📚 Year 9 CAIE Biology: Core Knowledge Review | Year 9 CAIE 生物：核心知识点梳理
This article provides a structured revision of the most important biological concepts covered in Year 9 of the Cambridge Lower Secondary programme. Understanding these core ideas will help you build a solid foundation for IGCSE Biology. Each section presents key facts and explanations, paired with Chinese translations to support bilingual learning.
本文系统梳理了剑桥初中阶段 Year 9 生物学最核心的知识点。掌握这些基础概念将为 IGCSE 生物学习打下扎实根基。每个小节都以中英双语形式呈现关键事实与解释，助力双语学习。
1. Characteristics of Living Organisms | 生物的特征
All living things carry out seven life processes, often remembered by the acronym MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition. These processes define what it means to be alive, and a non-living thing does not perform all of them.
所有生物都会进行七种生命活动，常用缩写 MRS GREN 来记忆：运动、呼吸、感应、生长、生殖、排泄和营养。这些过程定义了生命，而非生物不会全部表现这些特征。
Movement can be internal (such as cytoplasm streaming) or external (such as walking). Sensitivity means detecting and responding to changes in the environment, for example a plant shoot growing towards light (phototropism). Respiration is the release of energy from food, not to be confused with breathing.
运动可以是内部的（如细胞质流动）或外部的（如行走）。感应是指探测并响应环境变化，例如植物茎向光生长（向光性）。呼吸作用是从食物中释放能量，不要与呼吸（通气）混淆。
Reproduction allows organisms to produce offspring, either sexually or asexually. Excretion is the removal of toxic waste products made by cells, such as carbon dioxide and urea. Nutrition involves taking in materials for energy, growth and repair.
生殖使生物产生后代，分为有性生殖和无性生殖。排泄是去除细胞产生的有毒废物，如二氧化碳和尿素。营养则是摄入物质以提供能量、促进生长和修复。
2. Cells and Organisation | 细胞与组织
The cell is the basic structural and functional unit of all living organisms. Animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells have the same organelles plus a cellulose cell wall, a large permanent vacuole and chloroplasts for photosynthesis.
细胞是所有生物体结构和功能的基本单位。动物细胞含有细胞核、细胞质、细胞膜、线粒体和核糖体。植物细胞除了这些，还有纤维素细胞壁、大型中央液泡和用于光合作用的叶绿体。
The nucleus controls the cell’s activities and stores genetic material (DNA). Mitochondria are the sites of aerobic respiration, releasing energy. Ribosomes synthesise proteins, and the cell membrane controls what enters and leaves the cell.
细胞核控制细胞活动并储存遗传物质（DNA）。线粒体是有氧呼吸的场所，负责释放能量。核糖体合成蛋白质，细胞膜控制物质进出细胞。
In multicellular organisms, cells specialise to perform particular functions. Similar cells group together to form tissues, tissues form organs, and organs work together in organ systems, such as the digestive system or the circulatory system.
在多细胞生物中，细胞功能特化。相似细胞聚集形成组织，组织构成器官，器官协同工作形成器官系统，如消化系统或循环系统。
3. Movement of Substances | 物质进出细胞
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, and it does not require energy. Oxygen and carbon dioxide move into and out of cells by diffusion.
扩散是粒子从高浓度区域向低浓度区域的净移动，顺着浓度梯度，不需要能量。氧气和二氧化碳通过扩散进出细胞。
Osmosis is a special case of diffusion involving water molecules moving through a partially permeable membrane from a dilute solution to a more concentrated solution. It is vital for water uptake in plant roots and for maintaining turgor pressure.
渗透是扩散的一种特殊情况，指水分子通过半透膜从稀溶液向浓溶液移动。这对植物根系吸水和维持膨压至关重要。
Active transport moves substances against their concentration gradient, from low to high concentration, using energy from respiration. This process allows root hair cells to absorb mineral ions from the soil even when their concentration is lower outside the cell.
主动运输利用呼吸作用提供的能量，逆浓度梯度（从低浓度向高浓度）运输物质。这使得根毛细胞能从土壤中吸收矿物离子，即使胞外浓度更低。
4. Biological Molecules and Diet | 生物分子与饮食
The main nutrients in food are carbohydrates, proteins, lipids (fats), vitamins, minerals, dietary fibre and water. A balanced diet must contain these in the right proportions to provide energy and materials for growth.
食物中的主要营养素是碳水化合物、蛋白质、脂类（脂肪）、维生素、矿物质、膳食纤维和水。均衡膳食必须按合理比例包含这些成分，以提供能量和生长所需材料。
Carbohydrates, containing carbon, hydrogen and oxygen, are the main energy source. Simple sugars like glucose are used in respiration, while starch and glycogen are storage forms. Lipids provide long-term energy storage, insulation and protection of organs.
