GCSE AQA Biology: Microorganisms – Essential Revision | GCSE AQA 生物：微生物考点精讲

📚 GCSE AQA Biology: Microorganisms – Essential Revision | GCSE AQA 生物：微生物考点精讲

Microorganisms, or microbes, are tiny living organisms that are found all around us. They play essential roles in ecosystems, food production, and our own health. In AQA GCSE Biology, you need to understand the different types of microorganisms, the conditions they need to grow, how they are cultured safely, their roles in decay and nutrient cycles, and their uses and dangers in relation to human health and medicine.

微生物是微小的生物体，无处不在。它们在生态系统、食品生产以及我们自身健康中发挥着重要作用。在 AQA GCSE 生物学中，你需要掌握不同类型的微生物、它们生长所需的条件、如何安全培养、在分解和营养循环中的作用，以及它们在人类健康和医药中的应用与危害。

1. Types of Microorganisms | 微生物的类型

The four main groups of microorganisms are bacteria, fungi, viruses, and protists. Each has distinctive features and sizes, and they are found in almost every habitat on Earth.

微生物主要分为四类：细菌、真菌、病毒和原生生物。每种都有独特的特征和大小，几乎存在于地球上的每一个栖息地中。

Bacteria are unicellular prokaryotes, meaning they lack a true nucleus. They have a cell wall, cell membrane, cytoplasm, and a single circular strand of DNA that floats freely in the cytoplasm. Some bacteria also have a flagellum for movement. They reproduce rapidly by binary fission and can be harmful or beneficial.

细菌是单细胞原核生物，没有真正的细胞核。它们有细胞壁、细胞膜、细胞质和一条在细胞质中自由漂浮的环状DNA。有些细菌还有用于运动的鞭毛。它们通过二分裂快速繁殖，可能有害也可能有益。

Fungi can be unicellular (e.g., yeast) or multicellular (e.g., moulds, mushrooms). Their cells have a nucleus, cell wall made of chitin, and they feed by secreting enzymes onto food and absorbing the digested products (saprotrophic nutrition). They reproduce by spores.

真菌可以是单细胞（如酵母菌）或多细胞（如霉菌、蘑菇）。它们的细胞有细胞核、由几丁质构成的细胞壁，通过向食物分泌酶并吸收消化产物来获取营养（腐生营养）。它们通过孢子繁殖。

Viruses are not considered living by many scientists because they do not carry out any life processes independently. They consist of genetic material (DNA or RNA) enclosed in a protein coat. They can only reproduce by infecting host cells and using the host’s machinery to make copies of themselves.

病毒被很多科学家认为不是生物，因为它们不能独立进行任何生命活动。它们由遗传物质（DNA或RNA）和蛋白质外壳组成。它们只能通过入侵宿主细胞并利用宿主的机制进行复制。

Protists are a diverse group of unicellular eukaryotic organisms. Some, like algae, are plant-like and photosynthesise; others, like amoeba, are animal-like and feed on other organisms. Some protists are parasites that cause disease, such as the malarial parasite Plasmodium.

原生生物是一类多样的单细胞真核生物。有些像藻类那样能进行光合作用；有些像变形虫那样以其他生物为食。有些原生生物是引起疾病的寄生虫，例如引起疟疾的疟原虫。

2. Bacterial Growth and Binary Fission | 细菌生长与二分裂

Bacteria multiply by binary fission, a simple form of asexual reproduction. The single circular DNA replicates and the cell splits into two genetically identical daughter cells. Under ideal conditions, some bacteria can divide every 20 minutes, leading to exponential growth.

细菌通过二分裂进行繁殖，这是一种简单的无性生殖。单条环状DNA复制后，细胞分裂成两个遗传上相同的子细胞。在理想条件下，有些细菌每20分钟就能分裂一次，导致指数增长。

To calculate the number of bacteria after a given time, use the formula: number of bacteria = starting number × 2ⁿ, where n is the number of divisions. For example, if one bacterium divides every 30 minutes for 3 hours, n = 6, so the number becomes 1 × 2⁶ = 64.

计算一定时间后的细菌数量，公式为：细菌数量 = 起始数量 × 2ⁿ，其中 n 是分裂次数。例如，如果1个细菌每30分钟分裂一次，持续3小时，n = 6，所以数量变为 1 × 2⁶ = 64。

In reality, growth slows as nutrients run out, waste products build up, and space becomes limited. A typical bacterial growth curve shows a lag phase, exponential (log) phase, stationary phase, and death phase.

