📚 IGCSE Biology: Last-Minute Revision Notes | IGCSE 生物：考前冲刺笔记
Welcome to your last-minute revision powerhouse. This guide distils the entire IGCSE Biology syllabus into sharp, examiner-friendly essentials. Every section pairs a key concept in English with its direct Chinese translation, helping you reinforce knowledge and nail those final marks.
欢迎来到你的考前冲刺能量站。这份指南将 IGCSE 生物的全部考点浓缩成考官青睐的核心要点。每个知识点都配有中英对照讲解，帮助你巩固理解，在最后一刻稳稳拿下分数。
1. Cell Structure and Transport | 细胞结构与运输
All living organisms are built from cells. Plant cells have a rigid cellulose cell wall, a large permanent vacuole, and chloroplasts for photosynthesis, whereas animal cells lack these three structures. Both share a nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes.
所有生命体都由细胞构成。植物细胞有坚硬的纤维素细胞壁、一个大液泡和进行光合作用的叶绿体，动物细胞则没有这三样结构。两者共有细胞核、细胞质、细胞膜、线粒体和核糖体。
Magnification is calculated as: Magnification = Image size ÷ Actual size. Always convert units to the same scale before using the formula.
放大倍率计算公式：放大倍率 = 图像尺寸 ÷ 实际大小。使用公式前务必统一单位。
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient. It requires no energy and no membrane.
扩散是指粒子沿着浓度梯度从高浓度区域向低浓度区域的净运动。它不需要能量，也不需要膜参与。
Osmosis is the diffusion of water molecules through a partially permeable membrane from a high water potential to a low water potential. Water potential decreases when more solutes are dissolved.
渗透是水分子通过半透膜从高水势向低水势的扩散。溶解的溶质越多，水势越低。
Active transport moves substances against the concentration gradient, from low to high concentration. It requires carrier proteins and energy from respiration in the form of ATP.
主动运输将物质逆浓度梯度从低浓度运向高浓度。它需要载体蛋白和呼吸作用提供的能量（ATP）。
2. Biological Molecules and Enzymes | 生物分子与酶
Carbohydrates are made of simple sugars such as glucose (C₆H₁₂O₆). Starch and glycogen are polysaccharides. Lipids consist of three fatty acids bonded to one glycerol molecule; they release more energy per gram than carbohydrates. Proteins are composed of long chains of amino acids folded into specific shapes.
碳水化合物由单糖如葡萄糖（C₆H₁₂O₆）构成。淀粉和糖原是多糖。脂质由三个脂肪酸与一个甘油分子结合而成，每克释放能量比碳水化合物多。蛋白质由长链氨基酸折叠成特定形状。
Food tests: iodine solution turns blue-black with starch. Biuret reagent turns purple in the presence of protein. Benedict’s solution turns brick-red when heated with reducing sugars. Ethanol emulsion gives a cloudy white layer with lipids.
食物检测：碘液遇淀粉呈蓝黑色。双缩脲试剂遇蛋白质变紫。斐林/本尼迪克特试剂与还原糖加热后呈砖红色。乙醇乳浊液遇脂质出现浑浊白色层。
Enzymes are biological catalysts that speed up reactions without being used up. The lock-and-key model states that the active site is complementary to the shape of the substrate. If the shape of the active site changes, the enzyme can no longer function; this is called denaturation.
酶是生物催化剂，能加速反应却不被消耗。锁钥模型认为，酶的活性中心与底物形状互补。一旦活性中心形状改变，酶就会失效，这称为变性。
Enzyme activity rises with temperature up to an optimum and then falls rapidly as the enzyme denatures. Extreme pH also denatures enzymes. Each enzyme works best at a specific pH.
酶活性随温度上升直到最适温度，随后酶变性，活性急剧下降。极端 pH 也会使酶变性。每种酶都有其最适 pH 值。
3. Plant Nutrition and Transport | 植物营养与运输
Photosynthesis produces glucose and oxygen from carbon dioxide and water using light energy absorbed by chlorophyll. The word equation: carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll.
