📚 GCSE WJEC Biology: Immune System Revision Notes | GCSE WJEC 生物：免疫系统考点精讲
The immune system is your body’s defence network against pathogens. For GCSE WJEC Biology, you must understand both non‑specific and specific defences, how lymphocytes produce antibodies, the role of memory cells in immunity, the principles of vaccination and herd immunity, and why antibiotics only work against bacteria. This guide breaks down every key point with clear bilingual explanations, ready for your exam.
免疫系统是身体抵御病原体的防御网络。GCSE WJEC 生物学考试要求你理解非特异性防御和特异性防御、淋巴细胞如何产生抗体、记忆细胞在免疫中的作用、疫苗接种和群体免疫的原理以及为什么抗生素只对细菌有效。本指南用清晰的双语解释拆解每一个考点，为你备考指明方向。
1. Pathogens and Disease | 病原体与疾病
Pathogens are microorganisms that cause communicable (infectious) diseases. The four main groups you need to know are bacteria, viruses, fungi and protists. Bacteria can reproduce rapidly inside the body and release harmful toxins that damage tissues. Viruses are even smaller – they invade host cells, take over the cell’s machinery to make copies of themselves, and then destroy the host cell when they burst out. Fungi can produce spores and often cause skin infections, while protists (like the malaria parasite) can have complex life cycles involving vectors.
病原体是引起传染病（可传播疾病）的微生物。你需要知道的四大类病原体是细菌、病毒、真菌和原生生物。细菌能在人体内快速繁殖并释放损伤组织的毒素。病毒更小——它们侵入宿主细胞，霸占细胞的“生产车间”去复制自身，最后破胞而出时杀死宿主细胞。真菌能产生孢子，常引起皮肤感染；而原生生物（如疟原虫）则可能有需要媒介参与的复杂生活史。
Many diseases are spread by direct contact, airborne droplets, contaminated food and water, or through vectors such as mosquitoes. Understanding transmission helps scientists develop methods to control infections, which you may be asked about in the exam.
许多疾病通过直接接触、飞沫、受污染的食物和水，或通过蚊子等媒介传播。了解传播途径有助于科学家制定控制感染的方法，这也可能在考试中出现。
2. The Body’s Non‑Specific Defences | 人体的非特异性防御
The first line of defence includes physical and chemical barriers that prevent pathogens from entering the body. These are non‑specific because they work against any type of pathogen, not a particular one.
第一道防线包括物理屏障和化学屏障，它们能阻止病原体进入身体。这些屏障是非特异性的，因为它们对任何病原体都起作用，而不是只针对某一种。
- Skin – a tough physical barrier made of dead, keratinised cells that pathogens cannot easily penetrate.
- 皮肤——由死去的角化细胞构成的坚韧物理屏障，病原体难以穿透。
- Nasal hairs – trap larger particles and microbes before they reach the lungs.
- 鼻毛——在较大的颗粒和微生物到达肺部之前将其截留。
- Mucus and cilia in the trachea – goblet cells produce sticky mucus that traps pathogens, and cilia beat to sweep the mucus upwards to be swallowed or coughed out.
- 气管中的黏液和纤毛——杯状细胞分泌黏性黏液，黏住病原体；纤毛不停摆动，把黏液往上推，最后被吞咽或咳出。
- Stomach acid – hydrochloric acid (HCl) in the stomach kills most swallowed pathogens.
- 胃酸——胃里的盐酸杀死大多数被吞咽的病原体。
- Tears and saliva – contain enzymes such as lysozyme that break down bacterial cell walls.
- 眼泪和唾液——含有溶菌酶等能分解细菌细胞壁的酶。
If these barriers are damaged (e.g. a cut), pathogens can enter tissues, triggering the next stages of defence.
如果这些屏障受损（例如割伤），病原体就会进入组织，启动后续的防御阶段。
3. Phagocytosis | 吞噬作用
Once pathogens get past the surface barriers, white blood cells called phagocytes mount a rapid, non‑specific attack. Phagocytes (such as neutrophils and macrophages) can move out of blood capillaries towards the infected area by responding to chemical signals.