碳水化合物含有碳、氢、氧，是主要能量来源。像葡萄糖这样的单糖用于呼吸作用，而淀粉和糖原是储存形式。脂类提供长期能量储存、隔热和器官保护。
Proteins, made of amino acids, are needed for growth and repair of tissues, as well as for making enzymes and haemoglobin. Vitamins (e.g., vitamin C for healthy skin) and minerals (e.g., calcium for strong bones) are required in small amounts. Dietary fibre aids digestion and prevents constipation.
蛋白质由氨基酸组成，用于组织生长和修复，以及制造酶和血红蛋白。维生素（如维生素C维持皮肤健康）和矿物质（如钙强健骨骼）需求量小。膳食纤维帮助消化并预防便秘。
Chemical tests can identify these molecules: iodine solution turns blue-black with starch; Benedict’s solution turns brick-red with reducing sugars when heated; biuret reagent turns purple with proteins; ethanol emulsion test gives a cloudy white layer with lipids.
化学测试可鉴定这些分子：碘液遇淀粉变蓝黑色；本尼迪克特试剂与还原糖加热后呈砖红色；双缩脲试剂遇蛋白质变紫色；乙醇乳浊液测试遇脂肪出现乳白色浑浊层。
5. Enzymes and Digestion | 酶与消化
Enzymes are biological catalysts made of protein that speed up chemical reactions without being used up. Each enzyme has an active site with a specific shape that fits its substrate, like a lock and key. Factors such as temperature and pH affect enzyme activity, and extreme conditions can denature the enzyme.
酶是由蛋白质构成的生物催化剂，能加快化学反应而自身不被消耗。每种酶具有特定形状的活性部位，与其底物吻合，如同锁钥模型。温度和pH等因素影响酶活性，极端条件会导致酶变性。
Digestion breaks down large, insoluble food molecules into small, soluble ones so they can be absorbed into the blood. Amylase breaks down starch into maltose in the mouth and small intestine. Proteases break down proteins into amino acids in the stomach and small intestine. Lipases break lipids into fatty acids and glycerol, helped by bile from the liver.
消化过程将大的不溶性食物分子分解为小的可溶性分子，以便被血液吸收。淀粉酶在口腔和小肠中将淀粉分解为麦芽糖。蛋白酶在胃和小肠中将蛋白质分解为氨基酸。脂肪酶在肝脏胆汁的协助下将脂肪分解为脂肪酸和甘油。
Absorption mostly occurs in the small intestine, where the lining is folded into villi with microvilli, providing a huge surface area. Villi have a dense network of capillaries and a lacteal to transport absorbed nutrients.
吸收主要发生在小肠，小肠内壁折叠成绒毛和微绒毛，提供了巨大的表面积。绒毛拥有丰富的毛细血管网和一条乳糜管来运输吸收的营养物质。
6. Plant Nutrition and Photosynthesis | 植物营养与光合作用
Plants make their own food through photosynthesis, a process that converts light energy into chemical energy stored in glucose. The overall word equation is: carbon dioxide + water → glucose + oxygen, using light energy absorbed by chlorophyll.
植物通过光合作用制造自身食物，该过程将光能转化为储存在葡萄糖中的化学能。总文字方程式为：二氧化碳 + 水 → 葡萄糖 + 氧气，利用叶绿素吸收的光能。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Photosynthesis takes place in chloroplasts, mainly in the palisade mesophyll cells of leaves. The rate of photosynthesis is affected by light intensity, carbon dioxide concentration and temperature. Leaves are adapted for photosynthesis with a large surface area, thin shape, stomata for gas exchange, and a network of veins for transport.
光合作用在叶绿体中进行，主要发生在叶片的栅栏叶肉细胞中。光合作用速率受光照强度、二氧化碳浓度和温度影响。叶片适应光合作用，具有较大的表面积、薄片状形态、用于气体交换的气孔以及用于运输的叶脉网络。
Glucose produced is used in respiration, converted to starch for storage, or used to synthesise cellulose, amino acids and lipids. Mineral ions such as nitrate and magnesium are also required: nitrates for amino acids, magnesium for chlorophyll.
生成的葡萄糖用于呼吸作用，转化为淀粉储存，或用于合成纤维素、氨基酸和脂类。还需要硝酸盐和镁等矿物离子：硝酸盐用于合成氨基酸，镁用于叶绿素。
7. Respiration | 呼吸作用
Respiration is a chemical reaction that releases energy from food molecules, such as glucose, in all living cells. Aerobic respiration requires oxygen and produces a large amount of energy, carbon dioxide and water.