光合作用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。文字方程：二氧化碳 + 水 → 葡萄糖 + 氧气，需要光和叶绿素。
The balanced chemical equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Leaves are adapted for gas exchange through stomata, a broad surface area, and a thin structure for rapid diffusion.
配平的化学方程式为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。叶片通过气孔进行气体交换，具有大面积和薄结构以便快速扩散。
Xylem tissue transports water and dissolved minerals from roots to leaves. The transpiration stream is driven by evaporation of water from stomata and the cohesion-tension of water molecules. Phloem tissue transports sucrose and amino acids up and down the plant; this process is called translocation.
木质部将水和溶解的矿物质从根部运往叶片。蒸腾作用由气孔水分蒸发和水分子的内聚力-张力驱动。韧皮部将蔗糖和氨基酸在植物体内上下运输，这个过程称为转运。
Root hair cells absorb water by osmosis and mineral ions by active transport. Nitrate ions are needed for amino acid synthesis, magnesium ions for chlorophyll production.
根毛细胞通过渗透吸收水分，通过主动运输吸收矿物离子。硝酸盐离子用于合成氨基酸，镁离子用于制造叶绿素。
4. Human Nutrition and Digestion | 人体营养与消化
Humans need seven main nutrients: carbohydrates, proteins, lipids, vitamins, minerals, water, and dietary fibre. Fibre aids peristalsis and prevents constipation.
人体需要七类主要营养素：碳水化合物、蛋白质、脂质、维生素、矿物质、水和膳食纤维。纤维促进肠道蠕动，预防便秘。
Ingestion is taking in food; digestion is the mechanical and chemical breakdown of large insoluble molecules into small soluble ones; absorption is the movement of these nutrients into the blood; egestion removes undigested material.
摄食是吃进食物；消化是将大分子不溶性营养素机械和化学分解为小分子可溶物；吸收是这些营养物进入血液；排遗则排出未消化的废物。
Amylase breaks down starch into maltose and is produced in the salivary glands and pancreas. Protease digests proteins into amino acids; pepsin works in the acidic stomach, while trypsin functions in the alkaline small intestine. Lipase breaks lipids into fatty acids and glycerol, with the help of bile which emulsifies fats.
淀粉酶将淀粉分解为麦芽糖，由唾液腺和胰腺分泌。蛋白酶将蛋白质分解为氨基酸；胃蛋白酶在胃酸中工作，胰蛋白酶则在碱性小肠中起作用。脂肪酶在胆汁乳化脂肪的帮助下，将脂质分解为脂肪酸和甘油。
Villi in the small intestine increase surface area for absorption. They have a thin epithelium, dense capillary network, and a lacteal to transport absorbed fatty acids and glycerol via the lymphatic system.
小肠绒毛增大了吸收表面积。绒毛上皮薄，有丰富的毛细血管网和乳糜管，后者将吸收的脂肪酸和甘油经淋巴系统运输。
5. Circulation and Blood | 循环与血液
The human circulatory system is a closed double circuit: the pulmonary circulation carries blood to the lungs, and the systemic circulation takes oxygenated blood to the rest of the body. The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle.
人体循环系统是封闭的双循环：肺循环将血液送到肺部，体循环将充氧血输往全身。心脏有四个腔室：右心房、右心室、左心房和左心室。
Arteries carry blood away from the heart under high pressure; their walls are thick with muscle and elastic tissue. Veins return blood to the heart at low pressure and have valves to prevent backflow. Capillaries are one-cell thick to allow exchange of substances.
动脉在高压下将血液带离心脏，管壁厚，富含肌肉和弹性组织。静脉在低压下将血液送回心脏，内有瓣膜防止倒流。毛细血管仅一个细胞厚，利于物质交换。
Red blood cells contain haemoglobin, which binds oxygen to form oxyhaemoglobin in high oxygen concentration and releases it in low oxygen concentration. White blood cells defend against infection by producing antibodies and by phagocytosis. Platelets are involved in blood clotting.
