📚 GCSE OCR Biology: Microorganisms – Key Points Explained | GCSE OCR 生物：微生物 考点精讲
Microorganisms, or microbes, are tiny living organisms that can only be seen under a microscope. They are found everywhere – in soil, water, air and inside other organisms. Some are essential for processes like decomposition and food production, while others cause infectious diseases. In GCSE OCR Biology, you must know the types, structures, reproduction, roles in disease and industry, and how we control them. This detailed revision guide covers all the key concepts.
微生物无处不在—土壤、水、空气和其他生物体内。它们肉眼不可见，需借助显微镜观察。有些对分解和食品生产至关重要，有些则引发传染病。在 GCSE OCR 生物学中，你需要掌握微生物的类型、结构、繁殖、在疾病和工业中的作用，以及如何控制它们。本精讲涵盖所有核心考点。
1. What Are Microorganisms? | 什么是微生物？
Microorganisms are microscopic organisms that exist as single cells, cell clusters or acellular particles. They include bacteria, viruses, fungi and protists.
微生物是微观尺度下的生物体，以单细胞、细胞群体或非细胞颗粒形式存在，包括细菌、病毒、真菌和原生生物。
Bacteria are prokaryotic, unicellular organisms without a nucleus. Viruses are not made of cells; they consist of genetic material inside a protein coat. Fungi are eukaryotic and have a cell wall made of chitin, while protists are single-celled eukaryotes.
细菌是原核单细胞生物，无细胞核。病毒并非由细胞构成，而是包裹在蛋白质外壳中的遗传物质。真菌为真核生物，细胞壁由几丁质组成；原生生物则是单细胞真核生物。
Many microbes are harmless or beneficial, forming part of the normal microbiota of the human body, but pathogens are microbes that can cause infectious diseases.
许多微生物无害或有益，如正常人体菌群，但病原体是能引起传染病的微生物。
2. Structure of Bacteria | 细菌的结构
Bacterial cells possess a cell wall (made of peptidoglycan, not cellulose), a cell membrane, cytoplasm and a single circular chromosome of DNA lying free in the cytoplasm. They lack a nucleus.
细菌细胞具有细胞壁（由肽聚糖构成，不是纤维素）、细胞膜、细胞质和一条位于细胞质中的环形染色体 DNA，没有细胞核。
Many bacteria also contain small rings of DNA called plasmids, which can carry genes for antibiotic resistance. Some have a flagellum for movement.
许多细菌体内还含有称为质粒的小型环状 DNA，可携带抗生素抗性基因。部分细菌通过鞭毛运动。
Due to their simple structure, bacteria can reproduce rapidly in favourable conditions. Understanding their structure is key to explaining how antibiotics work.
由于结构简单，细菌在适宜条件下繁殖极快。理解其结构是解释抗生素如何起作用的关键。
3. Structure of Viruses | 病毒的结构
Viruses are much smaller than bacteria and are not considered living because they cannot carry out life processes on their own. They consist of a nucleic acid core (DNA or RNA) surrounded by a protein coat called a capsid.
病毒比细菌小得多，且因无法独立完成生命过程而不被视为生物。它们由核酸核心（DNA 或 RNA）以及包裹其外的蛋白质衣壳组成。
Some viruses, like HIV, also have an outer lipid envelope derived from the host cell membrane. Viruses lack cytoplasm, ribosomes and metabolic enzymes.
某些病毒（如 HIV）还拥有来自宿主细胞膜的外层脂质包膜。病毒没有细胞质、核糖体和代谢酶。
A virus must infect a host cell to reproduce, using the host’s machinery to replicate its genetic material and produce new virus particles.
病毒必须感染宿主细胞才能繁殖，利用宿主的机制复制遗传物质并制造新的病毒颗粒。
4. Fungal and Protist Pathogens | 真菌与原生生物的病原体
Fungi can be unicellular (yeast) or multicellular with thread-like hyphae (moulds). Their cell walls are made of chitin. Some fungi cause plant diseases such as rose black spot, which leads to purple or black leaf spots and early leaf loss.
真菌可以是单细胞（酵母）或由丝状菌丝构成的多细胞（霉菌）。其细胞壁由几丁质构成。一些真菌引起植物病害，如玫瑰黑斑病，导致叶片出现紫黑色斑点并提早落叶。
Protists are single-celled eukaryotes. An important example is Plasmodium, the protist parasite that causes malaria. It is transmitted by female Anopheles mosquitoes and invades red blood cells, causing periodic fevers.
原生生物为单细胞真核生物。重点例子是引起疟疾的原生寄生虫——疟原虫，经雌性按蚊传播，侵入红细胞并引起周期性发热。
Both fungal and protist pathogens can cause significant disease in plants and animals, and understanding their life cycles helps in developing control measures.
