📚 IGCSE CIE Biology: Last-Minute Revision Notes | IGCSE CIE 生物：考前冲刺笔记
These last-minute revision notes cover the most essential concepts, key definitions, common pitfalls and exam tips for the CIE IGCSE Biology syllabus. Use them to quickly recall core knowledge before your paper.
这份考前冲刺笔记涵盖了CIE IGCSE 生物大纲中最关键的概念、核心定义、常见错误和考试技巧，帮助你在考前快速回顾基础知识。
1. Cell Structure and Organisation | 细胞结构与组织
Animal cells share a basic structure: nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells have, in addition, a cellulose cell wall, a large permanent vacuole and often chloroplasts.
动物细胞的基本结构包括细胞核、细胞质、细胞膜、线粒体和核糖体。植物细胞除此之外还有纤维素细胞壁、大形永久液泡，并常含叶绿体。
Bacterial cells are prokaryotic; they lack a nucleus and membrane-bound organelles. Their genetic material is a single loop of DNA, and they may have plasmids.
细菌细胞是原核细胞；它们没有细胞核和膜包被的细胞器。遗传物质是一个环状DNA，并可能含有质粒。
Common specialised cells to remember: red blood cells (no nucleus, biconcave shape), root hair cells (long extension for water absorption), sperm cells (flagellum, many mitochondria) and palisade mesophyll cells (packed with chloroplasts).
需熟记的特化细胞：红细胞（无核、双凹形）、根毛细胞（长突起利于吸水）、精子细胞（鞭毛、大量线粒体）和栅栏叶肉细胞（富含叶绿体）。
A common error is to think that all plant cells have chloroplasts – for example, root hair cells and onion epidermal cells do not. Also remember that magnification = image size ÷ actual size.
常见错误是认为所有植物细胞都有叶绿体——例如根毛细胞和洋葱表皮细胞就没有。还要记住放大倍数 = 图像尺寸 ÷ 实际尺寸。
2. Biological Molecules | 生物分子
Carbohydrates are made of carbon, hydrogen and oxygen. Simple sugars (glucose) are monomers; starch and glycogen are polymers. The test for starch is iodine solution (blue-black). Reducing sugars are tested with Benedict’s solution, heated (brick-red precipitate).
碳水化合物由碳、氢、氧构成。单糖（葡萄糖）是单体；淀粉和糖原是聚合物。淀粉用碘液检验（蓝黑色）。还原糖用班氏试剂加热检验（砖红色沉淀）。
Lipids are made of fatty acids and glycerol. The emulsion test: add ethanol, shake, then pour into water – a milky white emulsion indicates lipid.
脂质由脂肪酸和甘油构成。乳剂检验：加入乙醇振荡，再倒入水中——乳白色乳浊液表明有脂质。
Proteins are made of amino acids (20 types). The biuret test (sodium hydroxide + copper sulfate) gives purple colour. Protein shape is crucial for function; denaturation (by heat or pH) loses this shape.
蛋白质由氨基酸构成（20种）。双缩脲检验（氢氧化钠+硫酸铜）呈紫色。蛋白质的形状对其功能至关重要；高温或极端pH引起的变性会破坏形状。
DNA is a double helix made of nucleotides (sugar-phosphate backbone + bases A, T, C, G). Base pairing: A–T, C–G. The sequence of bases codes for proteins.
DNA是双螺旋结构，由核苷酸组成（糖-磷酸骨架 + 碱基A、T、C、G）。碱基配对：A—T，C—G。碱基序列编码蛋白质。
3. Enzymes | 酶
Enzymes are biological catalysts, speeding reactions without being used up. They are proteins with an active site. The lock-and-key hypothesis explains specificity: the substrate shape is complementary to the active site.
酶是生物催化剂，能加快反应而自身不被消耗。它们是具有活性位点的蛋白质。锁钥假说解释了专一性：底物形状与活性位点互补。
Temperature affects enzyme activity: rate increases with temperature until an optimum, then the enzyme denatures (active site shape is lost). pH also has an optimum; extremes cause denaturation.
温度影响酶活性：速率随温度升高直到最适温度，随后酶变性（活性位点形状丧失）。pH也有最适点；极端pH导致变性。
Common exam investigation: breakdown of starch by amylase at different pHs, using iodine to monitor. Remember to control temperature with a water bath.
常见实验考察：淀粉酶在不同pH下分解淀粉，用碘液监测。记得用水浴控制温度。
4. Plant Nutrition and Photosynthesis | 植物营养与光合作用
Photosynthesis is the process by which plants produce glucose and oxygen from carbon dioxide and water, using light energy absorbed by chlorophyll. The word equation is:
光合作用是植物利用叶绿素吸收的光能，将二氧化碳和水转化为葡萄糖和氧气的过程。文字方程式为：
carbon dioxide + water → glucose + oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
The balanced chemical equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Limiting factors include light intensity, carbon dioxide concentration and temperature.
