📚 Year 9 CIE Biology: Core Knowledge Review | Year 9 CIE 生物：核心知识点梳理
This article provides a structured overview of the essential topics covered in Year 9 CIE Biology. It connects fundamental biological concepts, from the characteristics of life to the basics of genetics and evolution, forming a solid foundation for further IGCSE study.
本文系统梳理了 Year 9 CIE 生物课程的核心知识点。内容涵盖从生命特征到遗传进化基础的各个关键概念，为后续的 IGCSE 学习打下坚实基础。
1. Characteristics of Living Organisms | 生物的特征
All living organisms share seven life processes, often remembered by the acronym MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition. Movement refers to a change in position or location, not necessarily locomotion; plants move their leaves towards light. Respiration is the chemical breakdown of nutrient molecules to release energy for cellular work. Sensitivity is the ability to detect and respond to changes in the internal or external environment.
所有生物共有七大生命活动，常记作 MRS GREN：运动、呼吸、感知、生长、繁殖、排泄和营养。运动指位置或姿态的改变，不一定是整体移动；植物也能使叶片朝向光。呼吸是将营养物质分解以释放能量的化学过程。感知是指能察觉并响应内、外环境的变化。
Growth is a permanent increase in size and dry mass, achieved by cell division and enlargement. Reproduction allows organisms to produce offspring, ensuring the continuity of their species. Excretion is the removal of toxic waste products of metabolism, such as carbon dioxide and urea. Nutrition involves the intake of materials for energy, growth, and repair; plants make their own food by photosynthesis, whereas animals consume other organisms.
生长是体积和干质量的永久增加，通过细胞分裂和增大实现。繁殖使生物产生后代，保证物种延续。排泄是排出代谢产生的有毒废物，如二氧化碳和尿素。营养指摄入用于供能、生长和修复的物质；植物通过光合作用自制食物，动物则摄食其他生物。
2. Cell Structure and Function | 细胞结构与功能
Cells are the basic structural and functional units of all living organisms. Animal cells typically contain a nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes. The nucleus controls cell activities and contains genetic material. Cytoplasm is the jelly-like substance where most metabolic reactions occur. The cell membrane is selectively permeable, controlling the entry and exit of substances. Mitochondria are the sites of aerobic respiration, releasing energy.
细胞是所有生物的基本结构和功能单位。动物细胞通常含有细胞核、细胞质、细胞膜、线粒体和核糖体。细胞核控制细胞活动并携有遗传物质。细胞质是果冻状物质，多数代谢反应在此进行。细胞膜具选择透过性，控制物质的进出。线粒体是有氧呼吸的场所，释放能量。
Plant cells share the same basic components but also possess a rigid cell wall made of cellulose, a large permanent vacuole containing cell sap, and chloroplasts where photosynthesis occurs. The cell wall provides structural support and prevents bursting. The vacuole helps maintain turgor pressure. Chloroplasts contain chlorophyll, which absorbs light energy for photosynthesis.
植物细胞有相同的基本结构，但还有由纤维素组成的坚韧细胞壁、含细胞液的大液泡以及进行光合作用的叶绿体。细胞壁起支撑作用并防止细胞涨破。液泡维持细胞膨压。叶绿体含叶绿素，可吸收光能用于光合作用。
| Feature | Animal Cell | Plant Cell |
|---|---|---|
| Nucleus | Present | Present |
| Cytoplasm | Present | Present |
| Cell membrane | Present | Present |
| Mitochondria | Present | Present |
| Cell wall | Absent | Present (cellulose) |
| Chloroplasts | Absent | Present |
| Large vacuole | Absent | Present |
3. Movement of Substances | 物质的运输
Substances move across cell membranes by diffusion, osmosis, and active transport. Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, and does not require energy. Oxygen and carbon dioxide enter and leave cells by simple diffusion.
物质穿过细胞膜的方式有扩散、渗透和主动运输。扩散是粒子由高浓度区域向低浓度区域的净运动，顺浓度梯度进行，不消耗能量。氧气和二氧化碳通过简单扩散进出细胞。
Osmosis is a special type of diffusion involving water molecules. It is the net movement of water from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) across a partially permeable membrane. Plant cells rely on osmosis to maintain turgidity; animal cells can burst if too much water enters.
