GCSE Biology: Microorganisms – Key Revision Points | GCSE 生物：微生物考点精讲

📚 GCSE Biology: Microorganisms – Key Revision Points | GCSE 生物：微生物考点精讲

Microorganisms are a central topic in GCSE Biology. You need to know the different types of microbes, how they cause disease, how our body fights them off, and the vital roles they play in ecosystems and food production. This bilingual revision guide covers every key point you will encounter in your exams, with clear English explanations followed by Chinese translations to support your learning.

微生物是 GCSE 生物学的核心主题。你需要掌握不同类型微生物的特征、它们如何致病、人体如何防御感染，以及它们在生态系统和食品生产中的重要作用。本双语复习指南覆盖考试中所有关键考点，每个概念均采用英文讲解后跟中文翻译的方式，帮助你透彻理解。

1. What Are Microorganisms? | 什么是微生物？

Microorganisms, or microbes, are organisms that are too small to be seen with the naked eye. They exist all around us – in soil, water, air, and inside our bodies. In GCSE Biology, we study four main groups: bacteria, viruses, fungi, and protists.

微生物是指肉眼无法看到的微小生物。它们存在于我们周围的土壤、水、空气以及人体内部。在 GCSE 生物中，我们主要学习四大类微生物：细菌、病毒、真菌和原生生物。

Some microorganisms are harmful pathogens that cause communicable diseases, while many others are essential for processes such as decomposition, recycling nutrients, and producing foods like yoghurt and bread.

部分微生物是引发传染病的病原体，但许多微生物在分解作用、养分循环以及酸奶、面包等食品生产中发挥着关键作用。

2. Types and Structures of Microorganisms | 微生物的类型与结构

Understanding the basic structure of each type of microbe helps explain how they function and how we can control them. The table below compares bacteria, viruses, fungi and protists.

了解各类微生物的基本结构有助于理解它们的功能以及控制它们的方法。下表对细菌、病毒、真菌和原生生物进行了比较。

Feature	Bacteria 细菌	Viruses 病毒	Fungi 真菌	Protists 原生生物
Cell type 细胞类型	Prokaryotic 原核	Not cellular 非细胞	Eukaryotic 真核	Eukaryotic 真核
Genetic material 遗传物质	Circular DNA loop, plasmids 环状DNA、质粒	DNA or RNA inside protein coat 蛋白质外壳内的DNA或RNA	Linear chromosomes in nucleus 细胞核内线性染色体	Linear chromosomes in nucleus 细胞核内线性染色体
Cell wall 细胞壁	Peptidoglycan 肽聚糖	No cell wall 无细胞壁	Chitin 几丁质	Variable / no cell wall 不定或无细胞壁
Examples 例子	E. coli, Salmonella 大肠杆菌、沙门氏菌	Influenza virus, HIV 流感病毒、HIV	Yeast, Mucor 酵母菌、毛霉	Plasmodium (malaria) 疟原虫（疟疾）

Viruses are much smaller than bacteria and can only reproduce inside a living host cell. They are not considered living by many scientists because they do not show all life processes on their own.

病毒比细菌小得多，只能在活宿主细胞内繁殖。许多科学家认为病毒不属于生物，因为它们无法独自完成所有生命活动。

3. Reproduction and Growth of Microorganisms | 微生物的繁殖与生长

Bacteria reproduce asexually by binary fission: the cell replicates its DNA and splits into two identical daughter cells. Under ideal warm, moist and nutrient-rich conditions, bacteria can divide as often as every 20 minutes.

细菌通过二分裂进行无性繁殖：细胞复制其 DNA 后分裂成两个相同的子细胞。在温暖、潮湿和营养充足的理想条件下，细菌每 20 分钟就能分裂一次。

Fungi can reproduce asexually via budding (as in yeast) or by producing huge numbers of spores that disperse in the air. Viruses replicate by injecting their genetic material into a host cell, hijacking the cell’s machinery to mass-produce new virus particles, which eventually burst out of the cell.

真菌可通过出芽（如酵母）或产生大量在空气中传播的孢子进行无性繁殖。病毒通过将遗传物质注入宿主细胞，劫持细胞结构大量复制新病毒颗粒，最终使细胞破裂释放病毒。

4. Culturing Microorganisms and Aseptic Technique | 微生物培养与无菌技术

In the lab, microorganisms are grown on agar plates containing nutrients. To prevent contamination by unwanted microbes and to ensure safety, aseptic techniques must be used. This includes sterilising the inoculating loop by flaming, working near a Bunsen burner to create an updraft, and taping the lid of the Petri dish after inoculation.

