📚 KS3 CIE Food Chains and Food Webs: Mark Scheme Essentials | KS3 CIE 食物链与食物网：评分标准要点
This revision guide breaks down how KS3 CIE examiners award marks on food chains and food webs. It explains the exact wording, arrow direction, energy transfer rules, and common mistakes that decide whether you gain or lose marks. Use it alongside past paper questions to train your answers to match the mark scheme.
本复习指南拆解 KS3 CIE 考官在食物链与食物网题目中的评分方式。它解释准确的措辞、箭头方向、能量传递规则以及决定得分或失分的常见错误。结合历年真题使用本指南，训练你的答案符合评分标准。
1. Understanding the Command Words | 理解指令词
CIE KS3 questions use command words such as 'state', 'describe', 'explain', 'suggest' and 'complete'. 'State' requires a short fact, 'describe' requires what happens, 'explain' requires a reason, usually linked with 'because'. 'Suggest' asks for a sensible scientific idea, even if the exact case is unfamiliar.
CIE KS3 题目使用 'state'、'describe'、'explain'、'suggest' 和 'complete' 等指令词。'state' 需要一个简短事实，'describe' 需要描述发生什么，'explain' 需要给出原因，通常用 'because' 连接。'suggest' 要求提出合理的科学想法，即使具体情境不熟悉。
- State: one word or short phrase, no explanation.
- 描述：一个词或短语，不需要解释。
- Describe: say what is shown or what happens.
- 描述：说明显示了什么或发生了什么。
- Explain: give a scientific reason, often using 'because'.
- 解释：给出科学原因，通常使用 'because'。
- Complete: fill in missing names or arrows using given information.
- 补全：用所给信息填写缺失的名称或箭头。
2. Core Definitions and Acceptable Terms | 核心定义与可接受术语
Mark schemes award marks for correct scientific vocabulary. You must know the exact meaning of producer, consumer, herbivore, carnivore, omnivore, decomposer, predator, prey, food chain, food web and trophic level. Spelling must be close enough to recognise, but key biological words should be accurate.
评分标准给使用正确科学词汇的答案打分。你必须准确掌握生产者、消费者、草食动物、肉食动物、杂食动物、分解者、捕食者、猎物、食物链、食物网和营养级的含义。拼写必须足以辨认，但关键生物词汇应准确。
| Term | Meaning | Mark scheme note |
| Producer | Organism that makes its own food, usually by photosynthesis. | Accept 'plant' only if context is clear. |
| Consumer | Organism that eats other organisms for energy. | Do not accept 'eats plants' for all consumers. |
| Decomposer | Organism that breaks down dead material and waste. | Usually bacteria or fungi. |
中文释义：生产者是通常通过光合作用制造自身食物的生物。消费者是捕食其他生物获取能量的生物。分解者是分解死亡物质和废物的生物，通常是细菌或真菌。
3. Arrow Direction in Food Chains | 食物链中的箭头方向
rabbit → grass, the mark is not awarded because energy does not flow from rabbit to grass.
食物链中的箭头表示能量传递的方向。它必须从被吃的生物指向吃它的生物。例如：草 → 兔 → 狐狸。如果你画成兔 → 草，则不能得分，因为能量不会从兔流向草。
grass → rabbit → fox
草 → 兔 → 狐狸
The mark scheme may also say 'arrows must point in the direction of energy flow'. Never use an equals sign or a dash in place of an arrow.
评分标准还可能说明 '箭头必须指向能量流动的方向'。切勿用等号或破折号代替箭头。
4. Constructing Food Chains from Data | 根据数据构建食物链
You may be given a table listing organisms and what they eat. Start with a producer, then use the food source column to connect each consumer to its prey. Write the names in one line separated by arrows. Do not include decomposers in a feeding chain unless the question specifically asks about decay.
题目可能给出一个列出生物及其食物的表格。先从生产者开始，然后利用食物来源栏将每个消费者与其猎物连接起来。将名称写成一行，用箭头分隔。除非题目特别问到腐烂过程，否则不要将分解者写入捕食链。
. If the table also includes a fungus, it is a decomposer and must stay outside the chain.