渗透是水分子特有的一种扩散。它是水通过部分透性膜从水势较高（稀溶液）的区域向水势较低（浓溶液）的区域净移动。植物细胞依靠渗透维持坚挺；动物细胞若进水过多会胀破。
Active transport is the movement of particles against a concentration gradient, from low to high concentration, using energy from respiration. This process requires protein carriers in the membrane. Examples include the uptake of mineral ions by root hairs and the absorption of glucose in the small intestine.
主动运输是粒子逆浓度梯度的运动，即从低浓度到高浓度，需消耗呼吸作用提供的能量。该过程需要膜上的蛋白质载体。实例包括根毛吸收矿物离子和小肠吸收葡萄糖。
4. Biological Molecules and Enzymes | 生物分子与酶
The main groups of biological molecules are carbohydrates, proteins, and lipids (fats and oils). Carbohydrates provide the primary source of energy; glucose is a simple sugar, and starch is a large storage carbohydrate in plants. Proteins are made of amino acids and are needed for growth and repair of tissues. Lipids are used for long-term energy storage, insulation, and forming cell membranes.
主要的生物分子包括碳水化合物、蛋白质和脂类（脂肪与油）。碳水化合物是主要能源；葡萄糖是单糖，淀粉是植物中的大型储存碳水化合物。蛋白质由氨基酸构成，用于组织生长与修复。脂类用于长期储能、保温和构成细胞膜。
Enzymes are biological catalysts, which speed up chemical reactions without being used up. They are proteins with a specific three-dimensional shape. The ‘lock and key’ model explains enzyme action: the active site of the enzyme is complementary to the shape of the substrate molecule. An enzyme-substrate complex forms, and the reaction takes place, after which products are released.
酶是生物催化剂，能加速化学反应而自身不被消耗。它们是具有特定三维形状的蛋白质。“锁钥模型”解释了酶的作用：酶的活性中心与底物分子的形状互补。形成酶-底物复合物，发生反应后产物被释放。
Enzyme activity is affected by temperature and pH. As temperature rises, activity increases up to an optimum (around 37°C in humans), after which the enzyme denatures and loses its shape irreversibly. Extreme pH values also denature enzymes. Each enzyme works best at a specific pH; for example, stomach protease pepsin works best at acidic pH 2, while most other enzymes work near neutral pH 7.
酶活性受温度和 pH 影响。温度升高，活性增加直至最适温度（人体约 37°C），随后酶变性失活，形状不可逆改变。极端 pH 值也会使酶变性。每种酶有特定的最适 pH；例如胃蛋白酶在酸性 pH 2 时活性最佳，而多数其他酶在中性 pH 7 附近工作。
5. Plant Nutrition – Photosynthesis | 植物营养 – 光合作用
Photosynthesis is the process by which green plants use light energy to synthesize carbohydrates from carbon dioxide and water. The word equation is:
光合作用是绿色植物利用光能将二氧化碳和水合成为碳水化合物的过程。文字方程式为：
carbon dioxide + water → glucose + oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
The balanced chemical equation is:
化学方程式为：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Chlorophyll in chloroplasts traps light energy, which is used to split water molecules (photolysis) and convert carbon dioxide into glucose. Oxygen is released as a waste product. Limiting factors for photosynthesis include light intensity, carbon dioxide concentration, and temperature.
叶绿体中的叶绿素捕捉光能，用于分解水分子（光解）并将二氧化碳转化为葡萄糖。氧气作为废物释放。光合作用的限制因素包括光照强度、二氧化碳浓度和温度。
A leaf is adapted for photosynthesis: it is broad and flat to capture maximum light; thin to allow short diffusion distances for gases; has stomata to allow carbon dioxide to enter and oxygen to leave; and contains a network of veins (xylem and phloem) for water and sugar transport. The palisade mesophyll layer is packed with chloroplasts near the upper surface.
