A-Level AQA Biology: Microorganisms – Key Points | A-Level AQA 生物：微生物考点精讲

📚 A-Level AQA Biology: Microorganisms – Key Points | A-Level AQA 生物：微生物考点精讲

Microorganisms are the unseen engines of life, driving nutrient cycles, shaping ecosystems, and acting as both allies and enemies in human health. In AQA A-Level Biology, you are expected to understand their diversity, structure, growth, roles in biotechnology, and their interactions with hosts, including disease and immunity. This article compiles essential knowledge and exam tips to help you master the topic.

微生物是生命活动中看不见的引擎，它们驱动着营养循环，塑造着生态系统，并在人类健康中既是盟友又是敌人。在 AQA A-Level 生物学中，你需要理解微生物的多样性、结构、生长、在生物技术中的作用，以及它们与宿主的相互作用，包括疾病与免疫。本文汇集了必会知识点和应试技巧，助你全面掌握该专题。

1. Types of Microorganisms | 微生物的种类

Microorganisms are a diverse group of organisms that are typically unicellular or acellular and can only be visualised under a microscope. The main categories examined by AQA include bacteria, viruses, fungi, and protoctists. Each group has distinct cellular organisation and modes of life.

微生物是一类多样化的生物，通常为单细胞或无细胞结构，只能在显微镜下观察。AQA 考试中涉及的主要类别包括细菌、病毒、真菌和原生生物。每一类群都有独特的细胞组织方式和生命模式。

Bacteria are prokaryotic organisms with no membrane-bound nucleus or organelles, and they possess 70S ribosomes. They reproduce asexually by binary fission and can be classified by cell wall structure using Gram staining (Gram-positive or Gram-negative).

细菌是原核生物，没有膜包围的细胞核或细胞器，且拥有 70S 核糖体。它们通过二分裂进行无性繁殖，并可通过细胞壁结构用革兰氏染色（革兰氏阳性或阴性）区分。

Viruses are acellular, infectious particles consisting of a nucleic acid core (DNA or RNA) surrounded by a protein coat called a capsid, and sometimes a lipid envelope. They are obligate intracellular parasites that use host cell machinery to replicate.

病毒是无细胞的感染性颗粒，由核酸核心（DNA 或 RNA）和称为衣壳的蛋白质外壳组成，有时还有脂质包膜。它们是专性细胞内寄生物，利用宿主细胞的分子机器进行复制。

Fungi are eukaryotic organisms with a cell wall made of chitin, and they can be unicellular (yeasts) or multicellular (moulds). They feed by saprophytic nutrition, secreting enzymes to digest organic matter externally before absorption.

真菌是真核生物，细胞壁由几丁质构成，可以是单细胞（酵母菌）或多细胞（霉菌）。它们通过腐生营养方式获取养分，先分泌酶在体外分解有机物，再吸收产物。

Protoctists are eukaryotic, usually single-celled organisms, such as Plasmodium (cause of malaria) and amoebas. Some are pathogenic, while others are photosynthetic like algae.

原生生物是真核、通常单细胞的生物，例如疟原虫（疟疾病原体）和阿米巴。有些是致病性的，另一些像藻类一样能进行光合作用。

2. Bacterial Cell Structure | 细菌细胞结构

The bacterial cell is a model prokaryote. It lacks a nucleus; the genetic material is a single circular chromosome of DNA located in a region called the nucleoid. Plasmids, small loops of DNA carrying non-essential genes, often confer advantages such as antibiotic resistance.

细菌细胞是典型原核生物。它没有细胞核；遗传物质是一个单链环状 DNA，位于称为拟核的区域。质粒是携带非必需基因的小环状 DNA，常赋予细菌如抗生素耐药性等优势。

The cytoplasm contains 70S ribosomes (smaller than eukaryotic 80S), and may include storage granules such as glycogen or lipid droplets. Some bacteria possess a protective slime capsule that helps them evade the immune system, and flagella for locomotion.

细胞质中含有 70S 核糖体（比真核生物的 80S 小），还可能含有糖原或脂滴等储存颗粒。有些细菌具保护性的黏液荚膜，有助于逃避免疫系统，并有鞭毛用于运动。

The cell wall is made of peptidoglycan (murein), a polymer of sugars and amino acids. In Gram-positive bacteria the peptidoglycan layer is thick and retains crystal violet stain; in Gram-negative bacteria it is thin and covered by an outer membrane, giving a pink counterstain.

