IGCSE CIE Science: Animals Key Points Revision | IGCSE CIE 科学：动物考点精讲

📚 IGCSE CIE Science: Animals Key Points Revision | IGCSE CIE 科学：动物考点精讲

This comprehensive guide covers the essential animal-related topics in the IGCSE CIE Science syllabus, focusing on classification, nutrition, gas exchange, transport, excretion, coordination, and reproduction. Master these key points to excel in your exams.

本综合指南涵盖 IGCSE CIE 科学大纲中动物相关的重要主题，重点包括分类、营养、气体交换、运输、排泄、协调和繁殖。掌握这些要点，助你考试取得优异成绩。

1. Animal Classification | 动物分类

The animal kingdom is divided into two main groups: invertebrates (without a backbone) and vertebrates (with a backbone). In IGCSE CIE Science, the focus is on the five classes of vertebrates: fish, amphibians, reptiles, birds, and mammals. Each class has distinct features related to body temperature regulation, skin, respiratory organs, reproduction, and limbs.

动物界分为两大类：无脊椎动物（没有脊柱）和脊椎动物（有脊柱）。在 IGCSE CIE 科学中，重点放在五类脊椎动物上：鱼类、两栖类、爬行类、鸟类和哺乳类。每一类在体温调节、皮肤、呼吸器官、生殖方式和四肢方面都有明显特征。

Class	Key Features	Examples
Fish	Scales, gills, external fertilisation, cold-blooded	Salmon, shark
Amphibians	Moist skin, gills then lungs, external fertilisation, cold-blooded	Frog, toad
Reptiles	Dry scaly skin, lungs, internal fertilisation, lay leathery eggs, cold-blooded	Snake, lizard
Birds	Feathers, beak, lungs with air sacs, internal fertilisation, lay hard-shelled eggs, warm-blooded	Eagle, penguin
Mammals	Hair/fur, lungs, internal fertilisation, live birth, mammary glands, warm-blooded	Human, whale

Mammals and birds are endothermic (warm-blooded), meaning they maintain a constant internal body temperature regardless of the environment. Fish, amphibians, and reptiles are ectothermic (cold-blooded), so their body temperature varies with the surroundings.

哺乳类和鸟类是恒温动物（温血），意味着无论外界环境如何，都能保持稳定的内部体温。鱼类、两栖类和爬行类是变温动物（冷血），因此它们的体温随环境变化。

Classification is based on evolutionary relationships and shared characteristics. For exams, you must be able to use a dichotomous key to identify organisms and justify why an animal belongs to a particular class.

分类基于进化关系和共同特征。考试中，你必须能够使用二歧分类检索表来识别生物，并能说明为什么某种动物属于某一类别。

2. Nutrition and Digestion | 营养与消化

Animals are heterotrophs – they cannot make their own food and must consume other organisms. The human digestive system breaks down large insoluble molecules into small soluble ones that can be absorbed into the blood. This process involves mechanical digestion (chewing, churning) and chemical digestion (enzymes).

动物是异养生物——它们不能自己制造食物，必须摄取其他生物。人类消化系统将大的不溶性分子分解成小的可溶性分子，以便吸收到血液中。这个过程包括物理消化（咀嚼、搅拌）和化学消化（酶）。

The main organs of the alimentary canal are the mouth, oesophagus, stomach, small intestine, and large intestine. Accessory organs include the liver, gall bladder, and pancreas, which release enzymes and bile.

消化道的主要器官包括口腔、食道、胃、小肠和大肠。附属器官包括肝脏、胆囊和胰腺，它们分泌酶和胆汁。

Carbohydrates are broken down by carbohydrases (e.g., amylase) into simple sugars; proteins by proteases into amino acids; and fats by lipases into fatty acids and glycerol. Bile, produced by the liver and stored in the gall bladder, emulsifies fats, increasing surface area for enzyme action.

碳水化合物被碳水化合物酶（如淀粉酶）分解为单糖；蛋白质被蛋白酶分解为氨基酸；脂肪被脂肪酶分解为脂肪酸和甘油。胆汁由肝脏产生并储存在胆囊中，能乳化脂肪，增加酶作用的表面积。

The small intestine is the primary site of absorption. Its inner surface is covered with villi, which increase surface area. Each villus contains a network of blood capillaries and a lacteal for absorption of nutrients.

