Microorganisms in GCSE Edexcel Biology | GCSE Edexcel 生物：微生物考点精讲

📚 Microorganisms in GCSE Edexcel Biology | GCSE Edexcel 生物：微生物考点精讲

Microorganisms, often called microbes, are tiny living organisms that are too small to be seen with the naked eye. They include bacteria, viruses, fungi, and protists, and they play vital roles in human health, ecosystems, and industrial processes. In the Edexcel GCSE Biology specification, you need to understand their structures, life cycles, how we can culture and control them, and their importance in both disease and beneficial applications.

微生物，通常被称为微生物，是肉眼看不见的微小生物。它们包括细菌、病毒、真菌和原生生物，在人类健康、生态系统和工业过程中发挥着至关重要的作用。在 Edexcel GCSE 生物学大纲中，你需要理解它们的结构、生命周期、如何培养和控制它们，以及它们在疾病和有益应用中的重要性。

1. Introduction to Microorganisms | 微生物简介

Microorganisms are classified into several major groups based on their cell structure and mode of life. The four key types for GCSE are bacteria (prokaryotes), viruses (non-living particles), fungi (eukaryotes with chitin cell walls), and protists (a diverse group of single-celled eukaryotes). Unlike larger organisms, microbes can reproduce rapidly under favourable conditions and are found in almost every habitat on Earth.

微生物根据其细胞结构和生活方式分为几个主要类群。GCSE 涉及的四个关键类型是细菌（原核生物）、病毒（非生命颗粒）、真菌（具有几丁质细胞壁的真核生物）和原生生物（一类多样的单细胞真核生物）。与大型生物不同，微生物在适宜条件下可以快速繁殖，几乎存在于地球上的每一个栖息地。

Pathogens are microbes that cause infectious diseases. However, many microorganisms are harmless or even beneficial, such as those used in the production of yoghurt, bread, and antibiotics. Understanding how the body defends itself against pathogens and how we can prevent their spread is a core part of the topic.

病原体是引起传染病的微生物。然而，许多微生物是无害的甚至是有益的，例如用于生产酸奶、面包和抗生素的微生物。理解身体如何抵御病原体以及如何阻止它们传播是本主题的核心部分。

2. Structure and Reproduction of Bacteria | 细菌的结构与繁殖

Bacteria are single-celled prokaryotes. They lack a true nucleus, having instead a single loop of chromosomal DNA that floats freely in the cytoplasm. Many bacteria also possess small rings of DNA called plasmids, which can carry genes for antibiotic resistance. Their cell wall is made of peptidoglycan, and some species have a slime capsule for protection and a flagellum for movement.

细菌是单细胞原核生物。它们没有真正的细胞核，而是有一条环状的染色体DNA游离在细胞质中。许多细菌还有称为质粒的小型DNA环，它们可以携带抗生素抗性基因。它们的细胞壁由肽聚糖构成，有些物种还具有用于保护的黏液荚膜和用于运动的鞭毛。

Bacteria reproduce by a type of asexual reproduction called binary fission. Under optimal conditions (warmth, moisture, nutrients), a single bacterium can divide approximately every 20 minutes, leading to exponential growth. The population growth can be shown as a curve: lag phase, exponential (log) phase, stationary phase, and death phase.

细菌通过一种称为二分裂的无性生殖方式进行繁殖。在最佳条件下（温暖、潮湿、营养），一个细菌大约每20分钟就能分裂一次，导致指数式增长。种群增长可以展示为一条曲线：迟缓期、指数（对数）期、稳定期和死亡期。

3. Structure and Replication of Viruses | 病毒的结构与复制

Viruses are not considered living organisms because they cannot carry out life processes independently. They consist of a small piece of genetic material (DNA or RNA) enclosed within a protective protein coat called a capsid. Some viruses, like HIV, also have an outer lipid envelope derived from the host cell membrane. They are much smaller than bacteria and can only be seen with an electron microscope.

病毒不被视为生物，因为它们无法独立进行生命活动。它们由一小段遗传物质（DNA或RNA）包裹在称为衣壳的保护性蛋白质外壳中构成。一些病毒，如HIV，还有一层来自宿主细胞膜的外部脂质包膜。它们比细菌小得多，只能用电子显微镜观察。

Viruses replicate by attaching to a specific host cell, injecting their genetic material, and hijacking the host’s machinery to produce new virus particles. This lytic cycle eventually causes the host cell to burst (lyse), releasing many new viruses. Some viruses, like the herpes virus, can enter a lysogenic cycle where the viral DNA integrates into the host genome and remains dormant for long periods.

