📚 GCSE WJEC Biology: Food Chains – Key Points | GCSE WJEC 生物：食物链 考点精讲
Food chains and food webs are fundamental concepts in GCSE WJEC Biology, illustrating how energy and nutrients flow through ecosystems. Understanding these relationships is crucial for tackling questions about energy transfer, trophic levels, pyramids of number and biomass, and the effects of human activities on the environment.
食物链和食物网是 GCSE WJEC 生物学的核心概念，它们展示了能量和营养物质如何在生态系统中流动。理解这些关系对于回答有关能量传递、营养级、数量金字塔和生物量金字塔以及人类活动对环境的影响等问题至关重要。
1. Introduction to Food Chains | 食物链简介
A food chain is a linear sequence that shows how energy and nutrients are transferred from one organism to another through feeding. The arrows in a food chain always point from the food source to the consumer, indicating the direction of energy flow.
食物链是一个线性序列，展示了能量和营养物质如何通过摄食在生物之间传递。食物链中的箭头总是从食物指向消费者，表示能量流动的方向。
Every food chain begins with a producer, which is typically a green plant or alga that captures light energy from the Sun during photosynthesis to make glucose. All other organisms in the chain depend on this initial energy input.
每条食物链都从生产者开始，生产者通常是绿色植物或藻类，它们在光合作用过程中捕获太阳光能并制造葡萄糖。链中所有其他生物都依赖于这一初始的能量输入。
2. Producers, Consumers and Decomposers | 生产者、消费者和分解者
Producers are autotrophic organisms that convert light energy into chemical energy, forming the base of every food chain. In terrestrial ecosystems, plants are the dominant producers, while in aquatic systems, algae and phytoplankton play this role.
生产者是自养生物，能将光能转化为化学能，构成每条食物链的基础。在陆地生态系统中，植物是主要的生产者，而在水生系统中，藻类和浮游植物扮演这一角色。
Consumers are heterotrophic organisms that obtain energy by feeding on other organisms. Primary consumers (herbivores) eat producers, secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers. Omnivores feed at multiple trophic levels.
消费者是异养生物，通过捕食其他生物获得能量。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。杂食动物在多个营养级上取食。
Decomposers such as bacteria and fungi break down dead organic matter, returning nutrients to the soil for producers to reuse. Without decomposers, essential elements would remain locked in dead bodies and wastes.
分解者如细菌和真菌分解死去的有机物，将营养物质归还到土壤中供生产者重新利用。如果没有分解者，必需的元素将一直被锁在尸体和排泄物中。
3. Trophic Levels | 营养级
A trophic level describes the position an organism occupies in a food chain. Level 1 is always the producer, Level 2 is the primary consumer, Level 3 the secondary consumer, and so on. Omnivores can occupy more than one trophic level depending on their diet.
营养级描述生物在食物链中所处的位置。第 1 级总是生产者，第 2 级是初级消费者，第 3 级是次级消费者，以此类推。杂食动物根据其饮食可占据多个营养级。
ass is trophic level 1, the grasshopper is level 2, the frog is level 3, and the hawk is level 4 (tertiary consumer).
在典型的草地食物链中：草 → 蚱蜢 → 青蛙 → 鹰，草是第 1 营养级，蚱蜢是第 2 级，青蛙是第 3 级，鹰是第 4 级（三级消费者）。
Energy transfer between trophic levels is inefficient; on average, only about 10% of the energy stored in one level is passed on to the next. The rest is lost as heat through respiration, used for movement, or remains in waste products.
营养级之间的能量传递效率很低；平均只有约 10% 的能量从一个营养级传递到下一个营养级。其余能量通过呼吸作用以热的形式散失，用于运动，或存留在排泄物中。
4. Energy Flow and Energy Loss | 能量流动与能量损耗
All energy in a food chain originally comes from the Sun. Producers absorb only a small fraction (about 1-3%) of the sunlight that reaches them and convert it into chemical energy via photosynthesis.
食物链中的所有能量最初都来自太阳。生产者只吸收了到达它们的一小部分阳光（约 1-3%），并通过光合作用将其转化为化学能。
When a consumer eats, not all the chemical energy in the food is assimilated. Some is lost in faeces, some is used in respiration to release energy for heat and movement, and only a small proportion becomes new biomass.
当消费者进食时，食物中的化学能并非全部被同化。部分能量随粪便流失，部分在呼吸作用中被用于释放热量和运动，只有一小部分转化为新的生物量。
The energy transfer efficiency between trophic levels can be calculated using the following equation:
营养级之间的能量传递效率可以用以下公式计算：
Energy transfer efficiency (%) = (Energy in new biomass ÷ Energy consumed) x 100
rass and only 500 kJ becomes new rabbit biomass, the efficiency is (500 ÷ 5000) x 100 = 10%. This explains why food chains rarely have more than four or five trophic levels.
