📚 IGCSE CCEA Biology: Last-Minute Revision Notes | IGCSE CCEA 生物：考前冲刺笔记
This set of revision notes covers the essential topics for the CCEA IGCSE Biology examination. Use these concise summaries to reinforce key concepts, memorise definitions, and avoid common mistakes. Focus on understanding processes and linking ideas across topics.
这套复习笔记涵盖了 CCEA IGCSE 生物考试的核心主题。通过这些精炼总结，巩固关键概念，记忆定义，并避免常见错误。重点理解过程，并将各主题之间的联系串联起来。
1. Cell Structure and Function | 细胞结构与功能
All living organisms are made of cells, which are the basic structural and functional units of life. Eukaryotic cells, such as those of animals, plants and fungi, possess a true nucleus containing DNA. Prokaryotic cells, including bacteria, lack a nucleus and have free circular DNA in the cytoplasm.
所有生物体都由细胞构成，细胞是生命的基本结构和功能单位。真核细胞，如动物、植物和真菌细胞，具有真正的细胞核，内含 DNA。原核细胞，包括细菌，没有细胞核，细胞质中有游离的环状 DNA。
Animal cells contain a cell membrane, cytoplasm, nucleus, mitochondria (site of aerobic respiration), and ribosomes (site of protein synthesis). Plant cells share these organelles but also have a rigid cellulose cell wall, a large permanent vacuole filled with cell sap, and chloroplasts for photosynthesis. Fungal cells have a cell wall made of chitin, not cellulose.
动物细胞含有细胞膜、细胞质、细胞核、线粒体（有氧呼吸的场所）和核糖体（蛋白质合成的场所）。植物细胞同样拥有这些细胞器，但还具有坚硬的纤维素细胞壁、充满细胞液的大液泡以及进行光合作用的叶绿体。真菌细胞壁由几丁质构成，而非纤维素。
Key cell adaptations: Root hair cells have long extensions to increase surface area for water absorption. Red blood cells lack a nucleus to maximise space for haemoglobin. Sperm cells contain many mitochondria to provide energy for movement.
细胞关键适应性： 根毛细胞有长长的突起以增加吸收水分的表面积。红细胞没有细胞核，以最大化容纳血红蛋白的空间。精子含有大量线粒体，为运动提供能量。
2. Biological Molecules and Food Tests | 生物分子与食物检测
Carbohydrates, proteins, and lipids are the main organic molecules. Carbohydrates include monosaccharides (e.g., glucose), disaccharides (e.g., maltose), and polysaccharides (starch, glycogen, cellulose). Starch is the plant storage carbohydrate; glycogen is the storage form in animals and fungi.
碳水化合物、蛋白质和脂质是主要的有机分子。碳水化合物包括单糖（如葡萄糖）、二糖（如麦芽糖）和多糖（淀粉、糖原、纤维素）。淀粉是植物的储存碳水化合物；糖原是动物和真菌中的储存形式。
Proteins are made of amino acids joined by peptide bonds. They have many roles: enzymes, structural components, hormones, and antibodies. Lipids (fats and oils) are composed of fatty acids and glycerol; they provide long-term energy storage, insulation, and make up cell membranes.
蛋白质由通过肽键连接的氨基酸组成。它们具有多种功能：酶、结构组分、激素和抗体。脂质（脂肪和油）由脂肪酸和甘油组成；它们提供长期能量储存、保温并构成细胞膜。
| Food Test | Reagent | Positive Result |
|---|---|---|
| Starch | Iodine solution | Turns blue-black |
| Reducing sugar (glucose) | Benedict’s solution, heat | Brick-red precipitate |
| Protein | Biuret reagent | Lilac/purple colour |
| Lipid | Ethanol, then water | Cloudy white emulsion |
Remember: the Benedict’s test requires heating; non-reducing sugars (like sucrose) must be hydrolysed first. Biuret reagent detects peptide bonds, not individual amino acids.
记住：本尼迪克特试验需要加热；非还原糖（如蔗糖）必须先经过水解。双缩脲试剂检测肽键，而非单个氨基酸。
3. Enzymes | 酶
Enzymes are biological catalysts made of protein that speed up reactions without being used up. They have an active site with a specific shape, complementary to the substrate. This is the lock-and-key model.