病毒通过附着到特定的宿主细胞，注入其遗传物质，并劫持宿主的细胞器以产生新的病毒颗粒来进行复制。这种裂解周期最终导致宿主细胞破裂（裂解），释放出许多新病毒。有些病毒，如疱疹病毒，可进入溶源周期，此时病毒DNA整合到宿主基因组中并长期潜伏。

4. Fungi and Protists as Microbes | 真菌与原生生物微生物

Fungi can be unicellular (e.g., yeast) or multicellular (e.g., moulds, mushrooms). They are eukaryotes with cell walls made of chitin, not cellulose. Yeast is a single-celled fungus that reproduces asexually by budding. Multicellular fungi grow as a network of thread-like structures called hyphae, which form a mycelium. Fungi are saprotrophs, secreting enzymes to digest food externally and absorbing the broken-down nutrients.

真菌可以是单细胞的（如酵母菌）或多细胞的（如霉菌、蘑菇）。它们是真核生物，细胞壁由几丁质而非纤维素构成。酵母菌是一种通过出芽进行无性繁殖的单细胞真菌。多细胞真菌以称为菌丝的线状结构网络（形成菌丝体）方式生长。真菌是腐生生物，分泌酶在体外消化食物并吸收分解后的营养。

Protists are a diverse kingdom of single-celled eukaryotes. Some, like Plasmodium (causing malaria), are parasitic, while others are more like animal cells (protozoa) or plant cells (algae). Understanding their life cycles helps explain disease transmission. For instance, the malaria parasite has a complex life cycle involving both mosquitoes and humans.

原生生物是一个多样的单细胞真核生物界。有些是寄生的，如引起疟疾的疟原虫，而另一些更像动物细胞（原生动物）或植物细胞（藻类）。理解其生活周期有助于解释疾病传播。例如，疟原虫具有涉及蚊子和人类的复杂生活周期。

5. Aseptic Techniques for Culturing Bacteria | 培养细菌的无菌技术

In the laboratory, bacteria can be grown on sterile agar plates in an incubator. To prevent contamination from unwanted microbes and ensure safety, aseptic (sterile) techniques must be followed. Key steps include sterilising the inoculating loop by heating it in a Bunsen burner flame until red hot, dipping it in ethanol, and allowing it to cool before and after use. The Petri dish lid should be opened only slightly and taped shut, but not completely sealed, to allow oxygen to enter for aerobic bacteria and prevent anaerobic pathogen growth.

在实验室中，细菌可以在培养箱中的无菌琼脂平板上培养。为防止不受欢迎的微生物污染并确保安全，必须遵循无菌技术。关键步骤包括：将接种环在本生灯火焰上加热至红热以灭菌，浸入乙醇中消毒，并在使用前后冷却。培养皿盖应只略微打开并胶带封紧，但不要完全密封，以让氧气进入培养好氧细菌并防止厌氧病原体生长。

Plates are typically incubated at 25 °C in schools, not 37 °C (human body temperature), to reduce the risk of culturing harmful pathogens that thrive at body temperature. After incubation, distinct colonies can be observed. Each colony is assumed to have grown from a single bacterium, allowing the calculation of bacterial density in the original sample.

平板通常在学校以25 °C培养，而不是37 °C（人体温度），以降低培养在体温下旺盛生长的有害病原体的风险。培养后，可以观察到独立的菌落。每个菌落被认为是由单个细菌生长而成，从而可以计算原始样本中的细菌密度。

6. Sterilisation and Disinfection | 灭菌与消毒

Sterilisation refers to the complete elimination of all microorganisms, including bacterial spores. Methods include autoclaving (heating with steam under pressure, typically at 121 °C for 15 minutes), dry heat, gamma irradiation, and chemical sterilants. In microbiology labs, equipment and media must be sterilised before and after use to prevent contamination and ensure safe disposal.

灭菌是指完全消灭所有微生物，包括细菌芽孢。方法包括高压灭菌（在压力下用蒸汽加热，通常在121 °C持续15分钟）、干热、伽马辐照和化学灭菌剂。在微生物实验室中，设备与培养基使用前后必须灭菌，以防污染并确保安全处理。

Disinfection, in contrast, reduces the number of pathogens to a safe level but may not kill all spores. Common disinfectants include alcohol, bleach (sodium hypochlorite), and antiseptics used on skin. The effectiveness of different antibiotics and disinfectants can be tested by measuring the zone of inhibition around a treated paper disc on an agar plate.