细胞壁由肽聚糖（胞壁质）构成，这是一种糖和氨基酸的聚合物。在革兰氏阳性菌中，肽聚糖层较厚，能保留结晶紫染色；在革兰氏阴性菌中，肽聚糖层较薄，并被外膜覆盖，经复染后呈粉红色。

3. Viral Structure and Replication | 病毒结构与复制

Viruses are not considered living because they have no cellular machinery. They consist of a nucleic acid genome (either DNA or RNA, single- or double-stranded) enclosed in a capsid. Some viruses, like HIV, have an additional envelope derived from the host cell membrane, studded with glycoproteins for attachment.

病毒不被视为生物，因为它们缺乏细胞结构。它们由核酸基因组（DNA 或 RNA，单链或双链）包裹在衣壳内组成。一些病毒，如 HIV，还有一层来自宿主细胞膜的额外包膜，上面嵌有用于附着的糖蛋白。

The replication cycle typically involves attachment of viral attachment proteins to specific receptor sites on the host cell, penetration of the nucleic acid, replication of the viral genome using host enzymes, assembly of new virions, and release by lysis (lytic cycle) or by budding.

复制周期通常包括：病毒的附着蛋白与宿主细胞特定受体位点结合，核酸注入宿主细胞，利用宿主酶复制病毒基因组，组装新的病毒颗粒，最后通过裂解（裂解周期）或出芽方式释放。

Retroviruses like HIV use reverse transcriptase to transcribe their RNA into DNA, which then integrates into the host chromosome as a provirus. This latent stage can remain dormant before entering the lytic cycle.

像 HIV 这样的逆转录病毒使用逆转录酶将其 RNA 转录为 DNA，然后作为原病毒整合到宿主染色体中。这一潜伏阶段可以保持休眠状态，之后才进入裂解周期。

4. Culturing Microorganisms | 微生物培养

Aseptic techniques are critical when culturing microorganisms to prevent contamination and ensure safety. Common growth media include nutrient agar and broth, which supply carbohydrates, nitrogen sources, minerals, and water. Selective media may contain antibiotics or specific nutrients to isolate particular species.

在培养微生物时，无菌技术至关重要，以防止污染并确保安全。常用的生长培养基包括营养琼脂和肉汤，提供碳水化合物、氮源、矿物质和水分。选择性培养基可能含有抗生素或特定营养物，以分离特定菌种。

To obtain single colonies, a sterile inoculating loop is used to streak a microbial sample across an agar plate. Incubation temperature is typically 25°C in schools (to reduce the risk of growing human pathogens) or 37°C for clinical samples. Inoculated plates must be sealed and incubated upside down to prevent condensation dripping.

为获得单菌落，使用无菌接种环将微生物样本在琼脂平板上划线。学校中培养温度通常为 25°C（以降低致病菌生长风险），临床样本则用 37°C。接种后的平板必须密封并倒置培养，以防止冷凝水滴落干扰菌落。

Obligate aerobes require oxygen; obligate anaerobes are killed by oxygen; facultative anaerobes can grow with or without oxygen, though growth is better with oxygen. These demands dictate incubation atmospheres.

专性需氧菌需要氧气；专性厌氧菌会被氧气杀死；兼性厌氧菌在有氧或无氧条件下都能生长，但有氧时生长更好。这些需求决定了培养时的气体环境。

5. Aseptic Technique | 无菌技术

Aseptic technique prevents unwanted microorganisms from contaminating the culture and also protects the worker from pathogenic microbes. Key steps include disinfecting work surfaces with a suitable disinfectant, using a Bunsen burner to create an updraft and sterilisation zone, and flaming the necks of bottles and inoculating loops until red hot.

无菌技术可防止不需要的微生物污染培养物，同时保护操作者免受病原微生物的侵害。关键步骤包括用合适的消毒剂擦拭工作台面，使用本生灯产生上升气流和灭菌区域，并将瓶口和接种环灼烧至赤红。

When transferring liquids, lids should be opened as briefly as possible and passed through the flame to minimise airborne contamination. Agar plates should be opened only slightly and near the flame. Petri dish lids are secured with adhesive tape but not sealed entirely, as aerobic organisms need oxygen and anaerobic respiration can produce dangerous gas build-up.

转移液体时，瓶盖应尽可能短暂地打开并过火，以减少空气污染。琼脂平板只应微开并靠近火焰操作。培养皿盖用胶带固定，但不要完全密封，因为好氧生物需要氧气，且厌氧呼吸可能产生危险的气体积累。

6. Bacterial Growth Curve | 细菌生长曲线

In a closed batch culture, bacterial growth follows a characteristic sigmoid curve plotted as log cell number against time. The four major phases are lag, log (exponential), stationary, and death.