叶片适应光合作用：宽阔扁平以最大限度接收光；薄以减少气体扩散距离；具有气孔让二氧化碳进入、氧气排出；含有由木质部和韧皮部组成的叶脉网络以运输水和糖。栅栏组织紧靠上表面，密布叶绿体。
6. Human Nutrition – Digestion | 人体营养 – 消化
Digestion is the physical and chemical breakdown of large, insoluble food molecules into small, soluble molecules that can be absorbed into the bloodstream. Mechanical digestion includes chewing in the mouth and churning in the stomach. Chemical digestion is carried out by enzymes.
消化是将大而不可溶的食物分子物理和化学分解为可溶并能为血液吸收的小分子的过程。物理消化包括口腔咀嚼和胃的蠕动搅拌。化学消化由酶完成。
Carbohydrates are broken down by amylase (present in saliva and pancreatic juice) into simple sugars such as maltose. Proteins are digested by proteases: pepsin works in the acidic stomach, while trypsin acts in the alkaline small intestine. Lipids are emulsified by bile (produced by the liver, stored in the gall bladder) and then digested by lipase into fatty acids and glycerol. The small intestine is the main site of absorption, where villi and microvilli provide a huge surface area.
碳水化合物由淀粉酶（存在于唾液和胰液中）分解为麦芽糖等单糖。蛋白质由蛋白酶消化：胃蛋白酶在酸性胃中工作，胰蛋白酶在碱性的小肠中作用。脂类由胆汁（肝脏产生，储于胆囊）乳化，再被脂肪酶分解为脂肪酸和甘油。小肠是吸收的主要场所，绒毛和微绒毛提供了巨大的表面积。
7. Respiration and Gas Exchange | 呼吸作用与气体交换
Respiration is not breathing; it is the release of energy from food molecules such as glucose and occurs in every living cell. Aerobic respiration uses oxygen and produces a large amount of energy (ATP). The word equation is:
呼吸作用不是呼吸动作；它是从葡萄糖等食物分子中释放能量，发生于所有活细胞。有氧呼吸利用氧气并产生大量能量（ATP）。文字方程式为：
glucose + oxygen → carbon dioxide + water + energy
葡萄糖 + 氧气 → 二氧化碳 + 水 + 能量
Anaerobic respiration occurs when oxygen is short. In human muscle cells, it produces lactic acid and much less energy, leading to muscle fatigue and an oxygen debt. In yeast, anaerobic respiration produces ethanol and carbon dioxide; this is fermentation, used in bread-making and brewing.
无氧呼吸在缺氧时发生。在人体肌细胞中产生乳酸和较少能量，导致肌肉疲劳和氧债。酵母的无氧呼吸产生乙醇和二氧化碳，即发酵，用于制作面包和酿酒。
Gas exchange in humans occurs in the alveoli of the lungs. The alveoli have thin, moist walls, a large surface area, and a dense network of capillaries to maximise the diffusion of oxygen into the blood and carbon dioxide out. Breathing movements (inhaling and exhaling) are caused by the diaphragm and intercostal muscles changing the volume and pressure of the thorax.
人体气体交换在肺泡中进行。肺泡壁薄而湿润、表面积大且有密集的毛细血管网，以最大限度让氧气扩散入血、二氧化碳扩散出。呼吸运动（吸气和呼气）由膈肌和肋间肌改变胸腔容积和压力引起。
8. Transport in Plants | 植物的运输
Plants have two transport tissues: xylem and phloem. Xylem vessels are dead, hollow tubes strengthened with lignin; they transport water and dissolved mineral ions from the roots up to the stems and leaves. The movement of water through xylem is driven by transpiration, the evaporation of water from leaf surfaces, which creates a pulling force (transpiration pull).
植物有两种运输组织：木质部和韧皮部。木质部导管是已死的、由木质素强化的中空管，负责将水和溶解的矿物离子从根部向上运输到茎叶。水通过木质部的运动由蒸腾作用驱动——即水分从叶片表面蒸发，产生蒸腾拉力。
Phloem consists of living cells (sieve tubes and companion cells) and transports sucrose and amino acids from sources (e.g., leaves) to sinks (e.g., growing roots, fruits) in a process called translocation. Transpiration rate is affected by light intensity, temperature, humidity, and wind speed. Wilting occurs when water loss by transpiration exceeds water uptake.
