📚 IGCSE OCR Biology: Final Revision Guide | IGCSE OCR 生物：期末复习提纲
This revision guide distils the essential topics for the IGCSE OCR Biology end-of-term examination. It provides a concise walk through the core modules, from cell biology to ecology, emphasising key concepts, common misconceptions, and must-know processes. Use it alongside your specification and past papers to check your understanding and identify any gaps before the exam.
这份复习提纲精炼了 IGCSE OCR 生物期末考试的核心主题。它简明地梳理了从细胞生物学到生态学的主要模块，突出关键概念、常见误区以及必知过程。请结合考纲和历年真题使用本文，在考前检视自己的理解并找出薄弱环节。
1. Cell Structure and Function | 细胞结构与功能
All living organisms are built from cells, which can be prokaryotic (bacteria, no true nucleus) or eukaryotic (animal, plant, fungi, with a membrane-bound nucleus). Eukaryotic cells contain organelles such as mitochondria, ribosomes, and in plants, chloroplasts and a permanent vacuole.
所有生物体都由细胞构成，细胞分为原核细胞（如细菌，无真正细胞核）和真核细胞（如动物、植物、真菌，有膜包被的细胞核）。真核细胞含有线粒体、核糖体等细胞器，植物细胞还有叶绿体和一个中央大液泡。
Specialised cells are adapted for particular functions. For example, red blood cells lack a nucleus to maximise haemoglobin space, root hair cells have long extensions to absorb water and minerals, and sperm cells possess a tail for motility and many mitochondria for energy.
特化细胞为执行特定功能而发生适应。例如，红细胞无核以容纳更多血红蛋白，根毛细胞有长突起以吸收水分和矿物质，精子细胞具有鞭毛用于运动且富含线粒体提供能量。
Magnification and size calculations remain a vital skill. Recall: magnification = image size ÷ actual size. Always convert units to the same format (mm, μm, nm) before calculating and be prepared to estimate cell dimensions from scale bars.
放大倍率与大小计算是一项重要技能。记住：放大倍率 = 图像大小 ÷ 实际大小。计算前务必统一单位（mm、μm、nm），并能根据比例尺估测细胞尺寸。
2. Biological Molecules and Enzymes | 生物分子与酶
Carbohydrates, proteins, and lipids are the main biological molecules. Carbohydrates contain carbon, hydrogen, and oxygen and include sugars such as glucose (C₆H₁₂O₆) and starch. Proteins are chains of amino acids folded into specific shapes. Lipids are esters of fatty acids and glycerol and are used for long-term energy storage and insulation.
碳水化合物、蛋白质和脂质是主要的生物分子。碳水化合物含有碳、氢、氧，包括葡萄糖（C₆H₁₂O₆）和淀粉等糖类。蛋白质是由氨基酸链折叠而成的特定形状。脂质是脂肪酸与甘油的酯，用于长期储能和保温。
Food tests are examined regularly: Benedict’s solution for reducing sugars (blue to brick-red on heating), iodine for starch (orange-brown to blue-black), biuret for proteins (blue to purple), and ethanol emulsion for lipids (cloudy white emulsion).
食物测试经常考查：本尼迪克特试剂测还原糖（加热后由蓝色变为砖红色），碘液测淀粉（橙褐色变为蓝黑色），双缩脲试剂测蛋白质（蓝色变为紫色），乙醇乳浊液测脂质（出现浑浊白色乳浊液）。
Enzymes are biological catalysts that speed up reactions by lowering activation energy. The lock-and-key model explains enzyme specificity: the substrate fits into the enzyme’s active site. Factors affecting rate include temperature, pH, and substrate concentration. Denaturation is irreversible; extreme pH or high temperature break the bonds holding the enzyme’s shape.
