Microorganisms: GCSE CCEA Biology Revision | GCSE CCEA 生物：微生物 考点精讲

📚 Microorganisms: GCSE CCEA Biology Revision | GCSE CCEA 生物：微生物 考点精讲

Microorganisms, or microbes, are tiny living organisms that are too small to be seen with the naked eye. They include bacteria, viruses, fungi, and protists. In the CCEA GCSE Biology specification, understanding their structure, roles, and impact on human health and the environment is essential.

微生物是肉眼看不见的微小生物，包括细菌、病毒、真菌和原生生物。在 CCEA GCSE 生物学大纲中，理解它们的结构、作用以及对人类健康和环境的影响至关重要。

1. Types of Microorganisms | 微生物的类型

Microorganisms are classified into several groups based on their cell structure and genetic material. The main groups are bacteria, viruses, fungi, and protists. Each has distinct characteristics.

微生物根据细胞结构和遗传物质分为几个主要类别：细菌、病毒、真菌和原生生物，每一类都有独特的特征。

Bacteria are prokaryotic, unicellular organisms with no nucleus. Their genetic material forms a single circular chromosome and sometimes extra plasmids. They have a cell wall, cell membrane, and cytoplasm.

细菌是原核单细胞生物，没有细胞核。遗传物质是一条环状染色体，有时还有额外的质粒。它们有细胞壁、细胞膜和细胞质。

Viruses are not considered living cells. They consist of a protein coat (capsid) surrounding genetic material (DNA or RNA). They can only reproduce inside a host cell.

病毒不被视为活细胞。它们由蛋白质外壳包裹遗传物质（DNA或RNA）构成，只能在宿主细胞内繁殖。

Fungi can be unicellular like yeast or multicellular like moulds and mushrooms. Their cells have a nucleus and a cell wall made of chitin.

真菌可以是单细胞的（如酵母）或多细胞的（如霉菌和蘑菇）。细胞有细胞核，细胞壁由几丁质构成。

Protists are unicellular eukaryotes, such as amoeba and Plasmodium (the malaria parasite). They possess a nucleus and other membrane-bound organelles.

原生生物是单细胞真核生物，如变形虫和疟原虫。它们有细胞核和其他膜结构的细胞器。

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2. Bacteria: Structure and Reproduction | 细菌：结构与繁殖

Bacteria have a simple cell structure without membrane-bound organelles. Key structures include: circular DNA, plasmids, ribosomes, cell membrane, cell wall, and sometimes a slime capsule and flagella for movement.

细菌结构简单，没有膜结构的细胞器。主要结构包括：环状DNA、质粒、核糖体、细胞膜、细胞壁，有时还有荚膜和用于运动的鞭毛。

They reproduce asexually by binary fission, where one cell divides into two genetically identical daughter cells. This can occur very rapidly in warm, moist, nutrient-rich conditions.

它们通过二分裂进行无性繁殖，一个细胞分裂成两个基因相同的子细胞。在温暖、潮湿、营养丰富的条件下，繁殖速度极快。

Under favourable conditions, bacteria can divide every 20 minutes. To calculate population growth, use the formula: number of bacteria = starting number × 2ⁿ (n = number of divisions).

在适宜条件下，细菌每20分钟分裂一次。使用公式计算种群增长：细菌数量 = 起始数量 × 2ⁿ（n 为分裂次数）。

N = N₀ × 2ⁿ

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3. Viruses: Structure and Infection | 病毒：结构与感染

Viruses are acellular and much smaller than bacteria. They contain either DNA or RNA enclosed in a protein coat. Some have an additional lipid envelope.

病毒无细胞结构，比细菌小得多。它们包含DNA或RNA，外有蛋白质外壳，有些还有脂质包膜。

To replicate, a virus attaches to a specific host cell, injects its genetic material, and hijacks the cell’s machinery to produce new virus particles. The host cell eventually bursts, releasing the viruses.

病毒通过附着在特定宿主细胞、注入遗传物质，劫持细胞机制制造新病毒颗粒。宿主细胞最终破裂，释放病毒。

Because viruses lack cell structures and independent metabolism, antibiotics do not affect them. Antiviral drugs are designed to interfere with viral replication.

