📚 IGCSE OCR Biology: Microorganisms Exam Study Guide | IGCSE OCR 生物：微生物 考点精讲
Microorganisms are fundamental to life on Earth and a core topic in IGCSE OCR Biology. From their roles in disease to their essential functions in decomposition and biotechnology, a clear understanding of microbes can secure high marks in your exam. This guide breaks down every key area, uses precise scientific vocabulary, and highlights common pitfalls to help you revise efficiently.
微生物是地球生命的基础，也是 IGCSE OCR 生物学的核心主题。从它们在疾病中的角色到在分解与生物技术中不可或缺的功能，透彻理解微生物能让你在考试中稳拿高分。本指南拆解每一个关键领域，使用准确的科学术语，并指出常见误区，助你高效复习。
1. What Are Microorganisms? | 什么是微生物？
Microorganisms (microbes) are organisms that are generally too small to be seen without a microscope. They are found in every habitat on Earth, from deep-sea vents to human skin, and include bacteria, viruses, fungi, and protists.
微生物（微生物）是通常需要借助显微镜才能看到的微小生物。它们存在于地球上的每一个栖息地，从深海热液喷口到人类皮肤，包括细菌、病毒、真菌和原生生物。
Not all microorganisms are harmful; in fact, the vast majority are essential for processes such as decomposition, nitrogen fixation, and food production. Only a small fraction are pathogenic (disease-causing).
并非所有微生物都是有害的；事实上，绝大多数微生物对于分解、固氮和食品生产等过程至关重要。只有一小部分具有致病性（引发疾病）。
In your OCR IGCSE exam, you must be able to distinguish between the major groups based on their cellular structure, size, and mode of nutrition.
在 OCR IGCSE 考试中，你必须能够根据细胞结构、大小和营养方式区分这些主要类群。
2. Classification and Characteristics | 分类与特征
The four main groups of microorganisms are viruses, bacteria, fungi, and protists. Each group has distinct features that are regularly tested.
微生物主要分为四类：病毒、细菌、真菌和原生生物。每一类都有独特特征，经常出现在考题中。
Viruses are acellular and consist only of genetic material (DNA or RNA) surrounded by a protein coat (capsid). They are not considered living because they cannot carry out life processes independently and must invade host cells to replicate.
病毒是非细胞结构，仅由遗传物质（DNA 或 RNA）和蛋白质外壳（衣壳）组成。它们不被视为生物，因为它们无法独立进行生命活动，必须侵入宿主细胞才能复制。
Bacteria are unicellular prokaryotes. Their cells lack a nucleus; instead, genetic material floats freely in the cytoplasm as a circular chromosome. Many bacteria also possess small DNA loops called plasmids.
细菌是单细胞原核生物。它们的细胞没有细胞核，遗传物质以环状染色体的形式在细胞质中游离存在。许多细菌还具有称为质粒的小型 DNA 环。
Fungi can be unicellular (e.g., yeast) or multicellular (e.g., moulds, mushrooms). Their cells are eukaryotic and have cell walls made of chitin, not cellulose. Fungi feed by saprotrophic nutrition, secreting enzymes onto dead matter and absorbing the digested products.
真菌可以是单细胞（例如酵母菌）或多细胞（例如霉菌、蘑菇）。它们的细胞是真核细胞，细胞壁由几丁质组成，而非纤维素。真菌通过腐生营养方式获取养分，向死物分泌酶并吸收消化后的产物。
Protists are a diverse group of eukaryotic microorganisms, many of which are single-celled. Examples include Plasmodium (which causes malaria) and Amoeba. Some are photosynthetic, while others are heterotrophic.
原生生物是一类多样化的真核微生物，许多为单细胞。例子包括疟原虫（引起疟疾）和变形虫。有些能进行光合作用，有些则为异养。
3. Bacterial Structure and Prokaryotes | 细菌结构与原核生物
A typical bacterial cell contains a cell membrane, cytoplasm, cell wall (made of peptidoglycan, not cellulose), a circular chromosome of DNA, plasmids, and ribosomes. Flagella may be present for movement, and a slime capsule can protect against the host's immune system or drying out.
