计算能量传递效率百分比，公式为：

Efficiency (%) = (Energy available to next level ÷ Energy available to previous level) × 100

效率 (%) =（下一营养级可获得的能量 ÷ 上一营养级可获得的能量）× 100

For instance, if a field of wheat (producer) contains 50 000 kJ of energy and the mice (primary consumers) feeding on it gain 5 000 kJ, the efficiency is:

例如，如果一片麦田（生产者）含有50 000千焦能量，而以它为食的老鼠（初级消费者）获得了5 000千焦能量，则效率为：

(5 000 kJ ÷ 50 000 kJ) × 100 = 10%

Efficiencies rarely exceed 20% and are often much lower. Being able to perform these calculations is an important skill in IGCSE Biology, and questions often require you to show your working.

传递效率很少超过20%，通常要低得多。能够进行此类计算是IGCSE生物学的重要技能之一，考试题往往要求写出计算步骤。

9. Why Energy Loss Shapes Ecosystems | 能量损耗如何塑造生态系统

The low efficiency of energy transfer has profound consequences for ecosystem structure. Because so little energy reaches higher trophic levels, there is less biomass that can be supported at each successive level. This is why large predators such as lions, eagles and sharks are naturally rare and require large territories to obtain sufficient energy.

能量传递的低效率对生态系统结构有深远影响。由于到达更高营养级的能量极少，每个后续级别能够支持的生物量也越来越少。这就是为什么狮子、鹰和鲨鱼等大型捕食者自然数量稀少，且需要大片领地来获取足够能量的原因。

In addition, energy loss limits the length of food chains. The tiny amount of energy available beyond the fourth trophic level is generally insufficient to support an additional breeding population of consumers. Understanding energy flow also helps us appreciate why eating at lower trophic levels – consuming producers or primary consumers – is more energy‑efficient and can support a larger human population.

此外，能量损耗限制了食物链的长度。超过第四营养级后，微弱的能量通常不足以支撑另一个消费者繁殖种群。理解能量流动也有助于我们认识到，在较低营养级进食（食用生产者或初级消费者）更为节能，可以养活更多人口。

10. Human Impact on Energy Flow | 人类活动对能量流动的影响

Human activities can dramatically alter energy flow in ecosystems. For example, agriculture replaces diverse food webs with simplified monocultures, channelling more energy directly from producers to humans. However, this can reduce biodiversity and make ecosystems more vulnerable to pests and diseases. Overfishing removes top predators, disrupting pyramids and sometimes leading to population explosions of lower trophic level species. Climate change further influences energy flow by altering the rates of photosynthesis and respiration in producers.

人类活动可以显著改变生态系统中的能量流动。例如，农业用单一的种植方式取代多样化的食物网，使更多能量直接从生产者流向人类。然而，这会降低生物多样性，使生态系统更易遭受病虫害。过度捕捞会移除顶级捕食者，破坏金字塔结构，有时导致低营养级物种数量激增。气候变化通过改变生产者的光合作用和呼吸速率，进一步影响了能量流动。

Sustainable practices aim to maintain natural energy flows and ecosystem resilience. This includes protecting keystone species, restoring habitats and choosing food from lower trophic levels to reduce overall energy loss from the food system.

可持续实践旨在维持自然能量流动和生态系统恢复力，包括保护关键物种、恢复栖息地以及选择低营养级的食物，以减少食物系统中总体的能量损耗。

11. Exam Technique for Energy Transfer Questions | 能量传递考题解题技巧

When tackling IGCSE Edexcel Biology questions on this topic, keep these tips in mind:

在解答IGCSE爱德思生物学有关本题的考试时，请牢记以下技巧：

Always use the terms ‘producer’, ‘primary consumer’, ‘secondary consumer’ and ‘tertiary consumer’ precisely. Refer to ‘trophic levels’ rather than just ‘levels’. When explaining energy losses, mention specific processes such as respiration, egestion, excretion and uneaten parts – do not simply write ‘energy is lost as heat’.

要准确使用“生产者”“初级消费者”“次级消费者”“三级消费者”等术语。用“营养级”而不仅是“层次”。在解释能量损耗时，要提及具体的过程，如呼吸作用、排遗、排泄和未被食用的部分——不要只写“能量以热的形式散失”。

For calculations, always show your working. Write the formula first, substitute the numbers and then calculate. Include units (kJ) and a percentage sign where appropriate. In evaluation questions, link energy losses to pyramid shapes and food chain length. Use the 10% rule as a benchmark but recognise that real efficiencies vary.

计算题一定要写出步骤。先写公式，代入数字后再计算。附上单位（千焦）和百分号。在评估类问题中，要将能量损耗与金字塔形状和食物链长度联系起来。以10%法则为基准，但要认识到实际效率会有差异。

12. Summary of Key Points | 重点总结

Energy enters ecosystems through producers carrying out photosynthesis. Only about 10% of energy is transferred from one trophic level to the next; the rest is lost through respiration, egestion, excretion and uneaten material. This low efficiency explains why food chains rarely have more than four or five trophic levels and why pyramids of energy are always upright. Understanding energy transfer not only helps you answer exam questions accurately but also reveals the delicate balance that sustains life on Earth.

能量经由生产者进行光合作用进入生态系统。大约仅10%的能量从一个营养级传递到下一级；其余通过呼吸作用、排遗、排泄和未被取食的物质流失。这种低效率解释了为什么食物链很少超过四到五个营养级，以及为什么能量金字塔总是正立的。理解能量传递不仅能帮助你准确答题，还揭示了维持地球生命的精妙平衡。

Published by TutorHao | Science Revision Series | aleveler.com

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