📚 IGCSE AQA Biology: Mind Map Quick Revision | IGCSE AQA 生物：思维导图速记
This mind map quick revision guide breaks down the IGCSE AQA Biology syllabus into key interconnected topics, so you can visualise how ideas link together and rapidly recall essential knowledge fast in the exam hall. Each section is written as a mini mind map: one core idea, its branches, and the exact facts examiners reward.
本思维导图速记指南将 IGCSE AQA 生物大纲拆解为相互关联的关键主题，帮助你直观看到知识点之间的连接，并在考场上快速回忆核心内容。每一节都是一个迷你思维导图：一个中心概念、若干分支，以及考官真正给分的事实。
Use it in three passes: first read the headings only to build the skeleton, then read the bullet points to fill the branches, then cover the page and draw the map from memory. Repetition across three passes beats one long reread.
建议分三轮使用：第一轮只读标题，搭起骨架；第二轮读要点，填充分支；第三轮遮住页面，凭记忆画出导图。三轮重复的效果远好于一次长时间的重复阅读。
1. Cell Structure and Specialisation | 细胞结构与特化
All living organisms are made of cells. Both animal and plant cells contain a nucleus (controls activities), cytoplasm (site of metabolic reactions), a cell membrane (controls entry and exit), mitochondria (site of aerobic respiration) and ribosomes (protein synthesis).
所有生物都由细胞构成。动植物细胞均含有细胞核（控制活动）、细胞质（代谢反应场所）、细胞膜（控制进出）、线粒体（有氧呼吸场所）和核糖体（蛋白质合成）。
Plant cells have three additional structures: a rigid cellulose cell wall for support, a large permanent vacuole containing cell sap, and chloroplasts which absorb light for photosynthesis. Bacterial cells are much smaller, have no nucleus, and carry a single circular loop of DNA plus plasmids.
植物细胞还有三个额外结构：坚硬的纤维素细胞壁起支持作用，含有细胞液的大永久液泡，以及吸收光能进行光合作用的叶绿体。细菌细胞小得多，没有细胞核，只携带一条环状 DNA 和质粒。
Cells can differentiate to become specialised. Root hair cells have long extensions to increase surface area for water absorption; nerve cells are elongated to transmit electrical impulses over long distances; sperm cells have a tail for movement and many mitochondria for energy; red blood cells have no nucleus and a biconcave shape for more haemoglobin and a shorter diffusion path.
细胞可以分化从而变得特化。根毛细胞具有长突起以增加吸收水分的表面积；神经细胞细长以远距离传递电脉冲；精子细胞有尾部用于运动，并含大量线粒体供能；红细胞无细胞核，呈双凹圆盘形，以容纳更多血红蛋白并缩短扩散距离。
cation = image size ÷ actual size. Convert units before dividing, and remember 1 mm = 1000 µm.
放大倍数几乎必考，务必背下三角关系：放大倍数 = 图像大小 ÷ 实际大小。相除前先统一单位，并记住 1 mm = 1000 µm。
2. Biological Molecules and Food Tests | 生物分子与食物检测
Carbohydrates (starch and sugars), proteins and lipids are the three essential macromolecules. Carbohydrates are built from simple sugars, proteins from amino acids, and lipids from fatty acids and glycerol. These building blocks are joined by condensation reactions and released by hydrolysis.
碳水化合物（淀粉和糖）、蛋白质和脂质是三大必需大分子。碳水化合物由单糖构成，蛋白质由氨基酸构成，脂质由脂肪酸和甘油构成。这些单体通过缩合反应连接，并通过水解反应释放。
Each food test has a specific reagent and a specific colour change. Learn the starting colour as well as the final colour, because marks are often split between the two.
