📚 Why Species Become Extinct: CIE KS3 Mark Scheme Guide | 物种为何灭绝：CIE KS3 评分标准指南
This revision guide explains the main reasons why species become extinct and shows how CIE KS3 Science mark schemes expect you to answer extinction questions. It covers natural and human causes, key vocabulary, model answers and common mistakes.
本复习指南解释物种灭绝的主要原因，并展示 CIE KS3 科学评分标准希望你如何回答灭绝相关问题。内容涵盖自然原因、人为原因、关键术语、标准答案和常见错误。
1. What Extinction Means | 什么是灭绝
Extinction occurs when every individual of a species dies and no living members remain anywhere on Earth. In CIE KS3 Science, a species is considered extinct when there are no breeding individuals left to produce new offspring.
灭绝是指某个物种的所有个体都死亡，地球上不再有存活成员。在 CIE KS3 科学中，当一个物种没有能够繁殖后代的个体时，即被认为已经灭绝。
Extinction is different from being endangered. An endangered species still has living individuals, but its population is very small and it is likely to become extinct if the threats continue. Mark schemes often test whether you can use the words ‘extinct’ and ‘endangered’ accurately.
灭绝不同于濒危。濒危物种仍有存活个体，但种群数量非常少，如果威胁继续存在，就很可能灭绝。评分标准经常考查你能否准确使用“灭绝”和“濒危”这两个词。
| Term | Meaning |
| Extinct | No living individuals of the species remain. |
| Endangered | Very few individuals remain; the species is at risk of extinction. |
术语：灭绝——物种没有存活个体。濒危——物种存活个体极少，面临灭绝风险。
2. Natural Causes of Extinction | 自然原因导致的灭绝
Some species became extinct long before humans existed. Natural events such as volcanic eruptions, asteroid impacts, sudden climate shifts and disease can kill large numbers of organisms in a short time.
有些物种早在人类出现之前就已经灭绝。火山爆发、小行星撞击、气候突变和疾病等自然事件可以在短时间内杀死大量生物。
A natural cause becomes a cause of extinction when the species cannot adapt quickly enough to the change. If the environment changes faster than the species can evolve, the population may decline until no individuals remain.
当物种无法足够快地适应变化时，自然原因就会导致灭绝。如果环境变化的速度超过物种进化的速度，种群数量可能会下降，直到没有个体存活。
Mark schemes usually accept natural causes such as ‘volcanic eruption’, ‘asteroid impact’, ‘disease’ or ‘climate change’ provided you explain that the species could not survive or adapt. Simply naming the event may gain only one mark.
评分标准通常接受“火山爆发”“小行星撞击”“疾病”或“气候变化”等自然原因，但前提是你解释了物种无法生存或适应。只说出事件名称可能只能得 1 分。
3. Human Causes: Habitat Loss | 人为原因：栖息地丧失
Habitat loss is the most common reason mark schemes ask about when discussing human-caused extinction. Humans destroy habitats through deforestation, farming, building roads, mining and draining wetlands.
栖息地丧失是评分标准在讨论人为灭绝时最常问到的原因。人类通过砍伐森林、耕种、修建道路、采矿和排干湿地等活动破坏栖息地。
When a habitat is destroyed, organisms lose their food sources, shelter and breeding sites. Many individuals die, and the remaining population may become too small to reproduce successfully. Eventually the species can become extinct.
当栖息地遭到破坏时，生物会失去食物来源、庇护所和繁殖场所。许多个体会死亡，剩下的种群可能因数量太少而无法成功繁殖，最终可能导致物种灭绝。
A strong mark scheme answer links habitat loss to a specific effect. For example: ‘Deforestation removes trees that provide food and nesting sites, so the species cannot find enough food or a safe place to breed, leading to a fall in population and possible extinction.’
高分的评分标准答案会将栖息地丧失与具体影响联系起来。例如：“砍伐森林移除了提供食物和筑巢场所的树木，因此物种无法找到足够的食物或安全的繁殖地点，导致种群数量下降并可能灭绝。”
4. Human Causes: Hunting and Poaching | 人为原因：捕猎与偷猎
Hunting and poaching can drive species to extinction when more individuals are killed than can be replaced by reproduction. Poaching means hunting illegally, often for valuable body parts such as ivory, fur or horns.
当被捕杀的个体数量超过繁殖所能补充的数量时，捕猎和偷猎就可能导致物种灭绝。偷猎是指非法捕猎，通常是为了获取象牙、皮毛或角等有价值的身体部位。
Some species have been hunted for food, sport or traditional medicine. The dodo and passenger pigeon are often used as examples of species that were hunted to extinction, although habitat changes also played a role.
有些物种因食物、运动或传统医药而被猎杀。渡渡鸟和旅鸽常被用作被猎杀至灭绝的例子，尽管栖息地变化也起了作用。
In an exam answer, you should state that overhunting removes too many individuals, especially breeding adults. This reduces the population faster than new individuals are born, so the species cannot maintain its numbers.