酶是由蛋白质构成的生物催化剂，能加速反应而自身不被消耗。它们具有特定形状的活性位点，与底物互补。这就是锁钥模型。
Enzyme activity is affected by temperature and pH. As temperature rises, kinetic energy increases, raising the rate of reaction. Above the optimum temperature, the enzyme denatures – its active site changes shape irreversibly. Each enzyme works best at a specific pH; for example, pepsin in the stomach works optimally at pH 2, while most other enzymes prefer neutral conditions.
酶的活性受温度和 pH 影响。温度升高，动能增加，反应速率上升。超过最适温度，酶会变性——其活性位点不可逆地改变形状。每种酶在特定的 pH 下活性最高；例如，胃中的胃蛋白酶最适 pH 为 2，而大多数其他酶偏好中性条件。
Denaturation is often permanent, but changes in pH that do not denature the enzyme can be reversed. Inhibitors can also regulate enzyme action: competitive inhibitors resemble the substrate and block the active site; non-competitive inhibitors bind elsewhere and change the enzyme’s shape.
变性通常是永久性的，但未导致变性的 pH 变化是可逆的。抑制剂也能调节酶的作用：竞争性抑制剂与底物相似，阻塞活性位点；非竞争性抑制剂结合在其他位点，改变酶的形状。
4. Movement Across Cell Membranes | 物质跨膜运输
Substances move in and out of cells 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 the concentration gradient, without energy. Osmosis is the diffusion of water molecules through a partially permeable membrane from a dilute solution to a more concentrated one.
物质通过扩散、渗透和主动运输进出细胞。扩散是粒子从高浓度区域向低浓度区域的净移动，顺浓度梯度，不消耗能量。渗透是水分子通过半透膜从稀溶液向较浓溶液扩散。
In plant cells, if the external solution is dilute (hypotonic), water enters by osmosis, making the cell turgid. In a concentrated solution (hypertonic), water leaves, the cytoplasm shrinks and the membrane pulls away from the wall – this is plasmolysis. Animal cells lack a cell wall and may burst (lyse) in very dilute solutions or shrink (crenate) in concentrated solutions.
在植物细胞中，若外界溶液稀（低渗），水分通过渗透进入，细胞变得硬挺。在浓溶液（高渗）中，水分流失，细胞质收缩，细胞膜与细胞壁分离——这就是质壁分离。动物细胞没有细胞壁，在极稀溶液中可能胀破（溶血），在浓溶液中会皱缩。
Active transport moves substances against the concentration gradient, from lower to higher concentration, using energy from ATP. Carrier proteins in the membrane are needed. This process is vital for mineral ion uptake in root hairs and glucose absorption in the gut.
主动运输逆浓度梯度移动物质，从低浓度到高浓度，消耗 ATP 提供的能量。需要膜上的载体蛋白。这一过程对根毛吸收矿质离子和肠道吸收葡萄糖至关重要。
5. Nutrition and Digestion in Humans | 人体营养与消化
Humans require a balanced diet containing carbohydrates, proteins, lipids, vitamins, minerals, dietary fibre, and water. Digestion breaks down large insoluble molecules into small soluble ones that can be absorbed.
人类需要包含碳水化合物、蛋白质、脂质、维生素、矿物质、膳食纤维和水的均衡饮食。消化将大分子不溶物质分解为可吸收的小分子可溶物质。
Mechanical digestion (chewing, churning) increases surface area. Chemical digestion uses enzymes. In the mouth, amylase breaks down starch into maltose. In the stomach, pepsin (protease) acts on proteins and hydrochloric acid kills bacteria. In the small intestine, pancreatic amylase, proteases, and lipase continue digestion. Bile (produced by the liver, stored in the gall bladder) emulsifies fats, creating a larger surface area for lipase.
物理消化（咀嚼、搅拌）增加表面积。化学消化依靠酶。在口腔，淀粉酶将淀粉分解为麦芽糖。在胃中，胃蛋白酶作用于蛋白质，盐酸杀灭细菌。在小肠，胰淀粉酶、蛋白酶和脂肪酶继续消化。胆汁（肝产生，胆囊储存）乳化脂肪，为脂肪酶提供更大的表面积。
Absorption of digested food happens mainly in the ileum (small intestine), where villi and microvilli provide a vast surface area. Glucose and amino acids are absorbed into blood capillaries; fatty acids and glycerol are absorbed into lacteals (lymph vessels).
消化后的食物吸收主要发生在回肠（小肠），其中的绒毛和微绒毛提供了巨大的表面积。葡萄糖和氨基酸被吸收入毛细血管；脂肪酸和甘油被吸收入乳糜管（淋巴管）。
6. Respiration | 呼吸作用
Respiration is the process that releases energy from food (usually glucose) in all living cells. It is not the same as breathing. The energy released is used to make ATP, which powers processes like muscle contraction, cell division, and active transport.