每种食物检测都有特定试剂和特定颜色变化。起始颜色和最终颜色都要记，因为分数常常分别给在这两点上。
| Test | 检测 | Reagent | 试剂 | Positive result | 阳性结果 |
| Reducing sugar | 还原糖 | Benedict's solution, water bath | 本尼迪克特试剂，水浴加热 | Blue → brick red | 蓝 → 砖红 |
| Starch | 淀粉 | Iodine solution | 碘液 | Yellow-brown → blue-black | 黄褐 → 蓝黑 |
| Protein | 蛋白质 | Biuret reagent | 双缩脲试剂 | Blue → purple | 蓝 → 紫 |
| Lipid | 脂质 | Ethanol, then water | 乙醇，再加水 | Clear → white emulsion | 澄清 → 白色乳浊液 |
Key exam trap: Benedict's test needs heating in a water bath, while iodine and Biuret do not. Ethanol is flammable, so the ethanol emulsion test must never be placed near a flame.
关键易错点：本尼迪克特检测需要水浴加热，而碘液和双缩脲试剂不需要。乙醇易燃，因此乙醇乳化检测绝不能靠近明火。
3. Enzymes and Digestion | 酶与消化
Enzymes are biological catalysts made of protein. They speed up reactions by lowering the activation energy, and they are not used up. Each enzyme has a specific active site that is complementary to one substrate, which explains the lock-and-key model.
酶是由蛋白质构成的生物催化剂。它们通过降低活化能加快反应，且本身不被消耗。每种酶都有与特定底物互补的活性位点，这就是锁钥模型。
Substrate + Enzyme → Enzyme-Substrate Complex → Products + Enzyme
Temperature and pH both affect rate. As temperature rises, particles gain kinetic energy and collisions increase, until the optimum is passed and the active site denatures - the shape is permanently changed, so the substrate no longer fits. Extreme pH has the same denaturing effect.
温度和 pH 都会影响反应速率。温度升高时，粒子动能增大、碰撞增多，速率上升；一旦超过最适温度，活性位点变性，形状永久改变，底物不再匹配。极端 pH 同样会导致变性。
Digestive enzymes break large insoluble molecules into small soluble ones that can be absorbed. Amylase converts starch to maltose; protease converts proteins to amino acids; lipase converts lipids to fatty acids and glycerol.
消化酶把大分子不溶物分解为可吸收的小分子可溶物。淀粉酶把淀粉分解为麦芽糖；蛋白酶把蛋白质分解为氨基酸；脂肪酶把脂质分解为脂肪酸和甘油。
Bile, produced by the liver and stored in the gallbladder, is alkaline so it neutralises stomach acid, and it emulsifies fat into droplets to increase surface area for lipase. Digestive products are absorbed in the small intestine, whose lining is folded into villi with thin walls and a rich blood supply to maximise absorption.
胆汁由肝脏产生、储存在胆囊，呈碱性，可中和胃酸，并把脂肪乳化成小油滴以增大脂肪酶作用的表面积。消化产物在小肠吸收；小肠内壁折叠成绒毛，壁薄且血液供应丰富，从而最大化吸收效率。
4. Respiration and Gas Exchange | 呼吸作用与气体交换
Respiration is an exothermic reaction that releases energy from glucose in every living cell. Aerobic respiration needs oxygen, while anaerobic respiration happens without it and releases much less energy.
呼吸作用是放热反应，在每个活细胞中从葡萄糖释放能量。有氧呼吸需要氧气；无氧呼吸不需要氧气，释放的能量少得多。
Aerobic: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
Anaerobic (muscle): C₆H₁₂O₆ → 2C₃H₆O₃
Anaerobic (yeast): C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
The energy released is used for muscle contraction, active transport, protein synthesis, cell division and keeping warm. In animals, anaerobic respiration produces lactic acid, which causes cramp and must be broken down using extra oxygen after exercise - the oxygen debt.