配平的化学方程式：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。限制因素有光照强度、二氧化碳浓度和温度。
Leaf structure: broad lamina, thin, waxy cuticle, stomata for gas exchange. Palisade cells contain many chloroplasts; spongy mesophyll allows diffusion of gases.
叶片结构：宽阔的叶片、薄、有蜡质角质层、气孔进行气体交换。栅栏细胞含很多叶绿体；海绵叶肉利于气体扩散。
Mineral ions: nitrate ions are needed for amino acids/proteins; deficiency causes stunted growth and yellow older leaves. Magnesium ions are needed for chlorophyll; deficiency causes yellowing between veins.
矿质离子：硝酸盐离子用于合成氨基酸/蛋白质；缺乏导致生长迟缓和老叶变黄。镁离子用于合成叶绿素；缺乏导致叶脉间黄化。
5. Animal Nutrition and Digestion | 动物营养与消化
Digestion breaks large, insoluble molecules into small, soluble ones that can be absorbed. Mechanical digestion (chewing, churning) increases surface area. Chemical digestion uses enzymes.
消化将大分子不溶物质分解成可吸收的小分子可溶物质。物理性消化（咀嚼、搅动）增加表面积。化学性消化依靠酶。
Carbohydrases (amylase) break down starch to maltose; proteases (pepsin, trypsin) break proteins into amino acids; lipases break lipids into fatty acids and glycerol. The stomach produces hydrochloric acid (kills bacteria, optimal pH for pepsin).
碳水化合物酶（淀粉酶）将淀粉分解为麦芽糖；蛋白酶（胃蛋白酶、胰蛋白酶）将蛋白质分解为氨基酸；脂肪酶将脂肪分解为脂肪酸和甘油。胃分泌盐酸（杀菌，为胃蛋白酶提供最适pH）。
Absorption occurs mainly in the small intestine. Villi and microvilli provide a huge surface area. The epithelium is one-cell thick with a dense capillary network and a lacteal for fatty acid absorption.
吸收主要在小肠进行。绒毛和微绒毛提供了巨大的表面积。上皮细胞只有一层，有密集的毛细血管网和乳糜管用于吸收脂肪酸。
6. Transport in Plants and Animals | 植物与动物中的运输
In plants, xylem transports water and mineral ions (upwards) via transpiration pull; phloem transports sucrose and amino acids (translocation) in both directions.
在植物中，木质部通过蒸腾拉力向上运输水和无机盐；韧皮部通过转运作用双向运输蔗糖和氨基酸。
Transpiration is the loss of water vapour from leaves. Factors increasing transpiration: higher temperature, lower humidity, greater light intensity and more wind.
蒸腾作用是水蒸气从叶片散失的过程。增加蒸腾作用的因素：较高的温度、较低的湿度、较强的光照和较大的风。
In humans, the double circulatory system means blood passes through the heart twice: pulmonary circuit (to lungs) and systemic circuit (to body). The heart has four chambers. The left ventricle has the thickest wall because it pumps blood to the whole body.
在人体内，双循环系统意味着血液两次经过心脏：肺循环（到肺）和体循环（到全身）。心脏有四个腔室。左心室壁最厚，因为它将血液泵向全身。
| Blood vessel | Structure | Function |
|---|---|---|
| Artery | Thick muscular/elastic wall | Carries blood away from heart at high pressure |
| Vein | Thin wall, valves | Carries blood back to heart at low pressure |
| Capillary | One-cell thick, narrow | Exchange of materials with tissues |
Blood components: red blood cells transport oxygen (haemoglobin); white blood cells defend against disease (phagocytes, lymphocytes); platelets help clotting; plasma transports nutrients, hormones and waste.
血液成分：红细胞运输氧气（血红蛋白）；白细胞防御疾病（吞噬细胞、淋巴细胞）；血小板帮助凝血；血浆运输营养、激素和废物。
7. Respiration and Gas Exchange | 呼吸作用与气体交换
Respiration is NOT the same as breathing. It is the release of energy from glucose in cells. Aerobic respiration uses oxygen: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + lots of ATP. Anaerobic respiration in muscles produces lactic acid, and in yeast produces ethanol and carbon dioxide.
呼吸作用不同于呼吸/气体交换。它是细胞中葡萄糖释放能量的过程。有氧呼吸需要氧气：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 大量ATP。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。
During exercise, body cells need more energy, so breathing rate and depth increase to supply more oxygen and remove extra CO₂. After exercise, excess post-exercise oxygen consumption (EPOC) repays the oxygen debt.
