Energy Flow in Ecosystems | 生态系统中的能量流动

📚 Energy Flow in Ecosystems | 生态系统中的能量流动

Energy flow in ecosystems describes how energy is transferred from one organism to another through feeding relationships. All energy in most ecosystems originally comes from the Sun. Producers, mainly green plants and algae, capture light energy during photosynthesis and convert it into chemical energy stored in organic compounds. As consumers eat producers or other consumers, energy passes along food chains and food webs. However, at each trophic level, a large proportion of energy is lost through respiration, movement, heat and undigested material. This loss limits the length of food chains and shapes the structure of ecological communities. Understanding energy flow is fundamental to ecology and is a key topic in the IGCSE Edexcel Biology specification.

生态系统中的能量流动描述能量如何通过摄食关系从一个生物传递到另一个生物。大多数生态系统的能量最初都来自太阳。生产者，主要是绿色植物和藻类，通过光合作用捕捉光能，并将其转化为储存在有机化合物中的化学能。当消费者以生产者或其他消费者为食时，能量沿着食物链和食物网传递。然而，在每个营养级，很大一部分能量通过呼吸作用、运动、散热和未消化的物质而损失。这种损失限制了食物链的长度，并塑造了生态群落的结构。理解能量流动是生态学的基础，也是IGCSE Edexcel生物学考试中的核心主题。

1. The Sun as the Ultimate Energy Source | 太阳是最终的能量来源

Almost all ecosystems on Earth depend on energy from the Sun. Light energy travels through space and reaches the Earth’s surface. Only a small fraction of this solar energy is captured by producers during photosynthesis. Green plants and algae contain chlorophyll, a pigment that absorbs sunlight and uses its energy to combine carbon dioxide and water into glucose and oxygen. The glucose molecules store chemical potential energy, which becomes available to other organisms when they eat the plant material.

地球上几乎所有的生态系统都依赖来自太阳的能量。光能穿过太空到达地球表面。只有一小部分太阳能在光合作用过程中被生产者捕捉。绿色植物和藻类含有叶绿素，这种色素吸收阳光，并利用其能量将二氧化碳和水转化为葡萄糖和氧气。葡萄糖分子储存化学势能，当其他生物吃下植物材料时，这些能量就变得可用。

In some deep-sea ecosystems, such as hydrothermal vents, there is no sunlight. Here, chemosynthetic bacteria use energy from chemical reactions involving hydrogen sulfide to produce organic matter. This is an exception that is not part of the main IGCSE syllabus, but it is useful to know that energy can also enter ecosystems from chemical sources. For most terrestrial and aquatic ecosystems, however, the Sun is the driver of all energy flow.

在一些深海生态系统中，比如热液喷口，没有阳光。在这些环境中，化学合成细菌利用涉及硫化氢的化学反应产生的能量来制造有机物。这是一个例外，不属于IGCSE主要教学大纲，但知道能量也可以从化学来源进入生态系统是有帮助的。然而，对于大多数陆地和淡水生态系统来说，太阳是所有能量流动的驱动力。

2. Producers and Photosynthesis | 生产者与光合作用

Producers are organisms that make their own food using energy from the environment. In most ecosystems, producers are photoautotrophs – they use light energy to build organic molecules. The overall equation for photosynthesis is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. The glucose produced can be used immediately for respiration, stored as starch, or converted into other organic compounds such as cellulose and proteins. Only about 1% to 3% of the light energy falling on a leaf is actually converted into chemical energy; the rest is reflected, transmitted or lost as heat.

生产者是利用环境中的能量自己制造食物的生物。在大多数生态系统中，生产者是光能自养生物——它们利用光能来构建有机分子。光合作用的总方程式为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。产生的葡萄糖可以立即用于呼吸作用，以淀粉形式储存，或转化为其他有机化合物，如纤维素和蛋白质。实际上，照在叶片上的光能中只有大约1%到3%被转化为化学能；其余的被反射、透射或以热的形式散失。

In the IGCSE Edexcel exam, you may be asked to explain why the biomass of producers is greater than that of primary consumers. One key reason is the inefficiency of energy capture during photosynthesis. Only a small proportion of light energy becomes fixed in biomass, so the base of the food chain must be large to support higher trophic levels.

在IGCSE Edexcel考试中，你可能会被要求解释为什么生产者的生物量大于初级消费者。一个关键原因是光合作用过程中能量捕获的效率低下。只有一小部分光能被固定为生物量，因此食物链的基座必须足够大才能支撑更高的营养级。

3. Food Chains and Trophic Levels | 食物链和营养级

A food chain shows the linear pathway of energy transfer from one organism to another. Each step in a food chain is called a trophic level. Producers occupy the first trophic level. Primary consumers (herbivores) that eat producers occupy the second trophic level. Secondary consumers (carnivores that eat herbivores) occupy the third trophic level, and so on. Decomposers, such as bacteria and fungi, break down dead organisms and waste, returning nutrients to the soil, but they are not usually included in the main trophic level structure when calculating energy flow.