释放的能量用于肌肉收缩、主动运输、蛋白质合成、细胞分裂和维持体温。动物无氧呼吸产生乳酸，会导致肌肉酸痛，运动后必须用额外氧气分解，这就是氧债。
Gas exchange happens in the alveoli. They give a huge surface area, a moist thin wall one cell thick, a dense capillary network and good ventilation, so oxygen diffuses into the blood and carbon dioxide diffuses out along concentration gradients. Smoking damages alveoli and causes emphysema, reducing surface area for gas exchange.
气体交换在肺泡中进行。肺泡提供巨大的表面积、湿润且只有一层细胞厚的薄壁、密集的毛细血管网和良好的通气，因此氧气顺浓度梯度扩散入血，二氧化碳扩散出血液。吸烟会破坏肺泡并引起肺气肿，减少气体交换面积。
5. Transport in Cells and Organisms | 细胞与生物体内的运输
Diffusion is the net movement of particles from high to low concentration, down a gradient. Osmosis is the diffusion of water specifically across a partially permeable membrane, from a dilute solution to a concentrated one. Active transport moves substances against a gradient and requires energy from respiration.
扩散是粒子从高浓度到低浓度的净移动。渗透特指水分子通过半透膜，从稀溶液一侧向浓溶液一侧扩散。主动运输逆浓度梯度运输物质，需要呼吸作用提供的能量。
In plants, water and mineral ions enter through root hair cells by osmosis and active transport, rise in xylem vessels, and are lost as water vapour through stomata in transpiration. Sucrose and amino acids are transported in phloem in both directions.
在植物中，水和矿质离子通过渗透和主动运输进入根毛细胞，经木质部导管上升，最后以水蒸气形式经气孔蒸腾散失。蔗糖和氨基酸则通过韧皮部进行双向运输。
Transpiration rate rises with increased light intensity, temperature and wind speed, and falls with increased humidity. Stomata close in wilted conditions, which reduces water loss but also reduces carbon dioxide uptake for photosynthesis.
蒸腾速率随光照强度、温度和风速升高而升高，随湿度升高而降低。干旱萎蔫时气孔关闭，减少水分散失，但同时也减少光合作用所需的二氧化碳吸收。
In humans, the double circulatory system carries blood at high pressure. Arteries have thick elastic walls, veins have valves to prevent backflow, and capillaries are one cell thick for efficient exchange. Red blood cells contain haemoglobin and carry oxygen, white blood cells defend against pathogens, platelets clot blood, and plasma transports dissolved substances.
人体的双循环系统以较高压力输送血液。动脉管壁厚而富弹性，静脉有瓣膜防止血液倒流，毛细血管只有一层细胞厚以便高效交换。红细胞含血红蛋白运输氧气，白细胞防御病原体，血小板参与凝血，血浆运输溶解物质。
6. Photosynthesis and Plant Nutrition | 光合作用与植物营养
Photosynthesis is an endothermic reaction in which green plants use light energy trapped by chlorophyll in chloroplasts to convert carbon dioxide and water into glucose and oxygen.
光合作用是吸热反应，绿色植物利用叶绿体中叶绿素捕获的光能，把二氧化碳和水转化为葡萄糖和氧气。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Glucose made in photosynthesis is used for respiration, converted to starch for storage, converted to cellulose for cell walls, and combined with nitrate ions to form amino acids and proteins. Magnesium is needed to make chlorophyll; a deficiency causes yellow leaves.
光合作用产生的葡萄糖用于呼吸作用、转化为淀粉储存、转化为纤维素构成细胞壁，并与硝酸根离子结合形成氨基酸和蛋白质。镁是叶绿素合成的必需元素，缺乏会导致叶片变黄。
Three limiting factors control the rate: light intensity, carbon dioxide concentration and temperature. On a graph, the factor whose line is lowest and stops the rate rising is limiting; raising it will increase the rate.
限制光合速率的有三个因素：光照强度、二氧化碳浓度和温度。在图像上，最低且限制速率继续上升的那条线所代表的因素就是限制因素；提高它就能提升速率。
Practical work: pondweed bubbles can count oxygen release as a measure of rate, with a lamp at set distances for light intensity. To test a leaf for starch, boil it in water to kill tissue, boil in ethanol to remove chlorophyll, rinse, then add iodine - a blue-black result shows starch is present.
