IB Edexcel Biology: Microorganisms Masterclass | IB Edexcel 生物：微生物考点精讲

📚 IB Edexcel Biology: Microorganisms Masterclass | IB Edexcel 生物：微生物考点精讲

Microorganisms are a cornerstone of IB and Edexcel Biology, encompassing viruses, bacteria, fungi and protists. Understanding their structure, life cycles, ecological roles and interactions with humans is essential for tackling exam questions on infection, immunity, biotechnology and ecosystems. This masterclass distills the key concepts you need to master, with paired English–Chinese explanations to reinforce both language and subject knowledge.

微生物是 IB 与 Edexcel 生物学的基石，涵盖病毒、细菌、真菌和原生生物。理解它们的结构、生活史、生态作用以及与人类的相互作用，对于攻克感染、免疫、生物技术和生态系统等考题至关重要。本精讲提炼了必须掌握的核心概念，并提供英中双语对照，帮助巩固语言与学科知识。

1. Microorganism Classification and Basic Types | 微生物分类与基本类型

Microorganisms are broadly grouped into viruses, bacteria, fungi and protists. Viruses are acellular and exist at the boundary of life, while the others are cellular organisms.

微生物大致分为病毒、细菌、真菌和原生生物。病毒是非细胞的，处于生命的边缘，而其余几类都是细胞生物。

Bacteria belong to the domain Bacteria and are prokaryotic, lacking a true nucleus and membrane-bound organelles. Their cell wall typically contains peptidoglycan.

细菌属于细菌域，是原核生物，没有真正的细胞核和膜包裹的细胞器。它们的细胞壁通常含有肽聚糖。

Fungi are eukaryotic, mostly multicellular (except yeasts), with cell walls made of chitin. Protists are a heterogeneous collection of mainly unicellular eukaryotes, including autotrophic algae and heterotrophic protozoa.

真菌是真核生物，大多为多细胞（酵母菌除外），细胞壁由几丁质构成。原生生物是一类多样化的、主要单细胞的真核生物，包括自养型的藻类和异养型的原生动物。

Viruses, by contrast, consist of nucleic acid (DNA or RNA) enclosed in a protein coat and sometimes a lipid envelope; they are obligate intracellular parasites.

相比之下，病毒由核酸（DNA 或 RNA）包裹在蛋白质外壳中，有时还具有脂质包膜；它们属于专性胞内寄生物。

---

2. Viruses: Acellular Entities | 病毒：非细胞实体

A typical virus particle, or virion, comprises a capsid made of protein subunits called capsomeres surrounding the genetic material. Some viruses possess an outer lipid envelope derived from the host cell membrane, studded with glycoprotein spikes that aid attachment.

典型的病毒颗粒（病毒体）由蛋白质亚基（壳粒）组成的衣壳包裹遗传物质构成。某些病毒还具有源自宿主细胞膜的外层脂质包膜，上面镶嵌着帮助吸附的糖蛋白刺突。

Viral genomes may be single-stranded or double-stranded, DNA or RNA. This genetic simplicity means viruses lack ribosomes and metabolic enzymes; they rely entirely on the host’s machinery for replication.

病毒基因组可以是单链或双链的 DNA 或 RNA。这种基因上的简单性意味着病毒没有核糖体和代谢酶，它们完全依赖宿主的机器进行复制。

The lytic cycle involves immediate replication and lysis of the host cell, while the lysogenic cycle integrates the viral genome into the host chromosome as a prophage (in bacteriophages) or provirus (in animal viruses), allowing latent infection.

裂解周期涉及病毒即刻复制并裂解宿主细胞，而溶原周期则将病毒基因组整合到宿主染色体中，形成原噬菌体（噬菌体中）或原病毒（动物病毒中），从而实现潜伏感染。

Examples such as influenza (RNA virus with envelope) and HIV (retrovirus using reverse transcriptase) highlight structural and functional diversity relevant to exam questions.

流感病毒（有包膜的 RNA 病毒）和 HIV（使用逆转录酶的反转录病毒）等例子展示了与考试密切相关的结构和功能多样性。

---

3. Bacteria: Prokaryotic Wonders | 细菌：原核生物的奇迹

Bacteria are unicellular prokaryotes, typically 0.5–5 µm in diameter. Their cell envelope includes a plasma membrane, a cell wall containing peptidoglycan, and sometimes an outer membrane in Gram-negative species.