食物链展示了能量从一个生物传递到另一个生物的线性途径。食物链中的每一步称为一个营养级。生产者占据第一营养级。以生产者为食的初级消费者（食草动物）占据第二营养级。以食草动物为食的次级消费者（食肉动物）占据第三营养级，依此类推。分解者，如细菌和真菌，分解死去的生物和废物，将养分送回土壤，但在计算能量流动时，它们通常不被包括在主要的营养级结构中。

A typical exam question might ask you to identify the trophic levels of different organisms in a food chain or to draw arrows showing the direction of energy flow. Remember, the arrow points from the organism being eaten to the organism that eats it, showing the direction of energy transfer.

典型的考题可能要求你找出食物链中不同生物的营养级，或画出表示能量流动方向的箭头。记住，箭头从被食用的生物指向吃它的生物，表示能量传递的方向。

4. Energy Losses Between Trophic Levels | 营养级之间的能量损失

Not all the energy stored in one trophic level is passed on to the next. A large amount of energy is lost at each transfer. The main reasons for this loss include:

Respiration – organisms use energy for movement, growth, repair and maintaining body temperature (in mammals and birds). This energy is eventually lost as heat.
Uneaten parts – some parts of organisms, such as bones, roots or woody stems, are not consumed by the next trophic level.
Excretion and egestion – energy is lost in urine and faeces. Undigested material contains chemical energy that is passed to decomposers rather than to the next consumer.
Heat loss – metabolic processes release thermal energy, which dissipates into the environment.

并非某一营养级中储存的所有能量都传递到下一级。在每次传递中，大部分能量都会损失。造成这种损失的主要原因包括：

呼吸作用——生物用能量进行运动、生长、修复和维持体温（哺乳动物和鸟类）。这些能量最终以热的形式散失。
未被吃掉的部分——生物的某些部分，如骨骼、根或木质茎，不会被下一营养级吃掉。
排泄和排遗——能量通过尿液和粪便损失。未消化的物质含有化学能，传递给分解者而非下一个消费者。
热散失——新陈代谢过程释放热能，散失到环境中。

Because of these losses, only a small percentage of energy (typically about 10%) is transferred from one trophic level to the next. This inefficiency explains why most food chains have no more than four or five trophic levels.

由于这些损失，从一个营养级传递到下一个营养级的能量只有很小的百分比（通常约为10%）。这种低效率解释了为什么大多数食物链不超过四五个营养级。

5. The 10% Rule of Energy Transfer | 能量传递的10%规则

The ten percent rule is a simple way of estimating energy transfer efficiency between trophic levels. It states that, on average, only about 10% of the energy stored in one trophic level is converted into biomass in the next trophic level. The remaining 90% is lost through the processes listed above. In reality, the efficiency can vary between 5% and 20%, but for IGCSE questions, you should use 10% as a working estimate unless specific data is given.

百分之十规则是估算营养级之间能量传递效率的一种简单方法。它指出，平均而言，一个营养级中储存的能量只有大约10%被转化为下一营养级的生物量。剩下的90%通过上述过程损失。实际上，效率可在5%到20%之间变化，但在IGCSE考试中，除非有具体数据，否则你应使用10%作为估算值。

Using this rule, you can calculate the relative amounts of energy at each level. For example, if 10,000 kJ of energy is fixed by producers, then primary consumers could incorporate about 1,000 kJ, secondary consumers about 100 kJ, and tertiary consumers only about 10 kJ. This drastic decrease helps you understand why top predators are rare and require large territories.

利用这一规则，你可以计算每个营养级的能量相对值。例如，如果生产者固定了10,000千焦能量，那么初级消费者可同化约1,000千焦，次级消费者约100千焦，三级消费者仅约10千焦。这种急剧下降有助于理解为什么顶级捕食者数量稀少且需要广阔的领地。

6. Pyramids of Energy: Always Upright | 能量金字塔：永远为正立

A pyramid of energy shows the amount of energy present at each trophic level over a given period (usually one year or a growing season), measured in kJ m⁻² yr⁻¹. The bars are drawn with a width proportional to the energy content. Because energy is always lost between trophic levels, the pyramid of energy is always upright – each bar is smaller than the one below it. There are no inverted pyramids of energy in nature.

