📚 IGCSE CCEA Biology: Final Revision Outline | IGCSE CCEA 生物：期末复习提纲
This revision guide summarises key topics from the CCEA IGCSE Biology specification to help you structure your final review. Use it to check your understanding of essential concepts, from cell structure to ecology, and focus on the areas that need extra attention.
本复习指南总结了 CCEA IGCSE 生物课程的核心主题，帮助你规划期末复习。用它来检验你对细胞结构、生态等关键概念的理解，并集中精力攻克薄弱环节。
1. Cell Structure and Organization | 细胞结构与组织
All living organisms are made of cells. Animal and plant cells share common features – a cell membrane, cytoplasm, nucleus, mitochondria and ribosomes. Plant cells additionally have a cellulose cell wall, a large permanent vacuole and chloroplasts. Bacteria are prokaryotes: their DNA floats freely in the cytoplasm as a single circular chromosome and they lack a true nucleus.
所有生物都由细胞构成。动物细胞和植物细胞具有共同的结构——细胞膜、细胞质、细胞核、线粒体和核糖体。植物细胞还有纤维素细胞壁、一个大型中央液泡和叶绿体。细菌是原核生物：它们的 DNA 以单个环状染色体的形式游离在细胞质中，且没有真正的细胞核。
Microscopy lets us measure cells and organelles. The magnification formula is:
Magnification = Image size ÷ Actual size
显微镜使我们能够测量细胞和细胞器。放大倍数的计算公式为：
放大倍数 = 图像大小 ÷ 实际大小
ls contain many mitochondria for energy. Organization proceeds from cells → tissues → organs → organ systems.
细胞可以特化以执行特定功能，例如根毛细胞有巨大的表面积用于吸收水分，精子细胞含有大量线粒体提供能量。生命组织层次依次为：细胞 → 组织 → 器官 → 器官系统。
2. Biological Molecules | 生物分子
Carbohydrates, proteins and lipids are the main biological molecules. Starch and glycogen are polysaccharides that store energy in plants and animals respectively. Reducing sugars are tested with Benedict's solution (blue to brick‑red on heating), starch with iodine (turns blue‑black), proteins with Biuret reagent (blue to purple) and lipids with the ethanol emulsion test (cloudy white layer).
碳水化合物、蛋白质和脂质是主要生物分子。淀粉和糖原是多糖，分别用于植物和动物的能量储存。还原糖用本尼迪克特试剂检测（加热后由蓝色变为砖红色），淀粉用碘液检测（变为蓝黑色），蛋白质用双缩脲试剂检测（蓝色变为紫色），脂质用乙醇乳化试验检测（出现乳白色浑浊层）。
Proteins are made of long chains of amino acids folded into specific shapes. Enzymes are globular proteins that act as biological catalysts. DNA carries genetic information; it has a double helix structure made of two strands held together by complementary bases – adenine pairs with thymine, and cytosine pairs with guanine.
蛋白质由长链氨基酸折叠成特定形状。酶是球蛋白，起生物催化剂的作用。DNA 携带遗传信息；它呈双螺旋结构，两条链通过互补碱基对连接——腺嘌呤与胸腺嘧啶配对，胞嘧啶与鸟嘌呤配对。
3. Enzymes | 酶
Enzymes speed up metabolic reactions by lowering activation energy. They have an active site that is specific to their substrate – the lock‑and‑key model describes this. Enzyme activity depends on temperature and pH: as temperature rises, activity increases until an optimum is reached, after which denaturation occurs. Each enzyme has an optimum pH.
酶通过降低活化能来加速代谢反应。它们具有与底物特异性结合的活性位点——锁钥模型解释了这一点。酶活性取决于温度和 pH：温度升高时活性上升，达到最适温度后发生变性。每种酶都有其最适 pH。
Denaturation is the irreversible change in the shape of the active site, meaning the substrate can no longer bind. In experiments, you can investigate how factors like temperature affect the rate of an enzyme‑controlled reaction (e.g. breakdown of starch by amylase).
变性是活性位点形状发生不可逆改变，导致底物无法结合。在实验中，可以探究温度等因素如何影响酶促反应的速率（例如淀粉酶分解淀粉）。
4. Cell Membranes and Transport | 细胞膜与运输
The cell membrane is partially permeable, controlling the movement of substances in and out. Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, and requires no energy. Osmosis is the diffusion of water through a partially permeable membrane from a dilute to a more concentrated solution.
细胞膜具有选择通透性，控制物质进出。扩散是粒子从高浓度区域向低浓度区域的净运动，顺浓度梯度进行，不需要能量。渗透是水通过选择通透性膜从较稀溶液向较浓溶液的扩散。
Active transport moves substances against the concentration gradient, from low to high concentration, using energy from respiration and carrier proteins. This is vital for root hair cells absorbing mineral ions and for absorption of glucose in the kidney tubules.
