📚 IGCSE AQA Biology: Last-Minute Revision Notes | IGCSE AQA 生物：考前冲刺笔记
This set of last-minute notes covers the essential topics, key definitions, equations, and common pitfalls for the IGCSE AQA Biology exam. Use it to consolidate your understanding and sharpen your recall before the final paper. Every section is concise but complete, pairing the most exam-relevant facts with practical tips for answering questions.
这份考前冲刺笔记涵盖了 IGCSE AQA 生物学考试的核心主题、关键定义、方程式和常见易错点。用于考前巩固理解和强化记忆。每一部分都精炼而完整，将最重要的考点与答题技巧搭配呈现。
1. Cell Structure and Function | 细胞结构与功能
All living organisms are made of cells. You must be able to compare plant, animal, fungal and bacterial cells. Eukaryotic cells (plants, animals, fungi) have a nucleus and membrane-bound organelles, whereas prokaryotic cells (bacteria) lack a nucleus and have a single circular chromosome and plasmids. Plant cells possess a cellulose cell wall, a large permanent vacuole and chloroplasts for photosynthesis. Fungal cells have a cell wall made of chitin.
所有生物都由细胞构成。需要能够比较植物、动物、真菌和细菌细胞。真核细胞（植物、动物、真菌）具有细胞核和膜结合细胞器，而原核细胞（细菌）没有细胞核，只有一条环状染色体和质粒。植物细胞有纤维素细胞壁、大型中央液泡和进行光合作用的叶绿体。真菌细胞壁由几丁质构成。
When drawing cells, label structures like mitochondria, ribosomes, cytoplasm and cell membrane. Remember that mitochondria are the sites of aerobic respiration, and ribosomes are where proteins are synthesised. The nucleus contains genetic material. For calculations involving magnification, use the formula: magnification = image size ÷ actual size. Convert units carefully: 1 mm = 1000 µm.
画细胞图时要标注线粒体、核糖体、细胞质和细胞膜等结构。记住线粒体是有氧呼吸的场所，核糖体是蛋白质合成的位点。细胞核含有遗传物质。涉及放大倍数的计算，使用公式：放大倍数 = 图像大小 ÷ 实际大小。注意单位换算：1 毫米 = 1000 微米。
2. Transport Across Membranes | 跨膜运输
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. It is passive and does not require energy. Factors affecting the rate of diffusion include temperature, concentration gradient and surface area. Osmosis is the diffusion of water molecules through a partially permeable membrane from a dilute solution to a more concentrated solution. Active transport moves substances against the concentration gradient using energy from respiration.
扩散是微粒从高浓度区域向低浓度区域的净移动。这属于被动运输，不需要能量。影响扩散速率的因素包括温度、浓度梯度和表面积。渗透是水分子通过部分透性膜从稀溶液向较浓溶液扩散。主动运输利用呼吸作用产生的能量逆浓度梯度转运物质。
In experiments with potato cylinders or dialysis tubing, you can observe osmosis. If a potato strip placed in pure water increases in length and mass, water has entered by osmosis. In a concentrated sugar solution, the strip loses water and becomes flaccid. Active transport is crucial for root hair cells taking up mineral ions from the soil.
在马铃薯条或透析袋实验中可以观察渗透现象。若马铃薯条放入纯水后长度和质量增加，是因为水通过渗透进入；在浓糖水中，马铃薯条失水并变软。主动运输对根毛细胞从土壤吸收矿质离子至关重要。
3. Enzymes and Digestion | 酶与消化
Enzymes are biological catalysts made of protein. They speed up reactions without being used up. Each enzyme has an active site with a specific shape. The substrate fits into the active site like a key in a lock – the lock-and-key model. Enzyme activity is affected by temperature and pH. At low temperatures, reactions are slow; at the optimum temperature, activity is highest. High temperatures denature the enzyme, changing the shape of the active site permanently.
酶是由蛋白质构成的生物催化剂，可以加快反应速率而本身不被消耗。每个酶都有一个特定形状的活性位点。底物恰好与活性位点契合，就像钥匙插进锁里——锁钥模型。酶活性受温度和 pH 值影响。低温时反应慢；在最适温度时活性最高。高温会使酶变性，永久改变活性位点的形状。
Digestive enzymes break down large insoluble food molecules into small soluble ones. Amylase (produced in salivary glands and pancreas) breaks down starch into maltose. Proteases (stomach, pancreas) break down proteins into amino acids. Lipases (pancreas) break down fats into fatty acids and glycerol. Bile is not an enzyme but emulsifies fats to provide a larger surface area for lipase action. Bile also neutralises stomach acid to give the alkaline pH needed in the small intestine.
