📚 IGCSE CIE Biology: High-Yield Topic Summary | IGCSE CIE 生物：高频考点总结
This revision guide distils the most frequently examined topics in CIE IGCSE Biology (0610/0970). Focusing on key concepts, definitions, equations, and common misconceptions, it is designed to help you target marks efficiently. Each section pairs essential English explanations with equivalent Chinese summaries, ensuring clarity for bilingual learners.
本复习指南浓缩了 CIE IGCSE 生物 (0610/0970) 中最常考的主题。聚焦核心概念、定义、方程式和常见误区，旨在帮助你有针对性夺分。每个部分均以中英双语搭配讲解，便于理解透彻。
1. Cells and Microscopy | 细胞与显微镜
All living organisms are composed of cells. The two main types are prokaryotic cells (e.g. bacteria) which lack a nucleus, and eukaryotic cells (e.g. animal and plant cells) with a membrane-bound nucleus. Plant cells differ from animal cells by possessing a cellulose cell wall, a large permanent vacuole, and chloroplasts. Under the microscope, you should be able to identify these structures and calculate magnification using the formula: Magnification = image size ÷ actual size.
所有生物都由细胞构成。主要分为两类：原核细胞（如细菌）无成形细胞核，真核细胞（如动植物细胞）有被膜包围的细胞核。植物细胞与动物细胞的区别在于具有纤维素细胞壁、大液泡和叶绿体。在显微镜下，你应能认出这些结构，并用公式计算放大倍数：放大倍数 = 图像大小 ÷ 实际大小。
- Prokaryotes: circular DNA, plasmids, no mitochondria (mesosomes for respiration).
- Specialised cells: red blood cells (no nucleus, biconcave), root hair cell (long extension for absorption), ciliated cell (moves mucus).
- 原核生物：环状DNA、质粒、无线粒体（由中间体进行呼吸作用）。
- 特化细胞：红细胞（无核、双凹）、根毛细胞（突起用于吸收）、纤毛细胞（推动黏液）。
2. Biological Molecules and Enzymes | 生物分子与酶
Carbohydrates, lipids, proteins, and nucleic acids are fundamental. Starch and glycogen are polysaccharides; proteins are made of amino acids. The test for starch uses iodine solution (turns blue-black), for reducing sugars uses Benedict’s solution (heat, brick-red), for protein uses Biuret test (purple), and for lipids uses ethanol emulsion test (cloudy white).
糖类、脂类、蛋白质和核酸是基本物质。淀粉和糖原是多糖；蛋白质由氨基酸构成。检验淀粉用碘液（蓝黑色），还原糖用本尼迪克特试剂（加热，砖红色），蛋白质用双缩脲（紫色），脂类用乙醇乳液法（白色乳浊）。
Enzymes are biological catalysts that speed up reactions by lowering activation energy. They are proteins with an active site specific to a substrate. The lock-and-key model explains specificity. Enzyme activity is affected by temperature (optimum usually 37°C for human enzymes; denaturation at extreme heat) and pH (pepsin works best at pH 2, amylase around pH 7).
酶是生物催化剂，通过降低活化能加快反应速率。它们是蛋白质，活性部位对底物有专一性。锁钥模型解释了特异性。酶活性受温度（人体酶最适一般37°C，高温变性）和 pH（胃蛋白酶最适pH 2，淀粉酶约pH 7）影响。
3. Movement Across Membranes | 跨膜运输
Substances move across cell membranes by diffusion (net movement from high to low concentration, passive), osmosis (net movement of water through a partially permeable membrane from high water potential to low water potential), and active transport (movement against concentration gradient using energy from ATP, e.g. uptake of mineral ions by root hair cells).
物质跨膜运输方式：扩散（净移动由高浓度到低浓度，被动），渗透（水通过半透膜从高水势向低水势的净移动），主动运输（逆浓度梯度，消耗ATP能量，如根毛细胞吸收矿物质离子）。
In a hypertonic solution, an animal cell shrinks (crenation) while a plant cell becomes plasmolysed (cell membrane pulls away from cell wall). In a hypotonic solution, an animal cell may burst (lysis) but a plant cell becomes turgid, which is important for support.
在高渗溶液中，动物细胞皱缩，植物细胞发生质壁分离。在低渗溶液中，动物细胞可能破裂，植物细胞变得硬挺（膨胀），这对支撑很重要。
4. Photosynthesis | 光合作用
Photosynthesis is the process by which plants synthesise carbohydrates using light energy. The word equation: carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll. The balanced symbol equation:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
光合作用是植物利用光能合成碳水化合物的过程。文字方程式：二氧化碳 + 水 → 葡萄糖 + 氧气，需要光和叶绿素。符号方程式见上。
Limiting factors include light intensity, carbon dioxide concentration, and temperature. At low light intensity, the rate is limited; as it increases, the rate plateaus because another factor becomes limiting. Experiments often use pondweed to measure oxygen bubble production or a hydrogencarbonate indicator to track CO₂ levels.