细菌是单细胞原核生物，直径通常为 0.5–5 µm。它们的细胞被膜包括质膜、含肽聚糖的细胞壁，革兰阴性菌还有一个外膜。

Gram-positive bacteria retain crystal violet stain due to a thick peptidoglycan layer, whereas Gram-negative bacteria have a thin peptidoglycan layer and an outer lipopolysaccharide membrane, which provides resistance to certain antibiotics.

革兰阳性菌因肽聚糖层较厚而保留结晶紫染色，革兰阴性菌的肽聚糖层较薄且具有外膜脂多糖，这使其对某些抗生素具有抗性。

Bacterial genetic material is a single circular chromosome located in the nucleoid region, plus small plasmids that carry non-essential genes such as antibiotic resistance.

细菌的遗传物质是一个位于拟核区的单一环状染色体，外加携带非必需基因（如抗生素抗性基因）的小质粒。

Some bacteria possess flagella for motility, pili for adhesion and conjugation, and capsules that protect against desiccation and phagocytosis. These features are frequently tested in structure–function relationship questions.

部分细菌具有用于运动的鞭毛、用于黏附和接合的菌毛，以及抵御干燥和吞噬作用的荚膜。这些特征是结构和功能关系题中的常考内容。

---

4. Fungi: Eukaryotic Decomposers | 真菌：真核分解者

Fungi are eukaryotic organisms that secrete extracellular enzymes to digest organic matter externally before absorbing the nutrients. Their cell walls are composed of chitin, not cellulose.

真菌是真核生物，它们分泌胞外酶在体外将有机物消化后再吸收养分。它们的细胞壁由几丁质构成，而非纤维素。

They exist as unicellular yeasts (e.g., Saccharomyces cerevisiae) or as multicellular moulds forming a mycelium of hyphae. Hyphae may be septate (with cross-walls) or aseptate (coenocytic).

它们以单细胞的酵母菌（如酿酒酵母）或形成菌丝体的多细胞霉菌形式存在。菌丝可以有隔（有横壁）或无隔（多核体）。

Fungi reproduce by producing vast numbers of spores through asexual (e.g., sporangiospores, conidia) or sexual reproduction (e.g., ascospores, basidiospores). Spores are dispersed by wind or water, enabling rapid colonisation.

真菌通过无性（如孢囊孢子、分生孢子）或有性生殖（如子囊孢子、担孢子）产生大量孢子。孢子借助风或水传播，能快速定殖。

Ecologically, fungi are key decomposers and symbionts, forming mycorrhizal associations with plant roots. In industry, yeast is used in baking and alcohol fermentation, while Penicillium species produce antibiotics. Exam questions often link fungal biology to nutrient cycling and biotechnology.

在生态上，真菌是关键的分解者和共生体，与植物根系形成菌根联合。工业上，酵母用于烘焙和酒精发酵，青霉属物种则产生抗生素。考题常将真菌生物学与养分循环和生物技术联系起来。

---

5. Protists: Diverse Eukaryotes | 原生生物：多样化的真核生物

Protists are a polyphyletic group of mostly unicellular eukaryotes. They include plant-like algae, animal-like protozoa, and fungus-like slime moulds.

原生生物是一个多系群，主要由单细胞真核生物组成，包括植物样藻类、动物样原生动物和真菌样黏菌。

Algae, such as Chlorella and Euglena, possess chloroplasts and carry out photosynthesis, contributing significantly to global oxygen production. Euglena exhibits mixotrophy, capable of both photosynthesis and heterotrophic feeding.

藻类，如小球藻和眼虫，具有叶绿体并进行光合作用，对全球氧气生产贡献巨大。眼虫表现混合营养方式，既能光合作用也能异养摄食。

Protozoa, including Amoeba, Paramecium and Plasmodium, are heterotrophs that engulf food particles by phagocytosis. Plasmodium is the causative agent of malaria, with a complex life cycle involving mosquito and human hosts – a classic examination topic.

原生动物，包括变形虫、草履虫和疟原虫，是通过吞噬作用摄取食物颗粒的异养生物。疟原虫是疟疾的病原体，其复杂的生活史涉及蚊子和人类宿主——这是经典的考试主题。

Protists display varied locomotion structures: pseudopodia in Amoeba, cilia in Paramecium, and flagella in Euglena. These are useful for understanding evolutionary adaptations and are frequently assessed in practical investigations on pond water samples.

