📚 IGCSE AQA Science: Animal Biology Key Points | IGCSE AQA 科学：动物 考点精讲
This revision guide covers the essential animal biology topics for the IGCSE AQA Science syllabus. From cell structure to whole-organism systems, each section breaks down the key concepts you need to master. Whether you are studying Coordinated Science or Biology as a separate subject, these notes will help you tackle exam questions with confidence.
本复习指南涵盖 IGCSE AQA 科学大纲中动物生物学的核心主题。从细胞结构到整个生物体的系统，每个部分都拆解了你需要掌握的关键概念。无论你学习的是综合科学还是单独的生物学，这些笔记都将帮助你自信地应对考试题目。
1. Characteristics of Living Animals | 动物的生命特征
All animals share the seven life processes summarised by the acronym MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition. These processes distinguish living organisms from non-living matter.
所有动物都共有用首字母缩写 MRS GREN 概括的七个生命过程：运动、呼吸、感应、生长、生殖、排泄和营养。这些过程将生物体与非生命物质区分开来。
Animals are multicellular eukaryotes that lack cell walls and are heterotrophic, meaning they obtain organic nutrients by consuming other organisms. Most animals possess nervous and muscular systems, enabling rapid responses to stimuli.
动物是多细胞真核生物，没有细胞壁，属于异养生物，即它们通过摄食其他生物来获取有机营养。大多数动物具有神经系统和肌肉系统，能够对刺激做出快速反应。
Growth in animals usually occurs by cell division and cell enlargement, following a determined body plan. The ability to maintain a constant internal environment, known as homeostasis, is another fundamental characteristic of complex animals.
动物的生长通常通过细胞分裂和细胞增大进行，遵循一个确定的体态蓝图。维持恒定内环境的能力，即稳态，是复杂动物的另一个基本特征。
2. Animal Cells and Organisation | 动物细胞与组织层次
A typical animal cell contains a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. The nucleus holds genetic material, mitochondria carry out aerobic respiration, and ribosomes are the sites of protein synthesis.
一个典型的动物细胞包含细胞核、细胞质、细胞膜、线粒体和核糖体。细胞核容纳遗传物质，线粒体进行有氧呼吸，核糖体是蛋白质合成的场所。
Specialised animal cells are adapted for particular functions: red blood cells have a biconcave shape and lack a nucleus to maximise haemoglobin carriage; sperm cells possess a flagellum for movement and numerous mitochondria for energy; nerve cells are elongated to transmit electrical signals rapidly.
特化的动物细胞适应特定功能：红血球呈双凹圆盘形且无细胞核，以最大限度地携带血红蛋白；精子拥有用于运动的鞭毛和大量提供能量的线粒体；神经细胞则细长以快速传导电信号。
These cells are organised into tissues (e.g. muscular tissue, nervous tissue), tissues form organs (e.g. heart, stomach), and organs work together in organ systems (e.g. digestive system, circulatory system) to sustain life.
这些细胞组织起来形成组织（如肌肉组织、神经组织），组织构成器官（如心脏、胃），器官再协同工作构成器官系统（如消化系统、循环系统）以维持生命。
3. Nutrition and Digestion | 营养与消化
Animals require a balanced diet consisting of carbohydrates, proteins, lipids, vitamins, minerals, water and dietary fibre. Carbohydrates and lipids provide energy, proteins are essential for growth and repair, and vitamins and minerals support various metabolic roles.
动物需要均衡的膳食，包括碳水化合物、蛋白质、脂类、维生素、矿物质、水和膳食纤维。碳水化合物和脂类提供能量，蛋白质是生长和修复所必需的，维生素和矿物质则支持多种代谢功能。
The human digestive system breaks down large insoluble molecules into small soluble ones that can be absorbed. Mechanical digestion begins in the mouth, while chemical digestion relies on enzymes produced by glands and the gut lining.
人类消化系统将大分子不溶性物质分解为可被吸收的小分子可溶性物质。物理性消化从口腔开始，而化学性消化依赖于腺体和肠道内壁产生的酶。
| Enzyme | Substrate | Product | Site of Action |
|---|---|---|---|
| Amylase | Starch | Maltose / Glucose | Mouth, small intestine |
| Protease | Protein | Amino acids | Stomach, small intestine |
| Lipase | Lipids | Fatty acids, glycerol | Small intestine |
Absorption occurs mainly in the small intestine, where the inner wall is folded into villi and microvilli to increase surface area. Dissolved nutrients are transported into the blood or lymph.
