📚 4.6.3 Energy Transfer in Ecosystems | 生态系统中的能量传递
All organisms need energy to survive, grow and reproduce. In an ecosystem, this energy flows from the Sun through producers to consumers, but not all of it is transferred efficiently. Understanding how energy moves between trophic levels helps explain why most food chains are short and why pyramids of biomass are a more accurate representation of feeding relationships than pyramids of numbers. This article covers the key concepts required for Edexcel IGCSE Science, including trophic levels, pyramids of biomass, energy losses and calculations of transfer efficiency.
所有生物都需要能量才能生存、生长和繁殖。在生态系统中，能量从太阳经生产者流至消费者，但并非全部能量都能高效传递。理解能量在营养级之间如何流动，有助于解释为什么大多数食物链都很短，以及为什么生物量金字塔比数量金字塔更能准确表示摄食关系。本文涵盖Edexcel IGCSE科学所要求的关键概念，包括营养级、生物量金字塔、能量损失以及传递效率的计算。
1. The Flow of Energy in Ecosystems | 生态系统中的能量流动
Energy enters ecosystems as sunlight. Producers (plants and algae) capture a small fraction of this light energy during photosynthesis and convert it into chemical energy stored in their tissues. The chemical energy is then passed along food chains as organisms feed on one another. Unlike nutrients that can be recycled, energy flows in one direction and is eventually lost as heat to the environment.
能量以阳光的形式进入生态系统。生产者（植物和藻类）在光合作用中捕获一小部分光能，并将其转化为储存在组织中的化学能。当生物彼此捕食时，化学能沿着食物链传递。与可以循环利用的营养物质不同，能量是单向流动的，并最终以热量的形式散失到环境中。
2. Food Chains and Food Webs | 食物链与食物网
eat more than one type of food, so food webs give a more complete picture by linking many food chains together. Arrows in a food chain represent the direction of energy and biomass flow – from the eaten to the eater.
食物链展示一种简单的线性摄食关系，例如草 → 兔 → 狐狸。实际上，大多数生物不止吃一种食物，因此食物网通过连接多条食物链而给出更完整的图景。食物链中的箭头表示能量和生物量流动的方向——从被食者指向捕食者。
3. Trophic Levels | 营养级
Each step in a food chain is called a trophic level. Producers occupy trophic level 1. Primary consumers (herbivores) are at trophic level 2. Secondary consumers (carnivores that eat herbivores) are at trophic level 3, and tertiary consumers are at trophic level 4. Decomposers break down dead matter at every level, recycling nutrients but not passing energy along the chain.
食物链中的每一步都称为一个营养级。生产者占据第一营养级；初级消费者（食草动物）为第二营养级；次级消费者（捕食食草动物的食肉动物）为第三营养级；三级消费者为第四营养级。分解者在各个营养级分解死亡有机质，回收养分，但不沿着食物链传递能量。
4. Pyramids of Numbers | 数量金字塔
A pyramid of numbers shows the count of organisms at each trophic level. The bars are drawn to scale, with producers at the base. While these pyramids can be drawn easily, they are not always pyramid shaped: a single large tree can support thousands of insects, producing an inverted pyramid. Therefore, pyramids of numbers do not always give a reliable picture of the food chain's structure.
数量金字塔展示各营养级生物的个体数目。柱状图按比例绘制，生产者位于底部。虽然这种金字塔易于画出，但形状并不总是金字塔形：一棵大树能支撑成千上万只昆虫，从而形成倒置的金字塔。因此，数量金字塔并不总能可靠地表现食物链的结构。
5. Pyramids of Biomass | 生物量金字塔
Biomass is the total dry mass of living material at a trophic level. Pyramids of biomass generally have a classic pyramid shape because the mass of producers is usually greater than the mass of herbivores, which in turn is greater than the mass of carnivores. To draw a pyramid of biomass, the bar for each trophic level is drawn in proportion to its biomass (e.g. g/m²). These pyramids give a more accurate representation of energy content in each level.
生物量是指某一营养级中活生物体的总干质量。生物量金字塔通常呈经典的金字塔形状，因为生产者的质量一般大于食草动物的质量，而食草动物的质量又大于食肉动物的质量。绘制生物量金字塔时，每一营养级的柱状条按其生物量（例如克/平方米）的比例画出。这些金字塔能更准确地反映各营养级的能量含量。
6. Why Energy is Lost Between Trophic Levels | 为什么能量在营养级之间损失
Not all the energy consumed by a trophic level is available to the next level. Energy is lost in several ways: through respiration (released as heat), through movement, through uneaten body parts (bones, fur) and through waste products (faeces, urine). Typically, only about 10% of the energy is transferred from one trophic level to the next.
