📚 IGCSE WJEC Science: Animal Biology Key Points | IGCSE WJEC 科学：动物 考点精讲
Animal biology forms a major part of the IGCSE WJEC Science specification, covering cell structure, organ systems, and life processes. This revision guide breaks down the essential topics to help you master key concepts, from enzymes to the nervous system, with clear explanations and exam-focused tips.
动物生物学是 IGCSE WJEC 科学大纲的重要组成部分，涵盖细胞结构、器官系统以及生命活动过程。这份复习指南将拆解关键主题，从酶到神经系统，用清晰的解释和针对考试的提示，帮助你掌握核心概念。
1. Animal Cells and Specialisation | 动物细胞与特化
All animals are composed of eukaryotic cells. The main structures include a nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes. The nucleus contains genetic material in the form of chromosomes and controls cell activities. Mitochondria are the sites of aerobic respiration, releasing energy for the cell.
所有动物都由真核细胞组成。主要结构包括细胞核、细胞质、细胞膜、线粒体和核糖体。细胞核含有以染色体形式存在的遗传物质，并控制细胞活动。线粒体是有氧呼吸的场所，为细胞释放能量。
Animal cells can become specialised to carry out particular functions. For example, red blood cells are biconcave discs lacking a nucleus to maximise space for haemoglobin, which binds oxygen. Sperm cells have a tail for swimming and many mitochondria for energy. Nerve cells are long to transmit electrical impulses rapidly.
动物细胞可以特化以执行特定功能。例如，红细胞是双凹圆盘状，无细胞核，以最大化容纳血红蛋白的空间，血红蛋白能结合氧气。精子细胞有尾便于游动，并有大量线粒体提供能量。神经细胞很长，能快速传递电信号。
2. Levels of Organisation | 组织的层次
Cells of the same type group together to form tissues. A tissue is a collection of similar cells working together. Examples include muscle tissue (which contracts), nerve tissue (which carries electrical signals), and epithelial tissue (which covers surfaces and lines organs).
相同类型的细胞聚集在一起形成组织。组织是一群相似细胞协同工作的集合。例子包括肌肉组织（收缩）、神经组织（传导电信号）和上皮组织（覆盖表面和衬在器官内壁）。
Different tissues combine to form organs, such as the heart, stomach, and lungs. Organs work together in organ systems. The digestive system, for instance, includes the stomach, intestines, liver, and pancreas. The circulatory system includes the heart, blood vessels, and blood. Understanding this hierarchy from cells to systems is fundamental in WJEC exams.
不同的组织结合形成器官，例如心脏、胃和肺。器官在器官系统中协同工作。例如，消化系统包括胃、肠、肝和胰腺。循环系统包括心脏、血管和血液。理解从细胞到系统的这种层次结构是 WJEC 考试的基础。
3. Enzymes and Digestion | 酶与消化
Enzymes are biological catalysts produced by living cells. They speed up chemical reactions without being used up. Each enzyme has a specific active site that fits only one type of substrate – the lock and key model. Enzyme activity is affected by temperature and pH; extremes can denature the enzyme, changing the shape of its active site permanently.
酶是由活细胞产生的生物催化剂。它们能加快化学反应而自身不被消耗。每种酶都有一个特定的活性位点，只适合一种底物 —— 即锁钥模型。酶活性受温度和 pH 影响；极端条件会使酶变性，永久性地改变其活性位点的形状。
Digestion breaks down large insoluble food molecules into smaller soluble ones that can be absorbed. Amylase (produced in salivary glands and pancreas) breaks down starch into maltose. Proteases (in stomach and pancreas) break down proteins into amino acids. Lipases (pancreas) break down lipids into fatty acids and glycerol. Bile, produced by the liver and stored in the gall bladder, emulsifies fats and neutralises stomach acid for intestinal enzymes.
消化将大而不溶的食物分子分解成小而可溶的分子以便吸收。淀粉酶（由唾液腺和胰腺产生）将淀粉分解为麦芽糖。蛋白酶（在胃和胰腺中）将蛋白质分解为氨基酸。脂肪酶（胰腺）将脂肪分解为脂肪酸和甘油。肝脏产生的胆汁储存在胆囊中，能乳化脂肪并中和胃酸，为肠内的酶提供合适的 pH。
| Enzyme / 酶 | Site of production / 产生部位 | Substrate / 底物 | Products / 产物 |
|---|---|---|---|
| Amylase / 淀粉酶 | Salivary glands, pancreas / 唾液腺、胰腺 | Starch / 淀粉 | Maltose / 麦芽糖 |
| Protease / 蛋白酶 | Stomach, pancreas / 胃、胰腺 | Protein / 蛋白质 | Amino acids / 氨基酸 |
| Lipase / 脂肪酶 | Pancreas / 胰腺 | Lipids (fats) / 脂质 | Fatty acids + glycerol / 脂肪酸 + 甘油 |
4. The Circulatory System | 循环系统
The human circulatory system is a double circuit: the pulmonary circuit carries blood to the lungs to pick up oxygen, while the systemic circuit delivers oxygenated blood to the body. The heart has four chambers – right atrium, right ventricle, left atrium, and left ventricle. The left ventricle has thicker walls because it pumps blood all around the body at high pressure.