吸收主要在小肠中进行，小肠内壁折叠成绒毛和微绒毛以增大表面积。溶解的营养物质被转运进入血液或淋巴。
4. Gas Exchange and Respiration | 气体交换与呼吸
Gas exchange in animals involves the uptake of oxygen needed for cellular respiration and the removal of carbon dioxide, a waste product. In mammals, this takes place in the alveoli of the lungs.
动物的气体交换包括摄取细胞呼吸所需的氧气，并排出代谢废物二氧化碳。在哺乳动物中，这一过程发生在肺的肺泡中。
The breathing mechanism: when you inhale, the diaphragm contracts and flattens, intercostal muscles contract to raise the ribcage, increasing thoracic volume and lowering pressure so air is drawn in. Exhalation is largely passive.
呼吸机制：吸气时，膈肌收缩变平坦，肋间肌收缩抬起胸腔，胸腔容积增大、压力降低，空气被吸入。呼气主要是被动过程。
Aerobic respiration can be summarised as:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
Anaerobic respiration in animals produces lactic acid and yields much less energy:
Glucose → Lactic acid + energy
Anaerobic respiration leads to an oxygen debt, which is repaid by deep breathing after exercise to oxidise lactic acid.
无氧呼吸会导致氧债，运动后通过深呼吸氧化乳酸来偿还氧债。
5. Circulation and Blood | 循环系统与血液
The mammalian circulatory system is a closed double circuit. The right side of the heart pumps deoxygenated blood to the lungs (pulmonary circulation), while the left side pumps oxygenated blood to the rest of the body (systemic circulation).
哺乳动物的循环系统是封闭的双循环。心脏右侧将缺氧血泵至肺部（肺循环），左侧将含氧血泵至全身（体循环）。
The heart has four chambers: two atria and two ventricles. Valves prevent backflow of blood. The wall of the left ventricle is thicker because it must generate higher pressure to send blood around the whole body.
心脏有四个腔室：两个心房和两个心室。瓣膜防止血液倒流。左心室壁较厚，因为它需要产生更高的压力将血液输送到全身。
Blood components include:
- Red blood cells: transport oxygen. Haemoglobin binds oxygen reversibly.
- White blood cells: part of the immune system; phagocytes engulf pathogens, lymphocytes produce antibodies.
- Platelets: involved in blood clotting.
- Plasma: transports blood cells, nutrients, hormones, urea and heat.
血液成分包括：
- 红血球：运输氧气。血红蛋白可逆地结合氧气。
- 白血球：免疫系统的一部分；吞噬细胞吞噬病原体，淋巴细胞产生抗体。
- 血小板：参与血液凝结。
- 血浆：运输血细胞、营养物质、激素、尿素和热量。
6. Excretion and Homeostasis | 排泄与稳态
Excretion is the removal of metabolic waste products, which in animals include carbon dioxide (from respiration), urea (from breakdown of excess amino acids), and water. The main excretory organs are the lungs, kidneys and skin.
排泄是代谢废物的清除，动物体内的代谢废物包括二氧化碳（来自呼吸）、尿素（来自过量氨基酸的分解）和水。主要的排泄器官是肺、肾和皮肤。
The kidney contains millions of nephrons. Ultrafiltration occurs in the glomerulus, where small molecules (water, glucose, urea, ions) are forced out of the blood into the Bowman's capsule. Selective reabsorption in the tubule returns useful substances to the blood.
肾脏包含数百万个肾单位。超滤作用发生在肾小球，小分子（水、葡萄糖、尿素、离子）被压出血液进入鲍曼氏囊。肾小管中的选择性重吸收则将有用物质重新吸收回血液。
Homeostasis maintains stable internal conditions. Key examples are:
- Thermoregulation: skin adjusts blood flow, sweating and shivering to keep core temperature near 37 °C.
- Blood glucose regulation: insulin and glucagon from the pancreas control glucose levels.
稳态维持稳定的内环境。关键例子包括：
- 体温调节：皮肤通过调整血流量、排汗和颤抖来使核心温度保持在 37 ℃ 左右。
- 血糖调节：胰脏分泌的胰岛素和胰高血糖素控制血糖水平。
7. Nervous System and Coordination | 神经系统与协调
The nervous system enables rapid communication between receptors and effectors. It consists of the central nervous system (brain and spinal cord) and the peripheral nerves.
神经系统使感受器和效应器之间能够快速通讯。它由中枢神经系统（脑和脊髓）以及周围神经组成。
receptor → sensory neurone → relay neurone (in CNS) → motor neurone → effector → response.