红细胞含血红蛋白，在氧浓度高处与氧结合形成氧合血红蛋白，在低氧处释放氧。白细胞通过产生抗体和吞噬作用抵御感染。血小板参与血液凝固。
Plasma transports dissolved nutrients, carbon dioxide, hormones, and urea. Lymphocytes produce specific antibodies that lock onto antigens, while memory cells provide long-term immunity.
血浆运输溶解的营养物、二氧化碳、激素和尿素。淋巴细胞产生特异性抗体锁定抗原，记忆细胞则提供长期免疫。
6. Respiration and Gas Exchange | 呼吸与气体交换
Respiration is a chemical process that releases energy from glucose in every living cell. It is not the same as breathing. Aerobic respiration requires oxygen: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (a relatively large amount).
呼吸作用是每个活细胞从葡萄糖中释放能量的化学过程，不等于呼吸。有氧呼吸需要氧气：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 大量能量。
Anaerobic respiration in humans produces lactic acid and a small amount of energy. In yeast, it produces ethanol, carbon dioxide, and a small amount of energy. Oxygen debt is the amount of oxygen required to break down the lactic acid produced during vigorous exercise.
人体无氧呼吸产生乳酸和少量能量。酵母无氧呼吸产生乙醇、二氧化碳和少量能量。氧债是指剧烈运动后分解积累的乳酸所需的氧气量。
Gas exchange in humans occurs in the alveoli. Alveoli have a huge combined surface area, thin walls, and a film of moisture, all surrounded by a dense network of capillaries. Oxygen diffuses into the blood and carbon dioxide diffuses out down concentration gradients.
人体气体交换在肺泡进行。肺泡表面积巨大，壁极薄，表面有一层湿润的液体薄膜，并被密集的毛细血管网包围。氧气沿浓度梯度扩散入血，二氧化碳扩散出。
During inhalation, the intercostal muscles contract, moving the ribcage up and out, and the diaphragm contracts and flattens. The volume of the thorax increases, pressure decreases, and air rushes in.
吸气时，肋间肌收缩使胸腔向上向外移动，膈肌收缩变平。胸腔容积增大，压力降低，空气涌入。
7. Excretion and Homeostasis | 排泄与体内平衡
Excretion is the removal of toxic waste products of metabolism, such as carbon dioxide, urea, and excess water and salts. The kidneys filter blood to form urine. A nephron is the functional unit of the kidney.
排泄是清除代谢产生的有毒废物，如二氧化碳、尿素以及多余的水和无机盐。肾脏过滤血液形成尿液。肾单位是肾脏的功能结构。
In the nephron, ultrafiltration occurs in the glomerulus and Bowman’s capsule, forcing out water, urea, glucose, and ions while leaving large proteins and blood cells in the blood. Selective reabsorption then returns all glucose, some ions, and the amount of water the body needs back into the blood at the proximal convoluted tubule and loop of Henle.
肾单位中，肾小球和鲍曼氏囊进行超滤，压出水、尿素、葡萄糖和离子，大分子蛋白质和血细胞则留在血液中。随后在近曲小管和亨利氏袢进行选择性重吸收，将所有葡萄糖、部分离子和身体所需的水分重新吸收回血液。
The hypothalamus monitors blood temperature. When the body is too hot, vasodilation increases blood flow near the skin surface and sweat glands release sweat, cooling the body by evaporation. When cold, vasoconstriction conserves heat and shivering generates heat through muscle contraction.
下丘脑监测血温。过热时，血管扩张增加皮肤表层血流，汗腺排汗，通过蒸发降温。过冷时，血管收缩保存热量，肌肉战栗产热。
Blood glucose is regulated by insulin and glucagon. After a meal, the pancreas releases insulin, causing liver and muscle cells to take up glucose and convert it to glycogen. When blood glucose is low, glucagon stimulates glycogen breakdown back into glucose.
血糖由胰岛素和胰高血糖素调控。餐后胰腺释放胰岛素，使肝细胞和肌细胞摄取葡萄糖并转化为糖原。血糖低时，胰高血糖素刺激糖原分解成葡萄糖。
8. Coordination: Nervous System and Hormones | 协调：神经系统与激素
The nervous system transmits electrical impulses along neurones. A reflex arc involves a receptor, sensory neurone, relay neurone in the CNS, motor neurone, and effector (muscle or gland). This is a rapid, automatic response to a stimulus.