相比之下，消毒将病原体数量降低到安全水平，但可能无法杀死所有芽孢。常见消毒剂包括酒精、漂白剂（次氯酸钠）和用于皮肤的抗菌剂。不同抗生素和消毒剂的效果可以通过测量琼脂平板上处理过的纸碟周围的抑菌圈来检验。

7. Antibiotics and Antibiotic Resistance | 抗生素与抗生素耐药性

Antibiotics are chemicals that kill bacteria or stop them from growing, without harming human cells. Penicillin, discovered by Alexander Fleming, works by preventing bacteria from forming a cell wall. Since human cells lack a cell wall, they are unaffected. Antibiotics only target bacteria; they are ineffective against viruses, which is why they are not prescribed for viral infections like the common cold or flu.

抗生素是能杀死细菌或阻止其生长，而不伤害人体细胞的化学物质。由亚历山大·弗莱明发现的青霉素通过阻止细菌形成细胞壁来起作用。由于人体细胞没有细胞壁，它们不受影响。抗生素只针对细菌；对病毒无效，这就是为什么它们不用于治疗像普通感冒或流感这样的病毒感染。

Antibiotic resistance occurs when bacteria evolve mechanisms to survive exposure to an antibiotic. This can arise through random mutations or by acquiring resistance genes via plasmids. The overuse and misuse of antibiotics, such as not completing a prescribed course, accelerate the spread of resistant strains like MRSA. To minimise resistance, it is crucial to restrict antibiotic use to necessary cases and ensure patients always finish the full course.

抗生素耐药性发生在细菌进化出在抗生素暴露下存活的机制时。这可以通过随机突变或通过质粒获得抗性基因而产生。抗生素的过度使用和滥用，例如未完成处方疗程，会加速诸如MRSA等耐药菌株的传播。为最大程度减少耐药性，限制抗生素仅在必要时使用并确保患者始终完成完整疗程至关重要。

8. Vaccination and the Immune System | 疫苗与免疫系统

Vaccination involves introducing a harmless form of a pathogen (weakened, dead, or just its antigens) into the body to stimulate an immune response. White blood cells called lymphocytes produce specific antibodies that match the pathogen’s antigens. Memory cells are also generated, providing long-term immunity. If the actual pathogen later invades, the secondary immune response is rapid and strong, often preventing disease altogether.

疫苗接种涉及将无害形式的病原体（减毒、灭活或仅其抗原）引入体内以激发免疫应答。称为淋巴细胞的白细胞产生与病原体抗原匹配的特异性抗体。记忆细胞也随之生成，提供长期免疫。如果之后真正的病原体入侵，二次免疫应答迅速而强烈，通常可完全防止疾病发生。

Herd immunity occurs when a large portion of a population is vaccinated, reducing the spread of the disease and protecting those who cannot be vaccinated, such as newborns or individuals with weakened immune systems. Examples of vaccines studied at GCSE include the MMR vaccine and the HPV vaccine, which protects against cervical cancer.

群体免疫发生在大部分人群接种疫苗时，减少了疾病传播并保护了那些无法接种的人，如新生儿或免疫系统较弱者。在GCSE中学习的疫苗例子包括MMR疫苗和HPV疫苗（预防宫颈癌）。

9. Microorganisms in Decomposition and Nutrient Cycles | 微生物在分解与物质循环中的作用

Decomposers, mainly bacteria and fungi, break down dead organic matter and waste products, releasing nutrients back into the soil. This process is essential for the carbon cycle and nitrogen cycle. Bacteria decompose proteins into ammonia (ammonification), and nitrifying bacteria convert ammonia into nitrates, which plants can absorb for growth. Without these microbes, ecosystems would collapse due to nutrient lock-up.

分解者，主要是细菌和真菌，分解死亡的有机物和废物，将营养释放回土壤。这个过程对碳循环和氮循环至关重要。细菌将蛋白质分解为氨（氨化作用），硝化细菌将氨转化为植物可吸收用于生长的硝酸盐。如果没有这些微生物，生态系统将因营养锁定而崩溃。

In carbon cycling, decomposers respire, releasing carbon dioxide back into the atmosphere, which plants use in photosynthesis. Fungi like mushrooms are also key decomposers in woodland habitats. Experiments can explore decay by placing fresh grass in vacuum flasks with and without disinfectant, measuring temperature rise as a sign of microbial respiration.