示例数据：草被兔吃；兔被狐狸吃。食物链为草 → 兔 → 狐狸。如果表格还包括真菌，它是分解者，必须留在食物链之外。
5. Interpreting Food Webs | 解读食物网
A food web is made of several food chains linked together. Mark schemes test whether you can identify a producer, a primary consumer, a secondary consumer, an organism with two prey species, or what happens if one species is removed. Always follow the direction of the arrows.
食物网由多条相互连接的食物链组成。评分标准考查你是否能识别生产者、初级消费者、次级消费者、具有两种猎物的生物，或当某物种被移除时会发生什么。始终沿着箭头方向阅读。
he thrush is both a secondary consumer and a tertiary consumer in different chains. Removing snails would reduce food for thrushes, so thrush numbers may decrease.
例如，食物网显示：植物 → 蜗牛 → 画眉 → 鹰，以及植物 → 蚜虫 → 瓢虫 → 画眉，那么画眉在不同食物链中既是次级消费者又是三级消费者。移除蜗牛会减少画眉的食物，因此画眉数量可能下降。
6. Energy Transfer and Energy Loss | 能量传递与能量损失
Only about 10% of energy passes from one trophic level to the next. Most energy is lost as heat from respiration, movement, undigested food, and waste. This explains why food chains rarely have more than five trophic levels. In an 'explain' answer, write: energy is lost, so less energy is available to the next level.
只有约 10% 的能量从一个营养级传递到下一级。大部分能量以呼吸产热、运动、未消化食物和排泄物的形式散失。这就解释了为什么食物链很少超过五个营养级。在 'explain' 题中应写：能量被散失，因此可供下一营养级使用的能量更少。
A model answer: 'Energy is lost at each trophic level through respiration, heat and uneaten parts, so the top consumer receives too little energy to support another level.' This earns both energy loss and consequence marks.
参考答案：'能量在每一营养级通过呼吸作用、产热和未食用部分而散失，因此顶级消费者获得的能量太少，不足以支持更上一级。' 这样可同时获得能量散失和结果两个得分点。
7. Trophic Levels and Feeding Roles | 营养级与摄食角色
Trophic levels are feeding positions in a chain. Level 1 is the producer, level 2 is the primary consumer, level 3 is the secondary consumer, and level 4 is the tertiary consumer. Mark schemes may ask you to label these levels or place organisms in a pyramid of numbers or biomass.
营养级是食物链中的摄食位置。第 1 级是生产者，第 2 级是初级消费者，第 3 级是次级消费者，第 4 级是三级消费者。评分标准可能要求你标注这些营养级，或将生物放入数量金字塔或生物量金字塔中。
Pyramid of biomass is almost always pyramid-shaped because biomass decreases at higher trophic levels. Pyramid of numbers can be irregular if one large producer supports many small consumers, so read the data carefully.
生物量金字塔几乎总是呈金字塔形，因为生物量在较高营养级会减少。数量金字塔可能不规则，例如一株大型生产者养活许多小型消费者，因此要仔细阅读数据。
8. Common Misconceptions and Mark Deductions | 常见误区与扣分点
Examiners regularly deduct marks for the same mistakes. Common errors include: drawing the arrow the wrong way; writing 'plants eat sunlight' instead of 'producers make food by photosynthesis'; calling a decomposer a consumer; saying energy is 'lost' without saying how; and confusing predator with prey.
考官经常因相同错误扣分。常见错误包括：箭头方向画反；写 '植物吃阳光' 而不是 '生产者通过光合作用制造食物'；称分解者为消费者；只说能量 '损失' 而不说明方式；以及混淆捕食者与猎物。
- Wrong: rabbit → grass. Right: grass → rabbit.
- 错误：兔 → 草。正确：草 → 兔。
- Wrong: 'sunlight gives energy to plants by eating.' Right: 'plants absorb light energy for photosynthesis.'
- 错误：'阳光通过被吃给植物能量。' 正确：'植物吸收光能进行光合作用。'
- Wrong: 'energy disappears.' Right: 'energy is transferred to the surroundings as heat.'
- 错误：'能量消失。' 正确：'能量以热的形式传递到周围环境。'
9. Sample Mark Scheme Table | 示例评分标准表
This table shows how CIE style mark schemes allocate marks in short answer questions. Use it to check whether your answer would receive full credit.