由于病毒没有细胞结构和独立代谢，抗生素对它们无效。抗病毒药物旨在干扰病毒复制。

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4. Fungi and Protists in Detail | 真菌与原生生物详解

Fungi are heterotrophic, absorbing nutrients from dead or living organic matter. They play a vital role as decomposers. Yeast respires anaerobically to produce ethanol and carbon dioxide, used in baking and brewing.

真菌是异养生物，从死的或活的有机质中吸收营养。它们作为分解者扮演重要角色。酵母无氧呼吸产生乙醇和二氧化碳，用于烘焙和酿造。

Multicellular fungi like Mucor have a network of hyphae called mycelium. They reproduce via spores, which can be produced asexually in sporangia.

多细胞真菌如毛霉，具有由菌丝构成的菌丝体。通过孢子繁殖，孢子可在孢子囊中无性产生。

Protists are a diverse group, including plant-like algae (e.g., Euglena) and animal-like protozoa. Some protozoa are pathogens, such as Plasmodium causing malaria, transmitted by mosquito vectors.

原生生物种类多样，包括类似植物的藻类（如眼虫）和类似动物的原生动物。部分原生动物是病原体，如引起疟疾的疟原虫，由蚊子媒介传播。

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5. Beneficial Uses of Microorganisms | 微生物的有益用途

Microorganisms are essential in many industries and ecological processes. Yeast is used in bread-making (CO₂ production causes dough to rise) and in alcohol production (ethanol).

微生物在许多工业和生态过程中不可或缺。酵母用于制作面包（产生的CO₂使面团膨胀）和酒精生产（乙醇）。

Bacteria like Lactobacillus are used to make yoghurt and cheese. They ferment lactose in milk to lactic acid, which curdles milk proteins and gives a tangy flavour.

乳酸菌等细菌用于制作酸奶和奶酪。它们将牛奶中的乳糖发酵为乳酸，使牛奶蛋白凝固，产生独特酸味。

In agriculture, nitrogen-fixing bacteria live in root nodules of legumes, converting atmospheric nitrogen into nitrates for plant growth. Sewage treatment also relies on bacteria to decompose organic waste.

在农业中，固氮菌生活在豆科植物根瘤中，将大气氮转化为植物可用的硝酸盐。污水处理也依靠细菌分解有机废物。

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6. Pathogens and How They Cause Disease | 病原体及其致病机理

Pathogens are microorganisms that cause infectious diseases. Bacteria can produce toxins that damage cells, e.g., Salmonella causing food poisoning. Viruses invade and destroy host cells.

病原体是引起传染病的微生物。细菌可产生毒素损害细胞，如沙门氏菌引起食物中毒。病毒入侵并破坏宿主细胞。

Transmission can occur through direct contact, airborne droplets, contaminated food or water, and vectors like mosquitoes. The CCEA specification emphasises understanding the spread of malaria (protist), cholera (bacterium), and HIV (virus).

传播途径包括直接接触、飞沫传播、受污染的食物或水，以及蚊子等媒介。CCEA 大纲强调理解疟疾（原生生物）、霍乱（细菌）和 HIV（病毒）的传播。

Body defences: the first line includes skin, mucus, cilia, and stomach acid. The second line is the immune system: white blood cells engulf pathogens (phagocytosis), produce antibodies specific to antigens, and antitoxins to neutralise toxins.

人体防御：第一道防线包括皮肤、黏液、纤毛和胃酸。第二道防线是免疫系统：白细胞吞噬病原体（吞噬作用），产生针对抗原的特异性抗体，以及中和毒素的抗毒素。

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7. Aseptic Technique in the Lab | 实验室无菌操作技术

Aseptic technique prevents contamination by unwanted microorganisms. In CCEA practicals, you must describe how to culture bacteria safely on agar plates.

无菌技术可防止不需要的微生物污染。在 CCEA 实验操作中，必须描述如何在琼脂平板上安全培养细菌。

Key steps: sterilise the inoculating loop by heating it in a flame until red hot; open the Petri dish lid only slightly near the flame; streak the loop gently on the agar; seal the dish with tape (not completely airtight to avoid anaerobic pathogens); incubate at 25°C to prevent growth of human pathogens.