呼吸作用是在所有活细胞中从食物（通常是葡萄糖）释放能量的过程，与呼吸（通气）不同。释放的能量用于制造 ATP，驱动肌肉收缩、细胞分裂和主动运输等过程。
Aerobic respiration requires oxygen and produces a large amount of energy:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)
有氧呼吸 需要氧气，释放大量能量：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量（ATP）
Anaerobic respiration occurs without oxygen. In muscles, glucose is broken down into lactic acid, causing fatigue and oxygen debt. In yeast, glucose is converted to ethanol and carbon dioxide (fermentation). Anaerobic respiration yields much less ATP than aerobic respiration.
无氧呼吸 在无氧条件下发生。在肌肉中，葡萄糖分解为乳酸，导致疲劳和氧债。在酵母中，葡萄糖转化为乙醇和二氧化碳（发酵）。无氧呼吸产生的 ATP 远少于有氧呼吸。
| Feature | Aerobic | Anaerobic (Muscle) | Anaerobic (Yeast) |
|---|---|---|---|
| Oxygen | Required | Not required | Not required |
| Products | CO₂ + H₂O | Lactic acid | Ethanol + CO₂ |
| ATP yield | ~36-38 per glucose | 2 per glucose | 2 per glucose |
7. Photosynthesis and Plant Nutrition | 光合作用与植物营养
Photosynthesis is the process by which green plants use light energy to convert carbon dioxide and water into glucose and oxygen. It takes place in chloroplasts, using the pigment chlorophyll.
光合作用是绿色植物利用光能将二氧化碳和水转化为葡萄糖和氧气的过程，发生在叶绿体中，利用叶绿素色素。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Glucose produced may be used directly in respiration, converted to starch for storage, used to make cellulose for cell walls, or combined with nitrogen to form amino acids and proteins. Plants also need mineral ions: nitrates for amino acids, magnesium for chlorophyll, phosphates for DNA and cell membranes.
产生的葡萄糖可直接用于呼吸作用、转化为淀粉储存、用于制造细胞壁的纤维素，或与氮结合形成氨基酸和蛋白质。植物还需要矿质离子：硝酸盐用于氨基酸，镁用于叶绿素，磷酸盐用于DNA和细胞膜。
Limiting factors: light intensity, carbon dioxide concentration, and temperature all affect the rate of photosynthesis. At low light, the rate is limited by light; beyond a certain point, CO₂ or temperature becomes limiting. This is important in greenhouse management.
限制因素： 光照强度、二氧化碳浓度和温度都会影响光合作用速率。光照弱时，速率受光限制；超过一定水平后，CO₂ 或温度成为限制因素。这在温室管理中很重要。
Experiments often investigate the effect of light or CO₂ on pondweed. The volume of oxygen bubbles produced per minute measures the rate. A destarched plant can be used to test whether starch is produced after exposure to light.
实验通常探究光照或二氧化碳对水生植物的影响。每分钟产生的氧气气泡体积用于测量速率。可用脱淀粉植物检测光照后是否产生淀粉。
8. Genetics and Inheritance | 遗传学与遗传
Genes are sections of DNA that code for a specific protein. Alleles are different versions of the same gene. A diploid organism has two alleles for each gene, one from each parent. The genotype is the combination of alleles; the phenotype is the observable characteristic.
基因是编码特定蛋白质的 DNA 片段。等位基因是同一基因的不同形式。二倍体生物每个基因有两个等位基因，分别来自亲本。基因型是等位基因的组合；表型是可观察的特征。
A dominant allele (shown by a capital letter) masks the effect of a recessive allele (lowercase) in a heterozygous individual. Homozygous means two identical alleles; heterozygous means two different alleles.
显性等位基因（大写字母表示）在杂合子中掩盖隐性等位基因（小写）的效应。纯合子指两个相同的等位基因；杂合子指两个不同的等位基因。
Monohybrid crosses can be shown using Punnett squares. For example, crossing two heterozygous plants (Tt × Tt) for height (T = tall, t = dwarf) gives a 3:1 phenotypic ratio. Sex determination in humans: females are XX, males are XY; a 1:1 ratio results from the cross XX × XY.