呼吸作用是所有活细胞中从葡萄糖等食物分子释放能量的化学反应。有氧呼吸需要氧气，产生大量能量，同时生成二氧化碳和水。
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy)
Anaerobic respiration occurs when oxygen is insufficient. In animal cells, glucose is broken down to produce lactic acid and a small amount of energy. In yeast and some plants, anaerobic respiration produces ethanol, carbon dioxide and a small amount of energy; this is called fermentation and is used in baking and brewing.
无氧呼吸在氧气不足时发生。在动物细胞中，葡萄糖分解生成乳酸和少量能量。在酵母和一些植物中，无氧呼吸产生乙醇、二氧化碳和少量能量；这称为发酵，用于烘焙和酿造。
Energy released during respiration is used for processes such as muscle contraction, active transport, maintaining a constant body temperature, and building large molecules (anabolism). Respiration is not the same as breathing; breathing is the mechanical movement of air in and out of the lungs.
呼吸作用释放的能量用于肌肉收缩、主动运输、维持恒定体温以及合成大分子（合成代谢）等过程。呼吸作用不等同于呼吸（通气）；呼吸指的是空气进出肺部的机械运动。
8. Gas Exchange in Humans | 人体内的气体交换
Gas exchange is the delivery of oxygen to blood and the removal of carbon dioxide. It occurs in the alveoli, tiny air sacs in the lungs that provide a huge surface area, thin walls (one cell thick) and a rich supply of surrounding capillaries. The process relies on diffusion.
气体交换是指将氧气输送至血液并移除二氧化碳的过程。它发生在肺泡中——肺部微小的气囊，提供了巨大的表面积、薄壁（仅一个细胞厚）以及丰富的周围毛细血管网。该过程依赖扩散。
The pathway of air during inhalation: nasal cavity (or mouth) → pharynx → larynx → trachea → bronchi → bronchioles → alveoli. The trachea and bronchi are supported by C-shaped rings of cartilage to keep airways open. Mucus and cilia trap and move dust and microbes away from the lungs.
吸气时的空气通道：鼻腔（或口腔）→ 咽 → 喉 → 气管 → 支气管 → 细支气管 → 肺泡。气管和支气管由C形软骨环支撑，保持气道通畅。黏液和纤毛捕捉灰尘和微生物，并将其移出肺部。
During inhalation, the intercostal muscles contract and the diaphragm flattens, increasing the volume of the thorax and decreasing pressure, drawing air in. During exhalation, muscles relax, thorax volume decreases and pressure increases, forcing air out.
吸气时，肋间肌收缩，膈肌变平，胸腔容积增大，压力降低，空气被吸入。呼气时，肌肉放松，胸腔容积减小，压力升高，空气被排出。
9. Circulatory System | 循环系统
The human circulatory system consists of the heart, blood vessels and blood. It transports oxygen, nutrients, hormones and waste products, helps fight infection and distributes heat. The heart is a muscular pump with four chambers: left and right atria (upper) and left and right ventricles (lower).
人体循环系统由心脏、血管和血液组成。它运输氧气、营养物质、激素和废物，帮助抵抗感染并分配热量。心脏是一个肌肉泵，有四个腔室：左心房和右心房（上方），左心室和右心室（下方）。
Deoxygenated blood returns from the body to the right atrium, is pumped to the right ventricle, and then sent to the lungs via the pulmonary artery. Oxygenated blood returns from the lungs to the left atrium, is pumped to the left ventricle, and is then distributed to the body through the aorta. The left ventricle has a thicker muscle wall because it must pump blood all around the body.
缺氧血从身体回流至右心房，泵入右心室，再通过肺动脉输往肺部。富氧血从肺部返回左心房，泵入左心室，然后经由主动脉分布到全身。左心室肌肉壁更厚，因为它需要将血液泵往全身各处。
Arteries carry blood away from the heart under high pressure; they have thick, elastic muscular walls. Veins carry blood back to the heart under lower pressure; they contain valves to prevent backflow. Capillaries are microscopic vessels with walls just one cell thick, allowing efficient exchange of substances.
动脉在高压下将血液带离心脏，其壁厚实有弹性。静脉在较低压力下将血液导回心脏，内有瓣膜防止倒流。毛细血管是壁厚仅一个细胞的微小血管，便于物质高效交换。
Blood contains red blood cells (contain haemoglobin to bind oxygen), white blood cells (defence against pathogens), platelets (involved in clotting) and plasma (liquid that transports dissolved substances and heat).
血液包含红细胞（含有血红蛋白以结合氧气）、白细胞（防御病原体）、血小板（参与凝血）和血浆（运输溶解物质和热量的液体）。
10. Reproduction | 生殖
Reproduction can be sexual (fusion of male and female gametes resulting in variation) or asexual (one parent producing genetically identical offspring). In flowering plants, sexual reproduction occurs in the flower. The male gamete is the pollen grain produced in the anther. The female gamete is the ovule, found inside the ovary.