实际上，当营养耗尽、废物积累、空间受限时，生长会减缓。典型的细菌生长曲线包括延滞期、指数（对数）期、稳定期和死亡期。

3. Culturing Microorganisms and Aseptic Technique | 培养微生物与无菌操作

In the lab, microorganisms are grown on nutrient media such as agar plates or in broth. The medium provides carbohydrates, proteins, minerals, and sometimes growth factors. Agar is a jelly-like substance derived from seaweed that solidifies the medium.

在实验室中，微生物生长在琼脂平板或营养肉汤等培养基上。培养基提供碳水化合物、蛋白质、矿物质，有时还提供生长因子。琼脂是从海藻中提取的胶状物质，使培养基凝固。

To avoid contamination by unwanted microbes and to ensure safety, aseptic (sterile) techniques must be used. These include: sterilising all equipment and media before use (e.g., autoclaving at 121 °C), passing inoculating loops through a flame, securing the lid of Petri dishes with adhesive tape but not fully sealing to allow oxygen exchange, and incubating at a maximum temperature of 25 °C in schools to reduce the risk of growing harmful pathogens.

为避免杂菌污染并确保安全，必须使用无菌操作技术。包括：使用前对所有器材和培养基进行灭菌（例如在121 °C高压灭菌），将接种环通过火焰灭菌，用胶带固定培养皿盖子但不完全密封以允许氧气交换，在学校中最高在25 °C下培养以降低病原菌生长的风险。

When investigating the effect of antibiotics or disinfectants on bacterial growth, we measure the clear zone (zone of inhibition) around the substance. A larger clear zone indicates greater effectiveness. We calculate the area using πr², where r is the radius of the zone.

在研究抗生素或消毒剂对细菌生长的影响时，我们测量物质周围的抑菌圈（透明区）。抑菌圈越大表示效果越好。我们用 πr² 计算面积，其中 r 是半径。

Zone of inhibition area (mm²) = π × (radius in mm)²

抑菌圈面积（mm²）= π × （半径，mm）²

4. Pathogens and Disease Transmission | 病原体与疾病传播

Pathogens are microorganisms that cause infectious disease. They can be spread through direct contact, water, air (droplet infection), vectors (e.g., mosquitoes), or contaminated food. Once inside the body, they can damage cells directly or produce toxins.

病原体是引起传染病的微生物。它们可以通过直接接触、水、空气（飞沫传播）、媒介（如蚊子）或受污染的食物传播。进入人体后，它们可直接损伤细胞或产生毒素。

Viral diseases include measles (fever, rash, can be fatal), HIV/AIDS (attacks immune cells), and tobacco mosaic virus (affects plant leaves, reducing photosynthesis). Bacterial diseases include Salmonella (food poisoning), Gonorrhoea (a sexually transmitted disease), and bacterial pneumonia. Fungal diseases include rose black spot (plant disease) and athlete’s foot in humans. Protist diseases include malaria, caused by Plasmodium and spread by female Anopheles mosquitoes.

病毒性疾病包括麻疹（发烧、皮疹，可能致命）、艾滋病（攻击免疫细胞）和烟草花叶病毒（影响植物叶片，降低光合作用）。细菌性疾病包括沙门氏菌（食物中毒）、淋病（性传播疾病）和细菌性肺炎。真菌性疾病包括玫瑰黑斑病（植物病害）和人的足癣。原生生物疾病包括由疟原虫引起、由雌性按蚊传播的疟疾。

5. Human Defence Systems | 人体防御系统

The body has several non-specific defence mechanisms to prevent pathogens from entering and to destroy them quickly if they do. Physical barriers include the skin, which acts as a waterproof barrier and produces antimicrobial secretions. The respiratory tract is lined with mucus and cilia that trap and sweep away microbes. The stomach produces hydrochloric acid that kills most ingested pathogens.

人体有多个非特异性防御机制来阻止病原体进入，并在进入后迅速消灭它们。物理屏障包括皮肤，它是防水屏障并分泌抗菌物质。呼吸道内壁有黏液和纤毛，能捕获并扫除微生物。胃产生盐酸，可杀死大多数摄入的病原体。

The immune system provides specific responses. White blood cells (phagocytes) engulf and digest pathogens (phagocytosis). Lymphocytes produce antibodies that bind to specific antigens on the pathogen surface, marking them for destruction. Memory lymphocytes remain after an infection, providing long-term immunity. Antitoxins are produced to neutralise toxins released by bacteria.