限制因素包括光照强度、二氧化碳浓度和温度。光强低时限速，随其增强速率上升，继而平稳，因另一因素成为限制。实验常利用水草收集氧气泡，或用碳酸氢盐指示剂监测CO₂变化。
5. Human Nutrition and Digestion | 人体营养与消化
A balanced diet supplies carbohydrates, proteins, lipids, vitamins (C and D), minerals (calcium, iron), water, and dietary fibre. Digestion breaks down large insoluble molecules into small soluble ones that can be absorbed. Mechanical digestion occurs in the mouth (chewing) and stomach (churning). Chemical digestion involves enzymes: amylase (starch → maltose), protease (protein → amino acids), lipase (lipids → fatty acids and glycerol). Bile emulsifies fats but contains no enzymes.
均衡膳食提供糖类、蛋白质、脂类、维生素（C和D）、矿物质（钙、铁）、水和膳食纤维。消化把大分子不溶性物质分解为可吸收的小分子。物理消化发生在口腔（咀嚼）和胃（搅动）。化学消化依靠酶：淀粉酶（淀粉→麦芽糖）、蛋白酶（蛋白质→氨基酸）、脂肪酶（脂肪→脂肪酸和甘油）。胆汁乳化脂肪但不含酶。
Absorption mainly occurs in the ileum, where villi and microvilli increase surface area. The products of digestion are absorbed into the blood or lacteal (for fatty acids and glycerol). The colon reabsorbs water.
吸收主要在小肠回肠进行，绒毛和微绒毛增大表面积。消化产物进入血液，或脂肪酸和甘油进入乳糜管。大肠重吸收水分。
6. Transport in Animals | 动物运输
The circulatory system is composed of the heart, blood vessels, and blood. The heart is a double pump: the right side pumps deoxygenated blood to the lungs (pulmonary circulation), the left side pumps oxygenated blood to the body (systemic circulation). Valves prevent backflow. The pacemaker (sinoatrial node) initiates heartbeat.
循环系统由心脏、血管和血液组成。心脏是双泵：右心将缺氧血泵至肺（肺循环），左心将含氧血泵至全身（体循环）。瓣膜防止倒流。起搏点（窦房结）发动心跳。
Arteries carry blood away from the heart under high pressure, have thick muscular and elastic walls. Veins carry blood back to the heart, contain valves, and have thinner walls. Capillaries are one-cell thick for efficient exchange of substances. Blood components: red blood cells (transport oxygen via haemoglobin), white blood cells (defence), platelets (clotting), plasma (transports dissolved substances).
动脉将血液带离心室，壁厚而富有弹性，以承受高压。静脉将血液送回心脏，有瓣膜，壁较薄。毛细血管仅一层细胞，利于物质交换。血液成分：红细胞（通过血红蛋白运输氧）、白细胞（防御）、血小板（凝血）、血浆（运输溶解的物质）。
7. Transport in Plants | 植物运输
Xylem transports water and mineral ions from roots to leaves; it is composed of dead, hollow cells with lignin strengthening. The transpiration stream is driven by evaporation of water from stomata in leaves, creating a tension that pulls water up. Factors increasing transpiration: higher temperature, higher wind speed, lower humidity, increased light intensity (stomata open).
木质部由死去的中空细胞构成，有木质素加强，运输水和矿物质盐自根向上。蒸腾流由叶片气孔水分蒸发驱动，产生拉力使水上升。增大蒸腾作用的因素：温度升高、风速增大、湿度降低、光强增加（气孔开放）。
Phloem transports sucrose and amino acids (translocation) from sources to sinks. It consists of sieve tubes and companion cells. Translocation is active and requires energy. Ringing experiments can demonstrate phloem function.
韧皮部运输蔗糖和氨基酸（转运作用）从合成处到利用/储存处。由筛管和伴胞构成。转运过程为主动耗能。环割实验可证明韧皮部功能。
8. Gas Exchange and Respiration | 气体交换与呼吸作用
Gas exchange in humans occurs in the alveoli, which have a large surface area, thin walls (one cell thick), moist surface, and rich blood supply, allowing oxygen to diffuse into blood and carbon dioxide out. Breathing involves intercostal muscles and diaphragm; during inhalation, the diaphragm contracts and flattens, external intercostals contract, volume increases, pressure drops.
人体气体交换在肺泡进行，其表面积大、壁薄（单层细胞）、湿润、血供丰富，便于氧气弥散入血，二氧化碳排出。呼吸运动涉及肋间肌和膈肌；吸气时膈肌收缩变平，外肋间肌收缩，胸廓体积增大，气压降低。
Aerobic respiration releases more energy (ATP) using oxygen. Equation:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)
Anaerobic respiration in muscles produces lactic acid (and less ATP); in yeast, it produces ethanol and CO₂ (fermentation).