实验操作：可用水草气泡数计算氧气释放量作为速率指标，并用固定距离的灯改变光照强度。检测叶片淀粉时，先用水煮杀死组织，再用乙醇煮沸脱色，冲洗后加碘液；出现蓝黑色说明有淀粉。
7. Nervous System and Homeostasis | 神经系统与稳态
The nervous system detects stimuli, coordinates responses and allows rapid, short-lived electrical communication along neurones. The reflex arc is a fixed pathway that protects the body without conscious thought.
神经系统检测刺激、协调反应，并通过神经元进行快速、短暂的电信号传递。反射弧是一条固定通路，无需意识参与即可保护身体。
s → Receptor → Sensory neurone → Relay neurone (CNS) → Motor neurone → Effector → Response
At each synapse, a neurotransmitter diffuses across the gap and triggers an impulse in the next neurone, which explains why the signal travels in one direction only. Reflexes are faster because the relay neurone bypasses conscious decision-making in the brain.
在突触处，神经递质扩散通过间隙，触发下一个神经元的冲动，这也解释了信号为何只单向传递。反射更快，是因为中间神经元绕过了大脑的意识决策环节。
Homeostasis keeps the internal environment constant around an optimum. Body temperature is controlled by vasodilation, sweating and shivering; blood glucose is controlled by insulin lowering it and glucagon raising it, in a negative feedback loop. Type 1 diabetes results from insufficient insulin production, while Type 2 results from cells not responding to insulin.
稳态把内环境维持在最佳值附近。体温通过血管舒张、出汗和颤抖调节；血糖通过胰岛素降低、胰高血糖素升高，构成负反馈回路。1 型糖尿病由胰岛素分泌不足引起，2 型糖尿病则由细胞对胰岛素反应不良造成。
Water and ion balance is regulated by the kidneys through filtration and selective reabsorption, with ADH controlling the volume of water reabsorbed. Dialysis and kidney transplants are treatments for kidney failure.
水和离子平衡由肾脏通过过滤和选择性重吸收调节，抗利尿激素（ADH）控制水的重吸收量。透析和肾移植是肾衰竭的治疗手段。
8. Hormones, Reproduction and Inheritance | 激素、生殖与遗传
Hormones are chemical messengers released by glands into the blood, travelling to target organs with the correct receptors. Compared with nerves, hormonal responses are slower but longer lasting.
激素是腺体分泌进入血液的化学信使，随血液到达带有相应受体的靶器官。与神经相比，激素反应更慢但持续时间更长。
The menstrual cycle is driven by four hormones. FSH causes an egg to mature and stimulates oestrogen release; oestrogen builds the uterus lining and triggers an LH surge; LH causes ovulation; progesterone maintains the lining. Progesterone is also the basis of many contraceptive pills, while FSH is used in fertility treatment and IVF.
月经周期由四种激素驱动。卵泡刺激素（FSH）促使卵子成熟并刺激雌激素分泌；雌激素增厚子宫内膜并触发促黄体生成素（LH）高峰；LH 引发排卵；孕激素维持内膜。孕激素也是许多避孕药的成分基础，而 FSH 用于生育治疗和试管婴儿（IVF）。
Inheritance is about alleles: different versions of a gene. A dominant allele is expressed even when a recessive allele is present. Genotype is the combination of alleles present; phenotype is the observable characteristic.
遗传的核心是等位基因：同一基因的不同版本。显性等位基因即使同时存在隐性等位基因也会表达。基因型是所含等位基因的组合，表现型是可观察到的性状。
Use a Punnett square for crosses. Cystic fibrosis is caused by a recessive allele, so parents can be carriers without symptoms; Huntington's disease is caused by a dominant allele, so only one copy is needed. Sex in humans is determined by the X and Y chromosomes: XX is female and XY is male.