酶是生物催化剂，通过降低活化能加速反应。锁钥模型解释了酶的专一性：底物嵌入酶的活性位点。影响反应速率的因素包括温度、pH 和底物浓度。变性不可逆；极端 pH 或高温会破坏维持酶结构的化学键。
3. Movement Across Membranes | 跨膜运输
Substances move through cell membranes by diffusion, osmosis, and active transport. Diffusion is the net movement of particles from a region of higher concentration to lower concentration, down a gradient, without energy. Osmosis is the diffusion of water molecules through a partially permeable membrane from a dilute to a more concentrated solution.
物质通过扩散、渗透和主动运输穿过细胞膜。扩散是粒子从高浓度区域向低浓度区域的净运动，顺浓度梯度，不消耗能量。渗透是水分子通过部分透性膜从稀溶液向较浓溶液的扩散。
Active transport requires energy (ATP) to move substances against the concentration gradient, such as the uptake of mineral ions by root hair cells. Carrier proteins in the membrane change shape to transport molecules across.
主动运输需要能量（ATP）逆浓度梯度移动物质，例如根毛细胞吸收矿物离子。膜上的载体蛋白会改变形状来运输分子。
Water potential affects plant cells: in a hypertonic solution the cell becomes plasmolysed; in a hypotonic solution the cell becomes turgid. Animal cells lack a cell wall and may burst (lysis) or shrink (crenation) in extreme solutions.
水势影响植物细胞：在高渗溶液中细胞发生质壁分离；在低渗溶液中细胞变得坚挺。动物细胞缺乏细胞壁，在极端溶液中会破裂（溶解）或皱缩。
| Process | Energy needed? | Direction | Example |
|---|---|---|---|
| Diffusion | No | Down concentration gradient | Oxygen into blood |
| Osmosis | No | Down water potential gradient | Water uptake by roots |
| Active transport | Yes (ATP) | Against concentration gradient | Ion uptake in roots |
4. Photosynthesis and Plant Nutrition | 光合作用与植物营养
Photosynthesis converts light energy into chemical energy in the form of glucose. The word equation: carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll. The balanced symbol equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
光合作用将光能转化为以葡萄糖形式储存的化学能。文字方程式：二氧化碳 + 水 → 葡萄糖 + 氧气，需要光和叶绿素。平衡化学方程式：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。
The rate of photosynthesis is limited by several factors: light intensity, carbon dioxide concentration, and temperature. At low light, the rate is directly proportional to light intensity; as light becomes saturating, another factor becomes limiting. Greenhouse systems manipulate these conditions to maximise yield.
光合作用的速率受多种因素限制：光照强度、二氧化碳浓度和温度。在弱光下，速率与光照强度成正比；当光饱和后，另一因子成为限制因素。温室系统通过调控这些条件来最大化产量。
Plants need mineral ions, chiefly nitrate ions for protein synthesis and magnesium ions for chlorophyll. Deficiency symptoms include stunted growth and yellowing leaves. Root hairs actively absorb nitrate ions from the soil via active transport.
植物需要矿质离子，主要是用于合成蛋白质的硝酸根离子和用于叶绿素的镁离子。缺乏症状包括生长迟缓和叶片黄化。根毛通过主动运输从土壤中积极吸收硝酸根离子。
5. Human Nutrition and Digestion | 人体营养与消化
A balanced diet must supply all essential nutrients: carbohydrates, proteins, lipids, vitamins, minerals, fibre, and water. Carbohydrates provide energy, proteins are needed for growth and repair, lipids store energy and insulate, and vitamins and minerals act as co-factors for many processes.
均衡膳食必须提供所有必需营养素：碳水化合物、蛋白质、脂质、维生素、矿物质、膳食纤维和水。碳水化合物提供能量，蛋白质用于生长和修复，脂质储存能量并保温，维生素和矿物质作为许多过程的辅助因子。
Digestion breaks large insoluble molecules into small soluble ones that can be absorbed. Mouth: amylase starts starch digestion. Stomach: protease (pepsin) works in acidic pH. Small intestine: pancreatic enzymes and bile further digest; villi absorb products into the blood. Bile emulsifies lipids, increasing surface area for lipase.