生殖可以是有性的（雄性和雌性配子融合，产生变异）或无性的（单一亲本产生基因相同的后代）。有花植物的有性生殖发生在花中。雄性配子是花药产生的花粉粒。雌性配子是子房内的胚珠。
Pollination is the transfer of pollen from an anther to a stigma; it can be wind- or insect-pollinated. Fertilisation occurs when a pollen tube grows down the style, allowing the male nucleus to fuse with the ovule nucleus. The fertilised ovule develops into a seed, and the ovary becomes the fruit, aiding seed dispersal.
传粉是花粉从花药传到柱头的过程；可通过风媒或虫媒进行。受精发生时，花粉管沿花柱生长，使雄性细胞核与胚珠细胞核融合。受精的胚珠发育成种子，子房发育成果实，有助于种子传播。
In humans, the male reproductive system includes testes (produce sperm and testosterone), sperm ducts and penis. The female reproductive system includes ovaries (produce eggs and oestrogen), oviducts, uterus and vagina. Fertilisation typically occurs in an oviduct, and the embryo implants in the uterus wall where the placenta forms, providing oxygen and nutrients while removing waste.
在人类中，男性生殖系统包括睾丸（产生精子和睾酮）、输精管和阴茎。女性生殖系统包括卵巢（产生卵子和雌激素）、输卵管、子宫和阴道。受精通常在输卵管内发生，胚胎植入子宫壁，形成胎盘，提供氧气和营养并移除废物。
11. Inheritance and Variation | 遗传与变异
Inheritance is the transmission of genetic information from parents to offspring. DNA, located in the nucleus, is organised into chromosomes. A gene is a section of DNA that codes for a specific protein, and alleles are different versions of the same gene. Genotype is the combination of alleles, while phenotype is the observable characteristic.
遗传是亲本将遗传信息传递给后代的过程。DNA位于细胞核中，组织成染色体。基因是编码特定蛋白质的一段DNA，等位基因是同一个基因的不同版本。基因型是等位基因的组合，表现型是可观察的特征。
Some alleles are dominant and mask the effect of recessive alleles. In a monohybrid cross, the 3:1 phenotypic ratio appears in the F2 generation when both parents are heterozygous. Sex is determined by sex chromosomes: XX for female and XY for male.
有些等位基因为显性，会掩盖隐性等位基因的效应。在一个单基因杂合子杂交中，当双亲均为杂合时，F2代会出现3:1的表现型比例。性别由性染色体决定：XX为女性，XY为男性。
Variation within a species can be continuous (range of values, e.g., height), influenced by many genes and environment, or discontinuous (distinct categories, e.g., blood group), generally controlled by a single gene. Mutations are changes in the DNA sequence and can be harmful, neutral or beneficial, driving natural selection.
物种内的变异可以是连续性（数值范围，如身高），受多基因和环境共同影响；或是不连续（明显类别，如血型），通常由单一基因控制。突变是DNA序列的改变，可能有害、中性或有利，驱动自然选择。
12. Ecology and Ecosystems | 生态与生态系统
An ecosystem is a unit containing all living organisms (community) interacting with each other and with their non-living (abiotic) environment. Abiotic factors include light, temperature, water, pH and soil type. Biotic factors are the living components, such as predation and competition.
生态系统是由所有生物（群落）与其非生物（无机）环境相互作用构成的单元。非生物因素包括光照、温度、水分、pH值和土壤类型。生物因素则是捕食和竞争等生命组分。
Food chains and webs show the flow of energy through an ecosystem. Producers (plants) convert light energy into chemical energy via photosynthesis. Consumers are classified as primary, secondary and tertiary. Decomposers break down dead matter, returning nutrients to the soil.
食物链和食物网显示了能量在生态系统中的流动。生产者（植物）通过光合作用将光能转化为化学能。消费者分为初级、次级和三级消费者。分解者分解死物，将养分归还土壤。
Energy is lost at each trophic level, mainly as heat from respiration, which explains why food chains rarely exceed five levels. Pyramids of number and biomass can represent feeding relationships. Human activities such as deforestation, pollution and overfishing can disrupt ecosystems and reduce biodiversity, and conservation efforts aim to protect habitats and species.
能量在每一个营养级都会损失，主要以呼吸产热的形式，这解释了为什么食物链很少超过五级。数量和生物量金字塔可以表示摄食关系。森林砍伐、污染和过度捕捞等人类活动会破坏生态系统、降低生物多样性，保护措施则旨在保护栖息地和物种。
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