AQA GCSE生物 感染 病原体 免疫 抗生素考点
导语：AQA GCSE Biology 的 Infection and Response 单元把微生物学、人体免疫和药物治疗串成一条主线，在 Paper 1 里几乎每年都会出现。本文用考点清单的方式，把病原体类型、传播途径、常见疾病、人体防御、疫苗和抗生素整理成一份复习地图，中英对照，方便你在答题时直接调用关键术语和得分点。
This guide maps the whole AQA Infection and Response topic into clear exam-focused blocks: pathogen types, transmission routes, common diseases, body defences, vaccination and antibiotics. Each block pairs the Chinese explanation with the exact English terminology that mark schemes expect, so you can revise the science and the exam language at the same time.
1. 四类病原体 Types of Pathogens
病原体 pathogen 是能引起传染病的微生物。AQA 要求你区分四类：细菌 bacteria、病毒 viruses、真菌 fungi、原生生物 protists。细菌是单细胞生物，进入人体后快速繁殖并释放毒素 toxins，例如引起沙门氏菌食物中毒。病毒比细菌小得多，必须进入宿主细胞 host cell 才能复制，它们接管细胞内部的复制机器，最终把细胞破坏，所以病毒性症状往往来得很快。真菌可以是单细胞也可以是多细胞，部分真菌会侵入植物组织，例如玫瑰黑斑病 rose black spot。原生生物是单细胞真核生物，引起疟疾 malaria 的疟原虫就属于这一类，它依靠蚊子在不同人之间传播。
Pathogens are microorganisms that cause communicable diseases, and AQA expects you to name four groups: bacteria, viruses, fungi and protists. Bacteria are single-celled and reproduce rapidly inside the body, releasing toxins that damage tissues, which is how they cause food poisoning. Viruses are far smaller and can only reproduce inside a host cell; they take over the cell machinery and eventually destroy the cell, which is why viral symptoms appear quickly. Fungi may be single-celled or multicellular, and some grow into plant tissue causing diseases such as rose black spot. Protists are single-celled eukaryotes, and the protist that causes malaria is carried between people by mosquitoes.
2. 传播途径 How Pathogens Spread
病原体传播主要有四条路线：直接接触 direct contact、空气 airborne、水或食物 water or food、以及动物媒介 vectors。直接接触包括接触受感染的皮肤或体液，性传播疾病 gonorrhoea 就走这条路线。空气传播指感染者咳嗽或打喷嚏时把带病原体的飞沫释放到空气中，麻疹 measles 和流感属于这一类。被污染的水和食物会传播沙门氏菌和霍乱 cholera。媒介 vector 是把病原体从一个宿主带到另一个宿主的生物，蚊子传播疟疾就是最经典的例子。
Pathogens spread along four main routes: direct contact, airborne droplets, contaminated water or food, and animal vectors. Direct contact covers touching infected skin or exchanging body fluids, which is how the sexually transmitted disease gonorrhoea passes between people. Airborne transmission happens when an infected person coughs or sneezes, releasing droplets that carry pathogens, and this is the route for measles and influenza. Contaminated water and food spread bacteria such as salmonella and the cause of cholera. A vector is an organism that carries a pathogen from one host to another, and mosquitoes transmitting malaria is the classic example in the specification.
3. 病毒性疾病 Viral Diseases
病毒性疾病里，AQA 重点考三个：麻疹、艾滋病和烟草花叶病毒。麻疹由空气传播，症状包括红色皮疹和发热，严重时可引起肺炎甚至脑损伤，接种疫苗可以预防，儿童疫苗计划大幅降低了发病率。艾滋病由 HIV 引起，HIV 攻击并破坏人体的淋巴细胞 lymphocytes，使免疫系统逐渐失效，最终发展为 AIDS，此时患者容易感染其他疾病。HIV 通过体液传播，例如性接触和共用针具。烟草花叶病毒 TMV 感染植物，使叶片出现马赛克状斑驳，影响光合作用，从而降低作物产量。
Three viral diseases carry most of the marks: measles, HIV/AIDS and tobacco mosaic virus. Measles spreads through the air and causes a red skin rash and fever; in serious cases it leads to pneumonia or brain damage. Vaccination prevents it, and the childhood programme has cut cases dramatically. HIV attacks and destroys the lymphocytes of the immune system, so the body gradually loses its ability to fight infection and the patient develops AIDS, at which point other infections become life-threatening. HIV passes on through body fluids, including sexual contact and shared needles. Tobacco mosaic virus infects plants, giving leaves a mosaic pattern that reduces photosynthesis and therefore crop yield.