消化酶将大分子不溶性食物分解为小分子可溶性物质。淀粉酶（由唾液腺和胰腺分泌）将淀粉分解为麦芽糖。蛋白酶（胃、胰腺）将蛋白质分解为氨基酸。脂肪酶（胰腺）将脂肪分解为脂肪酸和甘油。胆汁不是酶，但能乳化脂肪，增大脂肪酶作用的表面积。胆汁还能中和胃酸，为小肠提供所需的碱性环境。
4. The Circulatory System and Blood | 循环系统与血液
Humans have a double circulatory system: one circuit to the lungs (pulmonary) and one to the rest of the body (systemic). The heart has four chambers: left and right atria, left and right ventricles. The left ventricle wall is thicker because it must pump blood all around the body. Blood flows from atria to ventricles, then out through arteries. Valves prevent backflow.
人类具有双循环系统：一条通往肺部（肺循环），一条通往全身（体循环）。心脏有四个腔室：左右心房和左右心室。左心室壁更厚，因为它需要将血液泵往全身。血液由心房流向心室，再经动脉泵出。瓣膜防止血液倒流。
Arteries carry blood away from the heart; they have thick muscular walls and a small lumen. Veins carry blood back to the heart; they have thinner walls, a larger lumen and valves. Capillaries are tiny vessels with walls one cell thick, allowing exchange of substances. Red blood cells contain haemoglobin which binds oxygen. White blood cells defend against pathogens. Platelets help blood clot.
动脉将血液带离心脏，管壁厚、肌肉发达、管腔小。静脉将血液送回心脏，管壁较薄、管腔较大且有静脉瓣。毛细血管管壁极薄，仅一个细胞厚，便于物质交换。红细胞中的血红蛋白结合氧气。白细胞抵御病原体。血小板参与凝血。
Cardiac output = stroke volume × heart rate
5. Respiration and Gas Exchange | 呼吸与气体交换
Aerobic respiration releases energy from glucose using oxygen. The overall word equation is: glucose + oxygen → carbon dioxide + water (+ energy). The balanced chemical equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O. Anaerobic respiration in muscles produces lactic acid and releases much less energy. In yeast, anaerobic respiration produces ethanol and carbon dioxide.
有氧呼吸利用氧气从葡萄糖中释放能量。总的文字方程式为：葡萄糖 + 氧气 → 二氧化碳 + 水（+ 能量）。化学方程式为：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O。肌肉中的无氧呼吸产生乳酸，释放的能量远少于有氧呼吸。酵母的无氧呼吸则产生乙醇和二氧化碳。
Gas exchange in mammals occurs in the alveoli of the lungs. Alveoli are adapted by having a large surface area, a thin wall (one cell thick), a moist lining and a rich blood supply. Inhaled air travels through the trachea, bronchi and bronchioles to reach the alveoli. Breathing involves the diaphragm and intercostal muscles changing the volume of the thorax. During inhalation, the diaphragm contracts and flattens, and the ribcage moves up and out.
哺乳动物的气体交换发生在肺泡中。肺泡的适应性结构包括表面积大、管壁薄（单细胞厚度）、表面湿润和丰富的血液供应。吸入的空气经过气管、支气管和细支气管到达肺泡。呼吸运动由膈肌和肋间肌改变胸腔容积来完成。吸气时，膈肌收缩变平，肋骨向上向外移动。
6. Nervous System and Hormones | 神经系统与激素
The nervous system uses electrical impulses for rapid, short-lived responses. A reflex arc involves a receptor, sensory neurone, relay neurone (in the spinal cord), motor neurone and an effector. Hormones are chemical messengers produced in endocrine glands and carried by the blood. They have slower but longer-lasting effects. Insulin, produced by the pancreas, lowers blood glucose by converting glucose to glycogen in the liver. Glucagon raises blood glucose.
神经系统利用电冲动进行快速而短暂的响应。反射弧包括感受器、感觉神经元、中间神经元（位于脊髓）、运动神经元和效应器。激素是由内分泌腺分泌、经血液运载的化学信使，作用较慢但更持久。胰岛素由胰腺分泌，能促进肝脏将葡萄糖转化为糖原，从而降低血糖。胰高血糖素则会升高血糖。
Adrenaline is released in ‘fight or flight’ situations, increasing heart rate and blood flow to muscles. Thyroxine regulates metabolic rate. The menstrual cycle is controlled by oestrogen and progesterone; FSH and LH are involved in egg maturation and ovulation. Contraceptive pills and fertility treatments all rely on manipulating these hormones.