人体循环系统是一个双循环系统：肺循环将血液运送到肺部以摄取氧气，体循环将含氧血液输送到全身。心脏有四个腔室 —— 右心房、右心室、左心房和左心室。左心室壁更厚，因为它以高压将血液泵送到全身各处。
Blood flows through arteries, veins, and capillaries. Arteries carry blood away from the heart; they have thick, elastic muscular walls to withstand high pressure. Veins return blood to the heart and contain valves to prevent backflow. Capillaries are tiny vessels with walls one cell thick, allowing exchange of substances. Heart rate is controlled by a group of cells called the pacemaker, located in the right atrium.
血液流经动脉、静脉和毛细血管。动脉将血液带离心脏；它们有厚实而有弹性的肌肉壁，以承受高压。静脉将血液送回心脏，并含有瓣膜防止回流。毛细血管是极细的血管，管壁仅一个细胞厚，便于物质交换。心率由位于右心房的起搏器细胞群控制。
5. Blood Components and Immunity | 血液成分与免疫
Blood is composed of plasma, red blood cells, white blood cells, and platelets. Plasma transports dissolved substances such as glucose, amino acids, carbon dioxide, urea, and hormones. Red blood cells, containing haemoglobin, bind oxygen in the lungs and release it in tissues. The reaction can be shown as:
血液由血浆、红细胞、白细胞和血小板组成。血浆运输溶解的物质，如葡萄糖、氨基酸、二氧化碳、尿素和激素。含有血红蛋白的红细胞在肺部结合氧气，并在组织处释放。反应可用下式表示：
haemoglobin + oxygen ⇌ oxyhaemoglobin
血红蛋白 + 氧气 ⇌ 氧合血红蛋白
White blood cells are part of the immune system. Phagocytes engulf and digest pathogens (phagocytosis), while lymphocytes produce antibodies specific to antigens on pathogens. Memory cells remain after an infection, providing long-term immunity. Platelets are involved in blood clotting, preventing excessive bleeding and entry of pathogens.
白细胞是免疫系统的一部分。吞噬细胞吞噬并消化病原体（吞噬作用），而淋巴细胞产生针对病原体抗原的特异性抗体。感染后记忆细胞留存，提供长期免疫力。血小板参与血液凝固，防止过多出血并阻止病原体进入。
6. Gas Exchange and Respiration | 气体交换与呼吸
Gas exchange in mammals occurs in the alveoli of the lungs. Alveoli are tiny air sacs surrounded by a dense network of capillaries. They have thin walls (one cell thick), a large surface area, and a moist lining, all adapting them for efficient diffusion of oxygen into the blood and carbon dioxide out.
哺乳动物的气体交换发生在肺的肺泡中。肺泡是微小的气囊，周围包裹着密集的毛细血管网。它们有薄壁（一个细胞厚）、大面积表面和湿润的内衬，这些特征都有利于氧气高效扩散进入血液、二氧化碳扩散出来。
Breathing involves the diaphragm and intercostal muscles. During inhalation, the diaphragm contracts and flattens, the external intercostal muscles contract to raise the ribcage, increasing the volume of the thorax and decreasing pressure, so air rushes in. Exhalation is largely passive at rest: the muscles relax, thoracic volume decreases, pressure increases, and air is pushed out.
呼吸涉及膈肌和肋间肌。吸气时，膈肌收缩变平，外肋间肌收缩提升胸腔，增加胸腔容积并降低压力，空气涌入。静息时的呼气主要是被动的：肌肉放松，胸腔容积减小，压力增大，空气被压出。
Aerobic respiration uses oxygen to release energy from glucose, producing carbon dioxide and water. The word equation is:
有氧呼吸利用氧气从葡萄糖中释放能量，产生二氧化碳和水。文字方程式为：
glucose + oxygen → carbon dioxide + water (+ energy)
葡萄糖 + 氧气 → 二氧化碳 + 水 (+ 能量)
7. Excretion and Homeostasis | 排泄与稳态
Excretion is the removal of metabolic waste products. The kidneys filter the blood, removing urea, excess water, and salts to form urine. They also regulate water balance (osmoregulation). Each kidney contains millions of nephrons, which filter blood under pressure (ultrafiltration) and then reabsorb useful substances like glucose, some water, and ions back into the blood.
排泄是去除代谢废物的过程。肾脏过滤血液，去除尿素、多余的水分和盐分形成尿液。肾脏还调节水平衡（渗透调节）。每个肾脏含有数百万个肾单位，在压力下过滤血液（超滤作用），然后将有用的物质，如葡萄糖、部分水和离子，重吸收回血液。
Homeostasis maintains a constant internal environment. The hormone ADH (anti-diuretic hormone) controls the amount of water reabsorbed in the kidneys. If the blood is too concentrated, the pituitary gland releases more ADH, making the collecting ducts more permeable to water, so more water is reabsorbed. Temperature regulation (thermoregulation) involves the skin: sweating cools the body, while shivering and vasoconstriction conserve heat.