消化将大的不可溶性分子分解成可吸收的小可溶性分子。口腔：淀粉酶开始消化淀粉。胃：蛋白酶（胃蛋白酶）在酸性 pH 下工作。小肠：胰酶和胆汁进一步消化；绒毛将产物吸收进血液。胆汁乳化脂质，增大脂肪酶作用面积。
The structure of a villus is directly linked to absorption: single layer of epithelial cells, rich blood capillary network, and a lacteal for lipid uptake. Microvilli on the cell surface amplify the surface area further.
绒毛的结构与吸收功能直接相关：单层上皮细胞、丰富的毛细血管网以及用于吸收脂质的乳糜管。上皮细胞表面的微绒毛进一步增加了吸收面积。
6. The Circulatory System | 循环系统
Humans have a double circulatory system: the right side of the heart pumps deoxygenated blood to the lungs (pulmonary); the left side pumps oxygenated blood to the rest of the body (systemic). The heart is a muscular pump with four chambers: right atrium, right ventricle, left atrium, and left ventricle. Valves prevent backflow.
人类拥有双循环系统：右心将缺氧血泵至肺部（肺循环）；左心将富氧血泵至全身（体循环）。心脏是一个肌肉泵，有四个腔室：右心房、右心室、左心房和左心室。瓣膜防止血液倒流。
Arteries carry blood away from the heart under high pressure and have thick, elastic walls. Veins return blood to the heart and possess valves; they have thinner walls and a wider lumen. Capillaries are one-cell thick, allowing exchange of substances between blood and tissues.
动脉将血液带离心脏，压力高，管壁厚而有弹性。静脉将血液送回心脏，含有静脉瓣；管壁较薄，管腔较宽。毛细血管仅一层细胞厚，便于血液与组织间的物质交换。
Blood consists of plasma, red blood cells, white blood cells, and platelets. Red blood cells transport oxygen bound to haemoglobin. White blood cells defend against pathogens. Platelets are involved in clotting. Be able to label a heart diagram and explain the sequence of blood flow.
血液由血浆、红细胞、白细胞和血小板组成。红细胞运输与血红蛋白结合的氧气。白细胞抵御病原体。血小板参与凝血。要求能标注心脏结构图并解释血流顺序。
7. Respiration and Gas Exchange | 呼吸作用与气体交换
Respiration is a chemical process that releases energy from glucose, which is then used to form ATP. Aerobic respiration uses oxygen: glucose + oxygen → carbon dioxide + water (+ energy). Anaerobic respiration in muscles produces lactic acid; in yeast, it produces ethanol and carbon dioxide (fermentation).
呼吸作用是一个从葡萄糖释放能量的化学过程，释放的能量用于合成 ATP。有氧呼吸使用氧气：葡萄糖 + 氧气 → 二氧化碳 + 水（+ 能量）。肌肉中的无氧呼吸产生乳酸；酵母中的无氧呼吸产生乙醇和二氧化碳（发酵）。
The breathing system moves air into and out of the lungs. Ventilation involves the diaphragm and intercostal muscles. During inhalation, the diaphragm contracts and flattens, the ribcage moves up and out, increasing thoracic volume and lowering pressure, drawing air in. Exhalation is largely passive at rest.
呼吸系统将空气吸入和排出肺部。肺通气涉及膈肌和肋间肌。吸气时，膈肌收缩变平，肋骨上移外扩，胸腔容积增大，气压降低，空气被吸入。静息时呼气主要依靠被动过程。
Gas exchange occurs in the alveoli: oxygen diffuses into blood and carbon dioxide diffuses out. Alveoli have thin walls, a large surface area, and a rich blood supply to maximise diffusion rate.