典型的细菌细胞包含细胞膜、细胞质、细胞壁（由肽聚糖组成，而非纤维素）、环状 DNA 染色体、质粒和核糖体。可能存在用于运动的鞭毛，荚膜可保护细菌免受宿主免疫系统攻击或防止干燥。
Bacteria are described as prokaryotic because they lack a nucleus and membrane-bound organelles such as mitochondria or chloroplasts. This is a key comparison point with eukaryotic plant and animal cells in the exam.
细菌被描述为原核生物，因为它们没有细胞核和膜包裹的细胞器，如线粒体或叶绿体。这是考试中与真核动植物细胞进行对比的关键点。
Plasmids can be transferred between bacteria, including genes for antibiotic resistance, which is crucial to understanding the spread of 'superbugs'.
质粒可以在细菌之间转移，包括抗生素抗性基因，这对理解“超级细菌”的传播至关重要。
Some bacteria are autotrophic and can photosynthesise (e.g., cyanobacteria), but many are heterotrophic and obtain nutrients from other organisms, either as decomposers or parasites.
有些细菌是自养的，能进行光合作用（如蓝细菌），但很多是异养的，作为分解者或寄生虫从其他生物获取营养。
4. Viruses: Living or Non-living? | 病毒：生命体还是非生命体？
Viruses are at the boundary of living and non-living. The exam expects you to explain that they lack cellular organisation, cannot respire, feed, or excrete, and do not grow. They reproduce only inside a host cell by hijacking the host's machinery.
病毒处于生命与非生命的边界。考试要求你解释它们缺乏细胞结构，不能呼吸、摄食或排泄，也不会生长。它们只在宿主细胞内通过劫持宿主机制进行繁殖。
The structure of a virus includes a core of genetic material (DNA or RNA) and a protein coat. Some have an additional lipid envelope stolen from the host cell, as in the influenza virus.
病毒的结构包括遗传物质核心（DNA 或 RNA）和蛋白质外壳。有些病毒还有一个从宿主细胞“窃取”的脂质包膜，例如流感病毒。
The lytic cycle is the main replication process: the virus attaches to the host, injects its genetic material, replicates new virus particles, and causes the cell to burst (lysis), releasing new viruses.
裂解循环是主要的复制过程：病毒附着在宿主上，注入遗传物质，复制新的病毒颗粒，并使细胞破裂（裂解），释放出新的病毒。
Since viruses do not respire or metabolise, antibiotics are ineffective against them. This is a classic OCR question — you must be able to justify why antibiotics cannot treat viral infections like the common cold or influenza.
由于病毒不进行呼吸或代谢，抗生素对它们无效。这是一个经典的 OCR 考题——你必须能够说明为什么抗生素无法治疗普通感冒或流感等病毒感染。
5. Fungi and Protists | 真菌与原生生物
Fungi are eukaryotic, have a body composed of thread-like hyphae (which form a mycelium), and reproduce by spores. The cell walls contain chitin, and they store carbohydrate as glycogen, not starch.
真菌是真核生物，身体由线状菌丝组成（菌丝形成菌丝体），通过孢子繁殖。细胞壁含几丁质，它们以糖原而非淀粉的形式储存碳水化合物。
l and carbon dioxide (C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂), which is exploited in baking and brewing.
酵母菌是一种单细胞真菌，既可以有氧呼吸也可以无氧呼吸。在无氧条件下，酵母菌将葡萄糖转化为乙醇和二氧化碳（C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂），这一特性被用于烘焙和酿造。
Protists are eukaryotic, mostly unicellular, and show immense variety. Some are plant-like (e.g., Chlorella with chloroplasts), others animal-like (e.g., Ameoba engulfing food by phagocytosis). The malaria parasite Plasmodium is a protist that requires both a mosquito and a human host.
