Year 9 Cambridge Biology: Core Knowledge Summary | Year 9 剑桥生物：核心知识点梳理

📚 Year 9 Cambridge Biology: Core Knowledge Summary | Year 9 剑桥生物：核心知识点梳理

Welcome to the ultimate revision guide for Year 9 Cambridge Biology. This resource gathers the essential topics you need to master, presented in clear English-Chinese paired explanations. From the microscopic world of cells to the complexity of human organ systems and ecological relationships, every concept is unpacked to help you prepare for assessments and future IGCSE study.

欢迎阅读 Year 9 剑桥生物终极复习指南。本资源汇集了需要掌握的核心主题，以清晰的中英对照方式呈现。从微观的细胞世界到复杂的人体器官系统与生态关系，每个概念都经过梳理，助力你应对评估并为 IGCSE 打下基础。

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1. Cell Structure | 细胞结构

All living organisms are made of cells, which are the basic structural and functional units of life. Animal cells typically contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells share these organelles but also have a rigid cell wall, a large permanent vacuole and often chloroplasts for photosynthesis.

所有生物都由细胞构成，细胞是生命的基本结构和功能单位。动物细胞通常包含细胞核、细胞质、细胞膜、线粒体和核糖体。植物细胞拥有这些细胞器的同时，还具备坚硬的细胞壁、中央大液泡，以及常用于光合作用的叶绿体。

The nucleus controls cell activities and stores genetic information in the form of DNA. Mitochondria are the sites of aerobic respiration, releasing energy. Ribosomes are responsible for protein synthesis. The cell membrane is selectively permeable, controlling the movement of substances in and out of the cell.

细胞核控制细胞活动，并以 DNA 形式储存遗传信息。线粒体是有氧呼吸的场所，释放能量。核糖体负责蛋白质合成。细胞膜具有选择透过性，控制物质进出细胞。

To view cells, we use a light microscope. Magnification is calculated as magnification = eyepiece lens magnification × objective lens magnification. The total magnification can reach up to ×400 in a school microscope.

我们使用光学显微镜观察细胞。放大倍数的计算方式是：放大倍数 = 目镜放大倍数 × 物镜放大倍数。学校显微镜的总放大倍数最高可达 400 倍。

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2. Cell Division and Growth | 细胞分裂与生长

Cells divide to allow organisms to grow, repair damaged tissues and replace worn-out cells. The most common type of cell division for growth is mitosis, which produces two genetically identical daughter cells. Before division, the DNA is replicated so each new cell receives a full set of chromosomes.

细胞分裂使生物体得以生长、修复受损组织和替换衰老细胞。最常见的生长分裂方式是有丝分裂，它产生两个遗传上完全相同的子细胞。分裂前，DNA 先进行复制，确保每个新细胞获得全套染色体。

In humans, body cells contain 46 chromosomes arranged in 23 pairs. Mitosis maintains this diploid number. In contrast, meiosis is a special type of division used to produce gametes (sperm and eggs) with half the chromosome number (haploid, 23 chromosomes).

人体细胞含有 46 条染色体，组成 23 对。有丝分裂维持这种二倍体数目。与此相对，减数分裂是一种特殊的分裂方式，用于产生配子（精子和卵子），其染色体数目减半（单倍体，23 条）。

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3. Classification of Living Organisms | 生物分类

Biologists classify living things into groups based on shared characteristics. The modern classification system includes five kingdoms: Animals, Plants, Fungi, Protists and Prokaryotes (Bacteria). Within each kingdom, organisms are further divided into phylum, class, order, family, genus and species.

生物学家根据共同特征对生物进行分类。现代分类系统包括五个界：动物界、植物界、真菌界、原生生物界和原核生物界（细菌）。每一界内，生物再依次分为门、纲、目、科、属、种。

The species is the basic unit of classification; members of the same species can interbreed to produce fertile offspring. The binomial naming system uses genus and species, e.g., Homo sapiens for humans, written in italics with the genus capitalised.

物种是分类的基本单位；同一物种的成员可以交配产生可育后代。双名法使用属名和种名，例如人类的 Homo sapiens（智人），以斜体书写，属名首字母大写。

Dichotomous keys are tools used to identify organisms by answering a series of questions about observable features, leading step by step to the correct identification.

二分检索表是一种鉴别工具，通过回答一系列有关可观察特征的问题，逐步找到正确的物种名称。

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4. Ecosystems and Food Chains | 生态系统与食物链

An ecosystem consists of a community of living organisms interacting with each other and their non-living (abiotic) environment. Energy enters most ecosystems through sunlight, which is captured by producers (green plants) during photosynthesis.