一旦病原体越过了体表屏障，一种叫做吞噬细胞的白细胞就会展开快速的非特异性攻击。吞噬细胞（如中性粒细胞和巨噬细胞）能够响应化学信号，从毛细血管中移动到感染区域。
The phagocyte recognises the pathogen as foreign, extends pseudopodia and engulfs it, forming a vesicle called a phagosome. Lysosomes containing powerful digestive enzymes fuse with the phagosome, forming a phagolysosome. The enzymes digest the pathogen harmlessly, and any indigestible debris is expelled from the cell.
吞噬细胞识别出病原体是“外来物”，伸出伪足将其吞入，形成一个叫做吞噬体的小泡。含有强力消化酶的溶酶体与吞噬体融合，形成吞噬溶酶体。酶将病原体无害地消化，不可消化的残渣则被排出细胞。
Phagocytosis is non‑specific – it does not distinguish between different types of foreign material. It is the same process for bacteria, viruses and other debris.
吞噬作用是非特异性的——它不区分不同种类的异物，对细菌、病毒和其他碎屑的过程都一样。
4. The Specific Immune Response: Lymphocytes | 特异性免疫应答：淋巴细胞
If an infection persists, a second type of white blood cell, the lymphocyte, provides a specific and highly targeted response. There are two main types: B‑lymphocytes (B cells) and T‑lymphocytes (T cells), though the WJEC course often focuses on the role of lymphocytes in producing antibodies.
如果感染持续，第二种白细胞——淋巴细胞——会提供特异且高度精准的应答。淋巴细胞主要有两种：B 淋巴细胞（B 细胞）和 T 淋巴细胞（T 细胞），不过 WJEC 课程常聚焦于淋巴细胞产生抗体的功能。
Each lymphocyte has receptor proteins on its surface that recognise one specific antigen – a molecule (often a protein) on the surface of a pathogen. When a lymphocyte meets its matching antigen, it becomes activated. Helper T cells can assist this activation by releasing signalling molecules.
每个淋巴细胞表面带有受体蛋白，能识别一种特定的抗原——病原体表面的分子（通常是蛋白质）。当淋巴细胞遇到与之匹配的抗原时，就被激活。辅助 T 细胞可以通过释放信号分子来协助激活过程。
Activated B cells divide rapidly to form two types of cells: plasma cells that secrete huge quantities of antibodies, and memory cells that remain in the body for years, sometimes for life.
激活的 B 细胞快速分裂，形成两种细胞：浆细胞，分泌大量抗体；记忆细胞，在体内留存多年，有时终身存在。
5. Antibodies and Antigens | 抗体与抗原
Antibodies are Y‑shaped proteins (also called immunoglobulins) produced by plasma cells. Each antibody has a variable region that is complementary in shape to a specific antigen. This is often compared to a lock and key – only the correct antibody can bind to a particular antigen.
抗体是浆细胞产生的 Y 形蛋白质（也称免疫球蛋白）。每个抗体都有一个可变区，其形状与特定抗原互补。常被比喻为“锁与钥匙”——只有正确的抗体才能与特定的抗原结合。
When antibodies bind to antigens on the surface of pathogens, they can agglutinate (clump) the pathogens together, making it easier for phagocytes to engulf them. They can also neutralise toxins or mark pathogens for destruction by other immune cells.
当抗体与病原体表面的抗原结合后，可使病原体凝集（团聚），让吞噬细胞更容易吞噬它们。抗体还能中和毒素，或给病原体打上标记，让其他免疫细胞来消灭。
Antibodies are highly specific – an antibody against the influenza virus will not work against a different virus. This specificity is the basis of immune recognition and the design of diagnostic tests such as the pregnancy test.
抗体具有高度特异性——针对流感病毒的抗体对不同的病毒无效。这种特异性是免疫识别和怀孕测试等诊断工具设计的基础。
6. Primary vs Secondary Immune Response | 初次与二次免疫应答
When the body encounters a pathogen for the first time, the primary response is relatively slow because the few lymphocytes with the right receptors must be activated, divide and differentiate. It can take several days to produce enough antibodies, and during this time the person may show symptoms of the disease.