原生生物展现出多样的运动结构：变形虫的伪足、草履虫的纤毛和眼虫的鞭毛。这有助于理解进化适应，并常在池塘水样实验探究中被考查。

---

6. Microbial Reproduction and Growth | 微生物的繁殖与生长

Bacteria reproduce asexually by binary fission, where the circular chromosome replicates followed by cell elongation and septum formation. Under optimal conditions, some species can divide every 20 minutes.

细菌通过二分裂行无性繁殖，环状染色体复制后细胞拉长并形成隔膜。在最佳条件下，某些物种每 20 分钟便可分裂一次。

The exponential growth of a bacterial population can be predicted by the formula Nₜ = N₀ × 2ⁿ, where N₀ is the initial cell number, n is the number of generations, and Nₜ is the final population. This relationship often appears in data-analysis questions.

细菌群体的指数增长可用公式 Nₜ = N₀ × 2ⁿ 预测，其中 N₀ 为初始细胞数，n 为世代数，Nₜ 为最终群体数量。这一关系常出现在数据分析题中。

In a closed culture, bacteria exhibit a typical growth curve: lag phase (cells adapt), exponential (log) phase (rapid division), stationary phase (nutrient depletion and waste accumulation balance growth and death), and death phase (cells die faster than they are produced).

在封闭培养中，细菌表现出典型的生长曲线：延迟期（细胞适应）、指数期（快速分裂）、稳定期（营养耗尽和废物积累使生长与死亡平衡）和死亡期（细胞死亡速度快于新生速度）。

Viruses replicate strictly inside host cells via the lytic or lysogenic pathway, while many fungi can reproduce asexually by budding or sporulation. Yeast divides asymmetrically by budding, a process observed in fermentation experiments.

病毒只能在宿主细胞内通过裂解或溶原途径复制，而许多真菌可通过出芽或形成孢子进行无性繁殖。酵母以出芽方式不对称分裂，这在发酵实验中可以观察到。

---

7. Microorganisms and Infectious Disease | 微生物与传染病

Pathogenic microorganisms cause disease by damaging host tissues directly, producing toxins, or triggering excessive immune responses. Key bacterial diseases include tuberculosis (Mycobacterium tuberculosis), cholera (Vibrio cholerae) and food poisoning (Salmonella).

病原微生物通过直接损伤宿主组织、产生毒素或引发过度的免疫反应导致疾病。重要的细菌性疾病包括结核病（结核分枝杆菌）、霍乱（霍乱弧菌）和食物中毒（沙门菌）。

Viral diseases such as influenza, HIV/AIDS, measles and COVID-19 (SARS-CoV-2) spread through droplets, contact or vectors. Fungal infections like athlete’s foot and thrush are common, while malaria (Plasmodium protist) and sleeping sickness (Trypanosoma protist) exemplify protozoal diseases.

流感、HIV/艾滋病、麻疹和 COVID-19（SARS-CoV-2）等病毒性疾病通过飞沫、接触或媒介传播。真菌感染如足癣和鹅口疮很常见，而疟疾（疟原虫）和昏睡病（锥虫）则是原生动物疾病的典型。

Understanding the mode of transmission (direct contact, airborne, vector-borne, contaminated water or food) is crucial for devising prevention strategies. This is heavily tested in the context of disease control and global health.

理解传播方式（直接接触、空气传播、媒介传播、污染的水或食物）对于制定预防策略至关重要。这在疾病控制和全球健康的背景下考查频繁。

Pathogens often bind to specific host cell receptors, invade, and evade the immune system. For example, HIV targets CD4+ T helper cells, crippling adaptive immunity. These mechanisms are linked to molecular recognition and cell signalling, core themes in both IB and Edexcel syllabi.

病原体常与特定的宿主细胞受体结合、侵入并逃避免疫系统。例如，HIV 靶向 CD4+ 辅助 T 细胞，摧毁适应性免疫。这些机制与分子识别和细胞信号传导相联系，是 IB 和 Edexcel 大纲的核心主题。

---

8. Antibiotics, Resistance and Control | 抗生素、耐药性与控制

Antibiotics are chemical substances that kill bacteria (bactericidal) or inhibit their growth (bacteriostatic). Penicillin disrupts cell wall synthesis, while tetracyclines inhibit protein synthesis by binding to ribosomes.

