📚 Microorganisms for GCSE WJEC Biology: Key Points | GCSE WJEC 生物：微生物 考点精讲
Microorganisms, also known as microbes, are tiny living organisms that are invisible to the naked eye. They include bacteria, viruses, fungi, and protists. In GCSE WJEC Biology, understanding their structure, growth, role in disease and vital functions in ecosystems and industry is essential.
微生物，也称微生物，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GCSE WJEC生物中，了解它们的结构、生长、在疾病中的作用以及在生态系统和工业中的重要功能至关重要。
1. Introduction to Microorganisms | 微生物简介
Microorganisms are found everywhere—in soil, water, air, and inside other living organisms. Many are harmless or beneficial, while some can cause diseases. The study of microorganisms is called microbiology.
微生物无处不在——存在于土壤、水、空气以及其他生物体内。许多微生物是无害或有益的，而有些则能引起疾病。研究微生物的科学称为微生物学。
2. Types of Microorganisms | 微生物的类型
There are four main groups: bacteria (single-celled, no nucleus, e.g., Lactobacillus), viruses (non-living particles, require host cells, e.g., influenza virus), fungi (can be single-celled like yeast or multicellular like moulds, have a nucleus), and protists (single-celled with nucleus, e.g., Plasmodium causing malaria).
主要有四类：细菌（单细胞，无细胞核，例如乳酸菌），病毒（非生命颗粒，需要宿主细胞，例如流感病毒），真菌（可以是单细胞如酵母，或多细胞如霉菌，有细胞核），原生生物（单细胞且有核，例如引起疟疾的疟原虫）。
3. Bacterial Growth and Reproduction | 细菌的生长与繁殖
Bacteria reproduce asexually by binary fission: one cell splits into two identical daughter cells. Under ideal conditions, the population doubles at a constant rate. The number of bacteria after n divisions can be calculated using 2ⁿ starting from a single cell.
细菌通过二分裂方式进行无性繁殖：一个细胞分裂成两个相同的子细胞。在理想条件下，种群以恒定速率成倍增长。从一个细胞开始，经过 n 次分裂后的细菌数量可以用 2ⁿ 来计算。
= 512 bacteria. Growth follows a curve with lag, exponential, stationary and death phases.
例如：如果一个细菌每20分钟分裂一次，3小时后（9次分裂）将有 2⁹ = 512 个细菌。生长曲线包括延迟期、指数期、稳定期和死亡期。
4. Culturing Microorganisms in the Lab | 实验室培养微生物
To study microbes, they are grown on agar plates containing nutrients. It is vital to use aseptic technique to prevent contamination: sterilise equipment, work near a Bunsen burner flame, and seal plates with tape but not fully to allow oxygen for aerobic bacteria. Incubate at 25°C in school labs to avoid growing harmful pathogens that thrive at body temperature.
为了研究微生物，将其培养在含有营养物质的琼脂平板上。必须使用无菌技术以防止污染：灭菌设备，在酒精灯火焰附近操作，用胶带密封平板但不完全封闭以允许需氧菌获得氧气。在学校实验室中，在25°C下培养，以避免培养出在体温下旺盛生长的有害病原体。
Calculating bacterial growth on agar: count colonies and multiply by dilution factor to estimate original concentration (colony-forming units per cm³, CFU/cm³).
计算琼脂上的细菌生长：计数菌落数并乘以稀释倍数以估算原始浓度（每立方厘米菌落形成单位，CFU/cm³）。
5. Pathogens and Disease Transmission | 病原体与疾病传播
Pathogens are microorganisms that cause infectious diseases. They can be spread by direct contact (e.g., HIV, Ebola), air (droplet infection, e.g., influenza, tuberculosis), contaminated water and food (e.g., cholera, Salmonella), or by vectors such as mosquitoes (e.g., malaria).
病原体是引起传染病的微生物。它们可以通过直接接触传播（如 HIV、埃博拉），通过空气（飞沫感染，如流感、肺结核），通过污染的水和食物（如霍乱、沙门氏菌），或通过媒介生物如蚊子（如疟疾）传播。
6. The Body's Defence Against Pathogens | 人体对病原体的防御
The body has non-specific defences: skin as a physical barrier, blood clotting to seal wounds, stomach acid that kills many microbes, and mucus and cilia in airways that trap and sweep away particles. White blood cells can ingest pathogens (phagocytosis) and produce antibodies as part of specific immune response.