关键步骤：将接种环在火焰上灼烧至红热灭菌；在火焰附近稍微打开培养皿盖；轻轻在琼脂上划线；用胶带密封培养皿（不完全密闭，避免厌氧致病菌生长）；在25°C 下培养，防止人体病原体生长。

After incubation, visible colonies appear. Each colony arises from a single bacterium or cluster of bacteria. Disinfect the work surfaces and wash hands thoroughly afterwards.

培养后可见菌落。每个菌落源自单个细菌或细菌团。用后消毒工作台并彻底洗手。

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

Antibiotics are drugs that kill bacteria or prevent their reproduction. They work by targeting bacterial cell walls (e.g., penicillin) or protein synthesis, without harming human cells. They do not affect viruses.

抗生素是能够杀死细菌或阻止其繁殖的药物。它们通过靶向细菌细胞壁（如青霉素）或蛋白质合成，而不伤害人体细胞。对病毒无效。

Antibiotic resistance arises when bacteria mutate, allowing them to survive antibiotic treatment. These resistant strains multiply, and the resistance gene can be passed to other bacteria via plasmids. This reduces the effectiveness of antibiotics.

细菌发生突变后可能对抗生素产生耐药性，存活下来并繁殖。耐药基因可通过质粒传递给其他细菌，降低抗生素效力。

To slow resistance, it is crucial to complete the prescribed course of antibiotics and avoid unnecessary use. Antibiotics should not be used for viral infections like colds or flu.

延缓耐药性的关键在于完成处方疗程，避免非必要使用。不应使用抗生素治疗感冒或流感等病毒感染。

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9. Food Spoilage and Preservation | 食物腐败与保藏

Microorganisms cause food to decay by breaking down organic matter. This can be slowed or prevented by altering conditions that microbes need to grow: temperature, moisture, pH, and oxygen.

微生物通过分解有机物导致食物腐败。通过改变微生物生长所需的条件如温度、水分、pH 和氧气，可以延缓或防止腐败。

Methods include: freezing or refrigeration (slows metabolism), drying (removes water), adding salt or sugar (osmosis dehydrates microbes), pickling with vinegar (low pH denatures enzymes), and heat treatment like pasteurisation (kills pathogens).

方法包括：冷冻或冷藏（减缓代谢）、干燥（去除水分）、加盐或糖（渗透作用使微生物脱水）、用醋腌制（低 pH 使酶变性），以及巴氏消毒等热处理（杀灭病原体）。

Canning involves sealing food in airtight containers and heating to kill microorganisms and spores, then preventing recontamination. Vacuum packaging excludes oxygen, inhibiting aerobic bacteria.

罐藏是将食物密封在容器中加热杀灭微生物和孢子，并防止再次污染。真空包装排除氧气，抑制需氧菌。

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10. Microorganisms in the Nitrogen Cycle | 氮循环中的微生物

The nitrogen cycle describes how nitrogen is converted between its various chemical forms. This cycle is heavily driven by specialist bacteria, making it a core CCEA topic.

氮循环描述了氮在不同化学形态之间的转化过程。这一循环主要由特定细菌驱动，是 CCEA 的核心主题。

Nitrogen fixation: bacteria such as Rhizobium in root nodules and free-living Azotobacter convert atmospheric nitrogen (N₂) into ammonia (NH₃), which forms ammonium ions (NH₄⁺) in soil. Lightning also fixes small amounts.

固氮：根瘤中的根瘤菌与自由生活的固氮菌将大气氮（N₂）转化为氨（NH₃），在土壤中形成铵离子（NH₄⁺）。闪电也能固定少量氮。

Nitrification: ammonium ions are first oxidised to nitrites (NO₂⁻) by Nitrosomonas, then to nitrates (NO₃⁻) by Nitrobacter. Nitrates can be absorbed by plant roots.

硝化作用：铵离子先被亚硝化单胞菌氧化为亚硝酸盐（NO₂⁻），再被硝化杆菌氧化为硝酸盐（NO₃⁻）。硝酸盐能被植物根部吸收。

Decomposition: decomposer fungi and bacteria break down dead organic matter and animal waste, releasing ammonium ions back into the soil.

分解：分解者真菌

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