例如，如果一只兔子从草中摄取了 5000 kJ 能量，而只有 500 kJ 成为新的兔子生物量，那么效率为 (500 ÷ 5000) x 100 = 10%。这就解释了为什么食物链很少超过四到五个营养级。
5. Pyramids of Number and Biomass | 数量金字塔和生物量金字塔
Ecologists use pyramids to represent the numbers or biomass of organisms at each trophic level. A pyramid of number shows the population size of each species, while a pyramid of biomass shows the total dry mass of living tissue at each level.
生态学家使用金字塔来表示各营养级的生物数量或生物量。数量金字塔显示每个物种的种群大小，而生物量金字塔显示每个营养级生物组织的总干重。
Pyramids of number can sometimes be inverted, for example, when one large tree (producer) supports many insects (primary consumers). Pyramids of biomass are almost always upright because the total mass of producers is typically greater than that of herbivores.
数量金字塔有时会倒置，例如一棵大树（生产者）供养许多昆虫（初级消费者）。生物量金字塔几乎总是正立的，因为生产者的总质量通常大于食草动物的总质量。
| Feature 特征 | Pyramid of Numbers 数量金字塔 | Pyramid of Biomass 生物量金字塔 |
|---|---|---|
| Shows 显示 | Number of organisms per trophic level 每个营养级的生物数量 | Dry mass of organisms per trophic level 每个营养级生物干重 |
| Shape 形状 | Can be upright or inverted 可正立或倒置 | Nearly always upright 几乎总是正立 |
| Example 示例 | Oak tree → aphids → ladybirds 橡树 → 蚜虫 → 瓢虫 | Phytoplankton → zooplankton → fish 浮游植物 → 浮游动物 → 鱼类 |
In an aquatic ecosystem, the biomass pyramid can sometimes appear inverted in a quick snapshot because phytoplankton have a very high turnover rate. However, over a whole year, the total biomass of producers still exceeds that of consumers.
在水生生态系统中，由于浮游植物的周转速率非常高，在某个快速快照中，生物量金字塔有时可能看起来是倒置的。然而，在整年的时间尺度上，生产者的总生物量仍然超过消费者。
6. Bioaccumulation and Biomagnification | 生物累积与生物放大
Bioaccumulation refers to the build-up of a toxic substance in the tissues of an organism when it absorbs the substance faster than it can excrete or break it down. Persistent pesticides like DDT are classic examples.
生物累积是指当生物吸收有毒物质的速度快于其排泄或分解速度时，有毒物质在生物组织内的积累。DDT 等持久性杀虫剂是典型的例子。
Biomagnification is the increasing concentration of a toxin at successively higher trophic levels in a food chain. Because consumers eat many organisms from the level below, the toxin becomes more concentrated in their bodies, reaching dangerous levels in top predators.
生物放大是指毒素在食物链中随着营养级上升而浓度不断增加的现象。由于消费者吃掉了许多低营养级的生物，毒素在其体内变得更加浓缩，在顶级捕食者中可达危险水平。
osprey, DDT concentration can increase from 0.000003 ppm in water to 25 ppm in the osprey's tissues, which can cause eggshell thinning and reproductive failure.
例如，在水生生态系统中：水 → 浮游生物 → 小鱼 → 大鱼 → 鱼鹰，DDT 浓度可从水中的 0.000003 ppm 增加到鱼鹰组织中的 25 ppm，这会导致蛋壳变薄和繁殖失败。
7. Predator-Prey Relationships | 捕食者-猎物关系
The numbers of predators and prey in a community are closely linked and often show cyclical fluctuations. When prey numbers increase, the predator population also rises after a time lag because more food is available.
一个群落中捕食者和猎物的数量紧密相连，经常表现出周期性波动。当猎物数量增加时，由于有更多食物可用，捕食者种群数量在经历一段时滞后也会上升。
As predators increase, they consume more prey, causing the prey population to decline. This then leads to a decrease in the predator population due to food shortage, allowing prey numbers to rise again. This creates a repeating cycle.
随着捕食者数量增加，它们会吃掉更多猎物，导致猎物种群下降。随后由于食物短缺，捕食者数量减少，使得猎物数量再次上升。这就形成了一个重复的循环。
Graphs of predator-prey relationships typically show two waves, with the predator peak following the prey peak. This lag is due to the time needed for reproduction and population growth in response to increased food supply.
捕食者-猎物关系的图表通常显示两条波状曲线，捕食者的高峰跟随猎物高峰。这种滞后是由于繁殖和种群增长以响应食物供应增加需要时间。
8. Food Webs and Interdependence | 食物网与相互依赖
A food web is a network of interconnected food chains, giving a more realistic picture of feeding relationships within an ecosystem. Most animals feed on more than one organism, so a change in one species can affect many others.
食物网是相互连接的食物链网络，更真实地反映了生态系统中的捕食关系。大多数动物以多种生物为食，因此一个物种的变化可能影响许多其他物种。
Organisms in a food web are interdependent, meaning that the population size of one species depends on the population sizes of the other species it interacts with. Removing or adding a species can have knock-on effects throughout the web.
Published by TutorHao | GCSE Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图