小肠是主要的吸收部位。其内表面布满绒毛，增加了表面积。每个绒毛含有毛细血管网和一个乳糜管，用于吸收营养物质。

After absorption, the large intestine reabsorbs water and forms faeces. It is essential to know the functions of each organ and the specific enzymes involved for the CIE Science exam.

吸收之后，大肠重新吸收水分并形成粪便。对于 CIE 科学考试，你必须了解每个器官的功能以及涉及的具体酶。

3. Gas Exchange | 气体交换

All animals need a constant supply of oxygen for aerobic respiration and must remove carbon dioxide, a waste product. In humans, gas exchange occurs in the lungs, which are adapted to maximise diffusion of oxygen into the blood and carbon dioxide out of the blood.

所有动物都需要持续供应氧气进行有氧呼吸，并必须排出废物二氧化碳。在人体中，气体交换发生在肺内，肺的适应性结构能最大限度地促进氧气扩散到血液，二氧化碳从血液中扩散出去。

Air passes through the trachea, bronchi, and bronchioles before reaching the alveoli – tiny air sacs surrounded by capillaries. The alveoli provide a large surface area, thin walls (one cell thick), a moist lining, and a rich blood supply, all features that speed up diffusion.

空气经过气管、支气管和细支气管后到达肺泡——微小气囊，周围包裹着毛细血管。肺泡提供了巨大的表面积、薄壁（仅一个细胞厚）、湿润的内衬和丰富的血液供应，所有这些特征都能加快扩散速率。

Ventilation (breathing) involves the diaphragm and intercostal muscles. During inhalation, the diaphragm contracts and flattens, and the intercostal muscles raise the ribcage. This increases chest volume and lowers pressure, drawing air in. Exhalation is largely passive at rest, with muscles relaxing.

肺通气（呼吸）涉及膈肌和肋间肌。吸气时，膈肌收缩变平，肋间肌使胸廓上抬。这增加了胸腔容积，降低了压力，从而吸入空气。静息时的呼气在很大程度上是被动的，肌肉放松即可。

For CIE Science, be able to label a diagram of the respiratory system, explain how alveoli are adapted, and describe the composition differences between inspired and expired air (inspired: ~21% O₂, 0.04% CO₂; expired: ~16% O₂, 4% CO₂).

对于 CIE 科学，要能够标注呼吸系统示意图，解释肺泡的适应性，并描述吸入和呼出空气的成分差异（吸入：约 21% O₂，0.04% CO₂；呼出：约 16% O₂，4% CO₂）。

4. Transport System | 运输系统

Animals require a circulatory system to deliver oxygen, nutrients, and hormones to cells and to remove waste products like carbon dioxide and urea. Humans have a closed, double circulatory system, meaning blood passes through the heart twice on one complete circulation of the body.

动物需要一个循环系统，将氧气、营养物质和激素输送到细胞，并带走二氧化碳和尿素等废物。人类拥有封闭的双循环系统，即血液在一次完整的体循环中要两次经过心脏。

The heart is a muscular pump with four chambers: right atrium, right ventricle, left atrium, and left ventricle. The right side pumps deoxygenated blood to the lungs (pulmonary circulation); the left side pumps oxygenated blood to the rest of the body (systemic circulation). Heart valves prevent backflow.

心脏是一个肌性泵，由四个腔室构成：右心房、右心室、左心房和左心室。右侧将缺氧血液泵送至肺部（肺循环）；左侧将富氧血液泵送至身体其他部位（体循环）。心脏瓣膜可防止血液倒流。

Blood vessels include arteries (thick, elastic walls, carry blood away from heart), veins (thinner walls, have valves, carry blood toward heart), and capillaries (one-cell thick walls for exchange). Note that the pulmonary artery carries deoxygenated blood, and the pulmonary vein carries oxygenated blood – an important exam point.