气体交换在肺泡中进行：氧气扩散入血，二氧化碳扩散出。肺泡壁极薄、表面积大且血供丰富，从而最大化扩散速率。
8. Nervous System and Homeostasis | 神经系统与稳态
The nervous system enables rapid communication via electrical impulses. A reflex arc includes a receptor, sensory neurone, relay neurone (in CNS), motor neurone, and effector. The synapse is a gap where neurotransmitters diffuse to continue the impulse. Reflexes are automatic and protective.
神经系统通过电脉冲实现快速通信。反射弧包括感受器、感觉神经元、中间神经元（在中枢神经系统内）、运动神经元和效应器。突触是一个间隙，神经递质在此扩散以传递冲动。反射是自动的且具有保护性。
Homeostasis maintains a stable internal environment. Key examples include control of blood glucose concentration, body temperature, and water balance. Negative feedback is the fundamental mechanism: a change is detected and a corrective response is triggered to return the system to its set point.
稳态维持内环境的稳定。重要实例包括血糖浓度调节、体温调节和水分平衡调节。负反馈是基本机制：检测到变化后，引发纠正性反应，使系统恢复至设定点。
The skin aids thermoregulation: when hot, vasodilation and sweating increase heat loss; when cold, vasoconstriction, shivering, and hair erection reduce heat loss. The thermoregulatory centre is in the hypothalamus.
皮肤参与体温调节：炎热时，血管舒张和出汗增加散热；寒冷时，血管收缩、战栗和毛肌收缩减少热量散失。体温调节中枢位于下丘脑。
9. Hormonal Coordination | 激素协调
Hormones are chemical messengers secreted by endocrine glands and transported in the blood. They act more slowly than nerve impulses but have longer-lasting effects. Adrenaline prepares the body for ‘fight or flight’ by increasing heart rate and blood glucose. Insulin and glucagon regulate blood glucose from the pancreas.
激素是由内分泌腺分泌、经血液运输的化学信使。它们作用比神经冲动慢，但效应更持久。肾上腺素通过增加心率和血糖来让身体做好“战斗或逃跑”的准备。胰腺分泌的胰岛素和胰高血糖素共同调节血糖。
In type 1 diabetes, the pancreas fails to produce sufficient insulin, leading to high blood glucose. Treatment involves monitoring diet and insulin injections. A negative feedback loop maintains glucose: high glucose stimulates insulin release, promoting glycogen storage in the liver.
1 型糖尿病中，胰腺无法产生足够的胰岛素，导致高血糖。治疗包括监控饮食和注射胰岛素。负反馈环维持血糖：高血糖刺激胰岛素释放，促进肝脏储存糖原。
Plant hormones, such as auxin, control tropisms. Phototropism: auxin accumulates on the shaded side, causing cells to elongate more there, bending the shoot toward light. Gravitropism: auxin moves to the lower side of a root, inhibiting growth, causing the root to grow downward.
植物激素如生长素控制向性运动。向光性：生长素在背光侧积累，使该侧细胞伸长更多，导致茎尖弯向光源。向地性：生长素移至根的底侧抑制生长，使根向下生长。
10. Reproduction and Inheritance | 生殖与遗传
Sexual reproduction produces genetically diverse offspring through the fusion of gametes. In humans, the male gamete is sperm, produced in testes; the female gamete is the ovum, released from ovaries. Fertilisation occurs in the oviduct. The placenta allows exchange of substances between mother and fetus without mixing blood.
有性生殖通过配子融合产生遗传多样性后代。人类中，雄配子为精子，由睾丸产生；雌配子为卵细胞，由卵巢排出。受精发生在输卵管。胎盘允许母亲与胎儿之间进行物质交换而又不使血液混合。
DNA is a double helix containing genes on chromosomes. A gene is a section of DNA that codes for a specific protein. The genetic code uses four bases: A, T, C, G. Protein synthesis involves transcription (DNA to mRNA) and translation (mRNA to amino acid sequence).
