📚 Feeding Relationships and Energy Flow in Ecosystems | 生态系统的摄食关系与能量流动
All organisms need energy to survive, grow and reproduce. This energy enters most ecosystems through sunlight captured by producers during photosynthesis. From there, it flows through a series of feeding levels, known as trophic levels, passing from one organism to another via food chains and webs. Understanding these relationships helps us see how energy is transferred and lost at each stage, and why ecosystems can only support a limited number of top predators.
所有生物都需要能量来生存、生长和繁殖。在大多数生态系统中，这种能量通过生产者利用光合作用捕获阳光而进入。从那里开始，它流经一系列营养级，通过食物链和食物网从一个生物体传递到另一个生物体。理解这些关系有助于我们了解能量在每个阶段如何传递和损失，以及为什么生态系统只能支撑有限数量的顶级捕食者。
1. Producers, Consumers and Decomposers | 生产者、消费者和分解者
Producers are organisms that make their own food using energy from sunlight (or in some cases from chemical reactions). On land, the main producers are green plants; in oceans and freshwater, algae and phytoplankton are the key producers. They are also called autotrophs.
生产者是利用阳光（或在某些情况下利用化学反应）的能量自己制造食物的生物。在陆地上，主要生产者是绿色植物；在海洋和淡水中，藻类和浮游植物是关键的生产者。它们也被称为自养生物。
Consumers are organisms that cannot make their own food and must obtain energy by eating other organisms. They are called heterotrophs. Primary consumers feed on producers; secondary consumers eat primary consumers; tertiary consumers eat secondary consumers, and so on.
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。它们被称为异养生物。初级消费者取食生产者；次级消费者吃初级消费者；三级消费者吃次级消费者，依此类推。
Decomposers, mainly bacteria and fungi, break down dead organisms and waste materials, releasing nutrients back into the soil. These nutrients are then absorbed by plants, completing the cycle of matter. They are essential for recycling nutrients.
分解者主要是细菌和真菌，它们分解死去的生物和排泄物，将营养物质释放回土壤中。这些营养物质随后被植物吸收，完成物质循环。它们对于养分回收至关重要。
2. Food Chains and Food Webs | 食物链和食物网
hat eats it, representing the direction of energy flow. For example: grass → rabbit → fox.
食物链是一个简单的线性图，显示能量从一个生物体传递到另一个生物体。食物链中的每个箭头都从被吃的生物指向吃它的生物，代表了能量流动的方向。例如：草 → 兔 → 狐。
A food web is a network of interconnected food chains. It gives a more realistic picture of feeding relationships within an ecosystem, showing that most organisms eat more than one type of food and are eaten by more than one type of predator. Food webs help stabilise ecosystems because if one species declines, consumers can switch to other food sources.
食物网是由相互连接的食物链组成的网络。它更真实地展示了生态系统内的摄食关系，表明大多数生物不只吃一种食物，也不止被一种捕食者吃掉。食物网有助于稳定生态系统，因为如果某一物种数量下降，消费者可以转向其他食物来源。
3. Trophic Levels and Pyramids of Numbers | 营养级与数量金字塔
A trophic level is the position an organism occupies in a food chain. Producers occupy the first trophic level, primary consumers the second, secondary consumers the third, and so on. It is rare to find more than four or five trophic levels in a chain because energy becomes too limited.
营养级是生物在食物链中所处的位置。生产者占据第一营养级，初级消费者占据第二，次级消费者占据第三，依此类推。很少在一条链中发现超过四五个营养级，因为能量变得过于有限。
A pyramid of numbers represents the number of organisms at each trophic level in a food chain. The width of each bar is proportional to the number of individuals. Typically, the bar for producers is widest, and the bars get narrower as you go up. However, in some ecosystems, like a single oak tree supporting many insects, the pyramid may appear inverted, but the biomass pyramid usually corrects this.
数量金字塔表示食物链中每个营养级的生物数量。每个条形图的宽度与个体数量成正比。通常，生产者的条形最宽，越往上越窄。然而，在某些生态系统中，例如一棵橡树养活许多昆虫，金字塔可能看起来是倒置的，但生物量金字塔通常会纠正这一点。
4. Pyramids of Biomass and Energy | 生物量与能量金字塔
Biomass is the total mass of living material at a trophic level. A pyramid of biomass shows the dry mass of organisms at each level, usually taking a sample, drying it, and weighing it. Since biomass decreases at each stage, these pyramids are almost always upright pyramids, providing a more reliable picture than pyramids of numbers.