真菌和原生生物病原体可在动植物中引发重大疾病，弄清其生命周期有助于制定防控措施。
5. Reproduction of Microorganisms | 微生物的繁殖
Bacteria reproduce asexually by binary fission. The chromosome replicates, and the cell divides into two genetically identical daughter cells. Under ideal conditions (warmth, moisture, nutrients), populations can double in as little as 20 minutes, leading to exponential growth: 1 → 2 → 4 → 8 → 16 … 2ⁿ.
细菌通过二分裂进行无性繁殖：染色体复制，细胞分裂为两个基因相同的子代细胞。在理想条件下（温暖、潮湿、营养充足），每 20 分钟即可翻倍，呈指数增长：1 → 2 → 4 → 8 → 16 … 2ⁿ。
Viruses replicate inside host cells by attaching, injecting nucleic acid, using the host to synthesise viral components, assembling new viruses, and then lysing (bursting) the cell to release them.
病毒在宿主细胞内复制：吸附、注入核酸、利用宿主合成病毒组分、组装新病毒，最后裂解宿主细胞释放子代病毒。
Yeast fungi reproduce by budding, where a small outgrowth forms and pinches off to become a new cell. Moulds produce spores that disperse and germinate.
酵母真菌通过出芽繁殖，形成小芽体后断裂成为新细胞；霉菌产生孢子，孢子扩散并萌发。
6. Culturing Microorganisms in the Lab | 实验室培养微生物
In the laboratory, bacteria are grown on agar plates in Petri dishes using aseptic technique to prevent contamination. The inoculating loop is sterilised by heating, and the dish lid is partially opened to avoid airborne microbes falling in.
在实验室中，细菌在琼脂平板上培养，需使用无菌技术防止污染。接种环通过加热灭菌，培养皿盖只部分打开以减少空气中微生物落入。
In schools, cultures are incubated at 25 °C rather than 37 °C to reduce the risk of growing human pathogens. Colony numbers can be used to calculate bacterial concentration or to test the effectiveness of antibiotics using inhibition zones.
学校培养通常用 25 °C 而非 37 °C，以减少人类病原体生长的风险。菌落计数可用于计算细菌浓度，或通过抑菌圈大小测试抗生素效果。
The area of an inhibition zone is determined by πr²; a larger zone indicates a more effective antibiotic. Cross-contamination must be avoided at all stages.
抑菌圈面积由 πr² 计算，面积越大表明抗生素越有效。整个操作过程必须避免交叉污染。
7. Microorganisms and Disease | 微生物与疾病
Pathogenic microorganisms can spread in several ways: through airborne droplets (measles, influenza), direct contact (HIV via body fluids), contaminated food and water (Salmonella, cholera), or vectors (mosquitoes for malaria).
病原微生物可通过多种途径传播：飞沫传播（麻疹、流感）、直接接触（HIV 通过体液）、污染的食物和水（沙门氏菌、霍乱），或媒介传播（蚊子传播疟疾）。
Viral diseases include measles (fever, red rash, can lead to pneumonia), HIV (destroys white blood cells, leading to AIDS) and tobacco mosaic virus (causes mosaic pattern on leaves, reducing photosynthesis).
病毒性疾病包括麻疹（发热、红疹，可致肺炎）、HIV（破坏白细胞，导致艾滋病）和烟草花叶病毒（叶片出现马赛克斑纹，降低光合作用）。
Bacterial diseases include Salmonella food poisoning (diarrhoea, fever, stomach cramps from undercooked food) and gonorrhoea (sexually transmitted, thick yellow discharge, pain when urinating).
细菌性疾病包括沙门氏菌食物中毒（未熟食物引起腹泻、发热、腹痛）和淋病（性传播，稠黄色分泌物，排尿疼痛）。
Fungal rose black spot reduces photosynthesis and vigour. Malaria, caused by Plasmodium, causes recurring fever, shaking chills and can be fatal without treatment.
真菌玫瑰黑斑病会削弱光合作用与植株活力。疟疾由疟原虫导致，周期性发热、寒战，不治疗可致命。
8. Preventing the Spread of Infectious Diseases | 预防传染病传播
Simple hygiene measures, such as handwashing and disinfecting surfaces, greatly reduce pathogen transmission. Isolating infected individuals and safely disposing of clinical waste also prevent spread.
简单的卫生措施如洗手和表面消毒可大幅减少病原体传播。隔离感染者以及安全处理医疗废物也有助于防控。
Vaccination protects populations by providing immunity before exposure. For insect vector diseases like malaria, mosquito nets and insecticide spraying limit transmission. Safe sex practices and using sterile needles reduce the spread of HIV and gonorrhoea.
疫苗接种可在暴露前提供免疫保护。对蚊媒疾病如疟疾，使用蚊帐和喷洒杀虫剂可减少传播。安全性行为和无菌针具能降低 HIV 和淋病传播。
Pasteurisation of milk (heating to 72 °C for 15 seconds) kills harmful bacteria without spoiling the product. Chlorination of water inactivates pathogens like Vibrio cholerae.