下表展示 CIE 风格评分标准如何在简答题中给分。用它检查你的答案是否能获得满分。
| Question | Acceptable answer | Not acceptable / deduction |
| Name the producer in this chain. | Grass / plant. | Rabbit; 'tree' only if context wrong. |
| Explain why arrows point in one direction. | They show the direction of energy flow. | 'They show who is stronger' earns no mark. |
| Give one reason why food chains are short. | Energy is lost between levels, so too little remains for more levels. | 'Animals get full' or 'there are not enough animals'. |
中文译文：问题：指出该链中的生产者。可接受答案：草 / 植物。不可接受：兔；如果情境错误，'树' 也不可接受。问题：解释箭头为何指向一个方向。可接受答案：它们显示能量流动的方向。不可接受：'它们显示谁更强' 不得分。问题：给出食物链较短的一个原因。可接受答案：能量在营养级之间损失，因此剩余能量不足以支持更多营养级。不可接受：'动物吃饱了' 或 '动物数量不够'。
10. Exam Technique for 4-6 Mark Questions | 4-6 分题作答技巧
For longer questions, write in full sentences but keep each point on one line or as a clear step. Include a scientific term + a linking word + a consequence. Example: 'The hawk population would decrease because there is less food from mice, so fewer hawks can survive.'
对于较长题目，用完整句子书写，但每一点写在一行或作为一个清晰步骤。包含科学术语 + 连接词 + 结果。示例：'鹰的数量会减少，因为来自鼠类的食物减少，因此能存活的鹰更少。'
If the question says 'explain the effect of removing rabbits from this food web', write two or three linked effects: fewer rabbits means less food for foxes, so foxes decrease; more grass may grow, so other herbivores may increase. Each linked cause and effect can earn a separate mark.
如果题目说 '解释从该食物网中移除兔子的影响'，写出两到三个关联影响：兔子减少意味着狐狸食物减少，因此狐狸减少；草可能长得更多，因此其他草食动物可能增加。每个关联的因果都可以单独得分。
11. Checkpoint Style Practice and Answers | Checkpoint 风格练习与答案
Try this short practice question. The mark scheme style answer is given below.
尝试下面的简短练习题。下方给出评分标准式答案。
s → ladybirds. A gardener removes all slugs. Explain two possible effects on the food web.
问题：一个花园食物网包含生菜 → 蛞蝓 → 青蛙，以及生菜 → 蚜虫 → 瓢虫。园丁清除了所有蛞蝓。解释对食物网可能产生的两种影响。
Mark scheme: any two from: frogs decrease because less food from slugs; lettuces increase because fewer slugs eat them; aphids may decrease if ladybirds switch to eating them; ladybirds are unaffected because they eat aphids not slugs.
评分标准：以下任选两点：青蛙减少，因为来自蛞蝓的食物减少；生菜增多，因为吃它们的蛞蝓减少；如果瓢虫转而捕食蚜虫，蚜虫可能减少；瓢虫不受影响，因为它们吃蚜虫而不吃蛞蝓。
Writing 'frogs will die because no food' earns only one effect if no second mark. 'Slugs removed so frogs increase' is incorrect and earns zero because frogs lose a food source.
写 '青蛙会因为没有食物而死' 如果没有第二点，则只能得一个影响分。写 '移除蛞蝓所以青蛙增加' 是错误的，得零分，因为青蛙失去了一个食物来源。
12. Final Checklist Before the Test | 考前最终检查清单
Before you finish an answer, check: arrow direction, producer at the start, correct use of consumer levels, pyramid labels, energy loss explanation, and spelling of key words. This final scan often recovers several marks.
完成答案前，检查：箭头方向、起点为生产者、消费者营养级使用正确、金字塔标注、能量损失解释和关键词拼写。这一最后检查通常能挽回好几分。
- Does every arrow point from food to eater?
- 每个箭头是否从食物指向取食者？
- Have I written 'energy is lost as heat', not just 'energy is lost'?
- 我是否写了 '能量以热的形式散失'，而不只是 '能量损失'？
- Have I used producer and consumer terms instead of only animal names?
- 我是否使用了生产者和消费者等术语，而不仅仅是动物名称？
- If a question asks for two effects, have I given two separate linked effects?
- 如果题目要求两个影响，我是否给出了两个独立的关联影响？
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