4. 细菌、真菌与原生生物疾病 Bacterial, Fungal and Protist Diseases
细菌性疾病里最重要的是沙门氏菌和淋病。沙门氏菌来自受污染的食物，例如未煮熟的鸡肉和鸡蛋，症状是发热、腹部绞痛、呕吐和腹泻，多数人几天内恢复，但家禽养殖场通过疫苗接种来控制疫情。淋病 gonorrhoea 是性传播疾病，症状包括排尿疼痛和生殖器分泌物，过去常用青霉素治疗，现在部分菌株已产生抗药性，所以预防措施变得更加重要。真菌引起的玫瑰黑斑病会在叶片上形成黑斑，影响光合作用， gardeners 用杀菌剂和移除病叶来控制。疟疾由疟原虫引起，患者反复发热，蚊子叮咬时把病原体注入血液，防止蚊子繁殖和睡觉用蚊帐是最有效的预防方式。
Among bacterial diseases, salmonella and gonorrhoea matter most for the exam. Salmonella comes from contaminated food such as undercooked chicken and eggs and causes fever, abdominal cramps, vomiting and diarrhoea; most patients recover within days, and poultry vaccination is used to control outbreaks. Gonorrhoea is a sexually transmitted disease with symptoms of painful urination and discharge, once treated with penicillin, though some strains are now resistant, so prevention has become more important. The fungal disease rose black spot produces dark patches on leaves that reduce photosynthesis, and gardeners control it with fungicides and by removing infected leaves. Malaria is caused by a protist and produces repeated fever; the mosquito injects the pathogen when it bites, so stopping mosquitoes from breeding and sleeping under a net are the most effective prevention methods.
5. 人体的非特异性防御 Non-Specific Defences
人体第一道防线是非特异性的，也就是说它对所有病原体都起作用，而不是针对某一种。皮肤 skin 形成物理屏障，并分泌抗菌物质；呼吸道里的鼻腔黏液 mucus 会捕获病原体，纤毛 cilia 把黏液向上推出并被吞咽；气管和支气管分泌黏液和粘液纤毛系统共同作用。胃酸 stomach acid 杀死随食物进入的病原体。如果病原体突破这些屏障，血小板和凝血机制会封闭伤口，防止更多病原体进入。这些防御反应速度快，但不会产生免疫记忆。
The body's first line of defence is non-specific, meaning it works against every pathogen rather than one particular type. The skin acts as a physical barrier and secretes antimicrobial substances. In the respiratory tract, mucus traps pathogens and cilia sweep the mucus upwards to be swallowed, while the stomach produces acid that kills pathogens taken in with food. If pathogens break through these barriers, platelets and clotting seal the wound so fewer pathogens can enter. These defences act fast, but they create no immunological memory.
6. 免疫系统的特异性反应 The Immune Response
当病原体突破第一道防线，免疫系统启动特异性反应。白细胞 white blood cells 主要有三种作用方式。第一是吞噬作用 phagocytosis：吞噬细胞识别外来抗原 antigen，把病原体包围并消化。第二是产生抗体 antibodies：淋巴细胞识别特定抗原后分裂，产生与该抗原匹配的抗体，抗体结合病原体使其被标记，随后被吞噬细胞清除。第三是产生抗毒素 antitoxins：抗毒素中和细菌释放的毒素。抗体具有专一性，一种抗体只结合一种抗原，这也是疫苗和免疫记忆的基础。
When pathogens break through the first line of defence, the immune system responds specifically. White blood cells act in three main ways. First, phagocytosis: phagocytes recognise foreign antigens and engulf and digest the pathogens. Second, antibody production: lymphocytes recognise a specific antigen, divide, and release antibodies that lock onto that antigen and mark the pathogen for destruction by phagocytes. Third, antitoxin production: antitoxins neutralise the toxins released by bacteria. Antibodies are highly specific, so one antibody binds only one antigen, and this specificity is the foundation of both immunity and vaccination.
7. 疫苗与免疫 Vaccination and Immunity
疫苗 vaccination 把死亡或减毒的病原体、或病原体的一部分注入体内，刺激免疫系统产生抗体和记忆细胞 memory cells，但不会引起真正的疾病。当同一种病原体再次入侵时，记忆细胞可以快速产生大量抗体，反应更快、更强，所以接种者往往不会发病。麻疹和HPV疫苗是常见例子。人群接种率高时，病菌难以在人与人之间传播，未接种的人也被间接保护，这就是群体免疫 herd immunity。需要强调的是，疫苗预防的是传染病，对抗生素耐药性没有直接作用。
Vaccination introduces dead or weakened pathogens, or parts of a pathogen, into the body. This stimulates the immune system to produce antibodies and memory cells without causing the actual disease. If the same pathogen enters the body again, memory cells produce a large number of antibodies far more quickly, so the vaccinated person usually does not become ill. Measles and HPV vaccines are common examples. When a high proportion of a population is vaccinated, the pathogen struggles to spread from person to person, which indirectly protects people who are not vaccinated; this is herd immunity. Remember that vaccines prevent communicable diseases and have no direct effect on antibiotic resistance.