遗传杂交用庞氏方阵解决。囊性纤维化由隐性等位基因引起，因此父母可以无症状地成为携带者；亨廷顿舞蹈症由显性等位基因引起，只需一个拷贝就会发病。人类性别由 X 和 Y 染色体决定：XX 为女性，XY 为男性。
9. DNA, Genes and Protein Synthesis | DNA、基因与蛋白质合成
DNA is a polymer of nucleotides twisted into a double helix. Each nucleotide contains a sugar, a phosphate group and one of four bases: A, T, C and G. Bases pair specifically, A with T and C with G, held by hydrogen bonds.
DNA 是由核苷酸聚合而成的双螺旋结构。每个核苷酸含有一个糖、一个磷酸基团和四种碱基之一：A、T、C、G。碱基严格配对，A 与 T 配对，C 与 G 配对，通过氢键连接。
A gene is a short section of DNA that codes for a specific protein. The genome is the entire genetic material of an organism. Some characteristics are controlled by a single gene, while most are controlled by many genes interacting with the environment.
基因是编码特定蛋白质的一段 DNA 片段。基因组是一个生物体的全部遗传物质。有些性状由单个基因控制，而大多数性状由多个基因与环境共同作用决定。
Protein synthesis happens in two stages. In transcription, the DNA double helix unzips and a complementary mRNA strand is made in the nucleus. In translation, mRNA leaves the nucleus, attaches to a ribosome, and carrier molecules bring complementary amino acids which are joined into a chain, forming a protein whose shape determines its function.
蛋白质合成分两个阶段。转录阶段，DNA 双螺旋解开，在细胞核内合成互补的 mRNA 链。翻译阶段，mRNA 离开细胞核并结合到核糖体，搬运分子带来互补的氨基酸，依次连接成链，形成蛋白质，其形状决定其功能。
Mutations change the base sequence. Most have no effect, some change the protein shape and therefore its function, which may cause genetic disorders. Mutations in body cells are not inherited, but mutations in gametes can be.
突变改变碱基序列。大多数突变没有影响，部分会改变蛋白质形状进而影响功能，可能导致遗传病。体细胞突变不会遗传，而配子突变可以遗传给后代。
10. Variation, Evolution and Natural Selection | 变异、进化与自然选择
Variation can be continuous - height, mass and heart rate, showing a normal distribution - or discontinuous, such as blood group, which falls into distinct categories. Variation results from genetic causes, environmental causes and interactions between them.
变异可以是连续变异，如身高、体重和心率，呈正态分布；也可以是不连续变异，如血型，分属明确类别。变异来自遗传因素、环境因素以及两者的相互作用。
Natural selection follows a fixed chain of reasoning that examiners want to see in order: there is genetic variation within a population; individuals compete for limited resources; those with advantageous alleles survive and reproduce; they pass the alleles on; over many generations the advantageous alleles become more common.
自然选择有一条考官想要的标准推理链：种群内存在遗传变异；个体为有限资源而竞争；具有有利等位基因的个体存活并繁殖；它们把等位基因传给后代；经过多代，有利等位基因在种群中变得更普遍。
Evidence includes fossils showing gradual change, and antibiotic resistance in bacteria, where resistant strains survive treatment and multiply rapidly because bacteria reproduce quickly and mutate readily.
证据包括显示渐变过程的化石，以及细菌的抗生素耐药性：耐药菌株在治疗中存活并迅速繁殖，因为细菌繁殖快、易发生突变。
If populations become isolated and conditions differ, they may evolve separately until they can no longer interbreed to produce fertile offspring - this is speciation. Extinction occurs when a species cannot adapt to environmental change, new competitors or new predators.