能量金字塔显示了在特定时期内（通常为一年或一个生长季）每个营养级的能量含量，单位为千焦每平方米每年。条形图的宽度与能量含量成正比。由于能量在不同营养级之间总是损失，能量金字塔总是正立的——每一个柱条都比它下面的柱条短。自然界不存在倒置的能量金字塔。

Energy pyramids provide the most accurate picture of energy flow because they account for the rate of production and avoid the distortions that can occur in pyramids of numbers or biomass. The IGCSE exam may require you to interpret or sketch an energy pyramid, so practise drawing a three-level pyramid with labelled axes and units.

能量金字塔提供了能量流动最准确的图景，因为它们考虑了生产速率，并能避免数量金字塔或生物量金字塔中可能出现的失真。IGCSE考试可能要求你解读或绘制能量金字塔，因此要练习绘制带有标注坐标轴和单位的三层金字塔。

7. Pyramids of Numbers and Biomass | 数量金字塔和生物量金字塔

Besides energy pyramids, ecologists also construct pyramids of numbers and pyramids of biomass. A pyramid of numbers shows the count of organisms at each trophic level. It can be upright, inverted, or partially inverted, depending on the ecosystem. For example, a single large tree (producer) can support many insects (primary consumers), resulting in an inverted pyramid of numbers. A pyramid of biomass shows the dry mass of living material at each trophic level, usually in g m⁻² or kg m⁻². Most biomass pyramids are upright, but there are exceptions, such as in aquatic ecosystems where the biomass of phytoplankton may be less than that of zooplankton at a given moment due to rapid production and consumption.

除了能量金字塔，生态学家还构建数量金字塔和生物量金字塔。数量金字塔显示每个营养级的生物个体数。它可以呈正立、倒置或部分倒置，视生态系统而定。例如，一棵大树（生产者）可以支持许多昆虫（初级消费者），导致数量金字塔倒置。生物量金字塔显示每个营养级活物质的干重，单位通常为克每平方米或千克每平方米。大多数生物量金字塔是正立的，但也有例外，例如在水生生态系统中，由于浮游植物的快速生产和消耗，在某一特定时刻浮游植物的生物量可能少于浮游动物的生物量。

For IGCSE Edexcel, you should know how to compare these three types of pyramids. The pyramid of energy is the most reliable and is always upright. The pyramid of numbers can change shape easily, and the pyramid of biomass can occasionally be inverted, but the energy pyramid never is.

对于IGCSE Edexcel，你需要知道如何比较这三种金字塔。能量金字塔是最可靠的，始终为正立。数量金字塔的形状容易变化，生物量金字塔偶尔可能倒置，但能量金字塔永远不会倒置。

8. Why Food Chains Are Short | 为什么食物链很短

Most natural food chains consist of only four or five trophic levels. The main limiting factor is the inefficiency of energy transfer. At each step, around 90% of energy is lost. By the fourth or fifth trophic level, very little energy remains to support another level. A longer chain would mean that the top predator receives so little energy that it could not survive. Thus, energy loss restricts the length of food chains.

大多数自然食物链只有四五个营养级。主要限制因素是能量传递的低效率。在每一步中，约90%的能量会损失。到第四或第五营养级时，剩下的能量非常少，不足以支撑另一个营养级。更长的食物链意味着顶级捕食者获得的能量极少，以至于无法生存。因此，能量损失限制了食物链的长度。

This principle also explains why top carnivores such as lions or eagles are less numerous than herbivores. They require a large area of habitat to obtain enough energy. Human activities that shorten food chains (e.g., eating plants directly rather than feeding them to animals first) can feed more people because less energy is wasted.

这一原理也解释了为什么狮子或鹰等顶级食肉动物比食草动物数量少。它们需要大片栖息地才能获得足够的能量。人类缩短食物链的活动（例如，直接食用植物而不是先把它喂给动物）可以养活更多人，因为浪费的能量更少。

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

A common IGCSE question asks you to calculate the efficiency of energy transfer between two trophic levels. The formula is:

Efficiency (%) = (Energy in higher trophic level ÷ Energy in lower trophic level) × 100

IGCSE考试常见的一道题是要求计算两个营养级之间的能量传递效率。公式为：

效率 (%) = （较高营养级的能量 ÷ 较低营养级的能量） × 100

For instance, if producers contain 20,000 kJ and primary consumers contain 2,000 kJ, the efficiency is (2,000 / 20,000) × 100 = 10%. Always make sure the units match (e.g., kJ m⁻² yr⁻¹). You might also be given a table of energy values and asked to draw a pyramid of energy or complete missing values. Keep a calculator handy and show your working clearly.