单基因杂交可用庞尼特方格表示。例如，杂交两个杂合高株植物（Tt × Tt）得到表型比 3:1。人类性别决定：女性为 XX，男性为 XY；XX × XY 的杂交产生 1:1 的比例。
Codominance occurs when both alleles are expressed in the phenotype, e.g., ABO blood groups. Some characteristics show continuous variation (e.g., height) influenced by many genes and environment.
共显性是指两个等位基因在表型中都表现出来，如 ABO 血型。一些特征表现出连续变异（如身高），受许多基因和环境的影响。
9. Ecology and the Environment | 生态学与环境
An ecosystem includes all the organisms living in an area (community) and their physical environment. Producers (plants) make their own food by photosynthesis. Consumers eat other organisms; decomposers break down dead material and recycle nutrients.
生态系统包括一个区域内的所有生物（群落）及其物理环境。生产者（植物）通过光合作用制造食物。消费者食用其他生物；分解者分解死物质，循环养分。
Food chains show the flow of energy: producer → primary consumer → secondary consumer → tertiary consumer. At each trophic level, energy is lost through respiration, heat, and undigested material. Only about 10% is transferred to the next level, so food chains rarely exceed 4–5 levels.
食物链显示能量流动：生产者 → 初级消费者 → 次级消费者 → 三级消费者。每个营养级能量因呼吸、热和未消化物质而损失。大约只有 10% 传递到下一级，因此食物链很少超过 4-5 个层级。
The carbon cycle moves carbon between the atmosphere, organisms, soil, and fossil fuels. Photosynthesis removes CO₂; respiration, combustion, and decomposition release it. Nitrogen is cycled by nitrogen-fixing bacteria, nitrifying bacteria, and denitrifying bacteria. Deforestation and burning fossil fuels disturb these cycles and contribute to global warming.
碳循环使碳在大气、生物体、土壤和化石燃料之间移动。光合作用吸收 CO₂；呼吸作用、燃烧和分解释放 CO₂。氮通过固氮菌、硝化菌和反硝化菌循环。森林砍伐和化石燃料燃烧干扰这些循环，导致全球变暖。
10. Human Physiology – Transport, Excretion, and Nervous System | 人体生理——运输、排泄与神经系统
The circulatory system consists of the heart, blood vessels, and blood. The heart has four chambers: right atrium, right ventricle, left atrium, left ventricle. The right side pumps deoxygenated blood to the lungs; the left side pumps oxygenated blood to the body. Valves prevent backflow.
循环系统由心脏、血管和血液组成。心脏有四个腔：右心房、右心室、左心房、左心室。右心室将缺氧血泵送到肺部；左心室将富氧血泵送至全身。瓣膜防止血液倒流。
Arteries carry blood away from the heart under high pressure; they have thick, muscular walls. Veins carry blood back to the heart, have thinner walls, and contain valves. Capillaries are narrow, thin-walled vessels where exchange of materials occurs.
动脉从心脏输出高压血液，壁厚而富有弹性。静脉将血液送回心脏，壁较薄，并有瓣膜。毛细血管是狭窄的薄壁血管，是物质交换的场所。
Blood is composed of plasma, red blood cells (transport oxygen using haemoglobin), white blood cells (defence), and platelets (clotting). Excretion removes metabolic waste. The kidneys filter blood, reabsorb useful substances, and produce urine (containing urea, excess water, and salts).
血液由血浆、红细胞（运氧，含血红蛋白）、白细胞（防御）和血小板（凝血）组成。排泄作用是清除代谢废物。肾脏过滤血液，重吸收有用物质，并产生尿液（含尿素、多余水分和盐）。
The nervous system uses electrical impulses. A reflex arc includes a receptor, sensory neurone, relay neurone (in the CNS), motor neurone, and effector (muscle or gland). Synapses use chemicals (neurotransmitters) to pass the signal between neurones. This allows rapid, involuntary responses to stimuli.
神经系统利用电冲动。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）、运动神经元和效应器（肌肉或腺体）。突触使用化学物质（神经递质）在神经元间传递信号，实现对刺激的快速无意识反应。
Hormones such as insulin and glucagon regulate blood glucose. Insulin lowers blood glucose by promoting glucose uptake and conversion to glycogen; glucagon raises it by breaking down glycogen in the liver. This is negative feedback homeostasis.
激素如胰岛素和胰高血糖素调节血糖。胰岛素通过促进葡萄糖摄取和转化为糖原来降低血糖；胰高血糖素通过分解肝脏中的糖原来升高血糖。这是负反馈稳态。
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