DNA 是双螺旋结构，基因位于染色体上。基因是编码特定蛋白质的 DNA 片段。遗传密码由四种碱基 A、T、C、G 组成。蛋白质合成包括转录（DNA 转 mRNA）和翻译（mRNA 转氨基酸序列）。
Monohybrid inheritance can be explained using Punnett squares. A dominant allele masks a recessive allele. Homozygous means two identical alleles; heterozygous means two different alleles. Sex is determined by X and Y chromosomes: XX female, XY male.
单基因遗传可用旁氏方格解释。显性等位基因掩盖隐性等位基因。纯合指两个相同等位基因，杂合指两个不同等位基因。性别由 X 和 Y 染色体决定：XX 为女性，XY 为男性。
11. Ecology and Biodiversity | 生态学与生物多样性
An ecosystem comprises a community of organisms interacting with their physical environment. Energy enters as light and is captured by producers (plants). Energy flows through food chains, but much is lost at each trophic level through respiration, heat, excretion, and uneaten parts, which limits chain length.
生态系统由生物群落与其物理环境相互作用组成。能量以光的形式进入，被生产者（植物）捕获。能量沿食物链流动，但每一营养级通过呼吸、散热、排泄和未食部分损失大量能量，这限制了食物链的长度。
The carbon cycle describes how carbon moves between the atmosphere, organisms, and the Earth. Photosynthesis fixes carbon, respiration returns it, combustion and decomposition release CO₂. The water cycle involves evaporation, condensation, precipitation, and transpiration from plants.
碳循环描述了碳在大气、生物体和地壳之间的移动。光合作用固定碳，呼吸作用归还碳，燃烧和分解释放 CO₂。水循环包括蒸发、凝结、降水和植物的蒸腾作用。
Human activities affect biodiversity. Deforestation destroys habitats, reduces biodiversity, and contributes to atmospheric CO₂. Pollution by fertilisers causes eutrophication: algal blooms block light, decomposers use up oxygen, killing aquatic life. Conservation efforts protect ecosystems and endangered species.
人类活动影响生物多样性。森林砍伐破坏栖息地、降低生物多样性并增加大气 CO₂。化肥污染导致富营养化：藻华遮蔽光线，分解者耗尽水中氧气，导致水生生物死亡。保护工作旨在保护生态系统和濒危物种。
12. Practical and Investigative Skills | 实验与探究技能
OCR IGCSE Biology places strong emphasis on practical skills. You must be able to plan experiments with appropriate controls, independent, dependent, and control variables. Always refer to ‘control experiment’ for comparison and state the importance of repeatability and reproducibility.
OCR IGCSE 生物高度重视实验技能。你需能设计实验，设置合适的对照组、自变量、因变量和控制变量。务必提及用于比较的“对照实验”，并说明可重复性和可再现性的重要性。
Key practicals include: using a microscope, testing for biological molecules, investigating enzyme activity (e.g., amylase at different pH), diffusion using agar cubes, photosynthesis measuring oxygen bubbles, and transpiration using a potometer. Be ready to outline the method, identify sources of error, and suggest improvements.
关键实验包括：显微镜使用、生物分子检测、酶活性探究（如不同 pH 下淀粉酶）、琼脂块法观察扩散、用氧气泡测量光合作用、以及用蒸腾计测量蒸腾作用。做好准备简述方法、找出误差来源并提出改进建议。
Data handling: construct a results table, plot line graphs, and describe trends. If a graph plateaus, suggest a limiting factor. Use a line of best fit and be able to calculate rate from gradient. Units must be written correctly and consistently.
数据处理：构建结果表格、绘制线图并描述趋势。若图形出现平台，请提出限制因子。使用最佳拟合线，并能够从斜率计算速率。单位必须正确且一致地书写。
Safety is paramount. Always wear eye protection, handle chemicals and hot liquids with care, and mention any specific safety precautions in your experimental plan, such as using a Bunsen burner safely or dealing with biological stains.
安全至关重要。始终佩戴护目镜，小心处理化学品和热液体，并在实验方案中提及特定的安全注意事项，如安全使用本生灯或处理生物染色剂。
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