例如，如果生产者含有20,000千焦能量，初级消费者含有2,000千焦，那么效率为 (2,000 / 20,000) × 100 = 10%。务必确保单位一致（例如，千焦每平方米每年）。你可能会面对一个能量数值表，并被要求画出能量金字塔或填充缺失值。准备好计算器，并清楚地展示演算过程。

10. Energy Flow in Food Webs and Ecosystem Stability | 食物网中的能量流动与生态系统稳定性

A food web is a network of interconnected food chains. It shows multiple feeding relationships and gives a more realistic picture of energy flow in an ecosystem. In a food web, an organism can occupy more than one trophic level depending on its diet. Energy still flows from producers to various consumers, but the pathways are complex. If one species declines, others may switch their food source, making the ecosystem more stable.

食物网是相互连接的食物链网络。它展示多种摄食关系，能更真实地反映生态系统中的能量流动。在食物网中，一种生物根据其食谱可能占据不止一个营养级。能量仍然从生产者流向各类消费者，但途径复杂。如果一个物种数量下降，其他物种可能会转而取食别的食物，从而使生态系统更加稳定。

However, energy losses still apply at every feeding link. The total energy available to top predators is determined by the overall productivity of the base of the web. A reduction in producer biomass, whether due to deforestation or pollution, can have cascading effects throughout the food web.

然而，能量损失在每一条摄食联结中仍然适用。顶级捕食者可用的总能量由食物网基础的整体生产力决定。生产者生物量的减少，无论是由于砍伐森林还是污染，都可能在整个食物网中产生级联效应。

11. Human Impact on Energy Flow and Agriculture | 人类对能量流动的影响与农业

Humans can manipulate energy flow to increase food production. In intensive agriculture, farmers try to reduce energy losses by eliminating pests, providing optimum nutrients, and controlling the diet of livestock. For example, keeping animals indoors in warm conditions reduces heat loss, so more energy goes into growth. Pesticides reduce crop destruction, so more energy is available for human consumption. However, these methods require energy inputs (fossil fuels for heating, transport, fertilisers) and can have environmental costs.

人类可以调控能量流动来增加食物产量。在集约农业中，农民试图通过消灭害虫、提供最佳养分和控制牲畜饮食来减少能量损失。例如，在温暖的条件下把动物关在室内可以减少散热，这样更多的能量就用于生长。杀虫剂减少了作物的破坏，因此有更多能量可供人类消费。然而，这些方法需要能量投入（用于加热、运输、肥料的化石燃料），并可能带来环境代价。

Educated consumers can also make choices that use energy more efficiently. Eating at lower trophic levels – that is, consuming more plant-based foods and less meat – reduces the number of inefficient energy transfers between the Sun and the human diet. This concept often appears in IGCSE questions about sustainability and global food supply.

受过教育的消费者也可以做出更有效利用能量的选择。在低营养级进食——也就是说，多吃植物性食物、少吃肉——可以减少太阳到人类饮食之间低效的能量传递次数。这个概念经常在IGCSE有关可持续性和全球粮食供应的问题中出现。

12. Key IGCSE Exam Tips and Common Mistakes | IGCSE考试重点提示与常见错误

When answering energy flow questions, remember these points:

Always specify that energy is lost as heat during respiration, not just ‘lost’.
Use the correct units: energy is measured in joules (kJ, kJ m⁻² yr⁻¹), biomass in g or kg per unit area.
Do not confuse pyramids: only the pyramid of energy is always upright.
In calculation questions, show the formula and substitution steps to gain method marks even if the final answer is slightly off.
Avoid stating that energy is ‘destroyed’. Energy cannot be created or destroyed, only transferred and transformed.

在回答能量流动相关问题时，请记住以下几点：

始终明确能量在呼吸过程中以热能形式损失，而不只是说“损失”了。
使用正确单位：能量以焦耳为单位（千焦、千焦每平方米每年），生物量以每单位面积的克或千克为单位。
不要混淆金字塔：只有能量金字塔总是正立的。
在计算题中，展示公式和代入步骤，即使最终答案稍有偏差也能获得方法分。
避免说能量“被毁灭”。能量不能被创造或毁灭，只能被转移和转化。

Finally, practise past paper questions on energy flow, food chains, pyramids and efficiency calculations. The topic is always tested, and a clear understanding of the ten percent rule together with the reasons for energy loss will help you score high marks.

最后，练习有关能量流动、食物链、金字塔和效率计算的往年真题。这个主题总是会考，清楚理解百分之十规则以及能量损失的原因将有助于你获得高分。

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Energy Flow in Ecosystems | 生态系统中的能量流动