身体首次遭遇某种病原体时，初次应答比较缓慢，因为带有合适受体的淋巴细胞为数不多，需要激活、分裂和分化。可能需要几天才能产生足够的抗体，在此期间患者会表现出疾病症状。
After recovery, memory cells remain in the blood and lymph nodes. If the same pathogen invades again, these memory cells rapidly recognise the antigen and trigger a much faster, stronger secondary response. Antibody concentration rises quickly to a much higher level, and the pathogen is often eliminated before symptoms develop. This is why many people only catch diseases like chickenpox once.
康复后，记忆细胞留存在血液和淋巴结中。如果同一种病原体再次入侵，这些记忆细胞迅速识别抗原，引发更快、更强的二次应答。抗体浓度快速上升至更高水平，通常还没来得及出现症状，病原体就被清除了。这就是为什么许多疾病如水痘，人们只会得一次。
An exam question may provide a graph of antibody concentration over time and ask you to identify the primary and secondary responses.
考试中可能给出抗体浓度随时间变化的曲线图，要求你辨认初次应答和二次应答。
7. Active and Passive Immunity | 主动免疫与被动免疫
Immunity can be gained naturally or artificially, and it can be active (the body makes its own antibodies and memory cells) or passive (ready‑made antibodies are introduced).
免疫力可以是自然获得或人工获得的，也可以是主动免疫（身体自行产生抗体和记忆细胞）或被动免疫（引入现成的抗体）。
| Type | How immunity is acquired | 类别 | 如何获得免疫 |
|---|---|---|---|
| Natural active | Infection with the actual pathogen triggers the immune response and creates memory cells. | 自然主动 | 感染真正的病原体，触发免疫应答并产生记忆细胞。 |
| Artificial active | Vaccination – introducing a harmless form of the antigen stimulates the immune system to produce memory cells. | 人工主动 | 疫苗接种——将无害的抗原形式引入体内，刺激免疫系统产生记忆细胞。 |
| Natural passive | Antibodies cross the placenta from mother to fetus or are passed in breast milk. This gives immediate but temporary protection. | 自然被动 | 抗体通过胎盘从母体传给胎儿，或经由母乳传递。提供即时但暂时的保护。 |
| Artificial passive | Injection of ready‑made antibodies, e.g. antivenom for snake bites. Protection is immediate but does not last as no memory cells are made. | 人工被动 | 注射现成的抗体，例如蛇咬伤使用的抗蛇毒血清。保护作用即时但短暂，因为没有产生记忆细胞。 |
Active immunity lasts a long time because memory cells persist; passive immunity is short‑lived but works instantly.
主动免疫持续时间长，因为有记忆细胞存在；被动免疫时间短但能立即生效。
8. Vaccination and Herd Immunity | 疫苗接种与群体免疫
A vaccine typically contains dead or weakened pathogens, fragments of a pathogen, or inactivated toxins. These contain the antigens but do not cause the full disease. The body mounts a primary immune response and produces memory cells, so if the real pathogen later enters, the secondary response is rapid and effective.
疫苗通常含有死的或弱化的病原体、病原体碎片或灭活毒素。它们带有抗原，但不会引发完整疾病。人体产生初次免疫应答并生成记忆细胞，那么后来当真正的病原体入侵时，二次应答就会迅速且有效。
Herd immunity occurs when a large proportion of a population is vaccinated, making the spread of infection very unlikely. Even those who cannot be vaccinated (e.g. very young babies, people with weakened immune systems) gain indirect protection because the pathogen cannot circulate widely.
当人群中有很高比例的人接种了疫苗，疾病传播变得极不可能，这就形成了群体免疫。即使那些无法接种疫苗的人（如很小的婴儿、免疫功能低下者）也能获得间接保护，因为病原体无法广泛传播。
In the exam, you need to explain why vaccination programmes require a high uptake and why booster jabs (to increase antibody levels and memory cell numbers) may be needed.
考试中要能够解释为什么免疫接种计划需要高覆盖率，以及为什么可能需要加强针（以提高抗体水平和记忆细胞数量）。
9. Antibiotics and Their Limitations | 抗生素及其局限性
Antibiotics are medicines that kill bacteria or stop them from reproducing. Penicillin was the first widely used antibiotic. They work by targeting features unique to bacterial cells, such as cell wall synthesis, without harming human cells.
