📚 Microorganisms Key Points for IB & CIE Biology | IB CIE 生物：微生物 考点精讲
Microorganisms, or microbes, are organisms invisible to the naked eye and include bacteria, viruses, fungi and protists. This revision guide covers essential concepts required for IB and CIE Biology, from cell structure to industrial applications and disease. Understanding these tiny life forms is crucial for ecology, medicine and biotechnology.
微生物是用肉眼无法看到的生物，包括细菌、病毒、真菌和原生生物。本复习指南涵盖IB和CIE生物考试所需的核心概念，从细胞结构到工业应用和疾病。理解这些微小生命形式对生态学、医学和生物技术至关重要。
1. Classification of Microorganisms | 微生物的分类
Microorganisms are grouped primarily by cell type and genetic material. Bacteria and archaea are prokaryotes, lacking a nucleus and membrane-bound organelles. Viruses are acellular and cannot carry out metabolism independently. Fungi and protists are eukaryotes, with true nuclei; fungi have chitin cell walls, while protists show immense diversity.
微生物主要根据细胞类型和遗传物质分类。细菌和古菌是原核生物，没有细胞核和膜结合细胞器。病毒是非细胞结构，不能独立进行代谢。真菌和原生生物是真核生物，具有真正的细胞核；真菌细胞壁含几丁质，原生生物则表现出极大的多样性。
- Bacteria – prokaryotic, peptidoglycan cell wall
- Viruses – non-living, require host cells
- Fungi – eukaryotic, chitin cell wall, can be unicellular (yeast) or multicellular (moulds)
- Protists – eukaryotic, mostly unicellular (e.g. Amoeba, Paramecium)
- 细菌 – 原核，细胞壁含肽聚糖
- 病毒 – 非生命，需要宿主细胞
- 真菌 – 真核，细胞壁含几丁质，可为单细胞（酵母）或多细胞（霉菌）
- 原生生物 – 真核，大多单细胞（如变形虫、草履虫）
2. Bacterial Cell Structure | 细菌细胞结构
A typical bacterium possesses a cell wall made of peptidoglycan, which determines shape and provides protection. The cell membrane encloses the cytoplasm, where 70S ribosomes are found. The genetic material is a single circular chromosome of DNA located in the nucleoid region; additional small DNA loops called plasmids are often present.
典型的细菌具有由肽聚糖组成的细胞壁，它决定细菌形状并提供保护。细胞膜包裹着细胞质，其中含有70S核糖体。遗传物质是一条位于拟核区的环形DNA分子；通常还存在称为质粒的小DNA环。
Some bacteria have a capsule that enhances virulence, flagella for movement, and pili for adhesion and conjugation. Mesosomes (infoldings of the membrane) may aid in respiration. No mitochondria or chloroplasts are present.
某些细菌具有增强毒力的荚膜，用于运动的鞭毛，以及用于附着和接合的菌毛。膜内褶形成的间体可能辅助呼吸。细菌没有线粒体或叶绿体。
Key features: Cell wall (peptidoglycan) | Circular DNA | 70S ribosomes | Plasmids | No nucleus
关键特征：细胞壁（肽聚糖） | 环状DNA | 70S核糖体 | 质粒 | 无核膜
3. Viral Structure and Replication | 病毒结构与复制
Viruses consist of a nucleic acid core (DNA or RNA) surrounded by a protein coat called a capsid. Some have an outer lipid envelope derived from the host cell membrane, studded with glycoprotein spikes. Viruses are obligate intracellular parasites.
病毒由核酸核心（DNA或RNA）和包围它的蛋白质外壳（衣壳）组成。有些病毒还具有来自宿主细胞膜的脂质包膜，其上镶嵌着糖蛋白刺突。病毒是专性细胞内寄生物。
The lytic cycle involves attachment, injection of nucleic acid, replication of viral components, assembly and lysis of the host cell. In the lysogenic cycle, viral DNA integrates into the host chromosome as a prophage, replicating with the host until an induction event triggers the lytic pathway.
裂解周期包括附着、注入核酸、复制病毒组分、装配以及宿主细胞裂解。在溶原周期中，病毒DNA以原噬菌体形式整合到宿主染色体中，随宿主复制，直至诱导事件触发裂解途径。
Lytic: Attachment → Penetration → Biosynthesis → Assembly → Lysis
裂解：附着→穿入→生物合成→装配→裂解
4. Culturing Microorganisms and Aseptic Technique | 微生物培养与无菌技术
Microorganisms can be grown on nutrient agar plates or in broth. Aseptic technique is vital to prevent contamination and ensure safety: work near a Bunsen burner flame, sterilise inoculating loops by flaming, lift the Petri dish lid at an angle, and seal plates with adhesive tape but not fully to allow aerobic respiration.