生态系统由生物群落及其与非生物环境之间的相互作用构成。能量通过阳光进入大多数生态系统，由生产者（绿色植物）在光合作用过程中捕获。

Food chains show the transfer of energy from one organism to another. A simple food chain: grass → grasshopper → frog → snake. The arrows indicate the direction of energy flow. At each trophic level, some energy is lost through respiration, movement and heat, so the chain rarely exceeds four or five levels.

食物链显示能量从一个生物传递到另一个生物的过程。一个简单的食物链：草 → 蚱蜢 → 青蛙 → 蛇。箭头表示能量流动的方向。在每一营养级，部分能量因呼吸作用、运动和热量而流失，因此食物链很少超过四到五个环节。

Decomposers, such as bacteria and fungi, break down dead organisms and waste materials, recycling nutrients back into the soil for producers to use. This maintains the balance of ecosystems.

分解者（如细菌和真菌）分解死去的生物和废物，将养分循环回土壤中，供生产者再利用。这维持了生态系统的平衡。

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5. Human Digestive System | 人体消化系统

The digestive system breaks down large, insoluble food molecules into small, soluble ones that can be absorbed into the blood. Digestion involves both mechanical processes (chewing in the mouth, churning in the stomach) and chemical digestion using enzymes.

消化系统将大而不可溶的食物分子分解成可以被血液吸收的小而可溶的分子。消化过程包括物理消化（口腔咀嚼、胃的蠕动）以及利用酶进行的化学性消化。

Key organs and their functions: The mouth physically breaks food and contains salivary amylase to start starch digestion. The stomach produces hydrochloric acid and protease enzymes. The small intestine is the main site of digestion and absorption, with villi increasing the surface area. The large intestine absorbs water.

关键器官及其功能：口腔物理性磨碎食物，并含有唾液淀粉酶开始消化淀粉。胃分泌盐酸和蛋白酶。小肠是消化和吸收的主要场所，其绒毛结构大大增加了表面积。大肠吸收水分。

Digestive enzymes are specific: Amylase breaks down starch into maltose (and then into glucose); protease breaks down proteins into amino acids; lipase breaks down fats into fatty acids and glycerol. Bile, produced by the liver, emulsifies fats to aid lipase action.

消化酶具有专一性：淀粉酶将淀粉分解为麦芽糖（进而成葡萄糖）；蛋白酶将蛋白质分解为氨基酸；脂肪酶将脂肪分解为脂肪酸和甘油。肝脏分泌的胆汁可乳化脂肪，帮助脂肪酶发挥作用。

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6. Respiratory System | 呼吸系统

Respiration is the process of releasing energy from glucose. It should not be confused with breathing (ventilation). Aerobic respiration uses oxygen and produces carbon dioxide and water: glucose + oxygen → carbon dioxide + water (+ energy).

呼吸作用是从葡萄糖中释放能量的过程，不应与呼吸（通气）混淆。有氧呼吸利用氧气，产生二氧化碳和水：葡萄糖 + 氧气 → 二氧化碳 + 水（+ 能量）。

The human respiratory system includes the trachea, bronchi, bronchioles and alveoli. The alveoli are tiny air sacs in the lungs where gas exchange occurs. Oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli to be exhaled.

人体呼吸系统包括气管、支气管、细支气管和肺泡。肺泡是肺部微小的气囊，气体交换在此进行。氧气从肺泡扩散进入血液，二氧化碳则从血液扩散到肺泡中被呼出。

Inhaled air contains about 21% oxygen and 0.04% carbon dioxide, whereas exhaled air has less oxygen (16%) and more carbon dioxide (4%). This difference can be tested using limewater, which turns milky in the presence of carbon dioxide.

吸入的空气约含 21% 氧气和 0.04% 二氧化碳，而呼出的空气含氧量降低（16%），二氧化碳含量升高（4%）。这一差异可用石灰水测试，石灰水遇到二氧化碳会变浑浊。

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7. Circulatory System | 循环系统

The circulatory system transports oxygen, nutrients, hormones and waste products throughout the body. It consists of the heart, blood vessels and blood. The human heart has four chambers: two atria (upper) and two ventricles (lower), and it acts as a double pump.

循环系统将氧气、营养、激素和废物运送到全身各处。它由心脏、血管和血液组成。人的心脏有四个腔室：左右心房（上）和左右心室（下），它作为一个双泵工作。

The right side of the heart pumps deoxygenated blood to the lungs (pulmonary circulation), while the left side pumps oxygenated blood to the rest of the body (systemic circulation). Valves prevent backflow of blood. Arteries carry blood away from the heart; veins carry blood towards the heart; capillaries are tiny vessels where exchange occurs.

心脏右半部分将缺氧血泵送至肺部（肺循环），左半部分将富氧血泵送至全身（体循环）。瓣膜阻止血液倒流。动脉将血液

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