A-Level CIE Science: Animal Biology Key Points | A-Level CIE 科学：动物考点精讲

📚 A-Level CIE Science: Animal Biology Key Points | A-Level CIE 科学：动物考点精讲

Welcome to this comprehensive revision guide designed for A-Level CIE Science students. The animal biology component spans key physiological systems, from transport and gas exchange to neural and hormonal coordination. Mastering these topics is vital for answering both structured and extended-response questions. This article covers the core concepts, relationships, and terminology you need, presented in a clear bilingual format to reinforce understanding in both English and Chinese.

欢迎阅读本份专为 A-Level CIE 科学学生编写的复习指南。动物生物学部分涵盖了从运输、气体交换到神经与激素协调等关键生理系统。掌握这些主题对于回答结构题和长篇解答题至关重要。本文以清晰的双语形式梳理了核心概念、关系与术语，帮助你巩固中英文理解。

1. Transport in Mammals | 哺乳动物的运输系统

Mammals possess a closed, double circulatory system consisting of two separate circuits: pulmonary circulation (heart to lungs and back) and systemic circulation (heart to body tissues and back). This separation ensures that oxygenated and deoxygenated blood never mix, maintaining a high partial pressure gradient for efficient oxygen delivery to respiring tissues. The heart acts as a dual pump, with the right side handling deoxygenated blood and the left side pumping oxygenated blood under high pressure.

哺乳动物拥有闭管式双循环系统，由两个独立的回路组成：肺循环（心脏→肺→心脏）和体循环（心脏→身体组织→心脏）。这种分隔确保富氧血与缺氧血互不混合，维持了较高的氧分压梯度，从而高效地向呼吸旺盛的组织供氧。心脏作为双重泵发挥作用，右侧处理缺氧血，左侧以较高压力泵出富氧血。

The primary transport fluid, blood, is composed of plasma, red blood cells (erythrocytes), white blood cells (leucocytes), and platelets. Red blood cells contain the iron-rich protein haemoglobin, which reversibly binds oxygen to form oxyhaemoglobin. This is crucial for oxygen carriage from the lungs to tissues. Carbon dioxide is mainly transported as bicarbonate ions (HCO₃⁻) in plasma, with some carried as carbaminohaemoglobin.

主要的运输液体——血液由血浆、红细胞、白细胞和血小板组成。红细胞含有富含铁的血红蛋白，能可逆地与氧结合形成氧合血红蛋白，这对将氧气从肺部运送到组织至关重要。二氧化碳主要以碳酸氢根离子 (HCO₃⁻) 形式在血浆中运输，少量以氨基甲酸血红蛋白的形式携带。

2. The Mammalian Heart | 哺乳动物的心脏

The heart is a four-chambered muscular organ with two atria and two ventricles. The right atrium receives deoxygenated blood from the body via the vena cavae, and the right ventricle pumps it to the lungs through the pulmonary artery. Oxygenated blood returns via the pulmonary veins to the left atrium, then enters the left ventricle, which propels it through the aorta to the systemic circulation. Atrioventricular valves (tricuspid on the right, bicuspid/mitral on the left) prevent backflow into the atria, while semilunar valves guard the exits of the pulmonary artery and aorta.

心脏是四腔肌肉器官，拥有两个心房和两个心室。右心房通过腔静脉接收来自身体各部的缺氧血，右心室将其泵入肺动脉流向肺部。富氧血经肺静脉返回左心房，随后进入左心室，左心室将其通过主动脉输入体循环。房室瓣（右侧为三尖瓣，左侧为二尖瓣/僧帽瓣）防止血液倒流回心房，而半月瓣则守护肺动脉和主动脉的出口。

The cardiac cycle consists of diastole (relaxation and filling) and systole (contraction). A heartbeat is initiated by the sinoatrial node (SAN), the natural pacemaker, which sends an electrical impulse through the atrial walls, causing atrial systole. The impulse is delayed at the atrioventricular node (AVN) before travelling down the bundle of His and Purkinje fibres to trigger ventricular systole from the apex upwards. This coordination ensures efficient emptying of the chambers.

心动周期包括舒张期（放松与充盈）和收缩期（收缩）。心跳由天然起搏器——窦房结 (SAN) 启动，它发出电脉冲沿心房壁传导，引发心房收缩。脉冲在房室结 (AVN) 发生短暂延迟，然后沿着希氏束和浦肯野纤维传导，从心尖向上引发心室收缩。这种协调确保了心室的高效排空。

Cardiac output = Heart rate × Stroke volume

An increase in either heart rate (beats per minute) or stroke volume (volume ejected per beat) boosts cardiac output, supplying more oxygen to muscles during exercise.

心输出量 = 心率 × 每搏输出量。运动中心率或每搏输出量的增加都能提高心输出量，为肌肉供给更多氧气。

3. Blood Vessels and Blood | 血管与血液

Arteries carry blood away from the heart; they have thick, elastic walls to withstand high pressure and maintain a pulse. Arterioles branch into capillaries, whose walls are only one cell thick (

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