📚 IGCSE Edexcel Biology: Last-Minute Revision Notes | IGCSE Edexcel 生物：考前冲刺笔记
This concise revision guide covers the most essential topics for the IGCSE Edexcel Biology exam, from cell structure to ecosystems. Use these notes to quickly solidify your understanding and boost your confidence before the test.
这份精炼的复习笔记涵盖了 IGCSE Edexcel 生物考试最关键的主题，从细胞结构到生态系统。用这些笔记快速巩固理解，提升考前信心。
1. Characteristics of Living Organisms | 生物的特征
All living things share seven life processes captured by the acronym MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition.
所有生物都共享七个生命过程，可用首字母缩略词 MRS GREN 记忆：运动、呼吸、感应、生长、繁殖、排泄和营养。
Movement can be internal (e.g., cytoplasm streaming) or external; sensitivity refers to detecting and responding to changes in the environment.
运动可以是内部的（如细胞质流动）或外部的；感应指探测并响应环境变化。
Growth is a permanent increase in size and dry mass, while reproduction ensures the continuation of a species. Excretion removes metabolic waste, and nutrition supplies raw materials for energy and growth.
生长是体积和干重的永久性增加，而繁殖保证物种延续。排泄移除代谢废物，营养提供能量和生长所需的原料。
2. Cell Structure and Function | 细胞结构与功能
Eukaryotic cells possess a nucleus containing genetic material, whereas prokaryotic cells lack a nucleus and have DNA floating in the cytoplasm as a circular chromosome.
真核细胞拥有含遗传物质的细胞核，而原核细胞无核，DNA 以环状染色体的形式游离在细胞质中。
Key organelles include mitochondria (site of aerobic respiration), ribosomes (protein synthesis), and chloroplasts (photosynthesis in plants). Cell walls of plants are made of cellulose; fungi have chitin.
关键细胞器包括线粒体（有氧呼吸场所）、核糖体（蛋白质合成）、叶绿体（植物光合作用）。植物细胞壁由纤维素构成，真菌则为几丁质。
The cell membrane is selectively permeable, controlling the movement of substances. Vacuoles in plant cells store cell sap and help maintain turgor pressure.
细胞膜具有选择通透性，控制物质进出。植物细胞的液泡储存细胞液并维持膨压。
3. Biological Molecules and Enzymes | 生物分子与酶
Carbohydrates consist of simple sugars (glucose, C₆H₁₂O₆) and polysaccharides; proteins are made of amino acids; lipids are composed of fatty acids and glycerol.
碳水化合物由单糖（葡萄糖，C₆H₁₂O₆）和多糖组成；蛋白质由氨基酸构成；脂质由脂肪酸和甘油组成。
Enzymes are biological catalysts that lower activation energy. They are highly specific due to their active site shape, explained by the lock-and-key model.
酶是生物催化剂，可降低活化能。它们因活性位点形状而高度特异，可用锁钥模型解释。
Temperature and pH affect enzyme activity. Extremes can denature the enzyme, permanently changing the shape of the active site so the substrate no longer fits.
温度和 pH 影响酶活性。极端条件会使酶变性，永久改变活性位点形状，使底物不再契合。
4. Movement of Substances | 物质的移动
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, and is a passive process.
扩散是粒子沿浓度梯度从高浓度区域向低浓度区域的净移动，属于被动过程。
Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution to a more concentrated one. Active transport requires energy (ATP) to move substances against the concentration gradient.
渗透是水通过半透膜从稀溶液向浓溶液扩散。主动运输则需要能量（ATP）逆浓度梯度移动物质。
In plant cells, a hypertonic solution causes plasmolysis; an isotonic solution results in incipient plasmolysis; a hypotonic solution makes the cell turgid.
在植物细胞中，高渗溶液导致质壁分离；等渗溶液出现初始质壁分离；低渗溶液使细胞硬挺。
5. Photosynthesis | 光合作用
The overall word equation is: carbon dioxide + water → glucose + oxygen, using light energy absorbed by chlorophyll. The balanced chemical equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
总的文字方程式：二氧化碳 + 水 → 葡萄糖 + 氧气，利用叶绿素吸收的光能。平衡化学方程式：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。
Light intensity, carbon dioxide concentration and temperature are the main limiting factors. The inverse square law relates light intensity to distance from the source.
光照强度、二氧化碳浓度和温度是主要限制因素。光照强度与距光源距离遵循平方反比定律。
The glucose produced can be used immediately in respiration, converted into starch for storage, or used to synthesise cellulose, amino acids and lipids.
产生的葡萄糖可立即用于呼吸作用，转化为淀粉储存，或用于合成纤维素、氨基酸和脂质。
6. Cellular Respiration | 细胞呼吸
Aerobic respiration requires oxygen and releases a large amount of energy: glucose + oxygen → carbon dioxide + water. The aerobic yield is 38 ATP per glucose molecule.
有氧呼吸需要氧气，释放大量能量：葡萄糖 + 氧气 → 二氧化碳 + 水。有氧呼吸每分子葡萄糖产出 38 个 ATP。
Anaerobic respiration in animals produces lactic acid, while in plants and fungi it forms ethanol and carbon dioxide. Both yield only 2 ATP per glucose molecule.
动物无氧呼吸产生乳酸，而植物和真菌生成乙醇和二氧化碳。两者每分子葡萄糖仅产出 2 个 ATP。
Respiration is essential for metabolic reactions, muscle contraction, active transport and maintaining body temperature in endotherms.
呼吸作用对代谢反应、肌肉收缩、主动运输和恒温动物维持体温至关重要。
7. Transport in Humans | 人体内的运输
The heart is a double pump: the right side sends blood to the lungs (pulmonary circulation), the left side to the body (systemic circulation). The pacemaker (SAN) initiates the heartbeat.