抗生素是能够杀死细菌（杀菌）或抑制细菌生长（抑菌）的化学物质。青霉素干扰细胞壁合成，四环素类则通过与核糖体结合抑制蛋白质合成。

Antibiotic resistance arises through mutations or horizontal gene transfer (conjugation, transformation, transduction) of resistance genes. Overuse and misuse in medicine and agriculture accelerate this process, leading to multidrug-resistant strains such as MRSA.

抗生素耐药性源于突变或耐药基因的水平基因转移（接合、转化、转导）。医疗和农业中的过度使用和误用加速了这一过程，导致出现耐甲氧西林金黄色葡萄球菌（MRSA）等多重耐药菌株。

Laboratory control measures include aseptic technique, sterilisation (autoclaving at 121 °C), disinfection, and pasteurisation. These are vital for preventing contamination and ensuring reliable experimental results.

实验室的控制措施包括无菌操作、灭菌（121 °C 高压灭菌）、消毒和巴氏消毒法。这对防止污染和确保实验结果可靠至关重要。

In fighting resistance, strategies involve using narrow-spectrum antibiotics, completing prescribed courses, and developing new drugs. The evolutionary arms race between bacteria and antibiotics provides an excellent example of natural selection that is frequently examined.

在抗击耐药性方面，策略包括使用窄谱抗生素、完成处方疗程以及研发新药。细菌和抗生素之间的进化军备竞赛提供了自然选择的绝佳实例，经常被考查。

---

9. Immune System and Vaccination | 免疫系统与疫苗接种

The immune system defends against microorganisms through innate (non-specific) and adaptive (specific) responses. Innate defences include physical barriers (skin, mucous membranes), phagocytes (neutrophils, macrophages), inflammation and antimicrobial proteins.

免疫系统通过先天（非特异性）和适应性（特异性）应答来防御微生物。先天防御包括物理屏障（皮肤、黏膜）、吞噬细胞（中性粒细胞、巨噬细胞）、炎症和抗微生物蛋白。

Adaptive immunity involves lymphocytes: B cells produce antibodies targeting specific antigens, while T cells include helper T cells (activate other immune cells) and cytotoxic T cells (kill infected cells). Memory cells enable long-lasting protection.

适应性免疫涉及淋巴细胞：B 细胞产生针对特定抗原的抗体，T 细胞包括辅助 T 细胞（激活其他免疫细胞）和细胞毒性 T 细胞（杀死感染细胞）。记忆细胞提供长期保护。

Vaccination exploits adaptive immunity by introducing a harmless form of an antigen (attenuated pathogen, inactivated toxin, subunit or mRNA) to stimulate the production of memory cells without causing disease. This triggers a faster, stronger secondary response upon real exposure.

疫苗接种利用适应性免疫，通过引入无害形式的抗原（减毒病原体、灭活毒素、亚单位或 mRNA），刺激记忆细胞产生而不致病。当遇到真正的病原体时，便能引发更快、更强的二次应答。

Herd immunity protects unvaccinated individuals when a high proportion of the population is immunised, breaking the chain of transmission. Questions on vaccines often require evaluation of efficacy, safety and public health implications.

当大部分人接种疫苗时，群体免疫可保护未接种个体，阻断传播链。关于疫苗的考题常要求评价其效力、安全性和公共卫生影响。

---

10. Industrial and Ecological Roles of Microbes | 微生物的工业与生态作用

Microorganisms are indispensable in biotechnology and nutrient recycling. Bacteria and fungi decompose organic matter, releasing carbon, nitrogen and other elements for reuse in ecosystems.

微生物在生物技术和养分再循环中不可或缺。细菌和真菌分解有机物，释放碳、氮等元素供生态系统重新利用。

In the nitrogen cycle, nitrogen-fixing bacteria (e.g., Rhizobium) convert N₂ into ammonia, nitrifying bacteria oxidise ammonia to nitrites and nitrates, and denitrifying bacteria return N₂ to the atmosphere. These transformations are central to soil fertility.

在氮循环中，固氮菌（如根瘤菌）将 N₂ 转化为氨，硝化细菌将氨氧化为亚硝酸盐和硝酸盐，反硝化细菌则将 N₂ 释放回大气。这些转化是土壤肥力的核心。

Fermentation by yeast and bacteria produces bread, cheese, yoghurt, and alcoholic drinks. The equation for alcoholic fermentation is: C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂, while lactic acid fermentation produces lactate.