运动时，细胞需要更多能量，因此呼吸频率和深度增加，以提供更多氧气并排出额外CO₂。运动后，过量氧耗偿还氧债。
Gas exchange in humans occurs in alveoli, which have large surface area, thin walls, moist surface and rich blood supply. Inspired air has more oxygen, less carbon dioxide and less water vapour than expired air.
人体的气体交换在肺泡中进行，肺泡表面积大、壁薄、湿润并供血丰富。吸入的空气比呼出的空气含氧量高、二氧化碳少、水蒸气少。
Smoking damages the gas exchange system: tar paralyses cilia, causing mucus build-up; carcinogens cause lung cancer; carbon monoxide reduces oxygen-carrying capacity; nicotine is addictive and increases heart rate.
吸烟损害气体交换系统：焦油麻痹纤毛，导致黏液堆积；致癌物导致肺癌；一氧化碳降低携氧能力；尼古丁成瘾并加快心率。
8. Excretion and Homeostasis | 排泄与稳态
Excretion is the removal of metabolic waste products: carbon dioxide (from respiration) via lungs, and urea (from breakdown of amino acids) via kidneys in urine.
排泄是代谢废物的去除：二氧化碳（来自呼吸作用）通过肺排出，尿素（氨基酸分解产生）通过肾脏以尿液排出。
The kidney contains millions of nephrons. Ultrafiltration occurs in the glomerulus/Bowman’s capsule; all small molecules (water, urea, glucose, ions) are forced into the filtrate. Selective reabsorption in the proximal convoluted tubule then returns all glucose, some ions and most water back to the blood. The collecting duct allows further water reabsorption under ADH control.
肾脏含有百万个肾单位。超滤作用发生在肾小球/鲍曼氏囊；所有小分子（水、尿素、葡萄糖、离子）被压入滤液。然后在近曲小管进行选择性重吸收，将所有葡萄糖、部分离子和大部分水送回血液。集合管在抗利尿激素控制下实现进一步的水重吸收。
Homeostasis includes temperature regulation. The skin contains receptors, sweat glands, hairs and capillaries. When hot: sweating, vasodilation, hairs lie flat. When cold: shivering, vasoconstriction, hairs stand up (goosebumps).
稳态包括体温调节。皮肤含有感受器、汗腺、毛发和毛细血管。热时：出汗、血管舒张、毛发平躺。冷时：发抖、血管收缩、毛发直立（鸡皮疙瘩）。
9. Coordination and Response | 协调与反应
The nervous system uses electrical impulses along neurones. A reflex arc quickly bypasses the brain: receptor → sensory neurone → relay neurone in spinal cord → motor neurone → effector (muscle or gland).
神经系统沿神经元传递电信号。反射弧快速绕过大脑：感受器 → 感觉神经元 → 脊髓中的联络神经元 → 运动神经元 → 效应器（肌肉或腺体）。
A synapse is a gap between neurones. Neurotransmitter chemicals diffuse across, ensuring impulses travel in one direction only.
突触是神经元之间的间隙。神经递质化学物质扩散通过，确保冲动单向传递。
The eye adjusts to light intensity: in bright light, the pupil constricts (circular muscles contract, radial relax); in dim light, it dilates. Accommodation – ciliary muscles contract to make the lens fatter for near objects.
眼睛对光强调节：强光下瞳孔缩小（环形肌收缩、放射肌舒张）；弱光下扩大。调节作用——睫状肌收缩使晶状体变凸，以看清近物。
Hormones like insulin (lowers blood glucose) and glucagon (raises it) maintain blood sugar. Adrenaline prepares the body for ‘fight or flight’, increasing heart rate and blood flow to muscles.
激素如胰岛素（降低血糖）和胰高血糖素（升高血糖）维持血糖稳定。肾上腺素让身体准备“战斗或逃跑”，增加心率和肌肉血流量。
Plant responses: auxin (plant hormone) in shoot tips causes phototropism – more auxin on the shaded side stimulates faster cell elongation, bending the shoot towards the light. In roots, high auxin inhibits growth, causing bending away from the light/downwards.
植物反应：茎尖的生长素导致向光性——背光侧更多生长素刺激细胞更快伸长，使茎弯向光源。在根中，高浓度生长素抑制生长，导致背离光源/向下弯曲。
10. Reproduction | 生殖
Asexual reproduction produces genetically identical offspring (clones) from one parent via mitosis. Examples: binary fission in bacteria, tubers in potatoes, runners in strawberry plants. Advantages: fast, no mate needed. Disadvantage: no genetic variation.