心脏是双泵：右侧将血液送至肺部（肺循环），左侧送至全身（体循环）。起搏器（窦房结）引发心跳。
Arteries carry blood away from the heart under high pressure; veins return blood at low pressure and contain valves to prevent backflow; capillaries are one-cell thick for efficient exchange.
动脉在高压下将血液带离心脏；静脉低压回血并含瓣膜防逆流；毛细血管仅一个细胞厚，利于高效交换。
Red blood cells contain haemoglobin for oxygen transport; white blood cells defend against pathogens; platelets aid clotting. Plasma transports carbon dioxide, hormones and nutrients.
红细胞含血红蛋白以运输氧气；白细胞抵御病原体；血小板辅助凝血。血浆运输二氧化碳、激素和营养物。
8. Transport in Plants | 植物体内的运输
Xylem vessels transport water and mineral ions from roots to leaves. They are dead, hollow tubes strengthened by lignin. Transpiration generates the pulling force.
木质部导管将水和无机离子由根运至叶。它们是死细胞构成的空管，由木质素强化。蒸腾作用产生拉力。
Phloem transports sucrose and amino acids from sources (leaves) to sinks (roots, fruits) in a process called translocation. Phloem cells are living and include companion cells.
韧皮部在转运过程中将蔗糖和氨基酸从源（叶）运至库（根、果实）。韧皮部细胞是活的，并包含伴胞。
Factors affecting transpiration rate: light intensity, temperature, humidity and wind speed. Measuring transpiration uses a potometer.
影响蒸腾速率的因素：光照强度、温度、湿度和风速。可用蒸腾计测量蒸腾速率。
9. Genetics and Inheritance | 遗传与遗传学
DNA is a double helix made of nucleotides, each containing a sugar (deoxyribose), a phosphate group and a base (A, T, C, G). A pairs with T, C pairs with G.
DNA 是双螺旋结构，由核苷酸构成，每个核苷酸含一个糖（脱氧核糖）、磷酸基团和碱基（A、T、C、G）。A 与 T 配对，C 与 G 配对。
A gene is a section of DNA that codes for a particular protein. Alleles are different versions of a gene. Genotype determines phenotype, influenced by the environment.
基因是编码特定蛋白质的一段 DNA。等位基因是同一基因的不同形式。基因型决定表型，并受环境影响。
Monohybrid crosses use Punnett squares. Homozygous dominant (e.g., AA), heterozygous (Aa) and homozygous recessive (aa) give 3:1 phenotypic ratios in the F₂ generation for complete dominance.
单性杂交使用庞纳特方格。纯合显性（如 AA）、杂合（Aa）和纯合隐性（aa）在完全显性下，F₂ 代表型比为 3:1。
10. Ecology and the Environment | 生态与环境
An ecosystem comprises a community of organisms interacting with their abiotic environment. Energy flows from the sun through producers, consumers and decomposers in food chains and webs.
生态系统由生物群落与其非生物环境相互作用构成。能量从太阳通过食物链和食物网中的生产者、消费者和分解者流动。
Carbon and nitrogen cycles recycle key elements. Carbon moves via photosynthesis, respiration, combustion and decomposition. The nitrogen cycle involves nitrogen fixation, nitrification, assimilation and denitrification.
碳循环和氮循环回收关键元素。碳通过光合作用、呼吸作用、燃烧和分解移动。氮循环包括固氮、硝化、同化和反硝化。
Human activities such as deforestation, burning fossil fuels and intensive farming can cause global warming, acid rain and eutrophication, reducing biodiversity.
人类活动如毁林、燃烧化石燃料和集约化农业可导致全球变暖、酸雨和富营养化，减少生物多样性。
11. Human Influences on the Environment | 人类对环境的影响
Pollution from sulfur dioxide and nitrogen oxides dissolves in water to form acid rain, damaging ecosystems and buildings. Greenhouse gases like CO₂ and methane trap heat in the atmosphere.
二氧化硫和氮氧化物污染溶于水形成酸雨，破坏生态系统和建筑物。CO₂ 和甲烷等温室气体将热量困在大气中。
Eutrophication occurs when excess fertilisers run off into water bodies, causing algal blooms that deplete oxygen levels and kill aquatic life.
过量肥料流入水体导致富营养化，引发藻类大量繁殖，耗尽氧气并杀死水生生物。
Conservation efforts include protecting habitats, captive breeding programmes, seed banks and legislation to limit pollution. Sustainable practices like reforestation can reduce environmental impact.
保护措施包括保护栖息地、人工繁殖计划、种子库和控制污染的立法。植树造林等可持续实践可减少环境影响。
12. Biotechnology and Genetic Engineering | 生物技术与基因工程
Microorganisms are used in the production of food, such as yeast in bread-making (anaerobic respiration produces CO₂ causing dough to rise) and bacteria in yoghurt production (lactic acid fermentation).
微生物被用于食品生产，如酵母在面包制作中（无氧呼吸产生 CO₂ 使面团发酵）和细菌在酸奶生产（乳酸发酵）。
Genetic engineering involves transferring a gene from one organism to another. Examples include inserting human insulin gene into bacteria to produce insulin, and creating genetically modified crops with pesticide resistance.
基因工程涉及将一个生物的基因转移到另一个生物。实例有将人胰岛素基因转入细菌生产胰岛素，以及创造具有抗虫性的转基因作物。
Restriction enzymes cut DNA at specific sites; ligase enzymes join DNA fragments. Vectors (e.g., plasmids) carry the gene into the host cell. Ethical issues include safety and labelling of GMOs.
限制酶在特定位点切割 DNA；连接酶连接 DNA 片段。载体（如质粒）将基因带入宿主细胞。伦理问题包括转基因生物的安全和标识。
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