IGCSE AQA Biology: Microorganisms – Key Exam Points | IGCSE AQA 生物：微生物 考点精讲

📚 IGCSE AQA Biology: Microorganisms – Key Exam Points | IGCSE AQA 生物：微生物 考点精讲

Microorganisms, or microbes, are tiny living organisms that are invisible to the naked eye. They include bacteria, viruses, fungi and protists. Many play essential roles in ecosystems, food production and nutrient cycling, while some cause diseases. Understanding their diversity, structure and functions is a core part of IGCSE AQA Biology.

微生物是肉眼看不见的微小生物体，包括细菌、病毒、真菌和原生生物。许多微生物在生态系统、食品生产和营养循环中发挥着重要作用，但也有一些会引发疾病。理解微生物的多样性、结构和功能是 IGCSE AQA 生物学的核心内容。

1. Introduction to Microorganisms | 微生物简介

Microorganisms are found almost everywhere – in soil, water, air and inside other organisms. They can be unicellular or multicellular, but most are unicellular. The study of microorganisms is called microbiology.

微生物几乎无处不在——存在于土壤、水、空气以及其他生物体内。它们可以是单细胞或多细胞生物，但大多数为单细胞。研究微生物的科学称为微生物学。

They are classified into major groups based on cell structure and genetic material. The four main groups relevant to IGCSE are bacteria, viruses, fungi and protists.

根据细胞结构和遗传物质，微生物可分为几大类。与 IGCSE 相关的四大类群是：细菌、病毒、真菌和原生生物。

Viruses are considered non-living because they cannot carry out life processes independently; they require a host cell to replicate.

病毒被认为是非生物，因为它们不能独立进行生命活动；它们需要宿主细胞才能复制。

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

Bacteria are prokaryotic, unicellular organisms with no true nucleus; their DNA is a single circular chromosome floating in the cytoplasm. They have cell walls made of peptidoglycan.

细菌是原核单细胞生物，没有真正的细胞核；其DNA是一条环状染色体，游离在细胞质中。它们的细胞壁由肽聚糖构成。

Viruses consist of genetic material (DNA or RNA) enclosed in a protein coat called a capsid; some have an outer lipid envelope. They are much smaller than bacteria.

病毒由遗传物质（DNA 或 RNA）和包裹它的蛋白质外壳（衣壳）组成；有些病毒还拥有外层脂质包膜。它们比细菌小得多。

Fungi include yeasts (unicellular) and molds or mushrooms (multicellular). They have a nucleus and cell walls made of chitin, not cellulose.

真菌包括酵母菌（单细胞）以及霉菌或蘑菇（多细胞）。它们具有细胞核，细胞壁由几丁质构成，而非纤维素。

Protists are a diverse group of eukaryotic, mostly unicellular organisms. Examples include amoeba, paramecium and the malaria parasite Plasmodium.

原生生物是一群多样化的真核生物，大多为单细胞。例子包括阿米巴原虫、草履虫以及引起疟疾的疟原虫。

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3. Bacteria: Structure, Shape and Reproduction | 细菌：结构、形态与繁殖

Bacterial cells contain cytoplasm, a cell membrane, a cell wall, ribosomes, and often a capsule or slime layer for protection. Some bacteria have flagella for movement and pili for attachment.

细菌细胞含有细胞质、细胞膜、细胞壁、核糖体，通常还有用于保护的荚膜或黏液层。有些细菌具有用于运动的鞭毛和用于附着的菌毛。

Bacteria reproduce asexually by binary fission, where one cell divides into two genetically identical daughter cells. Under ideal conditions, this can happen every 20 minutes.

细菌通过二分裂进行无性繁殖，一个细胞分裂成两个遗传上相同的子细胞。在理想条件下，每20分钟就可以分裂一次。

Bacterial shapes include cocci (spherical), bacilli (rod-shaped), spirilla (spiral) and vibrio (comma-shaped). Shape can be used to help identify bacteria.

细菌的形状包括球菌（球形）、杆菌（杆状）、螺旋菌（螺旋形）和弧菌（逗点状）。形态可用于辅助鉴定细菌。

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4. Viruses: Structure and Replication | 病毒：结构与复制

A virus particle, or virion, is not a cell. It has no cytoplasm, ribosomes or cell membrane. It simply carries a set of instructions to hijack host cell machinery.

病毒颗粒或毒粒并非细胞。它没有细胞质、核糖体或细胞膜。它只是携带一套指令，劫持宿主细胞的机器。

The viral life cycle (e.g. in bacteriophages) includes attachment, injection of nucleic acid, replication of viral parts, assembly and release, often destroying the host cell.

病毒的生活周期（例如噬菌体中）包括附着、注入核酸、病毒部件复制、组装和释放，通常会破坏宿主细胞。

Viruses are highly specific to their host cells because of the lock-and-key fit between viral surface proteins and host cell receptors.

病毒具有高度的宿主特异性，因为病毒表面蛋白与宿主细胞受体之间存在锁钥式的匹配。

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5. Fungi: Importance and Infection | 真菌：重要性与感染

Fungi are heterotrophic; they secrete digestive enzymes onto organic matter and absorb the digested nutrients. This makes them essential decomposers in ecosystems.

真菌为异养生物；它们向有机物质分泌消化酶，然后吸收已消化的营养物质。这使得它们成为生态系统中关键的分解者。

Yeast, a unicellular fungus, is used in baking (bread)

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