生物量是一个营养级中生物体的总质量。生物量金字塔显示每个营养级的干质量，通常通过取样、干燥并称重得出。由于生物量在每一阶段都会减少，这些金字塔几乎总是正金字塔，比数量金字塔更可靠。
A pyramid of energy shows the total energy stored in the organisms at each trophic level per unit area per year. It is even more accurate because it accounts for the energy lost through respiration, waste and uneaten parts. Energy pyramids are always upright and never inverted.
能量金字塔显示每年每单位面积每个营养级生物体储存的总能量。它更为精确，因为它考虑了通过呼吸、排泄物和未食用部分所损失的能量。能量金字塔总是正立的，从不倒置。
5. Energy Transfer and Loss Between Trophic Levels | 营养级之间的能量传递与损失
Only about 10% of the energy in one trophic level is passed on to the next. The rest is lost in various ways: much is used for respiration and released as heat; some is not eaten (e.g. bones, roots); some is egested as faeces and passes to decomposers; and some is lost in urine and other excretory products.
大约只有 10% 的能量从一个营养级传递到下一个营养级。其余的能量以各种方式损失：大量用于呼吸并以热的形式释放；一些未被食用（例如骨头、根）；一些随粪便排出并进入分解者；还有一些随尿液和其他排泄物损失。
Because so much energy is lost at each step, food chains rarely extend beyond four or five trophic levels. There is simply not enough energy left to support another level of consumers. This also explains why there are fewer top predators in an ecosystem than herbivores.
由于每一步能量损失极大，食物链很少超过四五个营养级。剩下的能量根本不足以支持下一级消费者。这也解释了为什么生态系统中的顶级捕食者数量远少于食草动物。
6. Efficiency of Energy Transfer | 能量传递效率
The efficiency of energy transfer between trophic levels can be calculated using the formula:
Efficiency (%) = (Energy in higher trophic level ÷ Energy in lower trophic level) × 100
ry consumers that feed on them store 1,200 kJ, the efficiency is (1200 ÷ 10000) × 100 = 12%. Edexcel IGCSE questions often ask you to interpret data and calculate such efficiencies.
能量传递效率可以使用以下公式计算：
效率 (%) = (较高营养级的能量 ÷ 较低营养级的能量) × 100
例如，如果植物储存了 10,000 kJ 的能量，而以它们为食的初级消费者储存了 1,200 kJ，则效率为 (1200 ÷ 10000) × 100 = 12%。Edexcel IGCSE 试题经常要求你解读数据并计算这种效率。
In agricultural systems, farmers aim to reduce energy losses to increase the efficiency of meat or milk production. They might keep animals indoors to minimise movement (reducing respiration loss) or feed them high-energy diets to limit the energy wasted on digestion.
在农业系统中，农民旨在减少能量损失，以提高肉类或奶类生产的效率。他们可能会将动物圈养在室内以减少活动（从而减少呼吸损失），或给它们喂食高能量饲料以减少用于消化的能量浪费。
7. Carbon Cycle and the Role of Feeding Relationships | 碳循环与摄食关系的作用
Feeding relationships are a vital part of the carbon cycle. Carbon is an essential element in all living things, found in carbohydrates, proteins, fats and nucleic acids. The main processes moving carbon through the ecosystem include:
摄食关系是碳循环的重要组成部分。碳是所有生物体中必不可少的元素，存在于碳水化合物、蛋白质、脂肪和核酸中。推动碳在生态系统中移动的主要过程包括：
Photosynthesis: Plants remove CO₂ from the atmosphere and convert it into organic carbon compounds.
光合作用：植物从大气中去除 CO₂，并将其转化为有机碳化合物。
Feeding: When consumers eat plants or other animals, the carbon compounds are passed along the food chain.
取食：当消费者吃掉植物或其他动物时，碳化合物沿食物链传递。
Respiration: All living organisms respire, releasing CO₂ back into the atmosphere.
呼吸作用：所有生物都进行呼吸，将 CO₂ 释回大气中。
Decomposition: When organisms die, decomposers break down their bodies and release CO₂ through respiration.