人体具有非特异性防御：皮肤作为物理屏障，血液凝固封闭伤口，胃酸杀死许多微生物，呼吸道中的黏液和纤毛能捕获并清除颗粒。白细胞可以通过吞噬作用摄入病原体，并作为特异性免疫反应的一部分产生抗体。
7. Immunity and Vaccination | 免疫与疫苗接种
When a new pathogen enters the body, white blood cells produce specific antibodies that bind to antigens on the pathogen, marking it for destruction. Memory cells are produced and remain in the blood, providing long-term immunity. Vaccination introduces weakened or dead pathogens, or just antigens, to stimulate antibody production and memory cells without causing disease.
当新的病原体进入人体时，白细胞会产生特异性抗体，这些抗体与病原体上的抗原结合，标记其以便消灭。记忆细胞会产生并留在血液中，提供长期免疫力。疫苗接种引入减弱或死亡的病原体，或仅引入抗原，刺激抗体产生和记忆细胞形成，而不会引起疾病。
Herd immunity occurs when a high percentage of the population is vaccinated, protecting those who are not immune.
当人口中很大比例接种疫苗时，会形成群体免疫，从而保护那些没有免疫力的人。
8. Antibiotics and Antibiotic Resistance | 抗生素与抗生素耐药性
Antibiotics are medicines that kill bacteria or stop them growing. They do not work against viruses. Penicillin, discovered by Alexander Fleming, is an example. However, overuse has led to antibiotic resistance: bacteria mutate, and resistant strains survive and multiply. MRSA is a resistant strain. To slow resistance, doctors prescribe antibiotics only when necessary, and patients must complete the full course.
抗生素是杀死细菌或阻止其生长的药物。它们对病毒无效。青霉素，由亚历山大·弗莱明发现，就是一个例子。然而，过度使用导致了抗生素耐药性：细菌发生突变，耐药菌株存活并繁殖。MRSA 就是一种耐药菌株。为了减缓耐药性，医生只在必要时开具抗生素，患者必须完成整个疗程。
9. Beneficial Microorganisms in Food Production | 食物生产中的有益微生物
Yeast is used in baking to make bread rise through anaerobic respiration, producing carbon dioxide. It is also used in brewing to produce ethanol. Bacteria like Lactobacillus are used to make yogurt by fermenting lactose into lactic acid, which thickens and sours the milk. Fungus Fusarium is used to produce mycoprotein, a meat substitute.
酵母用于烘焙，通过无氧呼吸产生二氧化碳使面包膨胀。它也用于酿造以产生乙醇。像乳酸菌这样的细菌用于制作酸奶，通过将乳糖发酵成乳酸，使牛奶变稠变酸。真菌镰刀霉用于生产菌蛋白，一种肉类替代品。
10. Decomposers and the Carbon Cycle | 分解者与碳循环
Microorganisms, especially bacteria and fungi, are decomposers. They break down dead organic matter, releasing nutrients back into the soil and releasing carbon dioxide into the atmosphere through respiration. This is a crucial part of the carbon cycle, maintaining the balance of carbon between living organisms, the atmosphere, and the soil.
微生物，尤其是细菌和真菌，是分解者。它们分解死去的有机物质，将养分释放回土壤，并通过呼吸作用将二氧化碳释放到大气中。这是碳循环的关键部分，维持了生物、大气和土壤之间碳的平衡。
11. Preventing Food Spoilage | 防止食物变质
Microorganisms cause food to decay. Methods to preserve food include refrigeration (slows growth), freezing, heating (pasteurisation), adding salt/sugar (osmotic effect removes water from microbes), vinegar (acidic pH) and vacuum packing (removes oxygen). These techniques reduce microbial activity and keep food safe for longer.
微生物导致食物腐烂。保存食物的方法包括冷藏（减缓生长）、冷冻、加热（巴氏消毒）、添加盐/糖（渗透作用从微生物中去除水分）、醋（酸性pH）和真空包装（去除氧气）。这些技术减少微生物活动，使食物更长时间保持安全。
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