抗生素是能杀死细菌或阻止其繁殖的药物。青霉素是第一种广泛使用的抗生素。它们通过靶向细菌细胞独有的特性（如细胞壁合成）来发挥作用，不损伤人体细胞。
Antibiotics do not work against viruses because viruses have no cell wall, no metabolic machinery of their own, and they live inside host cells where antibiotics cannot reach them easily. This is why doctors should not prescribe antibiotics for viral infections like the common cold or influenza.
抗生素对病毒无效，因为病毒没有细胞壁，没有自身的代谢机构，且生活在宿主细胞内部，抗生素难以到达。这就是为什么医生不该为普通感冒或流感等病毒感染开抗生素。
The overuse and misuse of antibiotics have led to the evolution of antibiotic‑resistant bacteria, such as MRSA. Resistant strains survive and reproduce, passing on the resistance genes. To slow this process, it is essential to complete the full course of prescribed antibiotics so all bacteria are killed.
抗生素的过度使用和滥用导致了耐药菌株（如 MRSA）的进化。耐药的菌株存活并繁殖，将抗性基因传递下去。为减缓这一过程，必须完整服用完医生开的抗生素疗程，以杀死所有细菌。
10. Monoclonal Antibodies | 单克隆抗体
Monoclonal antibodies are identical copies of a single type of antibody, produced from a clone of hybridoma cells. They are made by fusing a B‑lymphocyte (which makes the desired antibody) with a tumour cell (which divides endlessly). The resulting hybridoma cell can be grown in large quantities, producing huge numbers of identical antibodies specific to one antigen.
单克隆抗体是单一类型抗体的完全相同的拷贝，由杂交瘤细胞克隆产生。它们通过将 B 淋巴细胞（能产生所需抗体）与肿瘤细胞（能无限分裂）融合而制得。得到的杂交瘤细胞可以大量培养，产生海量的针对一种抗原的相同抗体。
One common application is in pregnancy testing. The test contains monoclonal antibodies that bind to the hormone hCG (human chorionic gonadotropin), which is only present in the urine of pregnant women. When urine is applied, hCG binds to the antibodies on a test strip, triggering a colour change that indicates a positive result.
一个常见应用是怀孕检测。测试条含有能结合人绒毛膜促性腺激素（hCG）的单克隆抗体，而 hCG 只存在于孕妇尿液中。滴入尿液后，hCG 与试纸上的抗体结合，引发颜色变化，显示阳性结果。
Monoclonal antibodies are also used to target specific cancer cells, to diagnose certain infections, and to deliver drugs directly to diseased cells, minimizing side effects.
单克隆抗体还用于靶向特定的癌细胞、诊断某些感染，以及将药物直接送达病变细胞，从而减少副作用。
11. Common Misconceptions and Exam Tips | 常见误解与考试技巧
Avoid these frequent mistakes: confusing phagocytes (non‑specific engulfing) with lymphocytes (specific antibody production); thinking antibiotics kill viruses; forgetting that passive immunity does not produce memory cells; mixing up antigens (on pathogen) and antibodies (produced by body). In the exam, use precise vocabulary – for example, say ‘agglutinate’ when describing the clumping of pathogens by antibodies.
避免以下常见错误：混淆吞噬细胞（非特性吞噬）和淋巴细胞（特异性产生抗体）；以为抗生素能杀死病毒；忘记被动免疫不会产生记忆细胞；搞混抗原（在病原体上）和抗体（机体产生）。考试中要使用准确的词汇——比如，在描述抗体导致病原体凝集时，要用“凝集”这个词。
If you are asked to interpret a graph of antibody concentration, label the axes mentally and explain why the secondary peak is higher and faster. When writing about vaccination, always link to memory cells and the secondary response. For monoclonal antibodies, emphasise their specificity and the method of hybridoma production.
如果题目要求解读抗体浓度曲线图，先在心中标出坐标轴，并解释为什么二次峰值更高更快。写疫苗接种时，一定要联系到记忆细胞和二次应答。关于单克隆抗体，则要强调其特异性以及杂交瘤生产方法。
Finally, remember that a well‑functioning immune system is crucial for health. A balanced diet, exercise and vaccinations all contribute to strong immunity – this can be a useful synoptic link in longer exam questions.
最后记住，运转良好的免疫系统对健康至关重要。均衡饮食、锻炼和接种疫苗都有助于巩固免疫力——在较长的考题里，这是很好的跨主题链接点。
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