肾上腺素在“战斗或逃跑”时释放，升高心率和肌肉血流量。甲状腺素调节代谢率。月经周期由雌激素和孕激素控制；FSH 和 LH 参与卵子成熟和排卵。口服避孕药和生育治疗都是通过调控这些激素来实现的。
7. Homeostasis and the Kidney | 稳态与肾脏
Homeostasis is the maintenance of a constant internal environment. The kidney plays a vital role by filtering blood and regulating water, ions and urea. Each kidney contains many nephrons. Ultrafiltration occurs in the glomerulus-Bowman’s capsule, where small molecules (water, glucose, urea, ions) are filtered out of blood. Selective reabsorption then reclaims all glucose and some ions and water in the proximal convoluted tubule. Water reabsorption is adjusted by ADH in the collecting duct.
稳态是指维持内部环境恒定。肾脏通过过滤血液并调节水分、离子和尿素的含量发挥关键作用。每个肾脏含有许多肾单位。超滤作用发生在肾小球-鲍曼氏囊，小分子（水、葡萄糖、尿素、离子）被滤出血液。然后在近曲小管进行选择性重吸收，回收全部的葡萄糖、部分离子和水。集合管中水分的重吸收受抗利尿激素（ADH）调节。
Diabetes is a failure of blood glucose regulation. Type 1 diabetes is caused by the pancreas not producing enough insulin; it is treated with insulin injections. In type 2 diabetes, body cells stop responding to insulin; it is often managed by diet and exercise. Negative feedback loops are a common biological control mechanism, as seen in thyroxine regulation and temperature control.
糖尿病是血糖调节失效所致。1 型糖尿病由胰腺无法产生足够胰岛素引起，需注射胰岛素治疗。2 型糖尿病则是体细胞对胰岛素不再敏感，通常通过饮食和运动控制。负反馈回路是生物体中普遍的控制机制，可见于甲状腺素调节和体温控制。
8. Plant Biology – Photosynthesis and Transport | 植物生物学 – 光合作用与运输
Photosynthesis uses light energy to convert carbon dioxide and water into glucose and oxygen. Word equation: carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll). Symbol equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. The rate is affected by light intensity, carbon dioxide concentration and temperature. The limiting factor concept is often tested: at any point, the rate is limited by the factor in shortest supply.
光合作用利用光能将二氧化碳和水转化为葡萄糖和氧气。文字方程式：二氧化碳 + 水 → 葡萄糖 + 氧气（需要光和叶绿素）。化学方程式：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。光合速率受光照强度、二氧化碳浓度和温度影响。限制因子的概念常被考查：任何时刻，速率都被处于最短缺的那个因素所限制。
Xylem transports water and mineral ions from roots upwards; it is composed of dead cells and strengthened by lignin. Transpiration is the loss of water vapour from leaves, driven by evaporation. Phloem transports sucrose and amino acids up and down the plant (translocation). Root hair cells absorb water by osmosis and minerals by active transport.
木质部将水和矿质离子从根部向上运输，由死细胞构成，并有木质素加固。蒸腾作用是由蒸发驱动的水蒸气从叶片散失的过程。韧皮部将蔗糖和氨基酸在植物体内进行双向运输（转运作用）。根毛细胞通过渗透吸收水分，通过主动运输吸收矿物质。
9. Genetics and Inheritance | 遗传与遗传
DNA is a polymer made of two strands forming a double helix. A gene is a section of DNA that codes for a particular protein. Alleles are different versions of a gene; they can be dominant or recessive. In monohybrid crosses, use Punnett squares to predict offspring ratios. If both parents are heterozygous (e.g. Bb), the expected phenotype ratio is usually 3:1 for a dominant-recessive trait.
DNA 是由两条链构成的双螺旋聚合物。基因是编码特定蛋白质的一段 DNA 序列。等位基因是同一基因的不同形式，有显性和隐性之分。在单基因杂交中，使用庞纳特方格预测子代比例。如果父母双方均为杂合子（如 Bb），对于显隐性性状，预期的表型比例通常为 3:1。
Sex is determined by the 23rd pair of chromosomes: XX for female and XY for male. Genetic disorders such as cystic fibrosis (recessive) and polydactyly (dominant) must be analysed through family pedigrees. Key terms: homozygous = two identical alleles, heterozygous = two different alleles, genotype = genetic makeup, phenotype = physical expression.