血管包括动脉（壁厚、有弹性，将血液带离心脏）、静脉（壁较薄，有瓣膜，将血液带回心脏）和毛细血管（壁仅一个细胞厚，用于物质交换）。需要注意的是，肺动脉输送缺氧血液，肺静脉输送富氧血液——这是一个重要的考点。

Blood consists of plasma, red blood cells, white blood cells, and platelets. Red blood cells contain haemoglobin, which binds oxygen to form oxyhaemoglobin. White blood cells defend against pathogens, and platelets help in clotting.

血液由血浆、红细胞、白细胞和血小板组成。红细胞含有血红蛋白，能与氧结合形成氧合血红蛋白。白细胞可防御病原体，血小板有助于凝血。

5. Excretion | 排泄

Excretion is the removal of toxic metabolic waste products from the body. The main excretory organ in mammals is the kidney, which filters blood to remove urea, excess water, and salts, forming urine. The skin also excretes small amounts of urea and salts through sweat, but its primary role is thermoregulation.

排泄是指将代谢产生的有毒废物从体内排出的过程。哺乳动物的主要排泄器官是肾脏，它过滤血液，将尿素、多余的水分和盐分以尿液的形式排出。皮肤也通过汗液排出少量尿素和盐分，但其主要作用是体温调节。

The kidney contains millions of functional units called nephrons. Each nephron performs ultrafiltration in the Bowman’s capsule, where small molecules (glucose, urea, salts, water) are forced out of the blood. Large molecules like proteins and blood cells remain in the blood.

肾脏含有数百万个称为肾单位的功能单位。每个肾单位在肾小囊中进行超滤作用，血液中的小分子（葡萄糖、尿素、盐分、水）被滤出。蛋白质和血细胞等大分子则留在血液中。

Selective reabsorption then occurs in the proximal convoluted tubule, where all glucose, some salts, and most of the water are reabsorbed back into the blood. The remaining fluid passes through the collecting duct, where water can be further reabsorbed depending on the body’s hydration levels, regulated by the hormone ADH.

然后在近曲小管中进行选择性重吸收，所有葡萄糖、部分盐分和大部分水分被重新吸收回血液。剩余的液体通过集合管，在那里根据身体的水合程度，可以在激素 ADH 的调节下进一步重吸收水分。

Urine, containing urea, excess salts, and water, flows through the ureters to the bladder for storage before being expelled. The liver plays a key role by converting excess amino acids into urea (deamination), which is then transported to the kidneys.

含有尿素、多余盐分和水分的尿液通过输尿管流到膀胱储存，之后排出体外。肝脏在排泄中起重要作用，它将多余的氨基酸转化为尿素（脱氨基作用），然后转运到肾脏。

6. Coordination and Response | 协调与反应

Animals respond to changes in their internal and external environments through two communication systems: the nervous system (quick, short-lived responses) and the endocrine system (slower, longer-lasting hormonal responses). Both systems use chemical signals but differ in speed and delivery.

动物通过两种通讯系统对内外部环境变化做出反应：神经系统（快速、短暂的反应）和内分泌系统（较慢、持续时间较长的激素反应）。两个系统都使用化学信号，但在速度和传递方式上不同。

The nervous system relies on neurones to transmit electrical impulses. A reflex arc includes a receptor, sensory neurone, relay neurone in the central nervous system, motor neurone, and effector (muscle or gland). Synapses use neurotransmitters to cross gaps between neurones, ensuring a coordinated response.

神经系统依靠神经元传递电脉冲。反射弧包括感受器、感觉神经元、中枢神经系统中的中间神经元、运动神经元和效应器（肌肉或腺体）。突触使用神经递质跨越神经元之间的间隙，确保做出协调的反应。

Hormones are chemical messengers secreted by endocrine glands directly into the blood. Adrenaline, released from the adrenal glands, prepares the body for ‘fight or flight’ by increasing heart rate and blood glucose. Insulin, produced by the pancreas, lowers blood glucose by promoting its conversion to glycogen in the liver.

激素是由内分泌腺分泌并直接释放到血液中的化学信使。肾上腺素由肾上腺释放，通过提高心率和血糖来让身体做好“战斗或逃跑”的准备。胰岛素由胰腺产生，通过促进肝脏将葡萄糖转化为糖原，从而降低血糖。

A key topic is negative feedback, which maintains homeostasis. For example, when blood glucose rises, insulin is released to bring it down; when it falls, glucagon is released to raise it. The body’s ability to control its internal environment is fundamental in animal physiology.