有氧呼吸利用氧气释放较多能量（ATP）。方程式见上。肌肉无氧呼吸产生乳酸（并较少ATP）；酵母无氧呼吸产生乙醇和CO₂（发酵）。
9. Disease and Immunity | 疾病与免疫
Pathogens include bacteria, viruses, fungi, and protoctists. The body’s defences include mechanical barriers (skin, hairs, mucus), chemical barriers (stomach acid, tears), and phagocytosis by white blood cells. Antibodies are produced by lymphocytes in response to specific antigens; this leads to memory cells that provide long-term immunity.
病原体包括细菌、病毒、真菌和原生生物。身体防御包括物理屏障（皮肤、鼻毛、黏液）、化学屏障（胃酸、泪液），以及白细胞吞噬。淋巴细胞针对特定抗原产生抗体，并形成记忆细胞，提供长期免疫。
Vaccination introduces harmless antigens to trigger an immune response and memory cells. Herd immunity protects unvaccinated individuals when a high percentage of the population is immune. Antibiotics kill bacteria but do not work against viruses.
疫苗接种引入无害抗原，激发免疫反应和记忆细胞。群体免疫在免疫比例足够高时保护未接种者。抗生素能杀灭细菌，但对病毒无效。
10. Coordination and Response | 协调与反应
The nervous system uses electrical impulses along neurones. A reflex arc involves receptor → sensory neurone → relay neurone (in CNS) → motor neurone → effector (muscle or gland). Synapses allow impulses to cross via chemical neurotransmitters. The endocrine system uses hormones, which are chemical messengers transported in the blood, causing slower but longer-lasting effects, e.g. adrenaline for ‘fight or flight’.
神经系统利用电冲动沿神经元传导。反射弧通路：感受器→感觉神经元→中间神经元（中枢内）→运动神经元→效应器（肌肉或腺体）。突触借化学递质传递冲动。内分泌系统利用激素，通过血液运输，作用慢但持久，如肾上腺素引起“战斗或逃跑”。
Plant responses: phototropism (growth towards light) is controlled by auxin, which accumulates on the shaded side causing elongation. Geotropism (growth in response to gravity) also involves auxin redistribution.
植物反应：向光性（向光生长）由生长素控制，其在背光侧积累引起细胞伸长。向地性也涉及生长素重新分布。
11. Inheritance and Selection | 遗传与选择
DNA is a double helix containing genes on chromosomes. Alleles are different forms of a gene. In monohybrid crosses, use a Punnett square to predict genotypic and phenotypic ratios. Key terms: homozygous (two identical alleles), heterozygous (two different alleles), dominant, recessive, codominance (both alleles expressed, e.g. AB blood group).
DNA为双螺旋结构，基因位于染色体上。等位基因是基因的不同形式。单基因杂交用旁氏表预测基因型和表现型比例。关键术语：纯合子（相同等位基因）、杂合子（不同等位基因）、显性、隐性、共显性（两者均表达，如AB血型）。
Sex determination: females XX, males XY. Natural selection: individuals with advantageous traits are more likely to survive and reproduce, passing alleles to offspring. Artificial selection (selective breeding) involves choosing desired traits. Examples include antibiotic resistance in bacteria.
性别决定：女性XX，男性XY。自然选择：具优势性状的个体更易存活和繁殖，将等位基因传给后代。人工选择（选育）挑选所需性状。例子如细菌的抗药性。
12. Ecology and Nutrient Cycles | 生态学与物质循环
Food chains show energy flow from producers to primary consumers to secondary consumers, etc. Energy is lost at each trophic level through respiration, uneaten parts, and excretion. Pyramids of numbers, biomass, and energy describe feeding relationships. The carbon cycle involves photosynthesis, respiration, combustion, and decomposition. The nitrogen cycle includes nitrogen fixation (by lightning or bacteria), nitrification, assimilation, and denitrification.
食物链显示能量从生产者到初级消费者等方向。每一营养级能量因呼吸、未食部分、排泄而损耗。数量、生物量、能量金字塔描述摄食关系。碳循环涉及光合作用、呼吸作用、燃烧和分解。氮循环包括固氮作用（闪电或细菌）、硝化作用、同化作用和反硝化作用。
Deforestation increases atmospheric CO₂, reduces biodiversity, and can cause soil erosion. Eutrophication occurs when excess fertilisers run off into water, causing algal bloom, oxygen depletion, and death of aquatic organisms. Conservation and sustainable practices are key to preserving ecosystems.
滥伐森林增加大气CO₂，减少生物多样性，引起土壤侵蚀。水体富营养化因过量肥料流入水域，导致藻类大量繁殖、缺氧和水生生物死亡。保护与可持续实践对维护生态系统至关重要。
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