酵母和细菌的发酵作用可生产面包、奶酪、酸奶和酒类饮品。酒精发酵方程式为：C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂，而乳酸发酵则产生乳酸盐。

Advances in genetic engineering use bacteria to produce human insulin, growth hormone and enzymes. Exam questions may ask you to design or analyse bioreactors, interpreting growth conditions and product yield.

基因工程中利用细菌生产人胰岛素、生长激素和酶。考题可能要求设计或分析生物反应器，解释培养条件和产品产量。

---

11. Key Experiments and Aseptic Techniques | 关键实验与无菌技术

Louis Pasteur’s swan-neck flask experiment disproved spontaneous generation by showing that broth remained sterile unless exposed to airborne microbes. This established the principle of biogenesis and the foundation of aseptic technique.

路易·巴斯德的鹅颈瓶实验反驳了自然发生说，显示肉汤除非接触空气微生物，否则能保持无菌。这确立了生源说的原理和无菌操作的基础。

In the lab, aseptic technique includes flaming the inoculating loop before and after use, working near a Bunsen burner to create an updraft, flaming the neck of culture tubes, and minimising lid opening time to prevent contamination.

在实验室中，无菌操作包括在使用前后灼烧接种环、在本生灯附近工作以产生上升气流、灼烧培养管管口，以及尽量减少开盖时间以防止污染。

A standard practical involves preparing a streak plate to isolate single colonies, incubating at an appropriate temperature (usually 25–30 °C for school labs to avoid pathogenic growth), and measuring zones of inhibition around antibiotic discs.

一个标准实验包括划线接种以获得单菌落，在适宜温度下培养（学校实验室通常为 25–30 °C，避免致病菌生长），并测量抗生素纸片周围的抑菌圈大小。

Designing fair tests requires standardising variables (e.g., inoculum volume, incubation time) and including controls. You should be able to calculate bacterial counts using serial dilutions and colony-forming units (CFU).

设计公平测试时需要标准化变量（如接种量、培养时间）并设置对照组。你应能运用梯度稀释和菌落形成单位（CFU）计算细菌数量。

---

12. Exam Strategies and Common Pitfalls | 考试策略和常见误区

When tackling microbiology questions, pay close attention to command terms: “describe” requires factual recall, “explain” needs causal links, and “compare” demands similarities and differences. In data response, always refer to specific numbers or trends from the graph.

解答微生物学问题时，要仔细注意指令词：“描述”需要事实性的回忆，“解释”需要因果联系，“比较”则需要相同点和不同点。在数据回答中，始终引用图表中的具体数字或趋势。

A common mistake is confusing the structures of viruses, bacteria and fungi. Use comparison tables to review cell wall composition, genetic material, and mode of reproduction. For instance, remember that fungi have chitin, not peptidoglycan.

一个常见错误是混淆病毒、细菌和真菌的结构。利用对比表复习细胞壁成分、遗传物质和繁殖方式。例如，记住真菌具有几丁质，而非肽聚糖。

Another pitfall is failing to link antibiotic action to specific bacterial features. Penicillin works only on actively dividing Gram-positive bacteria because it inhibits peptidoglycan cross-linking. Explain the consequence, not just the name of the target.

另一个误区是未能将抗生素作用与细菌的特定特征联系起来。青霉素仅作用于正在分裂的革兰阳性菌，因为它抑制肽聚糖交联。要解释结果，而非仅仅说出靶点名称。

When discussing vaccination, clearly distinguish between primary and secondary immune responses using graphs of antibody concentration versus time. Also, connect herd immunity to the basic reproduction number R₀.

在讨论疫苗接种时，要利用抗体浓度随时间变化的曲线图，清晰区分初次和二次免疫应答。同时，将群体免疫与基本再生数 R₀ 联系起来。

Finally, in essays on microbial ecology, integrate examples across levels from molecular (enzyme action) to ecosystem (carbon flux). This demonstrates synoptic thinking and depth, which examiners reward with top marks.

最后，在论述微生物生态时，从分子水平（酶作用）到生态系统水平（碳通量）整合实例。这展现了全局思维和深度，阅卷人会给予高分。

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）