主动运输逆浓度梯度（从低浓度到高浓度）移动物质，需要呼吸作用提供的能量和载体蛋白。这对根毛细胞吸收矿质离子和肾小管中葡萄糖的重吸收至关重要。
5. The Digestive System | 消化系统
Digestion breaks down large, insoluble molecules into small, soluble ones that can be absorbed. Mechanical digestion begins in the mouth (chewing) and continues in the stomach (churning). Chemical digestion uses enzymes: amylase breaks down starch to maltose, proteases digest proteins to amino acids, and lipases convert lipids into fatty acids and glycerol.
消化将大分子不溶性物质分解为可吸收的小分子可溶性物质。物理性消化从口腔（咀嚼）开始，在胃（搅拌）中继续。化学性消化依靠酶：淀粉酶将淀粉分解为麦芽糖，蛋白酶将蛋白质消化为氨基酸，脂肪酶将脂质转化为脂肪酸和甘油。
Bile, produced by the liver and stored in the gall bladder, emulsifies fats (increasing surface area) and neutralises stomach acid. The small intestine is adapted for absorption with villi and microvilli that provide a large surface area and a good blood supply.
胆汁由肝脏产生、储存在胆囊，能乳化脂肪（增加表面积）并中和胃酸。小肠适应吸收功能，其绒毛和微绒毛提供了巨大的表面积和丰富的血液供应。
6. The Circulatory System | 循环系统
The human circulatory system consists of the heart, blood vessels and blood. It is a double circulation: the right side pumps deoxygenated blood to the lungs (pulmonary circulation), and the left side pumps oxygenated blood to the rest of the body (systemic circulation). The heart has four chambers: left and right atria and ventricles.
人体循环系统由心脏、血管和血液组成。它是双循环系统：右心将缺氧血泵入肺部（肺循环），左心将富氧血泵往全身（体循环）。心脏有四个腔室：左、右心房和左、右心室。
Arteries carry blood away from the heart under high pressure; they have thick muscular walls. Veins return blood to the heart, contain valves to prevent backflow, and have thinner walls. Capillaries are one‑cell thick for efficient exchange of materials. Blood consists of red cells (carry oxygen), white cells (defence), platelets (clotting) and plasma (transports dissolved substances).
动脉在高压下将血液带离心脏，管壁厚且有肌肉。静脉将血液送回心脏，含有防止倒流的瓣膜，管壁较薄。毛细血管仅一层细胞厚，利于物质交换。血液由红细胞（运输氧气）、白细胞（防御）、血小板（凝血）和血浆（运输溶解物质）组成。
7. The Respiratory System | 呼吸系统
Respiration releases energy from glucose. Aerobic respiration uses oxygen and produces carbon dioxide and water, releasing a large amount of energy (ATP). The word equation is:
Glucose + Oxygen → Carbon dioxide + Water (+ energy)
呼吸作用从葡萄糖中释放能量。有氧呼吸利用氧气，产生二氧化碳和水，释放大量能量（ATP）。文字方程式为：
葡萄糖 + 氧气 → 二氧化碳 + 水（+ 能量）
Anaerobic respiration occurs without oxygen. In animals it produces lactic acid and releases much less energy. In yeast and plants, anaerobic respiration produces ethanol and carbon dioxide. The breathing system includes trachea, bronchi, bronchioles and alveoli. Alveoli are adapted for gas exchange: large surface area, thin walls, moist surface and rich blood supply.
无氧呼吸在缺氧时进行。在动物体内产生乳酸，释放的能量少得多。在酵母和植物中，无氧呼吸产生乙醇和二氧化碳。呼吸系统包括气管、支气管、细支气管和肺泡。肺泡适应气体交换：表面积大、壁薄、表面湿润、血液供应丰富。
8. Coordination and Response | 协调与反应
The nervous system enables rapid responses to stimuli. A reflex arc involves a receptor, sensory neurone, relay neurone (in the spinal cord), motor neurone and effector (muscle or gland). Synapses are gaps between neurones where chemical neurotransmitters pass the impulse.
神经系统能够对刺激产生快速反应。反射弧包括感受器、感觉神经元、中间神经元（在脊髓中）、运动神经元和效应器（肌肉或腺体）。突触是神经元之间的间隙，通过化学神经递质传递冲动。
Hormones are chemical messengers carried in the blood. Compared with nerves, hormone responses are slower but longer‑lasting. Adrenaline prepares the body for 'fight or flight' by increasing heart rate and blood flow to muscles. Insulin (from the pancreas) lowers blood glucose by promoting its uptake by cells and its conversion to glycogen in the liver.