在封闭的分批培养中，细菌生长遵循典型的 S 形曲线，以细胞数的对数值对时间作图。四个主要阶段为迟缓期、对数（指数）期、稳定期和衰亡期。

The lag phase shows little increase in cell numbers as bacteria adapt to the new environment and synthesise required enzymes. The log phase features rapid exponential growth, with population doubling at regular intervals; here, binary fission rate is maximal and depends on nutrient availability and temperature.

迟缓期中细胞数量几乎没有增加，因为细菌正在适应新环境并合成所需酶类。对数期呈现快速指数增长，菌群每隔一段时间即翻倍；此时二分裂速率达最大值，取决于营养供给和温度。

The stationary phase occurs when nutrient depletion and accumulation of toxic waste products cause the growth rate to equal the death rate. The death phase shows an exponential decline in viable cells, though some may survive longer by forming endospores or utilising stored materials.

稳定期出现于营养耗尽及有毒废物积累，导致生长速率与死亡速率相等。衰亡期活菌数呈指数下降，但部分细胞可能通过形成芽孢或利用储存物质存活更久。

Microbiologists often use the formula n = n0 × 2ᵏ, where n is final cell number, n0 is initial cell number, and k is the number of doublings over time t. The mean generation time can be calculated from the slope of the log phase.

微生物学家常使用公式 n = n0 × 2ᵏ，其中 n 为最终细胞数，n0 为初始细胞数，k 为在时间 t 内的倍增次数。平均世代时间可根据对数期斜率计算得出。

7. Microorganisms in Biotechnology | 生物技术中的微生物

Microorganisms are indispensable tools in industrial biotechnology. They are used in fermentation processes to produce foods such as yoghurt, bread, and cheese. Lactobacillus bacteria convert lactose into lactic acid, giving yoghurt its tangy taste and thick texture by coagulating milk proteins.

微生物是工业生物技术中不可或缺的工具。它们被用于发酵工艺以生产酸奶、面包和奶酪等食品。乳酸菌将乳糖转化为乳酸，通过凝集乳蛋白使酸奶具有酸味和浓郁质地。

In brewing and baking, the fungus Saccharomyces cerevisiae (yeast) ferments sugars to ethanol and carbon dioxide under anaerobic conditions. The CO2 causes dough to rise; the ethanol is retained in beer and wine.

在酿造和烘焙中，真菌酿酒酵母在无氧条件下将糖类发酵产生乙醇和二氧化碳。CO2 使面团膨发；乙醇保留在啤酒和葡萄酒中。

Recombinant DNA technology utilises bacteria such as E. coli to produce human proteins like insulin. A plasmid vector is cut with restriction enzymes, the insulin gene is inserted using ligase, and transformed bacteria multiply in fermenters, expressing the protein.

重组 DNA 技术利用如大肠杆菌等细菌来生产人胰岛素等蛋白质。质粒载体被限制酶切开，用连接酶插入胰岛素基因，转化后的细菌在发酵罐中增殖并表达蛋白质。

Large-scale fermentation requires controlled conditions: sterile medium, constant pH and temperature monitoring, aeration if aerobic, and aseptic sampling. Downstream processing then purifies the product.

大规模发酵需要受控条件：无菌培养基，持续监测 pH 和温度，好氧时需通气，以及无菌取样。下游工艺随后提纯产品。

8. Antibiotics and Resistance | 抗生素与耐药性

Antibiotics are chemical substances that selectively destroy or inhibit bacteria without harming human cells. Penicillin targets the enzyme transpeptidase, preventing cross-linking of peptidoglycan chains in bacterial cell walls, causing osmotic lysis. Thus, it is bactericidal against growing Gram-positive bacteria.

抗生素是能选择性地杀灭或抑制细菌而不伤害人体细胞的化学物质。青霉素作用于转肽酶，阻止细菌细胞壁肽聚糖链的交联，导致渗透裂解。因此它对生长中的革兰氏阳性菌是杀菌性的。

Broad-spectrum antibiotics affect a wide range of bacterial species, while narrow-spectrum ones target specific groups. Choosing the correct antibiotic and using a full course minimises the emergence of resistant strains.

广谱抗生素影响多种细菌，而窄谱抗生素针对特定菌群。选择正确的抗生素并完成全程用药，可最大限度地减少耐药菌株的出现。

Resistance arises through mutation and horizontal gene transfer. Resistant bacteria may produce enzymes such as β-lactamase that break down penicillin, modify target sites so antibiotics cannot bind, or use efflux pumps to expel the drug. Plasmids carrying multiple resistance genes (R factors) can spread rapidly in bacterial populations under selective pressure.