微生物可以在营养琼脂平板或肉汤中培养。无菌技术对于防止污染和保证安全至关重要：在酒精灯火焰附近操作，灼烧接种环灭菌，倾斜打开培养皿盖，用胶带封板但不完全密封以允许需氧呼吸。
Colony morphology differs between bacteria and fungi. Bacterial colonies appear small, shiny and often coloured; fungal colonies are fuzzy or powdery. Incubation is usually at 25–30 °C in schools to avoid growing human pathogens (37 °C).
细菌和真菌的菌落形态有所不同。细菌菌落较小、有光泽，常带有颜色；真菌菌落呈绒毛状或粉状。学校培养通常使用25–30 °C，以避免培养出人体病原体（37 °C）。
5. Bacterial Growth and Reproduction | 细菌的生长与繁殖
Bacteria mainly reproduce asexually by binary fission: the circular DNA replicates, the cell elongates and the septum divides the cell into two genetically identical daughter cells. Under ideal conditions, some species can double every 20 minutes.
细菌主要通过二分裂进行无性繁殖：环状DNA复制，细胞伸长，隔膜将细胞分裂成两个遗传上相同的子细胞。在理想条件下，某些物种每20分钟就能分裂一次。
The growth curve in a closed culture shows four phases: lag (adaptation), log/exponential (rapid division), stationary (nutrient depletion, waste accumulation; birth rate equals death rate) and death (cells die faster than they divide). Knowledge of the growth curve is essential for industrial fermentation and antibiotic production.
封闭培养的生长曲线分为四个阶段：迟缓期（适应）、对数期（快速分裂）、稳定期（营养耗尽，代谢废物积累；出生率等于死亡率）和衰亡期（死亡速度快于分裂速度）。理解生长曲线对于工业发酵和抗生素生产至关重要。
Growth curve: Lag → Log → Stationary → Death
生长曲线：迟缓期→对数期→稳定期→衰亡期
6. Microbial Metabolism – Respiration and Fermentation | 微生物代谢——呼吸与发酵
Many bacteria are aerobic and perform aerobic respiration, oxidising organic substrates to CO₂ and H₂O using oxygen as the terminal electron acceptor. In the absence of oxygen, facultative anaerobes switch to fermentation, while obligate anaerobes cannot survive in oxygen.
许多细菌是需氧的，进行有氧呼吸，以氧气为最终电子受体将有机物氧化为CO₂和H₂O。缺氧时，兼性厌氧菌转而进行发酵，而专性厌氧菌在氧气中无法存活。
Yeast (Saccharomyces cerevisiae) performs alcoholic fermentation: C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂ + ATP. Lactic acid bacteria (Lactobacillus) carry out lactic acid fermentation: C₆H₁₂O₆ → 2 CH₃CHOHCOOH + ATP. These pathways are exploited in food and biofuel industries.
酵母（酿酒酵母）进行酒精发酵：C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂ + ATP。乳酸菌（乳杆菌）进行乳酸发酵：C₆H₁₂O₆ → 2 CH₃CHOHCOOH + ATP。这些途径被用于食品和生物燃料工业。
7. Microbes in Nutrient Cycles | 微生物在营养循环中的作用
Decomposers (bacteria and fungi) break down dead organic matter, releasing carbon as CO₂ and nitrogen as ammonium (NH₄⁺). This mineralisation recycles nutrients essential for producers. Without microbes, ecosystems would collapse.
分解者（细菌和真菌）分解死去的有机物，将碳以CO₂形式、氮以铵根（NH₄⁺）形式释放。这种矿化作用循环了生产者必需的养分。没有微生物，生态系统将会崩溃。
In the nitrogen cycle, nitrogen-fixing bacteria (e.g. Rhizobium in root nodules) convert N₂ to NH₃, nitrifying bacteria oxidise NH₄⁺ to NO₂⁻ then NO₃⁻, and denitrifying bacteria return N₂ to the atmosphere. These transformations sustain soil fertility.
在氮循环中，固氮菌（如根瘤中的根瘤菌）将N₂转化为NH₃，硝化细菌将NH₄⁺氧化为NO₂⁻再氧化为NO₃⁻，反硝化细菌将氮气送回大气。这些转化维持着土壤肥力。
N₂ → NH₃ (fixation) → NO₂⁻ → NO₃⁻ (nitrification) → N₂ (denitrification)
N₂ → NH₃（固氮）→ NO₂⁻ → NO₃⁻（硝化）→ N₂（反硝化）
8. Industrial Applications of Microorganisms | 微生物的工业用途
Microbes are exploited on a large scale to produce foods, fuels and pharmaceuticals. Lactobacillus is used to make yoghurt and cheese by converting lactose to lactic acid, which coagulates milk proteins. Saccharomyces cerevisiae is employed in bread-making (CO₂ causes dough to rise) and in alcoholic beer and wine production.