激素是由血液携带的化学信使。与神经相比，激素反应较慢但持续时间更长。肾上腺素通过加快心率和增加肌肉血流量，使身体做好“战斗或逃跑”的准备。胰岛素（由胰腺分泌）通过促进细胞摄取葡萄糖和肝脏将葡萄糖转化为糖原来降低血糖。
9. Homeostasis and Excretion | 稳态与排泄
Homeostasis is the maintenance of a constant internal environment. Key examples include control of blood glucose, temperature and water balance. The skin helps regulate temperature: sweat evaporation cools the body; hair muscles trap air for insulation; blood vessels dilate or constrict.
稳态是指维持稳定的内部环境。关键例子包括血糖、体温和水分平衡的调节。皮肤帮助调节温度：汗液蒸发使身体降温；竖毛肌收缩保留空气隔热；血管扩张或收缩。
Excretion is the removal of metabolic waste products. The kidneys filter the blood, reabsorbing useful substances and excreting urea in urine. The nephron is the functional unit; ultrafiltration occurs in the Bowman's capsule, and selective reabsorption happens in the tubule. ADH controls water reabsorption according to the body's water status.
排泄是将代谢废物排出体外。肾脏过滤血液，重吸收有用物质，将尿素以尿液的形式排出。肾单位是功能性单位；超滤作用发生在鲍曼氏囊，选择性重吸收发生在肾小管。抗利尿激素（ADH）根据身体水分状况控制水的重吸收。
10. Reproduction | 生殖
Asexual reproduction involves one parent and produces genetically identical offspring (clones). Methods include binary fission in bacteria, tubers in potatoes and runners in strawberries. Sexual reproduction requires two gametes (sperm and egg) and produces variation.
无性生殖只需一个亲本，产生遗传上相同的后代（克隆）。方法包括细菌的分裂生殖、马铃薯的块茎和草莓的匍匐茎。有性生殖需要两个配子（精子和卵细胞），产生变异。
In humans, the male reproductive system produces sperm in the testes; the female system releases eggs from the ovaries and nurtures the developing embryo in the uterus. The menstrual cycle is controlled by hormones: FSH, LH, oestrogen and progesterone. Fertilisation occurs in the oviduct.
人体中，男性生殖系统在睾丸中产生精子；女性生殖系统从卵巢释放卵子，并在子宫中孕育胚胎。月经周期由激素调控：卵泡刺激素、黄体生成素、雌激素和孕激素。受精发生在输卵管。
11. Genetics and Inheritance | 遗传与变异
Genes are sections of DNA that code for proteins. Alleles are different versions of a gene; the dominant allele masks the effect of the recessive allele. Genotype describes the alleles present, while phenotype is the observable characteristic. A monohybrid cross can be shown using a Punnett square.
基因是编码蛋白质的 DNA 片段。等位基因是同一基因的不同版本；显性等位基因掩盖隐性等位基因的效应。基因型指拥有的等位基因，表现型则是可观察的特征。单因子杂交可用庞纳特方格表示。
Sex is determined by X and Y chromosomes: females are XX, males XY. Some diseases are inherited, such as cystic fibrosis (recessive) and Huntington's disease (dominant). Variation can be continuous (e.g. height) or discontinuous (e.g. blood group). Mutation is a rare, random change in DNA that may create new alleles.
性别由 X 和 Y 染色体决定：女性为 XX，男性为 XY。一些疾病是遗传的，如囊性纤维化（隐性）和亨廷顿病（显性）。变异可以是连续的（如身高）或不连续的（如血型）。突变是 DNA 中罕见、随机的改变，可能产生新的等位基因。
12. Ecology and Environment | 生态与环境
thesis by producers. Food chains show the flow of energy: producer → primary consumer → secondary consumer. Only about 10% s transferred between trophic levels; the rest is lost as heat and through life processes.
生态系统包括所有生物（群落）以及它们相互作用的环境。能量通过生产者的光合作用进入生态系统。食物链展示能量流动：生产者 → 初级消费者 → 次级消费者。营养级之间只有约 10% 的能量传递，其余以热能等形式散失。
The carbon cycle involves processes such as photosynthesis, respiration, combustion and decomposition. The nitrogen cycle relies on nitrogen‑fixing bacteria, nitrifying bacteria, and decomposers. Human activities such as deforestation and burning fossil fuels increase atmospheric carbon dioxide, contributing to global warming. Pollution can affect biodiversity through eutrophication and acid rain.
碳循环涉及光合作用、呼吸作用、燃烧和分解等过程。氮循环依赖固氮细菌、硝化细菌和分解者。森林砍伐和燃烧化石燃料等人类活动增加了大气中的二氧化碳，导致全球变暖。污染可通过富营养化和酸雨影响生物多样性。
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