在实验室中，微生物生长在含有营养的琼脂平板上。为了防止杂菌污染并确保安全，必须使用无菌操作技术，包括通过火焰灼烧接种环灭菌、在酒精灯附近操作形成上升气流，以及接种后用胶带封住培养皿盖。

In school labs, cultures are typically incubated at 25°C rather than 37°C to minimise the risk of growing pathogens that could be harmful to humans. Uncontaminated bacterial colonies are visible as circular spots on the agar surface.

学校实验室中，通常将培养物在 25°C 而非 37°C 下培养，以降低致病菌生长的风险。未被污染的细菌菌落在琼脂表面呈现圆形斑点。

5. Microorganisms as Pathogens | 病原微生物

Pathogens are microorganisms that cause infectious (communicable) diseases. Bacteria can release toxins that damage tissues; viruses take over and destroy host cells; fungi and protists can parasitise and cause serious illness. Examples include Salmonella food poisoning, measles, athlete’s foot and malaria.

病原体是引起传染性疾病的微生物。细菌可释放毒素损伤组织；病毒劫持并破坏宿主细胞；真菌和原生生物可寄生导致重病，例如沙门氏菌食物中毒、麻疹、脚癣和疟疾。

To cause disease, pathogens must enter the body, adhere to tissues, multiply and often produce toxins. The severity depends on the site of infection and the immune response of the host.

要致病，病原体需进入人体、附着于组织、大量繁殖并常产生毒素。疾病的严重程度取决于感染部位和宿主的免疫应答。

6. Spread and Prevention of Disease | 疾病的传播与预防

Communicable diseases can spread through direct contact, airborne droplets (sneezing/coughing), contaminated water or food, and vectors such as insects. For instance, malaria is spread by female Anopheles mosquitoes.

传染病可通过直接接触、空气飞沫（打喷嚏/咳嗽）、污染的水或食物以及媒介昆虫（如蚊子）传播。例如疟疾由雌性按蚊传播。

Prevention strategies include good hygiene, clean drinking water, vaccination, using mosquito nets, and isolating infected individuals. In the 19th century, Ignaz Semmelweis showed that hand washing dramatically reduced deaths from childbed fever, highlighting the importance of asepsis.

预防策略包括保持良好卫生、提供清洁饮用水、接种疫苗、使用蚊帐以及隔离感染者。19 世纪，塞麦尔维斯证明洗手能大幅降低产褥热死亡率，凸显了无菌操作的重要性。

7. Human Defence Systems Against Pathogens | 人体对病原体的防御系统

The human body has non-specific first lines of defence: the skin acts as a physical barrier, stomach acid kills swallowed microbes, and enzymes in tears destroy bacteria. If pathogens break through, the immune system responds with phagocytes that engulf and digest invaders, and lymphocytes that produce antibodies and antitoxins.

人体拥有非特异性第一道防线：皮肤起物理屏障作用，胃酸杀死吞入的微生物，泪液中的酶可破坏细菌。若病原体突破防线，免疫系统中的吞噬细胞会吞噬并消化入侵者，淋巴细胞则产生抗体和抗毒素。

Each antibody is specific to a particular antigen on the pathogen’s surface. Memory lymphocytes remain in the blood for a long time, enabling a faster and stronger response upon re-infection.

每种抗体专门针对病原体表面的特定抗原。记忆淋巴细胞可长期存留在血液中，当再次感染时能产生更快更强的免疫反应。

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

Antibiotics, such as penicillin, kill bacteria by targeting structures that human cells lack, like cell walls. They do not work against viruses because viruses have no cell walls and hide inside host cells. Doctors prescribe antibiotics only for bacterial infections to avoid resistance.

抗生素（如青霉素）通过攻击人类细胞不具备的结构（如细胞壁）来杀灭细菌。它们对病毒无效，因为病毒无细胞壁且隐藏在宿主细胞内。医生仅对细菌感染使用抗生素以避免耐药性。

Antibiotic resistance arises when a random mutation enables some bacteria to survive. These resistant strains multiply and spread, passing the resistance gene via plasmids. MRSA is a well-known example. To slow resistance, it is crucial to complete the full prescribed course of antibiotics.