一个关键主题是负反馈，它维持内稳态。例如，当血糖升高时，释放胰岛素使其降低；当血糖下降时，释放胰高血糖素使其升高。身体控制内环境的能力是动物生理学的基础。

7. Reproduction | 繁殖

Most animals reproduce sexually, which produces offspring with genetic variation. The male gamete (sperm) fertilises the female gamete (ovum) to form a zygote. In mammals, fertilisation is internal, and the embryo develops inside the mother’s uterus, receiving nutrients and oxygen via the placenta.

大多数动物进行有性生殖，产生的后代具有遗传变异。雄配子（精子）使雌配子（卵子）受精形成合子。哺乳动物为体内受精，胚胎在母体子宫内发育，通过胎盘获得营养和氧气。

The human male reproductive system produces sperm in the testes and delivers them via the sperm duct and urethra. The female system produces ova in the ovaries, and the fertilised egg implants in the uterus lining. The placenta allows diffusion of oxygen, nutrients, and waste between the mother’s blood and the fetal blood, without the two blood supplies mixing directly.

人类男性生殖系统在睾丸中产生精子，并通过输精管和尿道排出。女性生殖系统由卵巢产生卵子，受精卵着床于子宫内膜。胎盘允许氧气、营养和废物在母体血液和胎儿血液之间扩散，但两种血供不直接混合。

During the menstrual cycle, hormones regulate the thickening of the uterus lining (oestrogen), ovulation (LH surge), and maintenance of the lining (progesterone). If fertilisation does not occur, the lining breaks down and is shed (menstruation).

在月经周期中，激素调节子宫内膜的增厚（雌激素）、排卵（LH 高峰）和内膜的维持（孕激素）。如果未发生受精，内膜脱落，形成月经。

Puberty is the stage when secondary sexual characteristics develop under the influence of sex hormones. For CIE Science, be prepared to compare sexual and asexual reproduction and label structures of the reproductive systems.

青春期是在性激素影响下第二性征发育的阶段。在 CIE 科学考试中，要能够比较有性生殖和无性生殖，并能标注生殖系统结构。

8. Homeostasis and Temperature Regulation | 内稳态与体温调节

Homeostasis refers to the maintenance of a constant internal environment. In animals, this includes controlling temperature, blood glucose, water balance, and carbon dioxide levels. The skin is a crucial organ for temperature regulation in mammals.

内稳态是指维持稳定的内环境。在动物体内，这包括控制体温、血糖、水平衡和二氧化碳水平。皮肤是哺乳动物调节体温的关键器官。

When body temperature rises, thermoreceptors in the skin and brain trigger cooling mechanisms: vasodilation (widening of skin capillaries increases blood flow and heat loss), sweating (evaporation cools the body), and hair lying flat. When cold, vasoconstriction reduces blood flow, hair stands up to trap insulating air, and shivering generates heat by muscle contraction.

当体温升高时，皮肤和大脑中的温度感受器会触发降温机制：血管舒张（皮肤毛细血管扩张，增加血流量和散热）、出汗（蒸发带走体热）以及毛发平伏。寒冷时，血管收缩减少血流，竖毛肌收缩使毛发直立以困住绝缘空气，颤抖则通过肌肉收缩产生热量。

The hypothalamus in the brain acts as the body’s thermostat, integrating signals and coordinating responses. The endocrine system also aids homeostasis: for example, the anti-diuretic hormone (ADH) regulates water reabsorption in the kidneys.

大脑中的下丘脑充当身体的恒温器，整合信号并协调反应。内分泌系统也有助于内稳态：例如抗利尿激素（ADH）调节肾脏对水分的重吸收。

Exam questions often ask you to explain how the body responds to hot or cold conditions. Be specific and mention the role of antagonistic effectors – cooling and heating mechanisms work in opposite ways to return temperature to the set point.

考试题目常常要求你解释身体如何应对炎热或寒冷的环境。回答要具体，并提到拮抗效应器的作用——降温与升温机制以相反的方式运作，使体温回到设定点。

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IGCSE CIE Science: Animals Key Points Revision | IGCSE CIE 科学：动物 考点精讲