原生生物是真核生物，多数为单细胞，种类繁多。有些像植物（如小球藻具有叶绿体），有些像动物（如变形虫通过吞噬作用摄取食物）。疟疾寄生虫疟原虫是一种需要蚊子和人类两个宿主的原生生物。
6. Growth and Reproduction of Microorganisms | 微生物的生长与繁殖
Bacteria reproduce asexually by binary fission: the circular chromosome replicates, the cell elongates, and splits into two genetically identical daughter cells. Under ideal conditions, bacteria can divide every 20 minutes, leading to exponential growth.
细菌通过二分裂进行无性繁殖：环状染色体复制，细胞伸长，分裂成两个遗传物质相同的子细胞。在理想条件下，细菌每20分钟分裂一次，导致指数式增长。
pulation would be 1 × 2⁸ = 256. Always note the starting number and number of generations.
你可能需要计算给定时间后的细菌种群数量。例如，如果一个细菌每30分钟分裂一次，4小时后（8代）种群数量为 1 × 2⁸ = 256。务必注意起始数量和世代数。
n rate), and death phase. Limiting factors include nutrient depletion and accumulation of toxic waste.
实验室条件下的生长遵循典型的生长曲线：延滞期（适应期）、对数期（指数期）、稳定期（死亡速率等于分裂速率）和衰亡期。限制因素包括营养耗尽和有毒废物积累。
Yeast can reproduce by budding, an asexual method. Many fungi can also reproduce sexually by spore production, leading to genetic variation.
酵母菌通过出芽进行无性繁殖。许多真菌也能通过孢子产生进行有性繁殖，导致遗传变异。
7. Decomposition and Nutrient Cycling | 分解作用与营养循环
Microorganisms, particularly bacteria and fungi, act as decomposers (saprotrophs). They secrete extracellular enzymes onto dead organic material, breaking it down into smaller soluble molecules which they then absorb.
微生物，特别是细菌和真菌，充当分解者（腐生生物）。它们向死亡的有机物质分泌胞外酶，将其分解成较小的可溶分子，然后加以吸收。
This process recycles essential elements such as carbon and nitrogen back into the ecosystem, making them available for plants to take up. Without decomposers, nutrients would remain locked in dead bodies and waste.
这个过程将碳和氮等必需元素循环回生态系统，使之可被植物吸收利用。没有分解者，营养元素将被锁在死物和废物中。
Fungal hyphae penetrate the decomposing material, increasing surface area for enzyme secretion. In the OCR practical context, you may set up an experiment measuring decay rate at different temperatures, using indicators like changes in pH or CO₂ production.
真菌菌丝穿透分解材料，增加了酶分泌的表面积。在 OCR 实验背景下，你可能需要设计实验测量不同温度下的分解速率，使用 pH 变化或 CO₂ 产量等指标。
Composting is a practical application of microbial decomposition, where gardeners provide optimal conditions (moisture, oxygen, warmth) to speed up decay by bacteria and fungi.
堆肥是微生物分解的实际应用，园艺师提供最佳条件（湿度、氧气、温暖）以加速细菌和真菌的分解。
8. Microorganisms and Disease | 微生物与疾病
Pathogens are microorganisms that cause infectious diseases. Bacteria, viruses, fungi, and protists can all be pathogens. For example, Salmonella (bacterium) causes food poisoning, HIV is a virus, athlete's foot is caused by a fungus, and malaria by the protist Plasmodium.
病原体是引起传染病的微生物。细菌、病毒、真菌和原生生物都可成为病原体。例如，沙门氏菌（细菌）引起食物中毒，HIV 是病毒，脚气由真菌引起，疟疾由原生生物疟原虫引起。
The transmission routes vary: direct contact, airborne droplets, contaminated food/water, and vectors (e.g., mosquitoes transmit malarial protist). You need to be able to describe methods to prevent transmission, such as hygiene, sterilisation, vaccination, and vector control.