稳态维持恒定的内环境。抗利尿激素 (ADH) 控制肾脏重吸收的水量。如果血液太浓，垂体会释放更多 ADH，使集合管对水的通透性增加，从而重吸收更多水。体温调节（体温恒定）涉及皮肤：出汗使身体降温，而战栗和血管收缩能保存热量。
8. Nervous System and Reflexes | 神经系统与反射
The nervous system uses electrical impulses to bring about rapid responses. It consists of the central nervous system (CNS) – brain and spinal cord – and peripheral nerves. A reflex arc is a rapid involuntary response that bypasses conscious thought. Its pathway is:
神经系统利用电脉冲引起快速反应。它由中枢神经系统（CNS，脑和脊髓）以及周围神经组成。反射弧是一种不经过意识思考的快速不自主反应。其路径是：
s → receptor → sensory neurone → relay neurone (CNS) → motor neurone → effector → response
刺激 → 感受器 → 感觉神经元 → 联络神经元(CNS) → 运动神经元 → 效应器 → 反应
Synapses are gaps between neurones. An electrical impulse triggers the release of a neurotransmitter which diffuses across the gap and binds to receptors on the next neurone, continuing the impulse. The eye is a sensory organ; its structures include the cornea (refracts light), iris (controls light entry), lens (focuses light onto the retina), and retina (contains light-sensitive cells). Accommodation is the lens changing shape for near or distant vision.
突触是神经元之间的间隙。电冲动触发神经递质的释放，递质扩散通过间隙并与下一个神经元上的受体结合，使冲动继续传递。眼睛是一个感觉器官；其结构包括角膜（折射光线）、虹膜（控制进光量）、晶状体（将光线聚焦到视网膜上）和视网膜（含有感光细胞）。调节是晶状体改变形状以看清近处或远处物体的过程。
9. Hormones and Endocrine Control | 激素与内分泌控制
Hormones are chemical messengers produced by endocrine glands and transported in the blood. Compared with nervous responses, hormone action is slower but longer lasting. Important glands include the pituitary (master gland), thyroid (controls metabolic rate), pancreas (produces insulin and glucagon), adrenal glands (produce adrenaline), and ovaries/testes (sex hormones).
激素是由内分泌腺产生并通过血液运输的化学信使。与神经反应相比，激素作用较慢但持续时间更长。重要的腺体包括垂体（主控腺）、甲状腺（控制代谢率）、胰腺（产生胰岛素和胰高血糖素）、肾上腺（产生肾上腺素）和卵巢/睾丸（性激素）。
Insulin lowers blood glucose by stimulating cells to take up glucose and the liver to convert glucose to glycogen. Glucagon raises blood glucose by converting glycogen back to glucose. In type 1 diabetes, the pancreas produces little or no insulin. Adrenaline is released in ‘fight or flight’ situations, increasing heart rate, dilating pupils, and diverting blood to muscles.
胰岛素通过刺激细胞摄取葡萄糖，以及促进肝脏将葡萄糖转化为糖原，来降低血糖。胰高血糖素通过将糖原转化为葡萄糖来升高血糖。在 1 型糖尿病中，胰腺产生的胰岛素很少或没有。肾上腺素在“战斗或逃跑”的情况下释放，会加快心率、放大瞳孔并将血液转向肌肉。
10. Reproduction and Development | 生殖与发育
Sexual reproduction involves the fusion of male and female gametes (sperm and egg) to form a zygote. The male reproductive system includes the testes (produce sperm and testosterone), sperm ducts, and penis. The female system includes ovaries (produce eggs, oestrogen, and progesterone), oviducts (site of fertilisation), uterus (where the embryo develops), and vagina.
有性生殖涉及雄性和雌性配子（精子和卵细胞）融合形成受精卵。男性生殖系统包括睾丸（产生精子和睾酮）、输精管和阴茎。女性系统包括卵巢（产生卵细胞、雌激素和孕酮）、输卵管（受精部位）、子宫（胚胎发育处）和阴道。
The menstrual cycle is controlled by hormones. Oestrogen causes thickening of the uterine lining; LH (luteinising hormone) triggers ovulation. After ovulation, progesterone maintains the lining. If fertilisation occurs, the embryo implants and produces hCG, which keeps the corpus luteum producing progesterone. The placenta allows exchange of nutrients, oxygen, and waste between mother and embryo, but prevents mixing of blood.
月经周期受激素调控。雌激素使子宫内膜增厚；黄体生成素 (LH) 触发排卵。排卵后，孕酮维持内膜。如果受精发生，胚胎着床并产生 hCG，维持黄体产生孕酮。胎盘允许母亲和胚胎之间交换营养、氧气和废物，但阻止血液混合。
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