8. 抗生素、药物开发与考试技巧 Antibiotics, Drug Development and Exam Technique
抗生素 antibiotics 如青霉素能杀死体内的细菌，但完全不能杀死病毒，所以用抗生素治疗感冒或流感是错误的。抗生素耐药性 antibiotic resistance 是关键考点：细菌变异产生耐药菌株，被抗生素筛选存活并繁殖，导致感染难以治疗，因此医生要谨慎开药、患者必须完成整个疗程。药物开发 drug testing 分三阶段：先在实验室测试细胞和组织，再用动物测试毒性和有效性，最后进行人体临床试验 clinical trials，健康志愿者用于检验安全性，患者用于检验疗效，并采用双盲试验 double blind trial 避免偏见。考试技巧方面，Paper 1 常要求在描述疾病后解释传播方式，Paper 2 常用六分题让你评估疫苗接种或抗生素使用的利弊，答题时要写出具体病原体名称、症状、传播方式，再用因为所以的科学推理给出结论。复习时把每类病原体与一个真实疾病配对记忆，效率最高。
Antibiotics such as penicillin kill bacteria inside the body but cannot kill viruses, so using them against a cold or influenza is ineffective. Antibiotic resistance is a key exam point: random mutation produces resistant bacterial strains, which are selected by the antibiotic, survive and multiply, making infections harder to treat. This is why doctors prescribe carefully and patients must complete the full course. Drug development has three stages: laboratory testing on cells and tissues, animal testing for toxicity and effectiveness, and finally clinical trials in humans, where healthy volunteers test safety and patients test efficacy, often using a double blind trial to remove bias. For exam technique, Paper 1 often asks you to name the transmission route after describing a disease, while Paper 2 uses six-mark questions asking you to evaluate the benefits and risks of vaccination or antibiotic use. Write the specific pathogen, symptom and transmission route, then finish with a scientific conclusion linked by because or therefore. Pairing each pathogen group with one real disease is the fastest way to revise.
9. 预防传播与风险因素 Preventing Spread and Risk Factors
传染病防控有五个常用手段：良好的个人卫生 hygiene，例如勤洗手；隔离感染者 isolate infected individuals；安全处理或销毁受污染的材料；控制媒介昆虫，例如使用杀虫剂和蚊帐；以及在疫情中为人群接种疫苗。风险因素 risk factors 决定一个人是否更容易被感染或发展成重症，其中包括年龄、免疫状态、生活方式和营养状况。免疫功能低下的人感染风险更高，营养不良的人抵抗力更弱。需要注意的是，心脏病和癌症等非传染性疾病不由病原体引起，因此无法通过疫苗或抗生素预防，这个区别在判断题型时非常有用。
Five measures are commonly used to control communicable diseases: good personal hygiene such as washing hands regularly; isolating infected individuals; destroying or safely disposing of contaminated materials; controlling insect vectors with insecticides and bed nets; and vaccinating the population during an outbreak. Risk factors decide whether a person is more likely to be infected or to become seriously ill, and they include age, immune status, lifestyle and nutrition. Someone with a weakened immune system faces a higher risk of infection, while poor nutrition weakens resistance. Non-communicable diseases such as heart disease and cancer are not caused by pathogens, so they cannot be prevented by vaccination or cured by antibiotics, and this distinction helps you choose the right answer in exam questions.
10. 典型题目解析 Worked Exam Answer
下面用一道常见六分题演示答题结构。题目：Explain how vaccination protects a person from measles. 答题要点依次是：疫苗含有减毒或死亡的麻疹病毒；病毒表面带有抗原 antigen；淋巴细胞的受体识别该抗原并产生匹配的抗体；同时产生记忆细胞 memory cells；当真正的麻疹病毒再次进入身体时，记忆细胞迅速产生大量抗体；抗体结合病毒并使病毒被吞噬细胞清除，因此接种者不会发病。每个要点各占一分，缺少 antigen、memory cells、antibodies 这些具体术语会直接丢分。如果题目要求 evaluate，就必须补充另一面：疫苗可能引起轻微副作用，极少数人会出现过敏反应；如果接种率不够高，群体免疫无法形成，疫情仍可能扩散。
Here is how to structure a common six-mark answer. Question: explain how vaccination protects a person from measles. The mark points come in order: the vaccine contains weakened or dead measles virus; the virus carries antigens on its surface; receptors on lymphocytes recognise the antigen and produce matching antibodies; memory cells are produced at the same time; when the real measles virus enters the body again, memory cells rapidly release a large number of antibodies; the antibodies bind the virus so phagocytes can destroy it, which is why the vaccinated person does not become ill. Each point earns one mark, and omitting terms such as antigens, memory cells and antibodies loses marks immediately. If the command word is evaluate, you must also give the other side: vaccines can cause mild side effects and very rarely an allergic reaction, and without high vaccination coverage herd immunity fails and outbreaks can still spread.
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