在考试答案中，你应该说明过度捕猎会移除太多个体，尤其是繁殖期的成年个体。这使得种群减少的速度超过新个体出生的速度，因此物种无法维持其数量。
5. Human Causes: Pollution | 人为原因：污染
Pollution can poison organisms directly or damage their food, water and habitats. Chemicals from farms, factories and vehicles enter ecosystems through air, water and soil.
污染可以直接毒害生物，或破坏它们的食物、水和栖息地。来自农场、工厂和车辆的化学物质通过空气、水和土壤进入生态系统。
Pesticides may kill insects that other animals rely on for food. Oil spills coat animals and reduce their ability to move, feed or keep warm. Plastic waste can be eaten by animals and block their digestive systems. All these effects can reduce survival and reproduction.
杀虫剂可能杀死其他动物赖以生存的昆虫。石油泄漏会覆盖动物身体，降低它们移动、进食或保暖的能力。塑料废物可能被动物吞食并堵塞其消化系统。所有这些影响都会降低生存率和繁殖率。
Mark schemes often award a mark for naming a type of pollution and a second mark for explaining how it harms the species. Avoid vague phrases like ‘pollution harms animals’; instead write ‘chemical waste poisons the water, so fish die’.
评分标准通常会给说出污染类型 1 分，再给解释它如何伤害物种 1 分。避免使用“污染伤害动物”这样模糊的表述；而要写“化学废物毒化水体，使鱼类死亡”。
6. Climate Change and Extinction | 气候变化与灭绝
Climate change alters temperature, rainfall patterns and sea levels. Many species are adapted to specific conditions, so even a small change can make their habitat unsuitable.
气候变化会改变温度、降雨模式和海平面。许多物种适应特定的环境条件，因此即使是很小的变化也可能使它们的栖息地变得不适宜。
For example, rising temperatures can cause coral bleaching, where corals lose the algae they depend on for food and die. Warmer seas may also force fish to move to cooler water, leaving predators without food.
例如，气温升高会导致珊瑚白化，珊瑚失去赖以生存的藻类而死亡。海水变暖还可能迫使鱼类迁移到较冷的水域，使捕食者失去食物来源。
Some species can migrate to new areas, but many cannot move fast enough or have nowhere suitable to go. If they cannot adapt or migrate, climate change can lead to extinction.
有些物种可以迁移到新的区域，但许多物种无法足够快地移动，或没有合适的地方可去。如果它们无法适应或迁移，气候变化就可能导致灭绝。
A mark scheme answer should link climate change to a specific environmental change, such as drought, flooding, rising sea level or temperature increase, and then explain how this affects the species.
评分标准答案应将气候变化与具体的环境变化联系起来，例如干旱、洪水、海平面上升或气温升高，然后解释这如何影响物种。
7. Competition and Invasive Species | 竞争与入侵物种
A species may become extinct if a new competitor, predator or disease enters its habitat. Invasive species are organisms introduced by humans into areas where they do not naturally live.
如果新的竞争者、捕食者或疾病进入其栖息地，物种可能灭绝。入侵物种是由人类引入到其非自然分布区域的生物。
Invasive species can eat native species, compete with them for food and shelter, or spread diseases. Island species are especially vulnerable because they often have no defences against new predators.
入侵物种可以捕食本地物种、与其争夺食物和庇护所，或传播疾病。岛屿物种尤其脆弱，因为它们通常没有抵御新捕食者的能力。
In an exam answer, name the invasive species, explain what it does and describe the effect on the native species. For example: ‘Rats introduced to an island eat bird eggs, so fewer chicks hatch and the bird population falls.’
在考试答案中，要说出入侵物种的名称，解释它做了什么，并描述对本地物种的影响。例如：“引入岛屿的老鼠吃掉鸟蛋，因此孵化的雏鸟减少，鸟类数量下降。”
8. Extinction Is a Natural Process | 灭绝是自然过程吗
Extinction has happened throughout Earth’s history, and it is a natural part of evolution. Many species that once lived are now extinct because they could not compete or adapt to changing conditions.
灭绝在地球历史上一直发生，是进化的自然组成部分。许多曾经存在的物种现已灭绝，因为它们无法竞争或适应变化的环境。
However, scientists agree that the current rate of extinction is much higher than the natural background rate. Most of this increase is caused by human activities, which is why the topic appears so often in KS3 mark schemes.
然而，科学家一致认为当前的灭绝速度远高于自然背景灭绝速度。这种加速主要由人类活动造成，这也是该主题经常出现在 KS3 评分标准中的原因。
When a question asks whether extinction is natural, a good answer says that extinction can be natural, but human activities are making it happen much faster. This balanced statement often earns full marks.
当题目问灭绝是否是自然过程时，好的答案是：灭绝可以是自然过程，但人类活动使其发生速度大大加快。这种平衡的表述通常能得满分。
9. How Mark Schemes Award Marks | 评分标准如何给分
CIE KS3 Biology mark schemes usually use a points-based system. For a three-mark question on extinction, one mark is often for identifying a cause, a second for explaining how it affects the species, and a third for linking this to survival or reproduction.