免疫系统提供特异性应答。吞噬细胞（一种白细胞）吞噬并消化病原体（吞噬作用）。淋巴细胞产生抗体，与病原体表面的特定抗原结合，将其标记以便消灭。感染后体内留有记忆淋巴细胞，提供长期免疫力。同时产生抗毒素来中和细菌释放的毒素。

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

A vaccine contains a dead, weakened, or part of a pathogen. When injected, it triggers an immune response without causing disease. Lymphocytes produce antibodies, and memory cells are formed. On future exposure to the actual pathogen, the secondary response is rapid and strong, preventing illness.

疫苗含有死亡的、减毒的或部分病原体。注射后，它能激发免疫反应而不致病。淋巴细胞产生抗体，并形成记忆细胞。以后接触到真正的病原体时，二次反应迅速而强烈，从而防止生病。

Herd immunity occurs when a large proportion of the population is vaccinated, making it difficult for the pathogen to spread. This protects unvaccinated individuals, such as those with weakened immune systems. However, vaccination programmes require high uptake to be effective.

当大部分人群接种疫苗后，病原体难以传播，就形成了群体免疫。这可以保护未接种的人，例如免疫功能低下者。然而，疫苗接种计划需要高覆盖率才能有效。

7. Antibiotics and Painkillers | 抗生素与止痛药

Antibiotics are drugs that kill bacteria or stop their growth without harming human cells. They work by targeting features specific to bacteria, such as cell wall synthesis. Different antibiotics are effective against different types of bacteria. They cannot kill viruses because viruses lack the structures targeted by antibiotics.

抗生素是能杀死细菌或阻止其生长而不伤害人体细胞的药物。它们通过针对细菌特有的结构（如细胞壁合成）来发挥作用。不同的抗生素对不同类型的细菌有效。抗生素不能杀死病毒，因为病毒没有抗生素所针对的结构。

Painkillers such as aspirin and paracetamol relieve symptoms but do not kill pathogens. Doctors should not prescribe antibiotics for viral infections because they are ineffective and can contribute to antibiotic resistance.

止痛药（如阿司匹林和对乙酰氨基酚）可以缓解症状，但不能杀死病原体。医生不应为病毒感染开抗生素，因为抗生素无效且可能导致抗生素耐药性。

8. Antibiotic Resistance and Its Prevention | 抗生素耐药性及其预防

Bacteria can develop resistance to antibiotics through random mutations. A resistant bacterium survives and reproduces, passing on the resistance gene. Overuse and misuse of antibiotics (e.g., not completing a prescribed course) accelerate the spread of resistant strains. MRSA is a well-known example of an antibiotic-resistant bacterium that causes difficult-to-treat infections in hospitals.

细菌可通过随机突变产生对抗生素的耐药性。耐药细菌存活并繁殖，将耐药基因传递下去。抗生素的过度使用和不当使用（例如未完成疗程）会加速耐药菌株的传播。MRSA 是著名的耐抗生素细菌例子，在医院引起难以治疗的感染。

To slow down the development of resistance, it is essential to prescribe antibiotics only when necessary, to complete the full course, and to develop new antibiotics. Infection control measures in hospitals, such as hand washing and isolating infected patients, also help.

为了减缓耐药性的发展，必须只在必要时才使用抗生素，完成整个疗程，并开发新型抗生素。医院的感染控制措施，如洗手和隔离感染患者，也是有帮助的。

9. Development of New Drugs | 新药的开发

Many modern medicines originate from plants or other organisms. For example, the painkiller aspirin was developed from a compound found in willow bark, and the heart drug digitalis comes from foxgloves. Alexander Fleming discovered penicillin from the Penicillium mould, leading to the development of the first antibiotic.

许多现代药物来源于植物或其他生物体。例如止痛药阿司匹林是由柳树皮中的一种化合物发展而来，强心药地高辛来自毛地黄。亚历山大·弗莱明从青霉菌中发现了青霉素，从而开发出第一种抗生素。

Developing a new drug involves preclinical testing on cells and animals to check for toxicity, efficacy, and dosage. Clinical trials then test on healthy volunteers and patients to determine safety and effectiveness, often using double-blind placebo-controlled trials to avoid bias.