反射弧是最简单的神经通路，可对刺激做出快速、自动的反应。其顺序为：刺激 → 感受器 → 感觉神经元 → 中间神经元（位于中枢神经系统）→ 运动神经元 → 效应器 → 反应。
At synapses, an electrical impulse triggers the release of neurotransmitters, which diffuse across the gap and bind to receptors on the next neurone, generating a new impulse. This ensures unidirectional transmission.
在突触处，电冲动触发神经递质的释放，神经递质扩散过间隙并结合到下一个神经元的受体上，产生新的冲动。这确保了传导是单向的。
The eye is a sense organ; the cornea refracts light, the iris controls the pupil size, the lens focuses light onto the retina, where rod and cone cells convert light into electrical signals.
眼是感觉器官；角膜折射光线，虹膜控制瞳孔大小，晶状体将光线聚焦到视网膜上，视网膜上的视杆细胞和视锥细胞将光信号转换为电信号。
8. Hormonal Control | 激素调控
Hormones are chemical messengers secreted by endocrine glands directly into the blood. They travel to target organs where they produce a slower but longer-lasting response compared to nerve impulses.
激素是由内分泌腺直接分泌入血液的化学信使。它们随血液流到靶器官，产生比神经冲动更慢但更持久的反应。
Adrenaline is released from the adrenal glands in response to stress or danger, preparing the body for 'fight or flight'. It increases heart rate, raises blood glucose levels, and dilates pupils.
肾上腺素在应激或面临危险时由肾上腺释放，使身体做好“搏斗或逃跑”的准备。它使心率加快、血糖水平升高、瞳孔放大。
Insulin, produced by the pancreas, lowers blood glucose by promoting its uptake by cells and conversion to glycogen in the liver. Glucagon raises blood glucose by stimulating glycogen breakdown. A disruption leads to diabetes.
胰脏产生的胰岛素通过促进细胞摄取葡萄糖以及在肝脏中将葡萄糖转化为糖原来降低血糖。胰高血糖素则通过刺激糖原分解释放葡萄糖来提高血糖。一旦失调就会导致糖尿病。
9. Reproduction in Animals | 动物的生殖
Sexual reproduction involves the fusion of male and female gametes (sperm and egg) to form a zygote. This process, fertilisation, produces genetic variation in offspring.
有性生殖涉及雌雄配子（精子和卵子）融合形成受精卵。这一过程，即受精，使后代产生遗传变异。
In the human male reproductive system, sperm are produced in the testes and travel through the sperm ducts. The female reproductive system includes ovaries that release eggs, oviducts where fertilisation occurs, and a uterus where the embryo develops.
在男性生殖系统中，精子在睾丸中产生，经输精管输送。女性生殖系统包括释放卵子的卵巢、发生受精的输卵管，以及胚胎发育的子宫。
The menstrual cycle involves the building up and shedding of the uterine lining, regulated by hormones such as oestrogen and progesterone. If fertilisation occurs, the embryo implants and produces hCG to sustain pregnancy.
月经周期包括子宫内膜的增厚和脱落，受雌激素和孕激素等激素调控。如果受精发生，胚胎着床并分泌人绒毛膜促性腺激素以维持妊娠。
After birth, the placenta provides the foetus with oxygen and nutrients and removes wastes. The amnion secretes amniotic fluid to protect the developing baby.
出生前，胎盘为胎儿提供氧气和营养，并清除废物。羊膜分泌羊水以保护发育中的胎儿。
10. Inheritance and Evolution in Animals | 动物的遗传与进化
Genes are sections of DNA that code for proteins. Alleles are different versions of the same gene. An animal's genotype determines its phenotype, although the environment can also influence characteristics.
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。动物的基因型决定其表现型，尽管环境也会影响性状。
In a monohybrid cross, a single characteristic is controlled by one gene with two alleles. If a dominant allele is present, it masks the effect of a recessive allele. Homozygous organisms have two identical alleles; heterozygous have two different alleles.
在单基因杂交中，单个性状由一对等位基因控制。如果存在显性等位基因，它会掩盖隐性等位基因的效应。纯合子具有两个相同的等位基因；杂合子具有两个不同的等位基因。
Natural selection is the main driver of evolution. Animals with advantageous variations are more likely to survive, reproduce and pass on their alleles. Over generations, the population becomes better adapted to its environment. This can lead to the formation of new species.
自然选择是进化的主要驱动力。具有有利变异的动物更有可能存活、繁殖并传递其等位基因。经过多代，种群变得更适应环境。这可能导致新物种的形成。
Fossils, comparative anatomy and DNA analysis provide evidence for evolution. For example, the pentadactyl limb structure in vertebrates suggests a common ancestor.
化石、比较解剖学和 DNA 分析为进化提供了证据。例如，脊椎动物的五趾型肢结构暗示了共同祖先。
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