无性生殖通过有丝分裂从单一亲本产生遗传相同的后代（克隆）。例子：细菌的二分裂、马铃薯的块茎、草莓的匍匐茎。优点：快速，无需配偶。缺点：没有遗传变异。
Sexual reproduction involves fusion of male and female gametes (fertilisation) producing genetically varied offspring. In flowering plants, the male gamete is in the pollen grain; the female gamete is the ovule. After pollination and fertilisation, the ovule becomes a seed and the ovary develops into a fruit.
有性生殖涉及雌雄配子融合（受精），产生遗传多样的后代。在开花植物中，雄配子在花粉粒中；雌配子是胚珠。传粉与受精后，胚珠发育为种子，子房发育成果实。
In humans, the menstrual cycle is controlled by hormones: FSH stimulates egg maturation and oestrogen production; LH triggers ovulation; oestrogen repairs the uterus lining; progesterone maintains it. If fertilisation occurs, the embryo implants and produces hCG.
在人类中，月经周期受激素控制：FSH促进卵子成熟和雌激素分泌；LH触发排卵；雌激素修复子宫内膜；孕酮维持内膜。若受精发生，胚胎植入并产生hCG。
11. Genetics and Inheritance | 遗传与变异
Genes are sections of DNA coding for a protein. Alleles are different versions of a gene. A dominant allele always shows its effect; a recessive allele only shows in the homozygous state.
基因是编码蛋白质的DNA片段。等位基因是同一基因的不同形式。显性等位基因总能表现其效应；隐性等位基因只在纯合时表现。
Monohybrid crosses predict offspring ratios. Homozygous dominant (AA) × homozygous recessive (aa) gives all Aa (heterozygous). A cross between two heterozygotes gives a 3:1 phenotype ratio. Use Punnett squares.
单基因杂交可预测后代比例。纯合显性(AA) × 纯合隐性(aa)后代全为Aa（杂合）。两个杂合子杂交产生3:1表现型比例。使用庞纳特方格。
Sex determination: human females are XX, males XY. The father’s sperm determines the sex. A monohybrid cross X⁴X × X⁴Y gives a 1:1 ratio of female to male.
性别决定：人类女性为XX，男性为XY。父亲的精子决定后代性别。X⁴X × X⁴Y杂交产生的雌雄比例为1:1。
| Feature | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth, repair, asexual reproduction | Production of gametes |
| Number of divisions | One | Two |
| Daughter cells | Two, genetically identical | Four, genetically different |
| Chromosome number | Diploid (same as parent) | Haploid (half) |
Variation can be continuous (e.g. height, influenced by many genes and environment) or discontinuous (e.g. blood groups, single gene). Natural selection favours individuals with advantageous alleles, leading to evolution.
变异可以是连续的（如身高，受多基因与环境影响）或不连续的（如血型，单基因控制）。自然选择青睐具有有利等位基因的个体，从而导致进化。
12. Ecology and Ecosystems | 生态与生态系统
A food chain shows the flow of energy from producers to consumers. Arrows indicate the direction of energy transfer. Energy is lost at each trophic level through respiration, heat and waste, limiting chain length.
食物链显示能量从生产者向消费者的流动。箭头指示能量传递方向。每一营养级因呼吸、热量和废物而损失能量，这限制了食物链的长度。
The carbon cycle: carbon dioxide in the air is used in photosynthesis to make organic compounds in plants. These are passed to animals by feeding. Respiration in all organisms returns CO₂ to the atmosphere. Decomposition by microorganisms also releases CO₂. Combustion of fossil fuels adds extra CO₂.
碳循环：空气中的二氧化碳在光合作用中被用于制造植物中的有机化合物；这些通过摄食传递给动物。所有生物呼吸作用将CO₂返回大气。微生物的分解作用也释放CO₂。化石燃料的燃烧额外增加CO₂。
The nitrogen cycle involves nitrogen fixation (by lightning or nitrogen-fixing bacteria in root nodules of legumes), nitrification (ammonium to nitrites to nitrates), uptake by plants, and denitrification back to atmospheric nitrogen. Decomposers recycle nitrogen from dead organisms.
氮循环包括固氮作用（闪电或豆科植物根瘤中的固氮菌）、硝化作用（铵到亚硝酸盐到硝酸盐）、植物吸收，以及反硝化作用回到大气氮。分解者从死亡生物体中回收氮。
Population growth is limited by resources: exponential phase, stationary phase. Human population increase impacts the environment: deforestation, pollution, greenhouse effect, loss of biodiversity. Sustainable practices (e.g. conservation, recycling) can help.
种群增长受资源限制：指数期、平稳期。人口增长对环境产生影响：砍伐森林、污染、温室效应、生物多样性丧失。可持续做法（如保护、循环使用）可提供帮助。
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