性别由第 23 对染色体决定：XX 为女性，XY 为男性。遗传病如囊性纤维化（隐性）和多指症（显性）需通过家系图进行分析。关键术语：纯合子 = 两个相同等位基因，杂合子 = 两个不同等位基因，基因型 = 遗传组成，表现型 = 性状表现。
10. Evolution and Natural Selection | 进化与自然选择
Evolution occurs through natural selection. Individuals in a species show genetic variation. Those with adaptations better suited to the environment are more likely to survive and reproduce, passing on advantageous alleles. Over generations, the frequency of these alleles increases, leading to changes in the species. Evidence for evolution includes the fossil record and antibiotic resistance in bacteria.
进化通过自然选择发生。物种个体间存在遗传变异。具有更适合环境特征的个体更可能生存并繁殖，将有利等位基因传递给后代。经过多代，这些等位基因频率增高，导致物种发生变化。进化的证据包括化石记录和细菌的抗生素耐药性。
Speciation can arise when populations become isolated. Geographic isolation prevents gene flow, so each population evolves independently until they can no longer interbreed. Darwin’s finches are a classic example. Selective breeding is a human-driven process: individuals with desired traits are chosen to reproduce, producing breeds or strains.
种群隔离可以导致物种形成。地理隔离阻碍了基因交流，每个种群独立进化，直到彼此不能交配繁殖。达尔文雀是经典例子。选择性育种是人类驱动的过程：选择具有理想性状的个体进行繁殖，从而产生特定品种或品系。
11. Ecosystems and Material Cycles | 生态系统与物质循环
An ecosystem is a community of living organisms interacting with the abiotic environment. Food chains and food webs show feeding relationships; arrows indicate the direction of energy flow. The Sun is the primary source of energy. At each trophic level, about 10% of energy is passed on, the rest is lost through respiration, excretion and heat.
生态系统是由生物群落与非生物环境相互作用构成的。食物链和食物网展示了摄食关系，箭头表示能量流动方向。太阳是主要能量来源。在每个营养级，大约只有 10% 的能量传递到下一级，其余通过呼吸作用、排泄和以热的形式散失。
Materials such as carbon and water are recycled. In the carbon cycle, carbon dioxide is removed from the air by photosynthesis and returned by respiration, combustion and decomposition. Microorganisms play a key role in decay, breaking down dead material and recycling nutrients. The water cycle involves evaporation, transpiration, condensation and precipitation.
碳和水等物质是循环的。在碳循环中，二氧化碳通过光合作用离开大气，又通过呼吸作用、燃烧和分解回归。微生物在腐烂过程中起关键作用，分解死物质并使营养物再循环。水循环包括蒸发、蒸腾、凝结和降水等过程。
Biodiversity and global warming are important topics. Deforestation and burning fossil fuels increase atmospheric CO₂, enhancing the greenhouse effect. Peat bogs and wetlands store carbon; their destruction releases it. Sustainable practices such as reforestation help maintain balance.
生物多样性和全球变暖是重要议题。森林砍伐和化石燃料燃烧增加了大气中的二氧化碳，增强了温室效应。泥炭沼泽和湿地储存碳，其破坏会释放碳。植树造林等可持续措施有助于维持平衡。
12. Required Practicals Summary | 必做实验摘要
Exam questions frequently ask about required practicals. Key ones include: using a light microscope to observe cells; investigating osmosis in potato tissue; testing for biological molecules (starch with iodine, glucose with Benedict’s reagent, protein with biuret, lipids with ethanol emulsion); investigating how enzyme activity changes with pH or temperature (e.g. amylase and starch); measuring the rate of photosynthesis using pondweed and counting oxygen bubbles; and investigating population size using quadrats.
考题常涉及必做实验。重点包括：使用光学显微镜观察细胞；研究马铃薯组织中的渗透作用；检测生物分子（用碘液测淀粉，用本氏试剂测葡萄糖，用双缩脲测蛋白质，用乙醇乳浊液测脂类）；研究 pH 或温度如何影响酶活性（如淀粉酶与淀粉）；利用水草计数氧气泡测定光合作用速率；以及利用样方调查种群大小。
Always mention control variables and how you would ensure a fair test. When describing results, refer to trends and use data. For the osmosis practical, calculate percentage change in mass to compare results. For the photosynthesis practical, explain why a specific light intensity or CO₂ concentration is used. Practice drawing the apparatus and labelling it correctly.
答题时务必提及控制变量以及如何保证公平测试。描述结果时要联系趋势并使用数据。在渗透实验中，计算质量变化百分比以比较结果。在光合作用实验中，解释为什么使用特定的光照强度或二氧化碳浓度。练习绘制实验装置并正确标注。
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