某一营养级摄入的能量并非全部可供下一营养级使用。能量的损失有多种途径：通过呼吸作用（以热量形式释放）、通过运动、通过未被食用的身体部分（骨骼、毛皮）以及通过排泄物（粪便、尿液）。通常只有约10%的能量从一个营养级传递到下一个营养级。
7. The 10 Percent Rule | 百分之十法则
The '10% rule' states that, on average, about 10% of the energy stored in biomass at one trophic level is converted into biomass at the next level. The remaining 90% is used for life processes or lost as heat. This low efficiency limits the length of food chains – rarely do they exceed four or five trophic levels because there is not enough energy left to support another level.
“百分之十法则”指出，平均而言，一个营养级中储存于生物量中的能量大约只有10%转化为下一营养级的生物量。其余90%用于维持生命过程或以热量形式损失。这种低效率限制了食物链的长度——食物链很少超过四到五个营养级，因为剩余的能量不足以再支撑一个营养级。
8. Calculating Energy Transfer Efficiency | 计算能量传递效率
The efficiency of energy transfer between two trophic levels can be calculated using the following formula:
Efficiency (%) = (energy transferred to next level ÷ energy available at previous level) × 100%
onsumed by rabbits and 800 kJ becomes rabbit biomass, the efficiency is (800 ÷ 8000) × 100% = 10% perform similar calculations in your IGCSE exam using data provided in tables or diagrams.
两个营养级之间的能量传递效率可用以下公式计算：
效率（%）=（传递至下一级的能量 ÷ 上一级的可用能量）× 100%
例如，如果兔子摄取了8000千焦的草的能量，其中有800千焦转化为兔子的生物量，那么效率就是（800 ÷ 8000）× 100% = 10%。在IGCSE考试中，你可能会被要求利用表格或图表提供的数据进行类似的计算。
9. Pyramid of Energy | 能量金字塔
A pyramid of energy shows the amount of energy at each trophic level, usually in units of kJ/m²/year. Because energy flows obey the laws of thermodynamics, a pyramid of energy is always upright. The bars must be drawn to scale, and the pyramid never inverts. This is considered the most accurate way to represent trophic structure and energy flow.
能量金字塔显示每个营养级所含的能量，通常以千焦/平方米/年为单位。由于能量流动遵循热力学定律，能量金字塔始终是正立的。柱状条需按比例绘制，且金字塔绝不会倒置。这被认为是表示营养结构与能量流动的最准确方式。
10. Efficiency in Farming and Food Production | 农业与食物生产中的效率
Humans can improve energy transfer efficiency in food production. Reducing the number of trophic levels – for example, eating plants directly rather than feeding them to livestock – wastes less energy. Farmers also reduce energy losses in livestock by restricting animal movement and keeping them warm, so less energy is used for respiration and more is converted to biomass (meat, milk).
人类可以在食物生产中提高能量传递效率。减少营养级的数目——例如，直接食用植物而非用植物喂养牲畜——可以减少能量浪费。农民还通过限制牲畜的活动并为其保暖来减少能量损失，从而使更少的能量用于呼吸、更多的能量转化为生物量（肉、奶）。
11. The Role of Decomposers in Energy Flow | 分解者在能量流动中的作用
Decomposers (bacteria, fungi) break down dead organisms and waste, releasing the remaining chemical energy as heat through respiration. While they return mineral ions to the soil for producers to reuse, they do not transfer energy back into the food chain. Instead, they ensure that energy flow ends, while matter cycles. This is why a continuous input of sunlight is essential for most ecosystems.
分解者（细菌、真菌）分解死去的生物体和废物，通过呼吸作用将残留的化学能以热量形式释放出去。它们虽然将矿物质离子送回土壤供生产者再利用，但并不会将能量传回食物链。相反，它们使能量流动终结，而物质则循环不已。这就是为什么对于大多数生态系统来说，持续的阳光输入至关重要。
12. Key Points to Remember for the Exam | 考试重点记忆
ass are usually pyramid shaped, while pyramids of numbers can be odd shaped. Only about 10% late efficiency using the formula: (energy in next level ÷ energy in previous level) × 100% decomposers break down organic matter but do not transfer energy to higher trophic levels.
阳光几乎是所有食物链能量的最终来源。食物链中的箭头表示能量流动。生物量金字塔通常呈金字塔形，而数量金字塔可能形状不规则。营养级之间只有约10%的能量能够传递。能量以热量、运动、排泄物和未被食用的部分等形式损失。你必须会用公式（下一营养级能量 ÷ 上一营养级能量）× 100% 来计算效率。最后，分解者分解有机物质，但不会将能量传递给更高的营养级。
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