分解作用：当生物死亡时，分解者分解它们的尸体，通过呼吸作用释放 CO₂。
Combustion: Burning of fossil fuels releases stored carbon back into the atmosphere.
燃烧：燃烧化石燃料会将储存的碳释放回大气中。
Thus, the flow of carbon in an ecosystem depends directly on feeding relationships and decomposition.
因此，生态系统中碳的流动直接取决于摄食关系和分解作用。
8. Investigating Populations and Energy Flow Using Quadrats | 使用样方调查种群与能量流动
Biologists often use quadrats (square frames of known area) to estimate the population size of plants or slow-moving animals in a habitat. By taking random samples, they can calculate the population density and total biomass of producers and primary consumers, allowing estimations of energy flow.
生物学家经常使用样方（已知面积的正方形框架）来估算栖息地中植物或行动缓慢的动物的种群数量。通过随机取样，他们可以计算出生产者和初级消费者的种群密度及总生物量，从而估算能量流动。
For Edexcel IGCSE, you should know how to calculate population size per unit area:
total population = (Mean count per quadrat ÷ Area of each quadrat) × Total area of habitat
daisies. This data can then be used to estimate biomass and energy stored in that trophic level.
对于 Edexcel IGCSE，你应该知道如何计算单位面积的种群数量：
估算总种群 = (每个样方平均数量 ÷ 样方面积) × 栖息地总面积
例如，如果一个 1 m² 样方中雏菊的平均数量为 12，而田野面积为 800 m²，则雏菊总种群估算值为 (12 ÷ 1) × 800 = 9600 株雏菊。这些数据随后可用于估算该营养级的生物量和储存的能量。
9. Human Impact on Feeding Relationships and Energy Flow | 人类对摄食关系和能量流动的影响
Human activities such as deforestation, overfishing, and pollution can disrupt feeding relationships. Removing a top predator (e.g. through hunting) can cause an increase in prey populations, which may then overgraze producers and destabilise the entire ecosystem. The introduction of invasive species can also alter food webs dramatically.
诸如森林砍伐、过度捕捞和污染等人类活动可能会扰乱摄食关系。移除顶级捕食者（例如通过捕猎）可能导致猎物数量增加，进而可能过度啃食生产者，破坏整个生态系统的稳定。引入入侵物种也可能极大地改变食物网。
Eutrophication, covered in the Edexcel syllabus, is another consequence of human activity: excess fertilisers wash into water bodies, causing algal blooms. When algae die, decomposers multiply and use up oxygen, leading to the death of fish and other aquatic consumers.
Edexcel 大纲中涉及的富营养化是人类活动的另一个后果：过量的肥料冲刷进入水体，引起藻类大量繁殖。当藻类死亡时，分解者迅速增殖并消耗氧气，导致鱼类和其他水生消费者的死亡。
Conservation efforts, such as establishing marine protected areas or reintroducing native species, aim to restore natural feeding relationships and maintain balanced energy flow.
保护行动，如建立海洋保护区或重新引入本土物种，旨在恢复自然的摄食关系并维持平衡的能量流动。
10. Key Terms and Exam Tips | 关键术语与应试技巧
Make sure you can define and apply these terms in Edexcel IGCSE Biology Paper 1 and Paper 2:
确保你能在 Edexcel IGCSE 生物试卷 1 和试卷 2 中定义和应用这些术语：
Population: all the organisms of one species living in a habitat.
种群：生活在同一栖息地中的某一物种的所有个体。
Community: all the populations of different species living together in a habitat.
群落：生活在同一栖息地中的所有不同物种种群的集合。
Ecosystem: the community of organisms and the non-living (abiotic) components of their environment.
生态系统：生物群落与其环境中非生物（非生命）成分的总体。
Producer, consumer, decomposer, trophic level, food chain, food web, biomass.
生产者、消费者、分解者、营养级、食物链、食物网、生物量。
n energy-flow questions, remember to show your working clearly. Use tables to present data on numbers, biomass and energy. Be prepared to explain why pyramids of biomass and energy are more reliable than pyramids of numbers.
在绘制食物链时，一定要标明生物并使用正确方向的箭头（→）从食物指向取食者。在有关能量流动的问题中，记得清楚展示你的计算过程。使用表格来展示数量、生物量和能量数据。准备好解释为什么生物量金字塔和能量金字塔比数量金字塔更可靠。
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