在碳循环中，分解者呼吸，将二氧化碳释放回大气，供植物用于光合作用。像蘑菇这样的真菌也是林地生境中的关键分解者。实验可通过将新鲜草放入有消毒剂和无消毒剂的保温瓶中，测量温度上升作为微生物呼吸的标志，来探究腐烂过程。

10. Microorganisms in Food Production | 微生物在食品生产中的应用

Microorganisms are harnessed in traditional and industrial food production. Yoghurt is made by adding Lactobacillus bacteria to milk. These bacteria ferment lactose sugar into lactic acid, decreasing the pH. The lactic acid causes milk proteins to coagulate and thicken into yoghurt, also giving it a tangy flavour and preserving the milk by inhibiting spoilage bacteria.

微生物被用于传统和工业食品生产中。酸奶是通过在牛奶中添加乳酸菌制成的。这些细菌将乳糖发酵成乳酸，降低pH值。乳酸使牛奶蛋白凝固并增稠成酸奶，也赋予其独特的酸味并通过抑制腐败菌来保存牛奶。

In bread making, yeast (Saccharomyces cerevisiae) carries out anaerobic respiration (fermentation), producing carbon dioxide gas and ethanol. The CO2 bubbles cause the dough to rise, creating a light, spongy texture. The ethanol evaporates during baking. Industrial fermenters are used to grow large quantities of microorganisms under controlled conditions to produce products like mycoprotein, penicillin, and biogas.

在制作面包时，酵母菌进行无氧呼吸（发酵），产生二氧化碳气体和乙醇。二氧化碳气泡使面团膨胀，形成轻盈、海绵状的质地。乙醇在烘烤过程中蒸发。工业发酵罐用于在受控条件下大量培养微生物，生产诸如真菌蛋白、青霉素和沼气等产品。

11. Preventing the Spread of Infectious Diseases | 预防传染病传播

To control the spread of microbial diseases, simple hygiene measures are highly effective. Washing hands with soap, using clean drinking water, and proper sanitation break the chain of infection transmission. For insect-borne diseases like malaria, mosquito nets and insect repellent reduce vector contact. The ‘catch it, bin it, kill it’ campaign reminds people to use tissues to trap respiratory droplets.

为控制微生物疾病的传播，简单的卫生措施非常有效。用肥皂洗手、使用清洁饮用水和适当的卫生设施可切断感染传播链。对于像疟疾这样的虫媒疾病，蚊帐和驱虫剂减少了与媒介的接触。“接住、扔掉、杀死”运动提醒人们用纸巾捕获呼吸道飞沫。

Isolation of infected individuals and sterilisation of contaminated objects are also crucial. In hospitals, strict aseptic protocols prevent surgical wound infections. Understanding the differences in how bacteria, viruses, and fungi are transmitted allows for targeted prevention strategies, such as vaccination against viruses or antifungal creams for athlete’s foot.

隔离感染者并对污染物品消毒也至关重要。在医院，严格的无菌操作规程可防止手术伤口感染。了解细菌、病毒和真菌传播方式的不同，可以采取针对性预防策略，如针对病毒的疫苗接种或治疗脚气的抗真菌药膏。

12. Investigating the Effect of Antibiotics on Bacterial Growth | 探究抗生素对细菌生长的影响

A classic practical investigation in GCSE Biology involves testing the effect of different antibiotics (or antiseptics) on bacterial growth using the disc diffusion method. Agar plates are seeded evenly with a non-pathogenic bacterium like E. coli K-12. Sterile filter paper discs, each saturated with a different antibiotic solution, are placed on the agar surface.

GCSE生物学中一个经典的实践研究涉及利用纸片扩散法测试不同抗生素（或消毒剂）对细菌生长的影响。将非致病性细菌（如大肠杆菌K-12）均匀涂布在琼脂平板上。将浸有不同抗生素溶液的无菌滤纸片置于琼脂表面。

After incubation at 25 °C, clear zones (zones of inhibition) appear around the discs where the antibiotic has stopped bacterial growth. The diameter of these zones is measured and compared. Larger zones indicate greater effectiveness. This experiment also illustrates how resistant bacteria can survive, forming colonies within the zone, a point essential for discussing antibiotic resistance evolution.

在25 °C培养后，纸片周围会出现因抗生素阻止细菌生长而形成的透明圈（抑菌圈）。测量并比较这些圈的直径。较大的圈表明效果更强。该实验也展示了耐药细菌如何存活，并在抑菌圈内形成菌落，这对于讨论抗生素耐药性进化至关重要。

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Microorganisms in GCSE Edexcel Biology | GCSE Edexcel 生物：微生物 考点精讲