CIE KS3 生物学评分标准通常采用分点给分。对于灭绝相关的 3 分题，通常 1 分给识别原因，1 分给解释它如何影响物种，1 分给将其与生存或繁殖联系起来。
Look carefully at the command word. ‘State’ only needs a short fact. ‘Describe’ needs a more detailed account of what happens. ‘Explain’ requires reasons and cause-and-effect links.
仔细看指令词。“State”只需要简短事实。“Describe”需要更详细地描述发生了什么。“Explain”需要给出原因和因果联系。
| Command word | What you must do |
| State | Give a short answer, often one word or phrase. |
| Describe | Say what happens in detail, but no reasons needed. |
| Explain | Give reasons and say why something happens. |
指令词：State——给出简短答案；Describe——详细说明发生了什么；Explain——给出原因，说明为什么发生。
10. Model Answers for Common Questions | 常见题型的标准答案
Here is a common KS3 extinction question: ‘Explain two ways human activities can cause a species to become extinct.’ This question is worth four marks, two for each way.
这是一个常见的 KS3 灭绝题：“解释人类活动导致物种灭绝的两种方式。”该题 4 分，每种方式 2 分。
Model answer: ‘Habitat destruction removes food and shelter, so fewer individuals survive and the species cannot reproduce successfully. Hunting removes too many individuals, especially breeding adults, so deaths happen faster than births and the population falls to zero.’
标准答案：“栖息地破坏移除了食物和庇护所，因此存活个体减少，物种无法成功繁殖。捕猎移除了太多个体，尤其是繁殖期成年个体，因此死亡速度快于出生速度，种群数量降至零。”
Another common question: ‘Explain why an invasive species can cause extinction.’ A full-mark answer could say: ‘The invasive species has no natural predators in the new area, so its population grows quickly. It eats native species or competes with them for food, reducing their survival and reproduction until they disappear.’
另一个常见问题：“解释为什么入侵物种会导致灭绝。”满分答案可以是：“入侵物种在新地区没有天敌，因此其数量迅速增长。它捕食本地物种或与其争夺食物，降低它们的生存和繁殖率，直到它们消失。”
Notice that each model answer includes a cause and an explanation of how that cause leads to fewer births or more deaths. This is what examiners look for.
注意，每个标准答案都包含一个原因，并解释该原因如何导致出生减少或死亡增加。这正是考官寻找的内容。
11. Key Terms and Definitions | 关键术语与定义
Using the correct scientific vocabulary can improve your marks. Below are the key terms that often appear in CIE KS3 extinction mark schemes.
使用正确的科学词汇可以提高你的分数。以下是 CIE KS3 灭绝评分标准中经常出现的关键术语。
| English | 中文 | Definition |
| Extinction | 灭绝 | The permanent loss of all individuals of a species. |
| Endangered | 濒危 | At serious risk of becoming extinct. |
| Habitat | 栖息地 | The natural home or environment of an organism. |
| Biodiversity | 生物多样性 | The variety of living organisms in an area. |
| Invasive species | 入侵物种 | A species introduced to a new area where it spreads and harms native species. |
| Poaching | 偷猎 | Illegal hunting or capturing of wild animals. |
| Competition | 竞争 | When organisms struggle for the same limited resources. |
| Adaptation | 适应 | A feature that helps an organism survive in its environment. |
You do not need to memorise long definitions word-for-word, but you should be able to use these terms correctly in sentences.
你不必逐字记住很长的定义，但应能在句子中正确使用这些术语。
12. Exam Tips and Common Mistakes | 考试技巧与常见错误
One common mistake is writing ‘the species becomes endangered’ when the question asks about extinction. Extinction means the species has completely died out, not just become rare.
一个常见错误是在题目问灭绝时写成“物种变得濒危”。灭绝意味着物种已经完全消亡，而不只是变得稀有。
Another mistake is giving a cause without explaining its effect. For example, writing ‘pollution’ alone usually earns no mark for explanation. Always add how pollution kills organisms or reduces reproduction.
另一个错误是只给出原因而不解释其影响。例如，只写“污染”通常得不到解释分。一定要补充污染如何杀死生物或降低繁殖率。
Use cause-and-effect language in your answers: ‘because’, ‘so’, ‘therefore’, ‘this means that’, ‘which leads to’. This helps the examiner see the link between the cause and the extinction.
在答案中使用因果关系的语言，如“因为”“所以”“因此”“这意味着”“这导致”。这有助于考官看到原因与灭绝之间的联系。
Finally, always read the number of marks. A three-mark question needs three separate points or two points with a clear explanation. Do not write just one sentence and expect full marks.
最后，一定要看清楚分值。3 分题需要三个独立的要点，或两个要点加上清晰的解释。不要只写一句话就期望得满分。
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