神经系统沿神经元传递电脉冲。反射弧包括感受器、感觉神经元、中枢神经系统的中间神经元、运动神经元和效应器（肌肉或腺体）。这是对刺激快速、自动的反应。
At a synapse, an impulse triggers the release of neurotransmitter chemicals, which diffuse across the gap and bind to receptors on the next neurone, initiating a new impulse. Synapses ensure one-way transmission.
在突触处，冲动触发释放神经递质化学物质，递质扩散过间隙并与下一个神经元的受体结合，引发新的冲动。突触确保了单向传递。
Hormones are chemical messengers secreted by endocrine glands and transported in the blood. Insulin and glucagon regulate blood glucose. Adrenaline, released in ‘fight or flight’ situations, increases heart rate, dilates pupils, and boosts blood supply to muscles.
激素是由内分泌腺分泌、经血液运输的化学信使。胰岛素和胰高血糖素调节血糖。肾上腺素在“战或逃”时释放，加快心率、扩大瞳孔、增加肌肉血供。
The eye focuses light by changing the shape of the lens. For near objects, the ciliary muscles contract, suspensory ligaments slacken, and the lens becomes fatter (more convex). For distant objects, ciliary muscles relax, ligaments tighten, and the lens becomes thinner.
眼睛通过改变晶状体形状来聚焦。看近物时，睫状肌收缩，悬韧带松弛，晶状体变凸。看远物时，睫状肌舒张，悬韧带拉紧，晶状体变薄。
9. Reproduction and Development | 生殖与发育
Asexual reproduction involves a single parent and produces genetically identical offspring. Examples include binary fission in bacteria, budding in yeast, and runners in strawberry plants. Sexual reproduction involves the fusion of two gametes, creating genetic variation.
无性生殖只需一个亲代，产生基因完全相同的后代。例子包括细菌二分裂、酵母出芽和草莓的匍匐茎。有性生殖涉及两个配子融合，产生遗传变异。
In flowering plants, the male gametes are inside pollen grains produced by the anther. The female gamete is within the ovule inside the ovary. Pollination is the transfer of pollen from an anther to a stigma; fertilisation occurs when the pollen nucleus fuses with the ovule nucleus.
显花植物中，雄配子包含在花药产生的花粉粒内，雌配子在子房的胚珠内。传粉是花粉从花药转移到柱头的过程；受精是花粉核与胚珠核融合。
The human male reproductive system produces sperm in the testes. The female system releases an ovum from an ovary roughly every 28 days. If fertilisation occurs, the zygote implants in the uterus and develops a placenta for nutrient and waste exchange.
人类男性生殖系统在睾丸产生精子。女性约每28天从卵巢排出一个卵子。若受精，受精卵植入子宫，并发育出胎盘以交换营养和废物。
The menstrual cycle is controlled by hormones including oestrogen and progesterone. Oestrogen thickens the uterus lining; progesterone maintains it. A drop in progesterone triggers menstruation.
月经周期由雌激素和孕激素等激素调控。雌激素增厚子宫内膜，孕激素则维持内膜。孕激素下降引发月经。
10. Inheritance and Evolution | 遗传与进化
Genes are lengths of DNA that code for specific proteins. Alleles are different versions of the same gene. A dominant allele always expresses itself if present; a recessive allele is only expressed when two copies are present (homozygous).
基因是DNA片段，编码特定蛋白质。等位基因是同一基因的不同形式。显性等位基因只要存在就会表现出来，隐性等位基因只有在纯合时才会表达。
A monohybrid cross can be shown with a Punnett square. For example, Tt × Tt (where T is tall, t is short) produces offspring in a 3:1 phenotype ratio. Genotype ratio is 1 TT : 2 Tt : 1 tt.
单基因杂交可用庞纳特方格表示。例如 Tt × Tt（T 为高茎，t 为矮茎），后代表型比例为 3:1。基因型比例为 1 TT : 2 Tt : 1 tt。
Mutations are random changes to DNA. Some mutations are neutral, some harmful, and very rarely beneficial. Natural selection acts on variation: individuals with alleles best suited to the environment are more likely to survive, reproduce, and pass those alleles to the next generation.