当随机突变使某些细菌存活下来时，便会产生抗生素耐药性。这些耐药菌株繁殖传播，通过质粒传递耐药基因。MRSA 是一个典型例子。为减缓耐药性，必须完成整个抗生素疗程。

9. Vaccination and Herd Immunity | 疫苗接种与群体免疫

Vaccines contain weakened or inactive forms of a pathogen, or just its antigens. They trigger an immune response, causing lymphocytes to produce memory cells without causing illness. If the real pathogen later enters the body, memory cells can quickly produce large amounts of antibodies to prevent disease.

疫苗含有减毒或灭活的病原体，或仅其抗原。它们激发免疫应答，使淋巴细胞产生记忆细胞而不会致病。当真正的病原体后来入侵时，记忆细胞能迅速产生大量抗体阻止发病。

When a high percentage of the community is vaccinated, herd immunity protects those who cannot be vaccinated, such as very young infants or people with weak immune systems. This reduces the spread of the pathogen throughout the population.

当社区中大部分人接种疫苗后，群体免疫可以保护无法接种者（如婴幼儿或免疫力低下者），减少病原体在人群中的传播。

10. Useful Microorganisms in Food Production | 食品生产中有益微生物

Not all microbes are harmful. Yeast, a single-celled fungus, is used in baking and brewing. It respires anaerobically to produce carbon dioxide that makes bread rise and ethanol in alcoholic drinks. The word equation for anaerobic respiration in yeast is:

并非所有微生物都有害。酵母（一种单细胞真菌）用于烘焙和酿造。它进行无氧呼吸产生二氧化碳使面包膨胀，并产生酒精。酵母无氧呼吸的文字方程式为：

Glucose → Ethanol + Carbon dioxide (energy released)

葡萄糖 → 乙醇 + 二氧化碳（释放能量）

Bacteria such as Lactobacillus are used to turn milk into yoghurt and cheese. These bacteria ferment lactose into lactic acid, which thickens the milk and gives yoghurt its tangy taste. Industrial fermentation also produces insulin and antibiotics.

乳酸杆菌等细菌用于将牛奶制成酸奶和奶酪。这些细菌将乳糖发酵为乳酸，使牛奶变稠并赋予酸奶酸味。工业发酵还能生产胰岛素和抗生素。

11. Decomposition and the Carbon Cycle | 分解作用与碳循环

Decomposers, mainly bacteria and fungi, break down dead organic matter and waste, returning mineral ions to the soil. This is a crucial part of nutrient cycling. Aerobic respiration by decomposers releases carbon dioxide back into the atmosphere.

分解者主要是细菌和真菌，它们分解死去的有机物和废弃物，将矿物离子归还土壤。这是养分循环的关键环节。分解者进行有氧呼吸将二氧化碳释放回大气。

In the carbon cycle, carbon dioxide is removed from the air by photosynthesis in plants and algae. Animals eat plants and respire, releasing CO₂. Decomposers break down dead organisms, and combustion of fossil fuels adds CO₂. These processes maintain a balanced carbon cycle.

在碳循环中，植物和藻类通过光合作用从空气中吸收二氧化碳。动物摄食植物并进行呼吸释放 CO₂。分解者分解死去的生物体，化石燃料的燃烧也释放 CO₂。这些过程维持了碳循环的平衡。

12. The Nitrogen Cycle | 氮循环

The nitrogen cycle shows how nitrogen is converted between its various forms essential for life. Nitrogen-fixing bacteria in root nodules of leguminous plants, or free-living in soil, convert atmospheric nitrogen (N₂) into ammonia (NH₃). Ammonia is then converted to nitrites and then to nitrates by nitrifying bacteria.

氮循环展示了氮元素在各类生命必需形式间的转化。豆科植物根瘤中的固氮菌，或土壤中自由生活的固氮菌，将大气中的氮气 (N₂) 转化为氨 (NH₃)。氨随后被硝化细菌转化为亚硝酸盐再转化为硝酸盐。

Plants absorb nitrates to make proteins. When plants and animals die, decomposers break down the proteins into ammonia (ammonification). Denitrifying bacteria convert nitrates back to nitrogen gas under anaerobic conditions, completing the cycle.

植物吸收硝酸盐合成蛋白质。动植物死亡后，分解者将蛋白质分解为氨（氨化作用）。反硝化细菌在缺氧条件下将硝酸盐转化为氮气，完成循环。

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GCSE Biology: Microorganisms – Key Revision Points | GCSE 生物：微生物 考点精讲