如果种群被隔离且环境条件不同，它们可能各自进化，直到彼此无法交配产生可育后代，这就是物种形成。当物种无法适应环境变化、新竞争者或新捕食者时，就会灭绝。
11. Ecology, Cycles and Human Impact | 生态学、物质循环与人类影响
Ecology moves from individual organisms to populations, communities and ecosystems, then to the biosphere. Abiotic factors include light, temperature, moisture, pH and mineral content; biotic factors include food availability, predators, pathogens and competition.
生态学从个体、种群、群落、生态系统，一直到生物圈。非生物因素包括光照、温度、湿度、pH 和矿物质含量；生物因素包括食物供应、捕食者、病原体和竞争。
In a food chain, energy passes between trophic levels, but only about 10 percent is transferred. Energy is lost through respiration, movement, excretion, and as heat and undigested material, which is why food chains rarely have more than five levels.
在食物链中，能量在营养级之间传递，但只有约 10% 被转移。能量通过呼吸作用、运动、排泄，以及以热能和未消化物质的形式流失，因此食物链很少超过五级。
Material cycles recycle matter. In the carbon cycle, photosynthesis removes carbon dioxide, while respiration, combustion and decomposition release it. The water cycle moves water through evaporation, transpiration, condensation and precipitation, and the nitrogen cycle relies on nitrogen-fixing bacteria in root nodules and decomposers returning nitrogen compounds to the soil.
物质循环实现物质的再利用。碳循环中，光合作用固定二氧化碳，呼吸作用、燃烧和分解作用释放二氧化碳。水循环通过蒸发、蒸腾、凝结和降水完成。氮循环则依赖根瘤中的固氮细菌，以及分解者把含氮化合物归还土壤。
Human impact includes deforestation, burning fossil fuels adding carbon dioxide and methane, and pollution causing acid rain and eutrophication from fertiliser run-off. Bioaccumulation occurs when toxins build up along a food chain, and indicator species such as lichens show air quality while invertebrates show water quality.
人类影响包括森林砍伐、燃烧化石燃料增加二氧化碳和甲烷，以及污染造成酸雨和化肥径流引起的富营养化。毒素沿食物链累积形成生物富集；地衣等指示生物可反映空气质量，无脊椎动物可反映水质。
Conservation measures include breeding programmes, seed banks, nature reserves, reintroduction schemes and restricting deforestation. Sustainable management means using resources without preventing future generations from doing the same.
保护措施包括繁育计划、种子库、自然保护区、再引入项目和限制森林砍伐。可持续管理意味着使用资源的同时不损害后代使用同样的资源。
12. Biotechnology, Microorganisms and Exam Technique | 生物技术、微生物与应试技巧
Microorganisms are used in food production: yeast ferments sugar to ethanol and carbon dioxide for bread and beer, while bacteria convert milk into yoghurt and cheese. Optimum conditions of warmth, moisture and nutrients are needed, and unwanted microbes are controlled by sterilising equipment and using aseptic technique.
微生物用于食品生产：酵母发酵糖产生乙醇和二氧化碳，用于面包和啤酒；细菌把牛奶变成酸奶和奶酪。需要适宜的温度、湿度和营养，并通过消毒器材和无菌操作控制杂菌。
Biotechnology also uses genetic engineering: a human gene for insulin is inserted into a bacterial plasmid, the bacteria multiply rapidly, and pure human insulin is harvested. GM crops may carry genes for pest resistance or higher yield, but there are concerns about gene transfer to wild plants and effects on biodiversity.
生物技术还应用基因工程：把人胰岛素基因插入细菌质粒，细菌迅速繁殖，再提取纯人胰岛素。转基因作物可携带抗虫或高产基因，但人们担心基因转移到野生植物以及影响生物多样性。
Cloning in plants uses cuttings or tissue culture to produce genetically identical offspring quickly. Animal cloning, as in Dolly the sheep, uses an egg cell with its nucleus removed fused with a body cell nucleus and implanted into a surrogate mother.
植物克隆通过扦插或组织培养快速产生遗传上完全相同的
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