微生物被大规模用于生产食品、燃料和药物。乳酸菌通过将乳糖转化为乳酸，使牛奶蛋白凝固，用于生产酸奶和奶酪。酿酒酵母在面包制作中利用CO₂使面团膨胀，也用于啤酒和葡萄酒的酿造。
Fungal Penicillium chrysogenum secretes penicillin, the first antibiotic. Biofuels such as ethanol are produced by yeast fermentation of biomass. Enzymes like amylase and protease from bacteria and fungi are used in detergents and food processing. Single-cell protein from microorganisms offers a potential sustainable food source.
真菌产黄青霉菌分泌青霉素——第一种抗生素。生物燃料如乙醇通过酵母发酵生物质而生产。来自细菌和真菌的酶如淀粉酶和蛋白酶被用于洗涤剂和食品加工。微生物单细胞蛋白提供了潜在的可持续食物来源。
9. Biotechnology and Genetic Engineering using Bacteria | 利用细菌进行生物技术与基因工程
Bacterial plasmids are essential tools in gene technology. A target gene can be inserted into a plasmid vector using restriction enzymes and DNA ligase. The recombinant plasmid is then introduced into competent E. coli cells (transformation). Transformed bacteria replicate and express the protein, enabling large-scale production of human insulin, growth hormone and vaccines.
细菌质粒是基因技术中的重要工具。利用限制酶和DNA连接酶可将目标基因插入质粒载体。重组质粒随后被导入感受态大肠杆菌细胞（转化）。被转化的细菌复制并表达蛋白质，从而大规模生产人胰岛素、生长激素和疫苗。
Selection markers (e.g. antibiotic resistance genes) and reporter genes (e.g. GFP) help identify successfully transformed cells. PCR and gel electrophoresis are used to confirm the insert. These techniques are core to both IB and CIE practical assessments.
选择标记（如抗生素抗性基因）和报告基因（如绿色荧光蛋白）有助于鉴定成功转化的细胞。PCR和凝胶电泳用于验证插入片段。这些技术是IB和CIE实验考试的核心内容。
10. Pathogens and Infectious Diseases | 病原体与传染病
Pathogenic microorganisms cause disease by invading tissues, producing toxins or provoking excessive immune responses. Key examples: Mycobacterium tuberculosis (TB), Vibrio cholerae (cholera), HIV (AIDS), Plasmodium (malaria, a protist), and Candida (thrush, a fungus). Transmission can be direct (airborne droplets, contact) or indirect (vectors, contaminated food and water).
病原微生物通过侵入组织、产生毒素或引发过度的免疫反应而致病。重要例子包括：结核分枝杆菌（肺结核）、霍乱弧菌（霍乱）、HIV（艾滋病）、疟原虫（疟疾，一种原生生物）和念珠菌（鹅口疮，真菌）。传播方式可为直接（飞沫、接触）或间接（媒介、污染的食物和水）。
Understanding transmission modes underpins control measures such as vaccination, sterilisation, hand-washing, water treatment and vector control. Koch’s postulates provide criteria to establish a causative link between a microbe and a disease.
理解传播方式为控制措施（如疫苗接种、消毒、洗手、水处理和病媒控制）提供了基础。科赫法则提供了确立微生物与疾病因果关系的一系列标准。
| Pathogen | Disease | Transmission |
|---|---|---|
| Vibrio cholerae | Cholera | Contaminated water |
| Plasmodium spp. | Malaria | Female Anopheles mosquito |
| Influenza virus | Flu | Airborne droplets |
| 病原体 | 疾病 | 传播方式 |
|---|---|---|
| 霍乱弧菌 | 霍乱 | 污染的水 |
| 疟原虫属 | 疟疾 | 雌性按蚊 |
| 流感病毒 | 流感 | 飞沫传播 |
11. Antibiotics and Antibiotic Resistance | 抗生素与抗生素耐药性
Antibiotics are chemicals that kill or inhibit bacteria without harming human cells. They may target cell wall synthesis (penicillin), protein synthesis (tetracycline), nucleic acid replication or metabolic pathways. Viruses are not affected by antibiotics; antivirals are used instead.
抗生素是能杀死或抑制细菌而不伤害人体细胞的化学物质。它们可靶向细胞壁合成（青霉素）、蛋白质合成（四环素）、核酸复制或代谢途径。病毒不受抗生素影响，需使用抗病毒药物。
Antibiotic resistance arises from mutations or horizontal gene transfer (conjugation, transduction, transformation) that confer survival advantages. Overuse and misuse of antibiotics accelerate selection for resistant strains such as MRSA. Strategies to combat resistance include completing prescribed courses, restricting antibiotic use in agriculture and developing new drugs.
抗生素耐药性源于突变或水平基因转移（接合、转导、转化），这些赋予细菌生存优势。抗生素的过度使用和滥用加速了耐药菌株（如MRSA）的筛选。对抗耐药的策略包括完成处方疗程、限制农业中抗生素的使用以及开发新药。
Resistance mechanisms: Enzymatic degradation | Altered target site | Efflux pumps
耐药机制：酶促降解 | 靶位点改变 | 外排泵
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