传播途径各不相同：直接接触、空气飞沫、受污染的食物/水以及媒介（如蚊子传播疟原虫）。你需要能描述预防传播的方法，如卫生、灭菌、疫苗接种和病媒控制。
When a pathogen enters the body, the immune system responds with white blood cells: phagocytes engulf and digest pathogens (phagocytosis), while lymphocytes produce specific antibodies that bind to antigens on the pathogen.
当病原体进入体内时，免疫系统通过白细胞作出反应：吞噬细胞吞噬并消化病原体（吞噬作用），而淋巴细胞产生特定抗体，与病原体表面的抗原结合。
You may also be tested on the importance of aseptic techniques in healthcare to prevent hospital-acquired infections, such as using hand scrubs and sterile equipment.
你也可能被考到医疗保健中无菌技术的重要性，以防止医院获得性感染，例如使用洗手液和无菌设备。
9. Uses in Biotechnology and Food Production | 生物技术与食品生产中的用途
Microorganisms are harnessed industrially to produce foods and medicines. Yeast is used in bread-making: it anaerobically respires, producing CO₂ that makes the dough rise, and ethanol that evaporates during baking.
微生物被用于工业生产食品和药物。酵母菌用于面包制作：它进行无氧呼吸，产生的 CO₂ 使面团膨胀，乙醇则在烘焙过程中蒸发。
In yogurt production, bacteria such as Lactobacillus ferment lactose in milk to lactic acid, lowering pH and causing the milk proteins to coagulate into a thick, tangy product. The process requires a controlled warm temperature (around 40°C) to optimise enzyme activity.
在酸奶生产中，乳酸菌等细菌将牛奶中的乳糖发酵成乳酸，降低 pH 值，使牛奶蛋白凝固成浓稠、酸味的产物。该过程需要控制的温暖温度（约40°C）以优化酶活性。
The fungus Fusarium is used to produce mycoprotein (marketed as Quorn), a high-protein meat substitute grown in fermenters on a glucose syrup. This addresses food security with less environmental impact than rearing livestock.
镰刀菌真菌被用于生产菌蛋白（商业名称为 Quorn），这是一种高蛋白肉类替代品，在发酵罐中利用葡萄糖浆培养。这有助于保障粮食安全，比饲养家畜对环境的影响更小。
Bacteria can be genetically engineered to produce human insulin, growth hormone, or enzymes for laundry detergents. OCR often asks students to outline the steps: isolate the human gene, insert it into a bacterial plasmid using restriction and ligase enzymes, and culture the modified bacteria in a fermenter.
可对细菌进行基因工程改造，生产人胰岛素、生长激素或洗衣粉用酶。OCR 常要求学生概述步骤：分离人类基因，利用限制酶和连接酶将其插入细菌质粒，然后在发酵罐中培养改造后的细菌。
10. Antibiotics and Resistance | 抗生素与抗药性
Antibiotics are chemical substances that kill bacteria or stop their growth without harming host cells. They are produced naturally by some microorganisms (e.g., penicillin from the fungus Penicillium). They work by targeting structures or processes unique to bacteria, such as cell wall synthesis.
抗生素是能杀死细菌或阻止其生长而不伤害宿主细胞的化学物质。它们由某些微生物天然产生（例如盘尼西林来自青霉菌）。它们通过靶向细菌独有的结构或过程发挥作用，如细胞壁合成。
Antibiotics do not work against viruses, because viruses lack the bacterial targets and metabolic pathways. Inappropriate prescribing for viral infections contributes to antibiotic resistance, a major global health concern.
抗生素对病毒无效，因为病毒没有细菌的靶点和代谢途径。针对病毒感染的不当处方导致了抗生素耐药性，这是一项重大的全球健康问题。
Resistance arises by natural selection: in a bacterial population, a random mutation produces a resistant strain. When antibiotics are used, susceptible bacteria are killed, but resistant survivors multiply. Horizontal gene transfer can then spread the resistance gene to other bacteria via plasmids.