韧皮部由活细胞（筛管和伴胞）组成，将蔗糖和氨基酸从源（如叶片）运输到库（如生长的根、果实），这一过程称为输导。蒸腾速率受光照强度、温度、湿度和风速影响。当蒸腾失水超过吸水时，植物发生萎蔫。
9. Transport in Humans – The Circulatory System | 人体运输 – 循环系统
The circulatory system consists of the heart, blood vessels, and blood. The heart is a muscular organ that pumps blood around the body. The right side receives deoxygenated blood from the body and pumps it to the lungs (pulmonary circulation). The left side receives oxygenated blood from the lungs and pumps it to the rest of the body (systemic circulation). The septum separates the two sides, preventing mixing of oxygenated and deoxygenated blood.
循环系统由心脏、血管和血液组成。心脏是将血液泵往全身的肌肉器官。右心接受来自身体的缺氧血并将其泵至肺（肺循环）。左心接受来自肺的富氧血并泵到全身（体循环）。室间隔隔开两侧，防止富氧血和缺氧血混合。
Blood vessels include arteries (carry blood away from the heart, thick muscular walls, high pressure), veins (carry blood back to the heart, thinner walls, contain valves to prevent backflow), and capillaries (tiny, one-cell-thick walls to allow exchange of substances with tissues). Blood is composed of red blood cells (carry oxygen using haemoglobin), white blood cells (defence against disease), platelets (clotting), and plasma (transport of nutrients, hormones, and waste).
血管包括动脉（将血液带离心脏，壁厚有肌肉，压力高）、静脉（将血液送回心脏，壁较薄，有瓣膜防止倒流）和毛细血管（极细，单层细胞壁，便于与组织进行物质交换）。血液由红细胞（用血红蛋白运氧）、白细胞（防御疾病）、血小板（凝血）和血浆（运输营养、激素和废物）组成。
10. Reproduction and Inheritance Basics | 生殖与遗传基础
Reproduction can be sexual or asexual. Sexual reproduction involves the fusion of male and female gametes, leading to offspring that are genetically different from the parents; this increases variation. Asexual reproduction does not involve gametes; offspring are genetically identical clones produced by one parent, e.g., by mitosis.
生殖分有性和无性。有性生殖涉及雄性和雌性配子融合，产生与亲本遗传不同的后代，增加了变异。无性生殖不涉及配子，后代由一个亲本产生，是遗传相同的克隆，例如通过有丝分裂。
In humans, the male gamete is the sperm, produced in the testes, and the female gamete is the ovum (egg), produced in the ovaries. Fertilisation occurs in the oviduct, and the zygote implants in the uterus lining. The placenta allows exchange of substances between mother and fetus without mixing blood. The menstrual cycle prepares the uterus for pregnancy.
人类雄性配子是精子，在睾丸产生；雌性配子是卵细胞，在卵巢产生。受精发生在输卵管，受精卵植入子宫内膜。胎盘允许母体和胎儿间物质交换而不混合血液。月经周期为子宫做好准备以迎接妊娠。
Genes are sections of DNA that code for particular proteins; they are located on chromosomes in the nucleus. Humans have 46 chromosomes (23 pairs). Sex is determined by X and Y chromosomes: females have XX, males have XY. A gene may exist in different forms called alleles. Dominant alleles mask the effect of recessive alleles. Natural selection is the process whereby organisms better adapted to their environment tend to survive and produce more offspring, leading to evolution over time.
基因是编码特定蛋白质的 DNA 片段，位于细胞核内的染色体上。人类有 46 条染色体（23 对）。性别由 X 和 Y 染色体决定：女性为 XX，男性为 XY。一个基因可以有不同的形式，称为等位基因。显性等位基因掩盖隐性等位基因的效应。自然选择是指更适应环境的生物往往能生存并产生更多后代，随时间推移导致进化。
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