牛奶巴氏消毒（72 °C 加热 15 秒）可杀死有害细菌而不破坏产品质量。饮用水加氯处理可灭活霍乱弧菌等病原体。
9. Human Defence Systems and Vaccination | 人体防御系统与疫苗
The body’s first lines of defence are non-specific: the skin acts as a physical barrier, nasal hairs and mucus trap particles, and stomach acid destroys swallowed pathogens. Phagocytic white blood cells engulf and digest microbes.
人体的第一道防线是非特异性的：皮肤作为物理屏障，鼻毛和黏液捕获颗粒，胃酸杀死吞入的病原体。吞噬白细胞则会吞噬并消化微生物。
Specific immunity involves lymphocytes that recognise antigens on pathogens and produce antibodies. Antibodies bind to antigens, neutralising or agglutinating pathogens. Memory lymphocytes remain for years, enabling a faster response upon reinfection.
特异性免疫涉及识别病原体抗原并产生抗体的淋巴细胞。抗体与抗原结合，中和或凝集病原体。记忆淋巴细胞可存活多年，再次感染时能更快应答。
Vaccines contain weakened or inactivated pathogens or their antigens. They trigger the production of antibodies and memory cells without causing illness, resulting in immunity. Herd immunity occurs when a high proportion of a population is vaccinated, protecting non-immune individuals.
疫苗含有减毒或灭活的病原体或其抗原，可刺激产生抗体和记忆细胞而不引发疾病，获得免疫。当人群接种率很高时，群体免疫可保护未免疫的个体。
10. Antibiotics and Antibiotic Resistance | 抗生素与抗生素耐药性
Antibiotics, such as penicillin, are medicines that kill bacteria or stop their growth by targeting structures absent in human cells (e.g. the bacterial cell wall). They have no effect on viruses because viruses lack these targets and hide inside host cells.
抗生素（如青霉素）能杀死细菌或抑制其生长，它们作用于人体细胞所没有的结构（如细菌细胞壁）。抗生素对病毒无效，因为病毒没有这类靶点，且藏匿于宿主细胞内。
Bacteria can become resistant to antibiotics through random mutation. Resistant strains survive and reproduce in the presence of the antibiotic by natural selection. MRSA is a well-known example of a resistant bacterium.
细菌可通过随机突变对抗生素产生耐药性。在抗生素环境中，耐药菌株通过自然选择存活并繁殖。MRSA 就是一种著名的耐药菌。
To combat resistance, doctors should only prescribe antibiotics when necessary, and patients must complete the full course. Developing new antibiotics involves preclinical testing on cells and tissues, followed by clinical trials on healthy volunteers and patients.
为应对耐药性，医生应仅在必要时开具抗生素，患者必须完成整个疗程。开发新抗生素需经过临床前细胞和组织测试，再在健康志愿者和患者中进行临床试验。
11. Microorganisms in Food Production | 微生物在食品生产中的应用
Yeast (a fungus) is used to make bread. In aerobic conditions, yeast respires sugars to produce carbon dioxide, which makes dough rise. During baking, trapped gas expands, giving bread its spongy texture. Ethanol produced evaporates in the oven.
酵母（一种真菌）用于制作面包。有氧条件下，酵母利用糖类呼吸产生二氧化碳，使面团膨胀。烘烤时气泡扩张，面包便呈海绵状；产生的乙醇在烤箱中蒸发。
For beer and wine production, yeast ferments sugars anaerobically:
C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂
制作啤酒和葡萄酒时，酵母在无氧条件下发酵糖类：
C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂
To make yoghurt, bacteria such as Lactobacillus are added to milk. They ferment lactose into lactic acid, which lowers the pH, thickens the milk and gives the tangy taste while preserving the product.
制作酸奶时，向牛奶中加入乳酸菌等细菌。它们将乳糖发酵为乳酸，降低 pH，使牛奶变稠，产生酸味并起到防腐作用。
12. Decomposition and Nutrient Cycling | 分解与营养循环
Decomposer microorganisms, mainly bacteria and fungi, break down dead organic matter and waste, releasing enzymes to digest material externally and absorbing the nutrients. This process recycles essential elements.
分解者微生物主要是细菌和真菌，它们分解死亡的有机物和废物，通过分泌酶在体外消化物质并吸收营养。这一过程实现了必需元素的再循环。
In the nitrogen cycle, decomposers convert proteins and urea into ammonium ions (ammonification). Nitrifying bacteria then oxidise ammonium to nitrites and nitrates, which plants absorb through their roots to build proteins.
在氮循环中，分解者将蛋白质和尿素转化为铵离子（氨化作用），硝化细菌再将铵氧化为亚硝酸盐和硝酸盐，植物经根部吸收硝酸盐合成蛋白质。
Useful applications include composting garden waste and treating sewage. In anaerobic digesters, microbes decompose organic waste to produce methane, a renewable fuel.
其应用包括堆肥处理和污水处理。在厌氧消化器中，微生物分解有机废物产生甲烷，这是一种可再生燃料。
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