耐药性源于自然选择：在细菌种群中，随机突变产生耐药菌株。使用抗生素时，敏感的细菌被杀死，而耐药的幸存者大量繁殖。水平基因转移随后可通过质粒将耐药基因传播给其他细菌。
Methods to reduce the spread of resistance include finishing the full course of prescribed antibiotics, restricting antibiotic use in agriculture, and developing new drugs. Examination questions frequently ask you to interpret data on resistant infections.
减少耐药性传播的方法包括完成全程抗生素处方、限制农业中抗生素的使用以及开发新药。考题常要求你解读有关耐药感染的数据。
11. Practical Microbiology: Aseptic Techniques | 微生物学实验：无菌技术
When culturing microorganisms in the school laboratory, you must follow strict aseptic techniques to prevent contamination and ensure safety. Only non-pathogenic organisms like yeast or safe bacterial strains (e.g., Escherichia coli K12) should be used.
在学校实验室培养微生物时，必须遵循严格的无菌技术以防止污染和确保安全。只能使用非致病生物，如酵母菌或安全的细菌菌株（如大肠杆菌 K12）。
Key steps include: sterilising the inoculating loop by heating it to red-hot in a Bunsen flame before and after use; flaming the neck of culture bottles; lifting the lid of the Petri dish only at an angle; and sealing plates with tape (but not completely, to allow oxygen for aerobic growth).
关键步骤包括：使用前后把接种环在本生灯火焰上加热至红热以灭菌；灼烧培养瓶瓶口；只以一定角度打开培养皿盖；用胶带封皿但不要完全封死，以便好氧菌获得氧气。
Incubation should be carried out at a maximum temperature of 25°C in schools to discourage the growth of human pathogens. Plates are incubated upside down to prevent condensation dripping onto the culture.
学校中培养应在最高25°C的温度下进行，以防止人类病原体生长。培养皿倒置培养，避免冷凝水滴落到培养物上。
You may be asked to evaluate an experimental design, spotting errors such as an open Petri dish left on a bench, or an inoculating loop not flamed.
你可能需要评估实验设计，找出错误，例如培养皿敞开放置在实验台上，或接种环未灼烧。
12. Exam Preparation: Key Diagrams and Concepts | 考试准备：重要图表与概念
Make sure you can label a typical bacterial cell: cell wall, cell membrane, cytoplasm, circular chromosome, plasmid, ribosome, and flagellum. This diagram appears frequently in OCR IGCSE papers.
确保你能标注典型细菌细胞结构：细胞壁、细胞膜、细胞质、环状染色体、质粒、核糖体和鞭毛。这个图在 OCR IGCSE 试卷中频繁出现。
Be prepared to draw and interpret a bacterial growth curve, explaining each phase. Use the correct terms: lag, log (exponential), stationary, death.
准备好绘制并解释细菌生长曲线，说明每个阶段。使用正确术语：延滞期、对数（指数）期、稳定期、衰亡期。
ed to industrial applications. For lactic acid bacteria: glucose → lactic acid (+ energy).
记住酵母菌无氧呼吸的文字方程式：葡萄糖 → 乙醇 + 二氧化碳（+ 能量）。这常与工业应用相联系。乳酸菌：葡萄糖 → 乳酸（+ 能量）。
Understand the concept of saprotrophic nutrition: extracellular digestion followed by absorption. Compare this to holozoic nutrition you learn in animal biology.
理解腐生营养的概念：胞外消化后吸收。将之与动物生物学中的整体营养（吞噬）进行比较。
Finally, when discussing antibiotic resistance, always frame it as an example of evolution by natural selection, not that bacteria 'learn' to become resistant. Use phrases like 'random mutation' and 'selective pressure'.
最后，讨论抗生素耐药性时，一定要将其表述为自然选择的进化实例，而非细菌“学会”耐药。使用“随机突变”和“选择压力”等词。
Published by TutorHao | IGCSE Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图