耐药性通过突变和水平基因转移产生。耐药菌可能产生如 β-内酰胺酶等酶来分解青霉素，改变靶点使抗生素无法结合，或利用外排泵排出药物。携带多重耐药基因（R 因子）的质粒在选择性压力下可在细菌种群中迅速传播。

9. Microorganisms and Disease | 微生物与疾病

Pathogenic microorganisms cause disease by damaging host tissues directly, producing toxins, or triggering excessive immune responses. Transmission can be direct (contact, droplet infection) or indirect (contaminated food, water, vectors).

病原微生物通过直接损伤宿主组织、产生毒素或引发过度免疫反应而致病。传播途径可以是直接传播（接触、飞沫传染）或间接传播（污染的食物、水、媒介生物）。

Key examples required for AQA include: Mycobacterium tuberculosis (tuberculosis, airborne droplet transmission), Vibrio cholerae (cholera, water-borne, produces enterotoxin causing severe diarrhoea), and HIV (retrovirus targeting helper T cells, transmitted via bodily fluids).

AQA 考试需要的重要例子包括：结核分枝杆菌（结核病，空气飞沫传播），霍乱弧菌（霍乱，水媒传播，产生肠毒素导致严重腹泻），以及 HIV（逆转录病毒，攻击辅助性 T 细胞，通过体液传播）。

Endotoxins are lipopolysaccharides in the outer membrane of Gram-negative bacteria released upon cell lysis; exotoxins are soluble proteins secreted by living bacteria, such as the cholera toxin. Understanding toxin action links to the mechanisms of disease symptoms.

内毒素是革兰氏阴性菌外膜中的脂多糖，在细胞裂解时释放；外毒素是活菌分泌的可溶性蛋白，如霍乱毒素。理解毒素作用有助于联系疾病的症状机制。

The body’s first lines of defence include physical barriers like skin and mucous membranes, chemical barriers such as stomach acid and lysozyme in tears, and mechanical defences like cilia in the respiratory tract. If breached, the non-specific inflammatory response and specific immune system are activated.

人体的第一道防线包括皮肤和黏膜等物理屏障，胃酸和泪液中的溶菌酶等化学屏障，以及呼吸道纤毛等机械性防御。一旦被突破，非特异性炎症反应和特异性免疫系统将被激活。

10. Preventing and Treating Infections | 预防和治疗感染

Vaccination exploits the immune system’s capacity to develop immunological memory. Vaccines contain antigens derived from weakened or killed pathogens, toxoids, or recombinant surface proteins. Upon exposure, memory B and T cells are primed for a rapid secondary response, preventing disease.

疫苗接种利用了免疫系统形成免疫记忆的能力。疫苗含有源自减毒或灭活病原体、类毒素或重组表面蛋白的抗原。一旦暴露，记忆 B 细胞和 T 细胞可启动快速二次应答，预防疾病。

Herd immunity occurs when a high proportion of the population is immunised, disrupting transmission and protecting vulnerable individuals who cannot be vaccinated, such as those with compromised immune systems.

群体免疫在人群接种比例较高时形成，可阻断传播，保护那些无法接种疫苗的弱势个体，如免疫系统受损者。

Antiviral drugs work differently from antibiotics, often by inhibiting viral enzymes like reverse transcriptase or proteases (e.g., in HIV treatment). Antifungal agents target ergosterol in fungal cell membranes. Antimicrobial resistance monitoring and prudent prescribing are essential global health strategies.

抗病毒药的作用机制与抗生素不同，通常通过抑制病毒酶如逆转录酶或蛋白酶（例如 HIV 治疗）。抗真菌剂靶向真菌细胞膜中的麦角甾醇。监测抗微生物药物耐药性并审慎处方是全球重要的健康策略。

Disinfection and sterilisation methods include heat (autoclaving at 121°C for 15 minutes), chemical disinfectants, ionising radiation, and filtration. These are used to control microbial contamination in hospitals, labs, and food production.

消毒与灭菌方法包括高温（121°C 高压灭菌 15 分钟）、化学消毒剂、电离辐射和过滤法。这些方法用于控制医院、实验室和食品生产中的微生物污染。

Understanding the interplay between pathogenic microorganisms and host defences not only helps you ace the exam but also fosters an appreciation for how science informs public health campaigns and the development of life-saving therapies.

理解病原微生物与宿主防御之间的相互作用，不仅有助于在考试中取得高分，还能让你体会到科学如何为公共卫生运动提供依据，并推动挽救生命的疗法的研发。

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A-Level AQA Biology: Microorganisms – Key Points | A-Level AQA 生物：微生物 考点精讲