开发新药需要先在细胞和动物上进行临床前测试，检查毒性、效力和剂量。然后进行临床试验，在健康志愿者和患者身上测试安全性和有效性，通常采用双盲安慰剂对照试验以避免偏见。

10. Decay and the Carbon Cycle | 分解与碳循环

Microorganisms, particularly bacteria and fungi, are decomposers. They break down dead organic matter and waste, recycling nutrients back into the environment. During decay, enzymes are secreted to digest complex molecules into simpler, soluble substances that the microbes absorb. This process releases carbon dioxide, water, and mineral ions (especially nitrates and phosphates) into 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和废物，将营养物质循环回环境中。在分解过程中，它们分泌酶将复杂分子消化为简单的、可溶的物质，然后吸收。这个过程向土壤释放二氧化碳、水和无机盐离子（尤其是硝酸盐和磷酸盐）。

Decomposition is essential in the carbon cycle. Carbon from dead organisms is returned to the atmosphere as CO₂ through respiration of decomposers. In the absence of oxygen, some microorganisms produce methane (CH₄), which also releases carbon. Combustion of fossil fuels and respiration by living organisms also return CO₂ to the air.

分解作用在碳循环中至关重要。死生物体中的碳通过分解者的呼吸作用以 CO₂ 形式返回大气。在缺氧条件下，有些微生物产生甲烷（CH₄），也释放碳。化石燃料的燃烧和生物的呼吸也将 CO₂ 返回空气。

11. The Nitrogen Cycle and Microorganisms | 氮循环与微生物

Nitrogen is needed by all organisms to make proteins and DNA. Although the atmosphere is about 78% nitrogen gas (N₂), most organisms cannot use it directly. Microorganisms play key roles in converting nitrogen into usable forms.

所有生物都需要氮来合成蛋白质和DNA。虽然大气中约78%是氮气（N₂），但大多数生物无法直接利用。微生物在将氮转化为可吸收形式上起着关键作用。

Nitrogen-fixing bacteria, found in the soil and in root nodules of legumes, convert N₂ into ammonia (NH₃), which then forms ammonium ions (NH₄⁺). Nitrifying bacteria oxidise ammonium ions first into nitrites (NO₂⁻) and then into nitrates (NO₃⁻), which plants can absorb. Decomposers break down proteins in dead organisms and waste, producing ammonia (ammonification). Denitrifying bacteria convert nitrates back into N₂ gas, completing the cycle.

固氮菌存在于土壤和豆科植物的根瘤中，能将 N₂ 转化为氨（NH₃），进而形成铵离子（NH₄⁺）。硝化细菌将铵离子先氧化成亚硝酸盐（NO₂⁻），再氧化成硝酸盐（NO₃⁻），植物可以吸收。分解者分解死生物体和废物中的蛋白质，产生氨（氨化作用）。反硝化细菌将硝酸盐转化回 N₂ 气体，从而完成循环。

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

Humans have used microorganisms for thousands of years to make food and drink. Yeast (a fungus) is used in baking and brewing. In bread making, yeast ferments sugars in the dough, producing carbon dioxide that makes the bread rise, and ethanol that evaporates during baking. In alcoholic drinks, yeast converts sugars into ethanol and CO₂ under anaerobic conditions.

人类利用微生物制作食品和饮料已有数千年历史。酵母菌（一种真菌）用于烘焙和酿造。在制作面包时，酵母发酵面团中的糖，产生二氧化碳使面包膨胀，并产生乙醇，乙醇在烘烤时蒸发。在酒精饮料中，酵母在厌氧条件下将糖转化为乙醇和 CO₂。

Bacteria are used to make yogurt. Lactobacillus bacteria are added to warm milk, where they ferment lactose (milk sugar) into lactic acid. The acid lowers the pH, causing milk proteins to coagulate and thicken, giving yogurt its characteristic texture and tangy taste.

细菌被用来制作酸奶。将乳酸杆菌加入温牛奶中，它们将乳糖发酵成乳酸。酸使 pH 降低，导致牛奶蛋白凝固变稠，使酸奶具有特有的质地和酸味。

In cheese production, similar bacterial cultures produce lactic acid, helping to curdle the milk. Enzymes such as rennet may also be added. The type of microbe and conditions used influence the cheese flavour and texture.

在奶酪生产中，类似的细菌培养物产生乳酸，帮助牛奶凝结。也可能添加凝乳酶等酶。微生物的种类和条件影响奶酪的风味和质地。

Other applications include the production of mycoprotein (a protein-rich food made from the fungus Fusarium) and the use of microorganisms in industrial fermentation to make antibiotics, hormones (e.g., insulin), and enzymes for biological washing powders.

其他应用包括生产真菌蛋白（由镰刀菌制成的高蛋白食品），以及利用微生物在工业发酵中制造抗生素、激素（如胰岛素）和用于生物洗衣粉的酶。

Published by TutorHao | AQA GCSE Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

GCSE AQA Biology: Microorganisms – Essential Revision | GCSE AQA 生物：微生物 考点精讲