突变是DNA的随机变化。有些突变中性，有些有害，极少数有益。自然选择作用于变异：拥有最适应环境的等位基因的个体更可能存活、繁殖并将这些等位基因传给下一代。
Selective breeding (artificial selection) involves humans choosing parents with desirable traits, such as high milk yield in cattle, and breeding them over generations. This reduces genetic variation and can lead to inbreeding problems.
选择性育种（人工选择）是人类选择具有理想性状的亲本（如高产奶量的牛）并世代繁殖。这会降低遗传变异，可能导致近交退化。
11. Ecology | 生态学
A food chain shows the transfer of energy from producer to primary consumer to secondary consumer. Arrows represent the direction of energy flow. Only about 10% of energy passes from one trophic level to the next; the rest is lost as heat during respiration, in movement, and via excretion.
食物链展示能量从生产者到初级消费者再到次级消费者的传递。箭头代表能量流动方向。约仅10%的能量从某一营养级传递到下一级，其余以热、运动、排泄等形式散失。
The carbon cycle includes photosynthesis (plants take in CO₂), respiration (releases CO₂), decomposition (microorganisms break down dead matter, releasing CO₂), and combustion of fossil fuels. Deforestation and burning fossil fuels increase atmospheric CO₂, contributing to the greenhouse effect.
碳循环包括光合作用（植物吸收CO₂）、呼吸作用（释放CO₂）、分解作用（微生物分解死亡有机体释放CO₂）和化石燃料燃烧。毁林和燃烧化石燃料增加大气CO₂，加剧温室效应。
A habitat is the place where an organism lives; a population is all organisms of one species in that habitat; a community is all populations of different species living together. An ecosystem includes the community and the physical environment.
栖息地是生物生活的地方；种群是某一栖息地内同一物种的所有个体；群落是不同物种种群共同生活在一起；生态系统包括群落和物理环境。
Human population growth increases demand for food, water, and land, leading to deforestation and habitat loss. Sustainable practices such as reforestation, conservation, and using renewable resources are essential to maintain biodiversity.
人口增长增加了对食物、水和土地的需求，导致毁林和栖息地丧失。植树造林、自然保护和利用可再生资源等可持续实践对于维持生物多样性至关重要。
12. Exam and Practical Skills | 应考与实验技能
When describing a graph, always identify the trend (increase, decrease, plateau) and quote data values with units. Use the formula: rate = 1 ÷ time taken to compare the speed of enzyme-controlled or diffusion experiments.
描述图表时，务必指出趋势（上升、下降、平稳），并引用带单位的数据数值。使用公式：速率 = 1 ÷ 所用时间，来比较酶促反应或扩散实验的快慢。
In experimental design, identify the independent variable (what you change), the dependent variable (what you measure), and control variables (everything else that must be kept constant). A control experiment tests for the influence of a single factor by omitting only that factor.
实验设计中，明确自变量（你改变的变量）、因变量（你测量的量）和控制变量（必须保持恒定的所有因素）。对照实验通过只略去某个因素来检验该单一因素的作用。
For microscope drawings, always use a sharp pencil, draw clear outlines, label structures with straight ruling lines, and include a title and magnification. The field of view can be calculated using the eyepiece graticule calibrated against a stage micrometre.
显微镜绘图时，始终使用削尖的铅笔，绘制清晰轮廓，用直尺引线标注结构，并附上标题和放大倍率。视野可通过目镜测微尺结合台微尺校准后计算。
Common practicals: test a leaf for starch to show photosynthesis has occurred; use hydrogencarbonate indicator or a carbon dioxide sensor to measure respiration rates; and investigate the effect of temperature on the activity of enzymes such as amylase on starch.
常见实验：检验叶片淀粉证明光合作用发生；用碳酸氢盐指示剂或二氧化碳传感器测定呼吸速率；探究温度对酶（如淀粉酶分解淀粉）活性的影响。
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